JP2018063119A - Method for evaluating destruction strength of fiber-reinforced composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating FRP composite materials adequately for destruction strength by a numerical analysis alone, taking account of strength reduction due to the shape irregularity of fiber (especially, the swell of fiber) in FRP layers.SOLUTION: The method includes a model production step of producing a plurality of different swell models, each of the models representing a composite material having a different swell state, an analysis step of conducting a stress analysis on each of the plurality of swell models with variable load levels exerted on the plurality of swell models, and an evaluation step of evaluating each of the plurality of swell models for destruction strength. The evaluation step includes a destruction determination step of conducting a destruction determination by applying to the result of the stress analysis for the plurality of swell models a plurality of destruction rules, respectively, corresponding to a plurality of different destruction modes, and a tolerance determination step of determining swell state tolerance based on which of the plurality of swell models are determined to be nondestructive by the destruction determination.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a method for evaluating the fracture strength of a composite material formed by laminating FRP layers made of fiber-reinforced plastic.

  An FRP composite made by laminating an FRP layer made of fiber reinforced plastic (FRP: Fiber Reinforced Plastics) exhibits the highest strength against a load in the same direction as the direction in which the fibers are oriented in the FRP layer. . However, since the FRP composite material has low strength in directions other than the fiber orientation direction, and is particularly vulnerable to loads along the out-of-plane direction perpendicular to the lamination surface, delamination occurs between the FRP layers laminated in the out-of-plane direction. Prone to occur. The following patent document and non-patent document assume a case where the FRP composite material having the laminated structure as described above is destroyed by delamination along the out-of-plane direction, and a method for evaluating the fracture strength of the FRP composite material. Disclosure.

  In the fracture strength evaluation method described in Patent Document 1, first, the relationship between the load acting in the delamination direction between the FRP layers and the energy release rate caused by delamination is calculated by numerical analysis on the FEM model. Subsequently, a load corresponding to the energy release rate equal to the fracture toughness value measured by the fracture toughness value test using the actual FRP composite material is obtained from the above relationship, and calculated as the fracture strength. In addition, in the fracture strength evaluation method described in Patent Document 2, a measurement test is performed in which elastic modulus is measured at various locations in the plane of the actual FRP composite material under various inspection temperatures, and the distribution tendency of the elastic modulus in the plane. The fracture strength is evaluated by analyzing the temperature change of the elastic modulus.

  Patent Document 1 and Non-Patent Document 1 disclose a method for calculating an energy release rate corresponding to the fracture energy necessary for delamination to proceed in connection with the above-described evaluation of fracture strength. Specifically, a technique is disclosed in which numerical analysis based on VCCT (Virtual Clip Closure Technique) is performed on an FEM model in which a delamination portion of an FRP composite material is modeled.

JP 2013-011504 A International publication 2011/129235 gazette

Anthony Tirkettle et al., "Study on methods for modeling delamination caused by defects in cylindrical large-diameter members", European Conference 2005 on spacecraft structure, member and mechanism testing (ESA SP-581 2005) May)

  By the way, since the composite material made of FRP has high anisotropy, if the fiber oriented in the FRP layer is irregular in shape, the load direction is shifted from the fiber direction as a result. The strength of the composite with respect to the direction load is greatly reduced. As one form of the irregular shape of the fiber as described above, for example, undulation occurs in some fibers in the FRP layer as a defect at the time of manufacturing the FRP composite material, so that the undulated fiber deviates from the fiber orientation at the time of design. There are cases. As a result, it is considered that the strength of the FRP composite material having such manufacturing defects is reduced not only with respect to the load along the delamination direction but also with respect to the tensile load in the in-plane direction.

  However, in Patent Document 1 and Non-Patent Document 1, in order to accurately evaluate the fracture strength of the FRP composite material in consideration of the strength decrease due to the fiber shape irregularity in the FRP composite material having the manufacturing defects as described above. Ingenuity is not disclosed. As a result, when the swell of some fibers can occur in the FRP layer at the time of manufacturing the FRP composite material, it is possible to determine an allowable range that defines how much the swell of the fiber can secure the required breaking strength. This is not possible, and quality control at the time of manufacturing the FRP composite material becomes difficult.

  Furthermore, the calculation method of the energy release rate by VCCT of patent document 1 and nonpatent literature 1 has the following unsolved subjects. Specifically, the strength reduction caused by the irregular shape of the fiber described above also weakens the strength against a tensile load in the in-plane direction. Nevertheless, the energy release rate described above corresponds only to the destructive energy required for delamination to propagate along the interface between the layers, and therefore corresponds to delamination when evaluating the fracture strength. Only destruction mode is considered. As a result, with the methods described in Patent Document 1 and Non-Patent Document 1, it is difficult to evaluate the fracture strength of the FRP composite material in consideration of various other failure modes that can cause the FRP composite material to break.

  Further, in Patent Document 2, when the fracture strength is evaluated, the above-described decrease in strength due to the irregular shape of the fiber is taken into consideration, but the measurement test of the elastic modulus is not performed at a plurality of locations of the actual FRP composite material. In other words, it is difficult to evaluate the fracture strength only by numerical analysis. As a result, it takes time and cost to perform various tests on actual samples and test pieces of the FRP composite material. In addition, if it is necessary to perform some test on the actual sample or test piece of the FRP composite material, among the various patterns of irregular shape of the fiber found in the FRP composite material, the pattern that is not the object of the test It is difficult to evaluate the decrease in fracture strength. In the invention described in Patent Document 2, it is difficult to employ the VCCT described in Patent Document 1 and Non-Patent Document 1 in order to evaluate the strength reduction caused by the irregular shape of the fiber described above by numerical analysis. Is as described above.

  In view of the above-described problems, some embodiments according to the present invention have irregular shapes of fibers in the FRP layer only by numerical analysis that does not require performing various tests on the actual FRP composite material or test piece ( In particular, it is an object of the present invention to obtain a method for appropriately evaluating the fracture strength of an FRP composite in consideration of strength reduction due to fiber undulation.

(1) A method according to some embodiments of the present invention is a fiber formed by laminating a plurality of FRP layers formed of fiber reinforced plastics in an out-of-plane direction, and extending in the FRP layer in the in-plane direction. Is a method for evaluating the fracture strength of a composite material in which a part of the
A model creation step for creating a plurality of different undulation models representing the composite material each having a different undulation state;
An analysis step of performing stress analysis on each of the plurality of undulation models while changing the magnitude of a load acting on the plurality of undulation models;
An evaluation step for evaluating the breaking strength for each of the plurality of undulation models,
The evaluation step includes
A fracture determination step for performing a fracture determination by applying a plurality of fracture rules respectively corresponding to a plurality of different fracture modes, as a result of the stress analysis for the plurality of undulation models;
And an allowable range determining step of determining an allowable range of the swell state based on which of the plurality of undulation models is determined to be non-destructive by the destruction determination.

  In the fracture strength evaluation method of (1) above, the stress analysis results for a plurality of undulation models with a plurality of fracture laws respectively corresponding to a plurality of different fracture modes without performing various tests on the actual sample or specimen of the composite material. Is used to evaluate fracture strength. Therefore, according to the fracture strength evaluation method of (1) above, the fracture strength of the FRP composite material in consideration of not only the fracture mode corresponding to delamination but also various other fracture modes that can cause the fracture of the FRP composite material. Can be evaluated only by numerical analysis.

  Further, in the fracture strength evaluation method of (1) above, after performing a fracture determination on a plurality of undulation models based on a plurality of fracture rules, any of the plurality of undulation models is determined to be non-destructive by the above fracture determination. The allowable range of the swell state is determined based on the height. Therefore, according to the fracture strength evaluation method of (1) above, when the swell of some fibers can occur in the FRP layer during the production of the FRP composite material, the required rupture strength is ensured to what extent the swell of the fibers is. An acceptable range that defines what can be done can be determined. As a result, when manufacturing the FRP composite material, the quality control is based on whether the degree of undulation occurring in some fibers in the FRP layer is within the allowable range determined as described above. It becomes easy to perform quality control.

(2) According to an exemplary embodiment, in the method of (1), in the model creation step, the waviness state is a distribution state of the waviness of the fibers distributed over the out-of-plane direction of the composite material. Described by a waviness pattern that represents the waviness pattern that represents the waviness pattern and the waviness shape and dimensions of the individual fibers,
The plurality of undulation models are created using the undulation pattern candidates and the undulation parameter candidates that match the undulation pattern candidates.

  In the method (2), the undulation state of each of the plurality of undulation models is described by the undulation pattern and the undulation parameter, and the undulation parameter represents the undulation shape and size of each individual fiber. On the other hand, the undulation pattern expresses the distribution state of the undulation distributed over the out-of-plane direction in the composite material (distributed across a plurality of fiber layers laminated in individual FRP layers). In the method (2), the undulation parameter candidates used for the stress analysis and the fracture determination are parameter candidates consistent with the undulation pattern candidates describing the undulation state of each undulation model.

  Therefore, according to the above method (2), by expressing the waviness state with the waviness pattern and the waviness parameter, it becomes possible to perform analysis in accordance with the actual situation. Specifically, according to the above method (2), stress analysis and fracture are performed using undulation parameters that contradict the distribution of undulation distributed over a plurality of fiber layers laminated in each FRP layer. It is possible to prevent the determination from being executed. Furthermore, in the method (2) described above, for example, the undulation distribution described by the undulation pattern as the undulation distribution distributed over the plurality of fiber layers laminated in the individual FRP layers is changed into the individual state of the individual undulations. By decomposing, for example, it is possible to efficiently generate undulation parameter candidates for a very large number of fibers.

(3) A method according to some embodiments of the present invention is a fiber formed by laminating a plurality of FRP layers formed of fiber-reinforced plastics in an out-of-plane direction and extending in the FRP layer in the in-plane direction. Is a method for evaluating the fracture strength of a composite material in which a part of the
A measurement step for obtaining a measurement result obtained by measuring the internal state of the composite material;
Based on the measurement result, a model creation step of creating at least one undulation model representing the composite material having a undulation state;
An analysis step of performing stress analysis on the undulation model by applying a load based on a predetermined load condition to the at least one undulation model;
An evaluation step for evaluating the breaking strength of the at least one undulation model,
The evaluation step includes
And a failure determination step of performing a failure determination by applying a plurality of failure rules respectively corresponding to a plurality of different failure modes to the result of the stress analysis for the at least one swell model.

  In the fracture strength evaluation method of (3) above, in order to evaluate the fracture strength of a real sample of a composite material by numerical analysis, a plurality of fracture laws respectively corresponding to a plurality of different fracture modes are applied to at least one undulation model stress. Applied to analysis results. Therefore, according to the method of (3) above, in order to evaluate the fracture strength of the actual sample of the composite material by numerical analysis, not only the failure mode corresponding to delamination but also other failure that can cause the FRP composite material to be destroyed. It is possible to evaluate the fracture strength in consideration of various fracture modes.

(4) In an exemplary embodiment, in the method of (3) above, in the model creation step,
The waviness state is described by a waviness pattern that represents the distribution of the waviness of the fibers distributed over the out-of-plane direction of the composite material and waviness parameters that represent the shape and dimensions of the individual waviness of the fibers,
The at least one undulation model is created using the undulation pattern candidates and the undulation parameter candidates that match the undulation pattern candidates.

  In the above method (4), the undulation state of each of the plurality of undulation models is described by the undulation pattern and the undulation parameter, and the undulation parameter estimated in the undulation estimation step from the undulation distribution state represented by the undulation pattern Represents the shape and dimensions of the swell of the fiber. On the other hand, the undulation pattern detected in the distribution detection step expresses the distribution state of undulation distributed over the out-of-plane direction in the composite material (distributed across a plurality of fiber layers).

  Therefore, according to the above method (4), it is possible to perform analysis in accordance with the actual situation by expressing the undulation state by the undulation pattern and the undulation parameter. Further, according to the method (4), when evaluating the fracture strength by numerical analysis for an actual sample of a composite material, stress analysis and fracture determination for a plurality of undulation models can be performed as follows. . That is, not only considering the strength reduction due to the undulation of individual fibers, but also considering the influence of the relative relationship between the undulations of adjacent fibers in the out-of-plane direction on the strength reduction. Destruction determination can be performed. For example, the swell of the fiber is reduced in the strength of the composite material in the case where the undulations of the plurality of adjacent fibers in the out-of-plane direction are aligned in the in-plane direction as compared to the case where the positions are shifted from each other in the in-plane direction It is thought that the impact on

(5) In an exemplary embodiment, in the method of (4), the model creation step includes:
A distribution detection step for detecting which of the plurality of candidates for the undulation pattern corresponds to the distribution state of the undulation of the fiber distributed over the out-of-plane direction of the composite material from the measurement result;
By developing the distribution state of the undulation of the fiber represented by the candidate for the undulation pattern detected by the distribution detection step into the shape and size of the undulation of the individual fiber, the shape and size of the undulation of the individual fiber are obtained. An undulation estimation step for estimating candidate undulation parameters to be represented;
It is characterized by including.

  Further, in the method (5), the distribution state of the undulation of the fiber represented by the undulation pattern detected in the distribution detection step is developed into the shape and size of the undulation of the individual fiber, whereby the shape of the undulation of the individual fiber is obtained. And the waviness parameter representing the dimension is estimated. Therefore, in the method of (5) above, if it is possible to detect what kind of undulation pattern the internal state of the actually measured composite material sample corresponds to, the undulation distribution represented by the undulation pattern is expanded to the undulation of individual fibers. By doing so, the waviness parameter for each fiber can be efficiently estimated.

(6) In an exemplary embodiment, in the method of (5), the measurement step includes an image recognition step of recognizing a cross-sectional observation image obtained by photographing an end cross section of the composite material with a photographing device. Including
The distribution detecting step includes a step of detecting, from the result of the image recognition, which of the plurality of candidates for the undulation pattern corresponds to the distribution state of the undulation of the fiber distributed over the out-of-plane direction of the composite material. It is characterized by that.

  In the method of (6) above, image recognition of a cross-sectional observation image obtained by photographing the end cross section of the composite material with an imaging device is performed, and the undulation of fibers distributed over the out-of-plane direction of the composite material sample from the image recognition result It is detected which of the plurality of candidates for the undulation pattern corresponds to the distribution status of. That is, in the above method (6), the swell pattern candidate corresponding to the internal state of the composite material sample is detected from the image recognition result of the image obtained by photographing the end section of the composite material. Therefore, according to the method of (6) above, it is possible to specify the undulation pattern candidate corresponding to the actual undulation distribution inside the composite material sample without having to cut the composite material sample or cut out the test piece. .

  (7) In an exemplary embodiment, in the method of (5) or (6) described above, a load acting on the swell occurrence position specified by observing an end cross section of the composite material is assumed. The method further comprises the step of setting a load condition in the stress analysis based on the assumed result.

  In the method (7), it is possible to identify the position where the undulation occurs by observing the end cross section of the composite material, and set the load condition in the stress analysis by paying attention to the load acting on this position. . Therefore, in the above method (7), in order to prevent the load condition in the stress analysis from becoming more complicated than necessary, among the load forces important for evaluating the decrease in the strength of the composite material due to the undulation of the fibers inside the composite material, The load condition can be simplified based only on the load force acting on the specified swell occurrence position.

(8) In an exemplary embodiment, in the method of (5), the measuring step includes an inspection performing step of performing a nondestructive inspection on the composite material,
The distribution detecting step includes a step of detecting, from a result of the non-destructive inspection, which of a plurality of candidates of a waviness pattern corresponds to a distribution state of the waviness of the fiber distributed over the out-of-plane direction of the composite material. It is characterized by that.

  In the method (8), a non-destructive inspection is performed on the composite material, and the distribution state of the fiber undulation distributed over the out-of-plane direction of the composite material sample is a plurality of candidates for the undulation pattern. Which of the following is detected. That is, in the method (8), the swell pattern candidate corresponding to the internal state of the composite material sample is detected from the result of actual measurement of the inside of the composite material by nondestructive inspection. Therefore, according to the method of (8) above, it is possible to specify the undulation pattern candidate corresponding to the actual undulation distribution inside the composite material sample without having to cut the composite material sample or cut out the test piece. .

  Compared with the case of measuring the two-dimensional internal state by recognizing the captured image of the end section of the composite material sample as in (6) above, according to the method of (8) above, Additional technical advantages are obtained. That is, in the non-destructive inspection in the method (8), the internal state of the composite material sample can be examined as a three-dimensional state distribution. Therefore, it can be estimated with higher accuracy than the method (6).

  (9) In an exemplary embodiment, in the method of (8) above, in the inspection execution step, the ultrasonic inspection method using an ultrasonic flaw detector or the X-ray CT method using an X-ray scanner device is used. Non-destructive inspection is performed.

  In the method (9), a special device for detecting what kind of waviness pattern candidate the internal state of the composite material sample corresponds to is not used, like an ultrasonic flaw detector or an X-ray scanner device. It is possible to detect a corresponding undulation pattern candidate using an existing measuring device. In the method (9), the undulation inside the composite material is obtained by three-dimensionally analyzing the ultrasonic signal and the X-ray signal actually measured by the ultrasonic flaw detector and the X-ray scanner device according to a known signal analysis method. It is possible to estimate the state more accurately and more easily from a three-dimensional viewpoint rather than two-dimensional.

(10) In an exemplary embodiment, in the methods of (2) and (4) to (9), the waviness model is stacked in a solid element that models each of the FRP layers and in the out-of-plane direction. After combining the adhesive elements that model the interface between the plurality of FRP layers, the undulation pattern and the undulation parameter are reflected.
The stress analysis is performed according to a finite element method on the created waviness model.

  As described above, the FRP composite material is low in strength in directions other than the fiber orientation direction. In particular, since the FRP composite material is weak against a load along the direction to the out-of-plane direction, delamination occurs between the FRP layers laminated in the out-of-plane direction. Is likely to occur. Therefore, in the method (10), a swell model, which is a target for performing stress analysis according to the finite element method, is created as follows. That is, each FRP layer is modeled by a solid element, a boundary surface between FRP layers is modeled by an adhesive element, and a swell pattern and a swell parameter are reflected in a model in which the solid element and the adhesive element are combined. As a result, according to the above method (10), it is possible to skillfully model the above-described properties of the composite material formed by laminating the FRP layers.

(11) In an exemplary embodiment, in the methods of (2) and (4) to (10), the undulation parameter includes a shape function parameter that identifies a shape function for representing the shape of the undulation. And to describe one or more dimensions in the undulation shape defined by the shape function,
An interval length parameter that identifies the length of the interval in which the swell occurred;
In the section where the undulation occurs, a height parameter for identifying a separation width at a position where the fibers are most separated from a fiber arrangement at the time of design in the FRP layer,
An angular parameter for identifying an angular offset between the direction of the fiber and the fiber orientation angle at the time of design in the section where the undulation has occurred;
It includes any one or more of lamination direction position parameters for identifying the position of the swell of the fibers in the out-of-plane direction where the plurality of FRP layers are laminated.

  In the method (11), a shape function for representing the shape of the undulation is defined by the shape function parameter described above, and one or more dimensions in the undulation shape defined by the shape function are defined as the section length parameter and the height parameter described above. , Angle parameters, stacking direction position parameters, etc. Therefore, for example, if the shape function for representing the shape of the swell is a sine wave function, the wavelength and amplitude of the Sine curve represented by the sine wave function are defined by the section length parameter and the height parameter. The shape and dimensions of the swell can be uniquely specified. Further, for example, if the shape function for representing the shape of the swell is a trapezoidal function, the trapezoidal waveform represented by the trapezoidal function is defined by the angle parameter, the section length parameter, and the height parameter. Shapes and dimensions can be uniquely identified. As described above, according to the above method (11), the shape and size of the undulation of each fiber can be uniquely specified using only a mathematically simplified model.

  Further, the following technical advantages can be obtained when the waviness parameter includes the stacking direction position parameter. That is, in the vicinity of the surface layer in the thickness direction of the composite material formed by laminating the FRP layers, the influence of the undulation of individual fibers on the decrease in strength of the composite material becomes large. Compared with this, the influence of the undulation of the fibers located deeper than the surface layer in the thickness direction of the composite material on the strength reduction of the composite material is relatively small. Therefore, by expressing the position of the undulation of individual fibers in the thickness direction of the composite with the position parameter in the lamination direction, the influence of the undulation of individual fibers on the decrease in strength of the composite is undulated. It can be modeled inside the model.

  (12) In an exemplary embodiment, in the methods (2) and (4) to (11), the plurality of candidates for the undulation pattern are along an out-of-plane direction in which the plurality of FRP layers are stacked. The fiber layer in the FRP layer is opened to include a first pattern corresponding to a swell distribution in which a resin reservoir containing no fiber is formed in the FRP layer.

  When the FRP layer constituting the composite material is manufactured, the volume ratio of the fiber and the resin in the FRP layer is not uniform, and a resin pool in which the volume ratio of the resin is partially very high in the FRP layer can be obtained. The resin strength may significantly reduce the fracture strength of the FRP layer. Therefore, in the method (12), as one of a plurality of candidates for the undulation pattern, the fiber layer in the FRP layer is opened along the stacking direction of the FRP layer, so that the fiber is included in the FRP layer. A first pattern representing a waviness distribution in which no resin puddle is formed is defined. As a result, according to the method of (12) above, the volume ratio of the fiber and the resin in the FRP layer was not uniform, and a resin pool with a very high resin volume ratio was partially formed in the FRP layer. It is possible to evaluate the fracture strength of the composite material in consideration of the decrease in fracture strength due to the above.

(13) In an exemplary embodiment, in the method of (12), the swell parameter defined for the first pattern is:
A resin pool size parameter for identifying a size of the resin pool formed in the FRP layer is further included.

  In the method (13), the volume ratio between the fibers and the resin in the FRP layer becomes non-uniform so that the size of the resin pool formed in the FRP layer is defined as the resin pool dimension parameter. As a result, according to the above method (12), when evaluating the fracture strength of the composite material in consideration of the strength decrease due to the resin pool, the magnitude of the strength decrease according to the size of the resin pool is set. Appropriate modeling within the swell model is possible.

  (14) In an exemplary embodiment, in the methods of (2) and (4) to (13), a plurality of candidates for the waviness pattern are generated in the out-of-plane direction in each of the FRP layers. And including a second pattern in which undulations of fibers overlap in the same direction vertically across the plurality of FRP layers, and in-plane direction positions where undulations occur in the fibers in each of the FRP layers are aligned over the plurality of FRP layers. Features.

  In the method of (14), as an example of the undulation pattern, the undulations of the fibers generated in the out-of-plane direction in each FRP layer overlap in the same direction vertically across the plurality of FRP layers, and the fibers in each FRP layer A case is defined where the in-plane direction positions where waviness occurs are aligned over a plurality of FRP layers. As a result, according to the above method (14), the distribution state of undulation corresponding to such undulation pattern candidates can be appropriately modeled in the undulation model.

  As described above, according to some embodiments of the present invention, the shape of the fiber in the FRP layer (particularly, the fiber shape) can be determined only by numerical analysis without performing various tests on the actual FRP composite material or test piece. In consideration of strength reduction due to undulation, a method for appropriately evaluating the fracture strength of the FRP composite material can be obtained.

It is a figure which shows the structure of the fracture strength evaluation apparatus which concerns on some embodiment of this invention. It is a figure which illustrates the structure of the composite material used as the evaluation object by the fracture strength evaluation apparatus which concerns on some embodiment of this invention. It is a figure which shows some examples of the waviness pattern which describes a waviness state. It is a figure which shows the example of the waviness parameter which describes a waviness state. It is a figure which shows a mode that the tolerance | permissible_range of a waviness parameter is calculated from the destruction determination result with respect to a some waviness model. It is a flowchart which shows the processing flow of the destruction evaluation method performed according to some embodiment of this invention. It is a figure which shows the structure of the fracture strength evaluation apparatus which concerns on another embodiment. It is a figure which shows a mode that the end surface image of a composite material is image | photographed with an imaging device. It is a figure which shows the example of the end surface image of the composite material image | photographed with the imaging device. It is a flowchart which shows the processing flow of the destruction evaluation method performed according to another embodiment. It is a figure which shows the structure of the fracture strength evaluation apparatus which concerns on another embodiment. It is a flowchart which shows the processing flow of the destruction evaluation method performed according to another embodiment. It is a figure which shows a mode that a nondestructive inspection is implemented with respect to a composite material with an ultrasonic flaw detector or an X-ray scanner apparatus.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state. On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of the other constituent elements.

  Hereinafter, an apparatus 100 for evaluating the fracture strength of a composite material formed by laminating FRP layers according to some embodiments of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 shows that according to some embodiments, even when the strength of the FRP composite material is reduced due to the undulation of some of the fibers in the FRP layer, the fracture strength of the FRP composite material can be evaluated with high accuracy. The structure of the apparatus 100 which can implement the various fracture strength evaluation methods is shown. A fracture strength evaluation apparatus 100 shown in FIG. 1 is implemented by mounting a fracture strength evaluation method according to some embodiments of the present invention as a software program and reading the software program on a computer.

  Moreover, an example of the composite material used as the evaluation object at the time of evaluating fracture strength with the apparatus 100 shown in FIG. 1 is shown in FIG. Referring to FIG. 2, a fiber reinforced composite material (FRP composite material) 20 is an FRP layer 22 (22 (a) to 22 (22) to 22) formed in a plate shape using a fiber reinforced plastic material (FRP). (N)) is laminated and several tens of sheets are laminated and fired in an autoclave. FRP is obtained by impregnating a resin into a reinforcing fiber 21 such as glass fiber or carbon fiber having high strength and elastic modulus and solidifying it. That is, the composite material 20 is formed by laminating a plurality of FRP layers 22 (22 (a) to 22 (n)) made of fiber reinforced plastic in the out-of-plane direction. In some embodiments of the present invention to be described later, some of the many fibers 21 extending in the in-plane direction in the FRP layer 22 (22 (a) to 22 (n)) have undulations. ing. Note that the degree and state of the swell of the fiber 21 generated in the FRP layer 22 is modeled as a swell state to be described later.

  Referring to FIG. 1 again, the apparatus 100 for evaluating the fracture strength of the FRP composite material 20 illustrated in FIG. 2 generates a plurality of swell state candidates, which will be described later, as swell state candidates. A load condition setting unit 120 that sets a load condition to be set in a stress analysis performed on the model m (m (1) to m (N)) expressing the unit 110 and the FRP composite material 20. In addition, the apparatus 100 receives a swell state candidate output from the swell state candidate generation unit 110 and creates a model m (m (1) to m (N)) representing the FRP composite material 20; A stress analysis unit 140 that executes stress analysis necessary for evaluating the fracture strength on the model m (m (1) to m (N)) is provided. Moreover, the apparatus 100 receives the stress analysis result output from the stress analysis unit 140, and the fracture strength of the FRP composite material 20 expressed by the model m (m (1) to m (N)) based on the stress analysis result. Is provided with a breaking strength evaluation unit 150 for evaluating the breaking strength of the FRP composite material 20 for evaluating the FRP.

  Hereinafter, the roles of the swell state candidate generation unit 110, the load condition setting unit 120, the model creation unit 130, the stress analysis unit 140, and the fracture strength evaluation unit 150 constituting the apparatus 100 will be described. First, the swell state candidate generation unit 110 is a functional unit that generates a plurality of swell state candidates, and the plurality of swell state candidates may be generated in some of the fibers included in the FRP composite material 20. Describe various swell states. At that time, as will be described later, each of the swell state candidates describes the swell state of the fibers included in the FRP composite material 20 in the form of the shape and size of each swell and the state of swell distribution.

  The load condition setting unit 120 sets the direction and size of a load vector assumed to act on the FRP composite material 20 in the stress analysis performed on the model m representing the FRP composite material 20 as the load condition. At that time, the direction and magnitude of the load vector assumed to act on the FRP composite material 20 are set based on the three-dimensional coordinates set in the FRP composite material 20 formed by laminating a plurality of FRP layers. The three-dimensional coordinates are set based on the stacking direction of the FRP composite 20 and the fiber orientation direction in each FRP layer.

  In addition, the model creating unit 130 creates a plurality of different undulation models m (1) to m (N) that express the FRP composite material 20 having different undulation states. The stress analysis unit 140 performs stress analysis on the plurality of undulation models m (1) to m (N) while changing the magnitude of the load applied to the plurality of undulation models m (1) to m (N). Do each. Moreover, the breaking strength strengthening unit 150 evaluates the breaking strength for each of the plurality of undulation models m (1) to m (N).

  Furthermore, the fracture strength evaluation unit 150 includes a fracture determination unit 151 and a swell allowable range determination unit 152 described later. Here, the fracture determination unit 151 has a plurality of fracture rules R (1) to R (R) respectively corresponding to a plurality of different fracture modes with respect to the result of the stress analysis for the plurality of undulation models m (1) to m (N). It is comprised so that destruction determination may be performed by applying (M). Further, the swell allowable range determination unit 152 determines the allowable range of the swell state based on which of the plurality of swell models m (1) to m (N) is determined to be non-destructive by the above-described destruction determination. It is configured as follows.

  In one exemplary embodiment, a “waviness state” that models a wide variety of waviness conditions that may occur on some of the fibers within the FRP composite 20 is determined by the waviness pattern and waviness parameters described below. Described. The undulation pattern represents the distribution of the undulation of the fibers 21 distributed over the out-of-plane direction of the FRP composite 20, whereas the undulation parameter represents the shape and dimensions of the undulation of the individual fibers 21. Here, some specific examples of the distribution state of the undulation in the FRP composite material 20 respectively expressed by a plurality of candidates for the undulation pattern are shown in FIG.

  The five types of undulation pattern candidates shown in FIGS. 3A to 3E correspond to the following undulation distribution patterns. That is, in this waviness distribution pattern, the waviness of the fibers 21 generated in the out-of-plane direction in each FRP layer 22 overlaps in the same direction up and down across the plurality of FRP layers 22. Further, in this waviness distribution pattern, the in-plane direction positions where waviness is generated in the fibers 21 in each FRP layer 22 are aligned over the plurality of FRP layers 22. On the other hand, the two types of waviness pattern candidates shown in FIGS. 3F and 3G correspond to the following waviness distribution patterns. That is, in this waviness distribution pattern, the fiber 21 in the FRP layer 22 is opened along the out-of-plane direction in which the plurality of FRP layers 22 are laminated, so that no resin is contained in the FRP layer 22. A reservoir 25 is formed.

  Next, a specific example of the swell parameter will be described as follows. In some examples, the undulation parameter includes a shape function parameter that identifies a shape function for representing the undulation shape of the fiber 21 and describes one or more dimensions in the undulation shape defined by the shape function. Various dimensional parameters may be included. By doing so, by defining the shape function for representing the shape of the undulation by the shape function parameter described above, by defining one or more dimensions in the undulation shape determined by the shape function by the above-described dimension parameter, It becomes possible to uniquely specify the shape and dimensions of the swell. By defining the undulation parameters as described above, the undulation shape and dimensions of individual fibers can be uniquely specified using only a mathematically simplified model.

  For example, if the shape function for representing the shape of the swell is a sine wave function, if the wavelength and amplitude of the Sine curve represented by the sine wave function are defined by dimensional parameters, the shape and size of the undulation of each fiber is uniquely determined. Can be specified. Also, for example, if the shape function for expressing the shape of the swell is a trapezoid function, the trapezoid function can be expressed by defining the tilt angle of the left and right sides of the trapezoid in addition to the base and height of the trapezoid by the dimension parameter. Since the trapezoidal waveform is uniquely defined, the shape and size of the undulation of each fiber can be uniquely specified.

  In this embodiment, if the fiber orientation surface in the case where the fiber 21 is oriented along the in-plane direction at the time of designing the FRP composite material 20 is used as a reference surface, the above-described dimensional parameters are the following parameters: May be included. For example, the section length parameter L for identifying the length along the reference plane of the section where the undulation has occurred and the separation width at the position where the fiber 21 is farthest away from the reference plane in the out-of-plane direction in the section where the undulation has occurred. A height parameter H may be included. Further, an angle parameter θ for identifying an inclination angle when the direction of the fiber 21 is inclined in the out-of-plane direction due to the undulation in the section where the undulation occurs may be included. Moreover, the lamination direction position parameter for identifying the position of the wave | undulation of the fiber 21 in the out-of-plane direction where the several FRP layer 22 was laminated | stacked may be included.

  FIG. 4 shows an example of dimensional parameters when the shape function for expressing the swell shape of the fiber 21 is a sine wave function. As shown in FIG. 4, the wavelength of the sine wave representing the shape of the undulation is represented by the undulation length L, which corresponds to the section length parameter L among the dimensional parameters described above. Further, the amplitude of the sine wave representing the shape of the undulation is represented by the undulation height H, which corresponds to the height parameter H among the dimensional parameters described above. Further, the angle formed between the tangent line at a specific phase of the sine wave representing the shape of the swell and the reference plane is represented by the swell angle θ, which corresponds to the angle parameter θ among the above-described dimensional parameters.

  In the exemplary embodiment, the swell state candidate generation unit 110 generates a plurality of swell state candidates so that each swell state candidate includes one swell pattern candidate and one swell parameter candidate. And output to the model creation unit 130. At that time, the undulation state candidate generation unit 110 generates a plurality of undulation state candidates so that the undulation pattern candidates and the undulation parameter candidates included in the same undulation state candidate match each other. As a result, in this embodiment, the model creation unit 130 that has received the swell state candidate from the swell state candidate generation unit 110 uses a plurality of swell pattern candidates and swell parameter candidates that match the swell pattern candidates. Swell models m (1) to m (N) are created.

  In an exemplary embodiment, the model creation unit 130 may be configured to create a plurality of waviness models m (1) to m (N) as follows. First, the model creation unit 130 models each FRP layer 22 with a solid element, and models a boundary surface between the plurality of FRP layers 22 stacked in the out-of-plane direction with an adhesive element. Finally, the model creation unit 130 creates a plurality of undulation models m (1) to m (N) by combining the solid elements and the adhesive elements and reflecting the undulation pattern and the undulation parameters.

When the swell models m (1) to m (N) created in this way are output to the stress analysis unit 140, the stress analysis unit 140 firstly combines the FRP composite from the outside of the apparatus 100 shown in FIG. receive material characteristic parameter for the fiber 21 and the resin material constituting the timber 20 _(D in FIG. 1). The material property parameters include Young's modulus, Poisson's ratio, shear elastic modulus or other parameters for the fibers 21 and the resin material constituting the FRP composite 20. The value of the material property parameter is obtained by extracting a sample in which the fiber 21 is not wavy from a large number of test samples of the FRP composite 20, and using this sample as a basic material such as a uniaxial tensile / compression test and a bending test. It is obtained as an actual measurement value in advance by performing a test.

  Subsequently, the stress analysis unit 140 is finite with respect to the waviness models m (1) to m (N) based on the value of the material property parameter under the load condition set by the load condition setting unit 120. You may comprise so that the stress analysis by an element method may be performed. At that time, the stress analysis unit 140 changes the magnitude of the load to be applied to the plurality of undulation models m (1) to m (N) according to the set load condition, and then the plurality of undulation models m (1) to m (N ) To perform stress analysis. Subsequently, the stress analysis unit 140 outputs the result of the stress analysis performed on the undulation models m (1) to m (N) to the fracture strength evaluation unit 150.

  When the fracture strength evaluation unit 150 receives the result of the stress analysis, the fracture determination unit 150 performs the stress analysis on the undulation models m (1) to m (N), respectively, and obtains the stress analysis result C. Destruction rules R (1) to R (M) respectively corresponding to a plurality of destructive modes are applied to (1) to C (N). As a result, which of the swell models m (1) to m (N) leads to failure under the load condition set by the load condition setting unit 120 is based on the destruction rules R (1) to R (M). Determined. That is, the fracture determination unit 151 has a plurality of fracture rules R (1) to R (R) respectively corresponding to a plurality of different fracture modes with respect to the stress analysis results for the plurality of undulation models m (1) to m (N). Destruction is determined by applying M). Subsequently, the swell allowable range determination unit 152 determines the swell parameter allowable range based on which of the plurality of swell models m (1) to m (N) is determined to be non-destructive by the destructive determination. To do.

By the way, a plurality of destruction rules R (1) to R (R) serving as a reference for determining which of the undulation models m (1) to m (N) leads to the destruction under the load condition set by the load condition setting unit 120. Specific examples of (M) may include a failure rule based on the maximum stress theory as follows. First, what is represented by the following formula may be included as a failure rule corresponding to a failure mode when a load force acts along the orientation direction of the fibers 21 inside the FRP composite 20.

If the above inequality holds, the FRP composite 20 is determined to be non-destructive. In the above inequality, σ ₁₁ represents the magnitude of stress with respect to the load force when a load force is applied along the orientation direction of the fiber 21 inside the FRP composite 20, and S _11T is the orientation direction of the fiber 21. It is the material strength in the tensile direction of the FRP composite material 20 when a tensile load force is applied along. S _{11 C} is the material strength of the FRP composite material 20 in the compressive load direction when a compressive load force is applied along the orientation direction of the fibers 21.

As a failure law corresponding to a failure mode when a load force is applied in a direction orthogonal to the orientation direction of the fibers 21 inside the FRP composite material 20, there is one represented by the following equation.

If the above inequality holds, the FRP composite 20 is determined to be non-destructive. In the above inequality, σ ₂₂ represents the magnitude of stress with respect to the load force acting in the direction perpendicular to the orientation direction of the fibers 21 among the load forces acting in the in-plane direction of the FRP layer 22 inside the FRP composite 20. , S _22T is the material strength of the FRP composite material 20 in the tensile direction when a tensile force is applied along the direction of the load force. _S22C is the material strength of the FRP composite material 20 in the compressive load direction when a compressive load force is applied along the direction of the load force. S _33T is the material strength in the tensile direction of the FRP composite material 20 when a tensile load force is applied along the out-of-plane direction (the thickness direction of the FRP layer 22) perpendicular to the orientation direction of the fibers 21. _S33C is the material strength of the FRP composite material 20 in the compressive load direction when a compressive load force is applied along this out-of-plane direction (the thickness direction of the FRP layer 22).

Moreover, there exists what is represented by the following formula | equation as a failure law corresponding to the failure mode in case the load force acts along the shear direction inside the FRP composite material 20.
If the above inequality holds, the FRP composite 20 is determined to be non-destructive. In the above equation, σ ₁₂ represents the stress with respect to the shearing force along the in-plane direction, and σ ₂₃ and σ ₁₃ represent the stress with respect to the shearing force along the out-of-plane direction (the thickness direction of the FRP layer 22). In the above _{formula, S 12} represents the material strength of FRP composite 20 against shearing force along the plane _direction, the shear force _{S 23} and _{S 13} are along the out-of-plane direction (thickness direction of the FRP layer 22) The material strength of the FRP composite material 20 with respect to

Specific examples of the plurality of destruction rules R (1) to R (M) may include a destruction rule based on the square law. The square law is a destruction law corresponding to the failure mode I, the failure mode II, and the failure mode III, which are three types of failure modes when delamination is caused between the FRP layers 22 stacked one above the other. It is expressed by a formula.
If the above inequality holds, the FRP composite 20 is determined to be non-destructive. In the above formula, <> is a bracket of Macaulay, and σ _I , σ _II and σ _III represent stresses corresponding to failure mode I, failure mode II and failure mode III. S _I , S _II and S _III represent the material strength of the FRP composite material 20 corresponding to the fracture mode I, the fracture mode II and the fracture mode III.

  In addition, specific examples of the plurality of destruction rules R (1) to R (M) that serve as a criterion for determining which of the undulation models m (1) to m (N) leads to the destruction include the maximum stress theory described above. In addition to the destruction rule based on the square law and the destruction law based on the square law, the Tsai-Wu law, the Hashin law, the Puck law, the LaRC law, and the like may be included.

  Next, a specific example of the operation in which the swell allowable range determination unit 152 illustrated in FIG. 1 determines the allowable range of the swell parameter value will be described. FIG. 5 shows an example of the allowable range of the swell state determined by the swell allowable range determination unit 152. FIG. 5 shows a two-dimensional plot represented by two-dimensional coordinates, in which the height parameter L corresponding to the height of the waviness is the vertical axis and the angle parameter θ corresponding to the waviness angle is the horizontal axis. A plane is shown. Each of the circle mark and the cross mark plotted on the two-dimensional plot plane shown in FIG. 5 corresponds to each of a plurality of undulation models m (1) to m (N). Here, the circles shown in FIG. 5 correspond to the swell model determined not to be destroyed (non-destructive) by the destruction determination unit 151, and the crosses shown in FIG. It corresponds to the swell model determined to be.

From the above, in the example shown in FIG. 5, the region shown on the two-dimensional plot plane shown in FIG. 5 as the region including only the circle mark has the allowable range of the parameter pair composed of the height parameter L and the angle parameter θ. Represents. Therefore, according to the embodiment illustrated in FIG. 5, an allowable range that defines the extent to which the undulation height L and the undulation angle θ of the fiber 21 that can occur inside the FRP composite material 20 can ensure the required fracture strength. Can be determined as a two-dimensional range ε (L, θ) represented by a pair of the undulation height L and the undulation angle θ, and output to the outside as the output D _out shown in FIG. As a result, according to this embodiment, the undulation height L and the undulation angle θ generated in some of the fibers 21 in the FRP layer 22 are within the allowable range ε (L, θ) determined as described above. It becomes easy to perform quality control at the time of manufacturing the FRP composite material 20 based on whether or not it falls within the range.

  Next, the flow of processing of the fracture strength evaluation method executed by the apparatus 100 shown in FIG. 1 to evaluate the fracture strength of the FRP composite material 20 will be described with reference to the flowchart of FIG. The flowchart of FIG. 6 starts from step S501, and the load condition setting unit 120 sets a load condition that needs to be set when performing a stress analysis of the FRP composite material 20. Subsequently, the process proceeds to step S502, and the swell state candidate generation unit 110 generates a swell pattern candidate to be reflected in the swell model m (i) representing the FRP composite 20 in which swells have occurred in the fibers 21. Subsequently, the process proceeds to step S503, and the swell state candidate generation unit 110 generates swell parameter candidates to be reflected in the plurality of swell models m (i) representing the FRP composite material 20 in which the swells have occurred in the fibers 21. To do.

  Subsequently, the process proceeds to step S504, and the model creation unit 130 that has received the undulation pattern and the undulation parameter candidate from the undulation state candidate generation unit 110 includes a plurality of undulation models m each reflecting the undulation pattern and the undulation parameter candidate. Create (i). Subsequently, the process proceeds to step S505, and the stress analysis unit 140 that receives the undulation model m (i) created by the model creation unit 130 performs the following operation. First, a basic material test is performed in advance on a sample of the FRP composite material 20 in which no undulation is generated in the fiber 21 (step S511 in FIG. 6), and the material characteristic parameters regarding the FRP composite material 20 input from the outside are measured. A value is received (step S512 in FIG. 6). Subsequently, under the load condition set by the load condition setting unit 120, stress analysis by the finite element method is executed on the undulation model m (i).

  Subsequently, the process proceeds to step S506, and the fracture strength evaluation unit 150 that has received the result of the stress analysis for the undulation model m (i) from the stress analysis unit 140 performs the following operation. First, the value of the material characteristic parameter regarding the FRP composite material 20 input from the outside is received (step S512 in FIG. 6). Subsequently, a plurality of destruction rules R (1) to R (M) corresponding to a plurality of destruction modes are set (step S513 in FIG. 6). Subsequently, the fracture determination unit 151 in the fracture strength evaluation unit 150 has a plurality of fracture rules R for the stress analysis results C (i) for the plurality of undulation models m (i) based on the values of the material characteristic parameters. The destruction determination is performed by applying (1) to R (M). As a result, a fracture determination result D (i) indicating whether or not the swell model m (i) is broken under the load conditions described above is obtained.

  Subsequently, the process proceeds to determination step S507, and if the destruction determination result D (i) for the undulation model m (i) represents a non-destructive determination (determination that no destruction occurs), the process proceeds to step S508. The undulation parameter candidates included in the undulation model m (i) determined to be non-destructive are classified as acceptable parameter candidates. On the other hand, if the destruction determination result D (i) for the undulation model m (i) represents the destruction determination (determination that the destruction will occur), the process proceeds to step S514, and the undulation model m determined to be non-destructive. The swell parameter candidates included in (i) are classified as unacceptable parameter candidates.

  Subsequently, the process proceeds to step S509, and the fracture strength evaluation unit 150 determines a sufficient number of fracture determinations for clearly defining the boundary between the acceptable parameter candidates and the unacceptable parameter candidates for the swell parameter candidates. Determine if results are obtained. If the number of obtained destruction determination results is insufficient to clearly define the boundary between the acceptable parameter candidate and the unacceptable parameter candidate, the process of the flowchart of FIG. 6 returns to step S503. . When the processing of the flowchart of FIG. 6 returns to step S503, a new undulation parameter candidate is generated based on the undulation pattern candidate generated in step S502, and a new undulation is performed in step S504 using the new undulation parameter. The model m (i + 1) is created by the model creation unit 130. Then, the above-described processing from step S505 to step S509 is repeatedly executed based on the new undulation model m (i + 1). Conversely, if the number of destruction determination results is sufficient to clearly define the boundary between acceptable and unacceptable parameter candidates, the process of the flowchart of FIG. 6 proceeds to step S510, The allowable waviness parameter determining unit 152 determines the allowable waviness parameter range and finishes the execution of the flowchart.

  As described above, the fracture strength evaluation method executed in the embodiment described above with reference to FIGS. 1 to 6 includes a plurality of waviness models m (1) to m (1) each reflecting a plurality of waviness state candidates. N) is randomly generated, and stress analysis and fracture determination are performed. And in the said destruction strength evaluation method, the tolerance | permissible_range of the waviness state was calculated | required from the waviness state candidate corresponding to the waviness model determined to be nondestructive. That is, the fracture strength evaluation method described above with reference to FIG. 1 to FIG. 6 does not allow a test sample of the FRP composite material 20 to be manufactured, and allows the swell state to be allowed by numerical analysis simulation for a large number of randomly generated undulation models. The range was purely theoretical predictions.

  In contrast, in the fracture strength evaluation method according to the embodiment described later with reference to FIGS. 7 to 15, a plurality of different fractures are performed in order to evaluate the fracture strength by numerical analysis for the FRP composite material 20 created as an actual machine. A plurality of destruction rules R (1) to R (M) corresponding to the respective modes are applied to the stress analysis result for at least one undulation model m (j). Therefore, according to this fracture strength evaluation method, in order to evaluate the fracture strength of the actual machine of the FRP composite material 20 by numerical analysis, not only the failure mode corresponding to delamination but also the failure of the FRP composite material 20 can be caused. It is possible to evaluate the fracture strength in consideration of various fracture modes.

  FIG. 7 shows still another apparatus capable of performing a fracture strength evaluation method capable of highly accurately evaluating the fracture strength of the FRP composite material 20 in which waviness occurs in a part of the fibers 21 according to some embodiments. 200 configurations are shown. A fracture strength evaluation apparatus 200 shown in FIG. 7 is an apparatus that is implemented by mounting a fracture strength evaluation method described later with reference to FIGS. 7 to 10 as a software program and reading the software program on a computer. Also good. Hereinafter, the configuration and operation of the fracture strength evaluation apparatus 200 will be described in detail with reference to FIGS.

  The apparatus 200 shown in FIG. 7 has a configuration different from the apparatus 100 shown in FIG. 1 in the following points. First, the apparatus 200 includes an image recognizing unit 260, and the image recognizing unit 260 is connected to an end face image capturing apparatus 500 provided outside the apparatus 200. Further, the swell state candidate generation unit 110 in the apparatus 100 shown in FIG. 1 is replaced with the swell state analysis unit 210 in the apparatus 200 shown in FIG. 2, and the swell state analysis unit 210 performs analysis by the analysis of the swell state analysis unit 210. A plurality of undulation models m are generated by receiving estimated undulation patterns and undulation parameter candidates. Further, in the apparatus 200 shown in FIG. 2, the fracture strength evaluation unit 250 only calculates the fracture determination result for a single swell model m, and does not determine the allowable range of the swell state.

  Hereinafter, functions and roles of the respective parts constituting the apparatus 200 shown in FIG. 7 will be described. The image recognition unit 260 connected to the end face image capturing device 500 illustrated in FIG. 7 is a unit that acquires a measurement result obtained by measuring the internal state of the FRP composite material 20. Specifically, the image recognition unit 260 measures the internal state of the FRP composite material 20 by recognizing a cross-sectional observation image obtained by photographing the end cross section of the FRP composite material 20 ′ with the end face image photographing device 500. And it is comprised as a measurement means to output to the undulation state analysis part 210. For example, as the end face image photographing device 500, FIG. 8 shows two photographing devices 501 and 502 which may be cameras or optical microscopes. As shown in FIG. 8, the photographing apparatus 501 is arranged to photograph an end cross section of the FRP composite material 20 ′ viewed from the direction d1, and the photographing apparatus 502 includes the FRP composite material 20 ′ viewed from the direction d2. It arrange | positions so that it may image | photograph an edge part cross section. Also, examples of the cross-sectional image of the end portion of the FRP composite material 20 ′ taken by the end face image photographing device 500 are shown in FIGS.

  Upon receiving the measurement result of the internal state of the FRP composite material 20 ′ from the image recognition unit 260, the undulation state analysis unit 210 analyzes what undulation state the inside of the FRP composite material 20 ′ corresponds to. The waviness state in this case is described by a waviness pattern that represents the distribution of waviness of the fibers 21 ′ distributed over the out-of-plane direction of the FRP composite material 20 ′ and waviness parameters that represent the shape and dimensions of the waviness of the individual fibers 21 ′. Is done.

  More specifically, the undulation state analysis unit 210 first receives the measurement result of the internal state of the FRP composite material 20 from the image recognition unit 260 as the image recognition result. Subsequently, the undulation state analysis unit 210 determines whether the undulation distribution state of the fiber 21 ′ distributed over the out-of-plane direction of the FRP composite material 20 ′ is any of a plurality of undulation patterns from the measurement result received as the image recognition result. Detect if applicable. For example, when the image of the end section of the FRP composite material 20 ′ photographed by the end face image photographing device 500 is as shown in FIG. 9B, the fiber layer is opened up and down in FIG. 9B. Thus, it can be understood that the image recognition result received from the image recognition unit 260 corresponds to the undulation pattern shown in FIG. In addition, the undulation state analysis unit 210 develops the undulation distribution state of the fibers 21 ′ represented by the undulation pattern candidates detected as described above into the undulation shape and dimensions of the individual fibers 21 ′. It is configured to estimate undulation parameter candidates representative of the undulation shape and dimensions of the fiber 21 '. Therefore, according to this embodiment, if only the undulation pattern corresponding to the actually measured internal state of the composite material can be detected, the undulation distribution represented by the undulation pattern is expanded to the undulation of individual fibers. Thus, the waviness parameter for each fiber can be estimated efficiently.

  In addition, the model creation unit 230 creates at least one undulation model that represents the FRP composite 20 having a swell state based on the measurement result obtained by measuring the internal state of the FRP composite 20. Specifically, the model creating unit 230 recognizes the cross-sectional observation image obtained by photographing the end cross section of the FRP composite material 20 with the end face image capturing device 500, and the image recognizing unit 260 recognizes the image of the FRP composite material 20. Get the measurement result of the internal state. Then, the model creation unit 230 creates at least one undulation model m representing the FRP composite material 20 having the undulation state from the measurement result of the internal state of the FRP composite material 20 obtained as the image recognition result as described above. To do.

The stress analysis unit 250 that has received at least one undulation model m from the model creation unit 230 is configured to perform a stress analysis on the undulation model by applying a load based on a predetermined load condition to the at least one undulation model m. The Further, the fracture strength evaluation unit 250 that has received the stress analysis result C from the stress analysis unit 240 is configured to evaluate the fracture strength of at least one swell model m. Specifically, the fracture strength evaluation unit 250 adds a plurality of fracture rules R (1) to R (M) respectively corresponding to a plurality of different fracture modes to the stress analysis result C for at least one undulation model m. Is applied to determine the destruction and output the output _Dout to the outside.

  Next, the flow of processing of the fracture strength evaluation method executed by the apparatus 200 shown in FIG. 7 for evaluating the fracture strength of the FRP composite material 20 ′ will be described with reference to the flowchart of FIG. 10. The flowchart of FIG. 10 starts from step S701, and the load condition setting unit 120 sets a load condition that needs to be set when performing a stress analysis of the FRP composite material 20 '. For example, the load condition setting unit 120 assumes a load acting on the waviness generation position specified by observing the end section of the FRP composite material 20 ′, and sets it in the stress analysis based on the assumed result. Determine the load condition. Subsequently, the process proceeds to step S <b> 702, and the image recognition unit 260 recognizes the cross-sectional observation image obtained by photographing the end cross section of the FRP composite material 20 ′ with the end face image photographing device 500, thereby recognizing the FRP composite material 20. Are measured and output to the swell state analysis unit 210.

  Subsequently, the process proceeds to step S703, and the undulation state analysis unit 210 undulates the distribution state of the swell of the fibers 21 ′ distributed over the out-of-plane direction of the FRP composite 20 ′ from the image recognition result received from the image recognition unit 260. Which of a plurality of pattern candidates is detected is detected. Subsequently, the undulation state analysis unit 210 develops the undulation distribution state of the fibers 21 ′ represented by the undulation pattern candidates detected as described above into the undulation shapes and dimensions of the individual fibers 21 ′. The candidate of the undulation parameter representing the shape and size of the undulation of the fiber 21 'is estimated.

  Subsequently, the process proceeds to step S704, and the model creation unit 230, which has received the undulation pattern and the undulation parameter candidate from the undulation state analysis unit 210, includes a plurality of undulation models m reflecting the undulation pattern and the undulation parameter candidate. create. Subsequently, the process proceeds to step S705, and the stress analysis unit 240 that receives the undulation model m (i) created by the model creation unit 230 performs the following operation. First, a material related to the FRP composite material 20 ′ that is actually measured by performing a basic material test in advance on a sample of the FRP composite material 20 ′ in which no undulation occurs in the fiber 21 ′ (step S709 in FIG. 10). The value of the characteristic parameter is received (step S710 in FIG. 10). Subsequently, under the load condition set by the load condition setting unit 120, stress analysis by the finite element method is executed on the undulation model m.

  Subsequently, the process proceeds to step S706, and the fracture strength evaluation unit 250 that has received the result of the stress analysis for the undulation model m from the stress analysis unit 240 performs the following operation. First, the value of the material characteristic parameter regarding the FRP composite material 20 ′ input from the outside is received (step S <b> 710 in FIG. 6). Subsequently, a plurality of destruction rules R (1) to R (M) corresponding to a plurality of destruction modes are set (step S711 in FIG. 6). Subsequently, the fracture determination unit 151 in the fracture strength evaluation unit 150 has a plurality of fracture rules R (1) to R (R) for the result C of the stress analysis for the plurality of undulation models m based on the value of the material characteristic parameter. Perform destruction determination by applying M). As a result, a fracture determination result D indicating whether or not the swell model m is broken under the load conditions described above is obtained.

  Subsequently, the process proceeds to determination step S707, and if the destruction determination result D for the undulation model m represents a nondestructive determination (determination that no destruction occurs), the process proceeds to step S708 and is determined to be nondestructive. The swell parameter candidates included in the swell model m are classified into acceptable parameter candidates. On the other hand, if the destruction determination result D for the bend model m represents the destruction determination (determination that the destruction will occur), the process proceeds to step S712, and the undulation parameter m included in the undulation model m determined to be non-destructive. Classify candidates as unacceptable parameter candidates.

  FIG. 11 shows still another embodiment in which a fracture strength evaluation method capable of highly accurately evaluating the fracture strength of the FRP composite material 20 ″ in which waviness occurs in a part of the fibers 21 ″ according to some embodiments. The structure of the apparatus 300 of FIG. A fracture strength evaluation apparatus 300 shown in FIG. 11 is an apparatus realized by mounting a fracture strength evaluation method, which will be described later with reference to FIGS. 11 to 13, as a software program, and reading the software program on a computer. Also good. Hereinafter, the configuration and operation of the fracture strength evaluation apparatus 300 will be described in detail with reference to FIGS.

  The apparatus 300 shown in FIG. 11 has a different configuration from the apparatus 200 shown in FIG. 7 in the following points. First, the apparatus 200 illustrated in FIG. 7 includes the image recognition unit 260 connected to the end face image capturing apparatus 500, whereas the apparatus 300 illustrated in FIG. 11 includes the three-dimensional signal analysis unit 360. The three-dimensional signal analysis unit 360 is connected to a nondestructive inspection apparatus 600 provided outside the apparatus 300.

  In the example shown in FIG. 11, the nondestructive inspection apparatus 600 may be configured as an ultrasonic flaw detection apparatus or an X-ray scanner apparatus for three-dimensionally scanning and examining the inside of the FRP composite material 20 ″. In the apparatus 300 shown in FIG. 11, a nondestructive inspection for observing the internal state of the FRP composite 20 "according to an ultrasonic flaw detection method using an ultrasonic flaw detection apparatus 600 or an X-ray CT method using an X-ray scanner apparatus. Is implemented. The three-dimensional signal analysis unit 360 performs three-dimensional signal analysis processing on signal data obtained by three-dimensionally scanning the inside of the FRP composite material 20 ″ with the nondestructive inspection apparatus 600, thereby performing the FRP composite material 20. ”Is measured as a measuring means for measuring the internal state three-dimensionally and outputting it to the undulation state analysis unit 310. The undulation state analysis unit 310 undulates the distribution state of the undulation of the fiber 21 ″ distributed over the out-of-plane direction of the FRP composite 20 ″ from the result of three-dimensional signal analysis processing of the signal data measured by the nondestructive inspection. It is configured to detect which of a plurality of pattern candidates is applicable.

  As described above, in the apparatus 300 shown in FIG. 11, the non-destructive inspection is performed on the FRP composite material 20 ″, and the undulation of the fibers 21 ″ distributed over the out-of-plane direction of the composite material sample from the result of the nondestructive inspection. It is detected which of the plurality of candidates for the undulation pattern corresponds to the distribution status of. That is, in this method, the undulation pattern candidate corresponding to the internal state of the composite material is detected from the result of actual measurement of the inside of the FRP composite material 20 ″ by nondestructive inspection. For example, undulation pattern candidates corresponding to the actual undulation distribution inside the composite material can be identified without having to cut the composite material or cut out the test piece.

  Compared to a case where a two-dimensional internal state is measured by recognizing a captured image of an end cross section of a composite material as in the apparatus 200 illustrated in FIG. 7, the apparatus 300 illustrated in FIG. Additional technical advantages. That is, in the non-destructive inspection in the apparatus 300 shown in FIG. 11, the internal state of the composite material can be examined as a three-dimensional state distribution. 7 can be estimated with higher accuracy than the apparatus 200 shown in FIG.

  Next, the flow of processing of the breaking strength evaluation method executed by the apparatus 200 shown in FIG. 11 to evaluate the breaking strength of the FRP composite material 20 ″ will be described with reference to the flowchart of FIG. 10 differs from the flowchart of Fig. 10 only in the following points: In the flowchart of Fig. 10, in step S702, a process of capturing an end face image of the FRP composite material 20 'and outputting the image analysis result to the waviness state analysis unit 210 is performed. In contrast, in the flowchart of FIG. 12, instead of this processing, the FRP composite material 20 ″ is subjected to a nondestructive inspection as shown in FIG. A signal analysis result measured and analyzed three-dimensionally is output to the undulation state analysis unit 210. Except for the above differences, the flowchart shown in FIG. The procedure is the same as the execution procedure of the flowchart in Fig. 10. The description is omitted in Fig. 13. In Fig. 13, the nondestructive inspection device 600 configured as an ultrasonic flaw detector or an X-ray scanner device is replaced with the FRP composite material 20. A state in which the internal state of the “FRP composite material 20” is three-dimensionally scanned along the direction d (Scan) from the upper point position d (point) is depicted.

20 (20 ′, 20 ″) FRP composite material 21 (21 ′, 21 ″) Reinforcing fiber 22 (22 (a)) FRP layer 25 Resin reservoir 100, 200, 300 Fracture strength evaluation device 110 Waviness state candidate generation unit 120 Load Condition setting unit 130, 230 Model creation unit 140, 240, 340 Stress analysis unit 150, 250, 350 Fracture strength evaluation unit 151 Fracture determination unit 152 Waviness tolerance range determination unit 210, 310 Waviness state analysis unit 260 Image recognition unit 360 Three-dimensional Signal analysis unit 500 (501, 502) End face image photographing device 600 Non-destructive inspection device

Claims (14)

A method for evaluating the fracture strength of a composite material formed by laminating a plurality of FRP layers formed of fiber reinforced plastics in an out-of-plane direction, and a part of fibers extending in the in-plane direction in the FRP layer has undulations. And
A model creation step for creating a plurality of different undulation models representing the composite material each having a different undulation state;
An analysis step of performing stress analysis on each of the plurality of undulation models while changing the magnitude of a load acting on the plurality of undulation models;
An evaluation step for evaluating the breaking strength for each of the plurality of undulation models,
The evaluation step includes
A fracture determination step for performing a fracture determination by applying a plurality of fracture rules respectively corresponding to a plurality of different fracture modes, as a result of the stress analysis for the plurality of undulation models;
An allowable range determination step for determining an allowable range of the swell state based on which of the plurality of undulation models is determined to be non-destructive by the determination of destruction;
The fracture strength evaluation method characterized by including. In the model creation step,
The waviness state is described by a waviness pattern that represents the distribution of the waviness of the fibers distributed over the out-of-plane direction of the composite material and waviness parameters that represent the shape and dimensions of the individual waviness of the fibers,
2. The fracture strength evaluation method according to claim 1, wherein the plurality of undulation models are created using the undulation pattern candidates and the undulation parameter candidates that match the undulation pattern candidates. 3. A method for evaluating the fracture strength of a composite material formed by laminating a plurality of FRP layers formed of fiber reinforced plastics in an out-of-plane direction, and a part of fibers extending in the in-plane direction in the FRP layer has undulations. And
A measurement step for obtaining a measurement result obtained by measuring the internal state of the composite material;
Based on the measurement result, a model creation step of creating at least one undulation model representing the composite material having a undulation state;
An analysis step of performing stress analysis on the undulation model by applying a load based on a predetermined load condition to the at least one undulation model;
An evaluation step for evaluating the breaking strength of the at least one undulation model,
The evaluation step includes
A fracture determination step of performing a fracture determination by applying a plurality of fracture rules respectively corresponding to a plurality of different fracture modes to the result of the stress analysis for the at least one undulation model;
The fracture strength evaluation method characterized by including. In the model creation step,
The waviness state is described by a waviness pattern that represents the distribution of the waviness of the fibers distributed over the out-of-plane direction of the composite material and waviness parameters that represent the shape and dimensions of the individual waviness of the fibers,
The fracture strength evaluation method according to claim 3, wherein the at least one undulation model is created using the undulation pattern candidate and the undulation parameter candidate that matches the undulation pattern candidate. The model creation step includes:
A distribution detection step for detecting which of the plurality of candidates for the undulation pattern corresponds to the distribution state of the undulation of the fiber distributed over the out-of-plane direction of the composite material from the measurement result;
By developing the distribution state of the undulation of the fiber represented by the candidate for the undulation pattern detected by the distribution detection step into the shape and size of the undulation of the individual fiber, the shape and size of the undulation of the individual fiber are obtained. An undulation estimation step for estimating candidate undulation parameters to be represented;
The fracture strength evaluation method according to claim 4, comprising: The measurement step includes an image recognition step of recognizing a cross-sectional observation image obtained by photographing an end cross section of the composite material with a photographing device,
The distribution detecting step includes a step of detecting, from the result of the image recognition, which of the plurality of candidates for the undulation pattern corresponds to the distribution state of the undulation of the fiber distributed over the out-of-plane direction of the composite material. ,
The fracture strength evaluation method according to claim 5. Assuming a load acting on the waviness occurrence position specified by observing the end cross section of the composite material, further comprising the step of setting the load condition in the stress analysis based on the assumed result,
The fracture strength evaluation method according to claim 5 or 6, characterized in that: The measurement step includes an inspection execution step of performing a nondestructive inspection on the composite material,
The distribution detecting step is a step of detecting, from the result of the non-destructive inspection, which of the plurality of candidates of the waviness pattern corresponds to the distribution state of the waviness of the fiber distributed over the out-of-plane direction of the composite material. The fracture strength evaluation method according to claim 5, further comprising: 9. The fracture strength evaluation according to claim 8, wherein, in the inspection execution step, the nondestructive inspection is performed according to an ultrasonic flaw detection method using an ultrasonic flaw detection device or an X-ray CT method using an X-ray scanner device. Method. The waviness model is obtained by combining solid elements that model each FRP layer and adhesive elements that model boundary surfaces between the FRP layers stacked in the out-of-plane direction. Created by reflecting the swell parameter,
10. The fracture strength evaluation method according to claim 2, wherein the stress analysis is executed in accordance with a finite element method on the created swell model. 10. The waviness parameter includes a shape function parameter that identifies a shape function for representing the shape of the waviness, and describes one or more dimensions in the waviness shape defined by the shape function,
An interval length parameter that identifies the length of the interval in which the swell occurred;
In the section where the undulation occurs, a height parameter for identifying a separation width at a position where the fibers are most separated from a fiber arrangement at the time of design in the FRP layer,
An angular parameter for identifying an angular offset between the direction of the fiber and the fiber orientation angle at the time of design in the section where the undulation has occurred;
A stacking direction position parameter for identifying the position of the undulation of the fibers in the out-of-plane direction in which a plurality of the FRP layers are stacked;
The fracture strength evaluation method according to any one of claims 2, 4 to 10, wherein any one or more of the following is included. The plurality of candidates for the undulation pattern is a resin reservoir in which fibers are not contained in the FRP layer by opening a fiber layer in the FRP layer along an out-of-plane direction in which the plurality of FRP layers are stacked. The fracture strength evaluation method according to any one of claims 2, 4 to 11, including a first pattern corresponding to the swell formed. The waviness parameter defined for the first pattern is:
The fracture strength evaluation method according to claim 12, further comprising a resin pool dimension parameter for identifying a dimension of the resin pool formed in the FRP layer. In the plurality of candidates for the undulation pattern, the undulations of the fibers generated in the out-of-plane direction in each of the FRP layers overlap in the same direction vertically across the plurality of FRP layers, and the undulations of the fibers in each of the FRP layers The fracture strength evaluation method according to any one of claims 2, 4 to 13, wherein the generated in-plane direction position includes a second pattern that is aligned over the plurality of FRP layers.