CN112685940B - Finite element modeling method for simulating bolt collision fracture failure - Google Patents
Finite element modeling method for simulating bolt collision fracture failure Download PDFInfo
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Abstract
The invention provides a finite element modeling method for simulating bolt collision fracture failure, which comprises the following steps of: and establishing a bolt center unit by using the beam unit, arranging a bolt shell unit, giving material parameters to the bolt shell unit, wherein the bolt center unit corresponds to nodes of the bolt shell unit one by one, and rigid connection is arranged between the corresponding nodes. And establishing a nut model, dividing the outer surface of the nut model into nut shell units, and endowing the nut shell units with material parameters and nut quality. A rigid connection is established between the corresponding nodes of the bolt housing unit and the nut housing unit. The bolt housing unit and the nut housing unit are added to the contact with the external part. A preload is provided to each beam unit generated in the bolt modeling step. The beam units are given material parameters, and the corresponding failure forces and the failure moment limit values are added to the material parameters. The model established by the modeling method is used for simulating the collision response, the simulation result is more accurate, the number of times of real vehicle collision is reduced, and the development cost is saved.
Description
Technical Field
The invention relates to the field of automobiles, in particular to a finite element modeling method for simulating bolt collision fracture failure.
Background
The bolt connection is used as an important connection mode of automobile parts, and the key part bolt loading condition and whether the bolt breaks and fails in the whole automobile collision simulation model have very important influence on the simulation result. If the local loading and deformation state of the bolt can be accurately simulated in the whole vehicle collision simulation model, and whether the key connection position is broken or not can be predicted, the whole vehicle simulation precision can be greatly improved, and the development cost can be reduced.
Currently, four methods are generally used in practical application.
The first type is to make units of parts to be bolted near the bolt holes into rigid bodies, and the rigid bodies are rigidly bound and restrained by using DYNA keywords CONSTRAINED _ RIGID _ BODIES.
The second type is to directly and rigidly connect the joints around the bolt holes of the parts to be bolted through one-dimensional rigid units rigidbody.
The former two methods are simple and effective in modeling and are widely applied to whole vehicle simulation. However, the two methods neglect the influence of the bolt body during modeling, approximate the bolt connection to be rigid connection, can not reflect the preload of the bolt and the loading condition of the bolt body in the collision process, and can not predict the fracture failure risk of the bolt in the key area.
And thirdly, the bolt body is established through a three-dimensional entity unit and is connected with surrounding parts to be connected through contact. In general, the size of the entity units in the whole vehicle model is required to be not smaller than 3.5mm, and the entity units are distributed for at least 3 layers, so that the method is only suitable for large bolts with the size of at least M14, the general type is not strong, and the units with the size of 3.5mm are too thick compared with the bolts, and the precision is difficult to ensure.
The fourth type of joint around the bolt hole of the component a to be connected is coupled to form a one-dimensional rigid body unit rigidbody a, the joint around the bolt hole of the component B to be connected is coupled to form another one-dimensional rigid body unit rigidbody B, and finally rigidbody a and rigidbody B are connected through a one-dimensional deformable beam unit. The method approximates the contact relation between the screw cap, the bolt head and the parts to be connected to rigid constraint, and simulates a screw rod by using a one-dimensional beam unit. This method cannot simulate the contact relationship between the bolt structure and surrounding parts, and can only simulate and monitor the screw loading condition by means of beam.
All four methods have quite large limitations, and the loaded condition of the bolt can not be accurately simulated under the condition of meeting the precision requirement.
Disclosure of Invention
The invention aims to provide a finite element modeling method for simulating bolt collision fracture failure, which accurately simulates the preload and load conditions of bolts in a whole vehicle simulation environment, improves the simulation precision of local stress and deformation of the bolts, and can predict the fracture failure of the bolts. The model established by the modeling method is used for simulating the collision response, the simulation result is more accurate, the reliability of the whole vehicle collision simulation prediction can be improved, the times of the real vehicle collision are reduced, and the development cost is saved.
The invention provides a finite element modeling method for simulating bolt collision fracture failure, which comprises the following steps of:
Modeling a bolt model: setting points and using beam units to establish a bolt center unit, arranging a bolt shell unit on the periphery of the bolt center unit, and giving material parameters to the bolt shell unit; the bolt center units are in one-to-one correspondence with the nodes of the bolt shell units, and rigid connection is arranged between the corresponding nodes of the bolt shell units and the bolt center units.
Modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units; and, give the nut shell unit material parameter, give the nut quality to the centroid of nut model.
And connecting the bolt model and the nut model: a rigid connection is established between the corresponding nodes of the bolt housing unit and the nut housing unit.
An external contact setting step: the bolt housing unit and the nut housing unit are added to the contact with the external part so that the bolt housing unit and the nut housing unit are brought into contact with the external part mold.
The method comprises the following steps of: a preload is provided to each beam unit generated in the bolt modeling step.
Bolt failure criterion setting: and (3) giving material parameters to the beam units in the bolt modeling step, adding corresponding failure force and failure moment limit values to the material parameters, and when the load of the bolts exceeds the limit values, enabling the beam units of the bolts to fail.
By adopting the scheme, the bolt morphology is considered, the bolt contact is accurately simulated, the preload of the bolt is considered, and the failure setting is performed on the bolt through a reasonable modeling method. The model established by the modeling method is used for simulating the collision response, can accurately simulate the real loading condition of the bolt in the whole vehicle collision environment, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of the bolt connection, is beneficial to improving the reliability of the whole car collision simulation, can reduce the frequency of development tests, shortens the development period and reduces the development cost.
According to another specific embodiment of the invention, in the modeling step of the finite element modeling method for simulating the collision fracture failure of the bolt, two circle centers of a bolt head plane and a screw head plane are respectively distributed, at least one beam unit is used for connecting the two circle centers and establishing a bolt center unit, a layer of bolt shell unit is arranged on the outer surface of the bolt center unit, and each node of the bolt shell unit is connected with the corresponding node of the bolt center unit by a rigid unit; wherein the bolt center unit is defined as a threaded portion and an unthreaded portion according to a sectional diameter, respectively; and the cross-sectional diameter of the threaded portion is the diameter at the thread root, and the cross-sectional diameter of the unthreaded portion is the true diameter of the screw.
By adopting the scheme, the center of the bolt, particularly the threaded part of the center of the bolt, is the position where fracture failure is most likely to occur. The simulation accuracy can be further improved by making two sections of the cross section of the beam unit different according to the threaded and unthreaded portions.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt impact fracture failure is disclosed in an embodiment of the present invention, in a bolt preload adding step, a friction coefficient between a bolt and an external part is determined according to actual material properties of the bolt and the external part, and a mounting moment calculated according to the friction coefficient is converted into an axial force to be applied to each beam unit of a bolt center unit.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt crash fracture failure is disclosed in the embodiment of the present invention, in which, in the bolt preload adding step, after an axial force is applied to each beam unit of a bolt center unit, dynamic release is performed before an actual calculation operation starts, and a preload is stably applied to a bolt model.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in an embodiment of the present invention, in the step of connecting a bolt model with a nut model, a node of an upper portion of the bolt model beyond an upper surface of the nut model and a node of an uppermost surface of the nut model are connected by a rigid unit to rigidly connect the bolt model with the nut model.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in an embodiment of the present invention, in the step of connecting a bolt model and a nut model, a nut shell unit on an upper surface of the nut model is made into a first rigid body unit, a bolt shell unit of an upper portion of the bolt model beyond a nut portion is made into a second rigid body unit, and the first rigid body unit and the second rigid body unit are rigidly connected to rigidly connect the bolt model and the nut model.
According to another specific embodiment of the present invention, a finite element modeling method for simulating bolt impact fracture failure is disclosed in the embodiment of the present invention, and the unit dimensions of a beam unit, a bolt housing unit, a nut housing unit and a rigid unit all satisfy the conditions: the characteristic degree of the three-dimensional solid unit is not less than 3.5mm, the characteristic length of the two-dimensional shell unit is not less than 3mm, and the characteristic length of the one-dimensional unit is not less than 2mm.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, wherein MAT9 materials are given to a bolt shell unit and a nut shell unit in a bolt model modeling step and a nut model modeling step; and MAT No. 100 material is given to the beam unit generated in the bolt modeling step.
According to another embodiment of the invention, the finite element modeling method for simulating the collision fracture failure of the bolt is disclosed in the embodiment of the invention, the size of a beam unit is not smaller than 2mm, and the size of a bolt shell unit is 3mm.
According to another embodiment of the present invention, a finite element modeling method for simulating bolt impact fracture failure is disclosed in the embodiment of the present invention, in which, in the external contact setting step, when the actual nut is a weld nut, the nut model is set as a weld-simulated connection.
The beneficial effects of the invention are as follows:
According to the invention, through a reasonable modeling method, the bolt morphology is considered, the bolt contact is accurately simulated, the preload of the bolt is considered, and the failure setting is performed on the bolt. The model established by the modeling method is used for simulating the collision response, can accurately simulate the real loading condition of the bolt in the whole vehicle collision environment, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of the bolt connection, is beneficial to improving the reliability of the whole car collision simulation, can reduce the frequency of development tests, shortens the development period and reduces the development cost.
Drawings
FIG. 1 is a flow chart diagram of a finite element modeling method for simulating bolt impact fracture failure in an embodiment of the invention;
FIG. 2 is a schematic diagram of a beam unit structure of a finite element modeling method for simulating bolt impact fracture failure in an embodiment of the present invention;
FIG. 3 is a schematic structural view of a bolt housing unit for use in a finite element modeling method for simulating bolt impact fracture failure in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram of a finite element modeling method for modeling bolt impact fracture failure according to an embodiment of the present invention;
FIG. 5 is a schematic structural view of a nut-shell unit for a finite element modeling method for simulating bolt impact fracture failure in an embodiment of the present invention;
FIG. 6 is a schematic diagram of a connection between a bolt model and a nut model for a finite element modeling method for simulating bolt impact fracture failure in accordance with an embodiment of the present invention;
FIG. 7 is a schematic diagram of a connection between a bolt model and a nut model for a finite element modeling method for simulating bolt impact fracture failure in accordance with an embodiment of the present invention;
FIG. 8 is a schematic diagram of the assembled structure of a bolt model and a nut model for a finite element modeling method for simulating bolt impact fracture failure in an embodiment of the present invention;
fig. 9 is an exploded structural schematic diagram of a bolt model and a nut model for a finite element modeling method for simulating bolt impact fracture failure in an embodiment of the present invention.
Reference numerals illustrate:
a: a moving direction of the first external part model;
b: a moving direction of the second exterior part model;
1: a bolt model;
2: a nut model;
3: a first external component model;
4: and a second exterior part model.
Detailed Description
Further advantages and effects of the present invention will become apparent to those skilled in the art from the disclosure of the present specification, by describing the embodiments of the present invention with specific examples. While the description of the invention will be described in connection with the preferred embodiments, it is not intended to limit the inventive features to the implementation. Rather, the purpose of the invention described in connection with the embodiments is to cover other alternatives or modifications, which may be extended by the claims based on the invention. The following description contains many specific details for the purpose of providing a thorough understanding of the present invention. The invention may be practiced without these specific details. Furthermore, some specific details are omitted from the description in order to avoid obscuring the invention. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
It should be noted that in this specification, like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
In the description of the present embodiment, it should be noted that the azimuth or positional relationship indicated by the terms "upper", "lower", "inner", "bottom", etc. are based on the azimuth or positional relationship shown in the drawings, or the azimuth or positional relationship in which the inventive product is conventionally put in use, are merely for convenience of describing the present invention and simplifying the description, and are not indicative or implying that the apparatus or element to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and therefore should not be construed as limiting the present invention.
The terms "first," "second," and the like are used merely to distinguish between descriptions and are not to be construed as indicating or implying relative importance.
In the description of the present embodiment, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present embodiment can be understood in a specific case by those of ordinary skill in the art.
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
Examples
A finite element modeling method for simulating bolt collision fracture failure is provided, analysis software is LS-dyan, as shown in figure 1, and the method comprises the following steps:
Modeling a bolt model: setting up and using a BEAM unit (the BEAM unit is shown as BEAM in analysis software LS-dyan) as shown in FIG. 2 to establish a bolt center unit, arranging a bolt shell unit as shown in FIG. 3 on the periphery of the bolt center unit, and giving material parameters to the bolt shell unit; wherein the bolt center units are in one-to-one correspondence with the nodes of the bolt shell units, and rigid connection is arranged between the corresponding nodes of the bolt shell units and the bolt center units, so that the bolt model shown in fig. 4 is obtained.
Specifically, in the step of modeling the bolt model, the bolt model is the most important part of the whole bolting connection modeling, and the contact and load conditions have very important influence on deformation and failure of the bolt model. The bolt model modeling should first connect the two points with several beam units in the center of both ends of the bolt model, i.e. the two centers of the bolt model head plane and the bolt model head plane. And a bolt shell unit is arranged on the periphery of the bolt center unit and used for simulating the basic shape of the bolt model.
It should be noted that along the length of the bolt pattern, the grid nodes of each layer of bolt housing units should correspond one-to-one to each node of the beam units.
Further, each layer of nodes on the outer surface of the bolt model is connected with the corresponding beam unit node through a one-dimensional rigid unit (the rigid unit is shown as Rigidbody in analysis software LS-dyan). The bolt shell unit on the outer surface is a null unit, MAT9 material is endowed, and the main function is to bear all contact between the bolt and the outside, and rigidity and strength are not provided.
The bolt pattern is in contact with other peripheral components through the outer surface shell element, and the load is transferred to the connected beam units through the central rigid unit (rigidbody), and the beam units bear various loads.
Modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units as shown in fig. 5; and, give the nut shell unit material parameter, give the nut quality to the centroid of nut model.
In particular, the nut is generally not prone to breakage, where only the shell elements need to be divided against the outer surface of the nut pattern. The operation method in the analysis software LS-dyan is that the nut shell unit on the outer surface of the nut model is also a null unit, the material parameter is MAT9 material, and the operation method mainly plays a role in bearing all contact between the nut and the outside. Notably, the nut centroid needs to be imparted to the quality of the real nut to ensure its real dynamics.
And connecting the bolt model and the nut model: a rigid connection is established between the corresponding nodes of the bolt housing unit and the nut housing unit, resulting in a model as shown in fig. 6 and 7.
An external contact setting step: the bolt housing unit and the nut housing unit are added to the contact of the external part so that the bolt housing unit and the nut housing unit are brought into contact with the external part mold.
The concrete operation method is that all the shell units are made into a set, and the set is added into the whole vehicle contact, so that the contact of the bolt model and the nut model with other parts is completed.
The method comprises the following steps of: a preload is provided to each beam unit generated in the bolt modeling step.
Bolt failure criterion setting: and (3) giving material parameters to the beam units in the bolt modeling step, adding corresponding failure force and failure moment limit values to the material parameters, and when the load of the bolts exceeds the limit values, enabling the beam units of the bolts to fail.
Specifically, the beam unit generated in the bolt model modeling step imparts material parameters to the main loaded portion of the bolt. For example, the operation method in the analysis software LS-dyan is to give MAT100 material, the parameters NRR/MRR in MAT100 material represent the axial tension/torsion moment limit which the bolt can bear, the parameters NRS/MSS and NRT/MTT represent the transverse shearing force/bending moment limit which the bolt can bear, the loading limit of the bolt is obtained by a table look-up or bolt bearing test method, and the corresponding failure force and failure moment limit are added in the material control card. When simulating calculations, if the bolt is loaded beyond the above limits, the bolt beam unit will be disabled.
As shown in fig. 8 and 9, the first exterior part model 3 and the second exterior part model 4 in fig. 8 are in contact with the bolt model, and one end of the bolt model 1 is connected with the nut model 2. The one-dimensional unit of the present invention is used to transmit forces and moments as evaluated in terms of contact. The two-dimensional shell element is used to simulate the actual contact of the bolts. The one-dimensional and two-dimensional units are connected through a rigid unit (rigidbody) so as to directly transfer the force and moment generated by contact to the one-dimensional unit of the main loaded unit. The external load sensitivity is evaluated, most of fracture failure of bolts in the collision process is shear fracture, and after the modeling of the invention is completed, the first external part model 3 and the second external part model 4 are connected if the bolt model 1 is connected in the whole vehicle collision process. The first exterior part mold 3 moves toward the a direction and the second exterior part mold 4 moves toward the b direction, and the first exterior part mold 3 and the second exterior part mold 4 are in contact with the bolt mold 1, where the shearing force generated on the bolts by the contact between the real bolts and the peripheral parts can be accurately simulated. In the invention, the bolt model 1 is divided into a plurality of layers from the aspect of fracture positions, and a plurality of one-dimensional units simulate different positions of the bolts, so that the actual fracture positions can be observed in actual simulation. Due to the simple two sheet metal models to which the bolt model 1 can be connected, several different component models can also be connected. After the bolt breaks under the complex connection environment, the accurate simulation of the breaking position of the bolt can provide a good guide for solving the actual engineering problem.
By adopting the scheme, the bolt morphology is considered, the bolt contact is accurately simulated, the preload of the bolt is considered, and the failure setting is performed on the bolt through a reasonable modeling method. The model established by the modeling method is used for simulating the collision response, can accurately simulate the real loading condition of the bolt in the whole vehicle collision environment, and can accurately simulate fracture failure after exceeding the allowable range. The invention improves the simulation precision of the bolt connection, is beneficial to improving the reliability of the whole car collision simulation, can reduce the frequency of development tests, shortens the development period and reduces the development cost.
According to another specific embodiment of the invention, in the modeling step of the finite element modeling method for simulating the collision fracture failure of the bolt, two circle centers of a bolt head plane and a screw head plane are respectively distributed, at least one beam unit is used for connecting the two circle centers and establishing a bolt center unit, a layer of bolt shell unit is arranged on the outer surface of the bolt center unit, and each node of the bolt shell unit is connected with the corresponding node of the bolt center unit by a rigid unit; wherein the bolt center unit is defined as a threaded portion and an unthreaded portion according to a sectional diameter, respectively; and the cross-sectional diameter of the threaded portion is the diameter at the thread root, and the cross-sectional diameter of the unthreaded portion is the true diameter of the screw.
Specifically, the center of the bolt, and particularly the threaded portion of the center of the bolt, is the location where fracture failure is most likely to occur. The cross-sectional definition of the beam element requires two-section distinction according to threaded and unthreaded portions. The threaded portion of the beam element cross-section diameter should be the minor diameter of the thread, i.e., the diameter at the root of the thread, and the unthreaded portion should be the true diameter of the screw.
It should be understood that at least one beam unit means that the more beam units the better the simulation effect, the more the beam units, and the number of beam units can be selected by those skilled in the art according to the design requirements.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt impact fracture failure is disclosed in an embodiment of the present invention, in a bolt preload adding step, a friction coefficient between a bolt and an external part is determined according to actual material properties of the bolt and the external part, and a mounting moment calculated according to the friction coefficient is converted into an axial force to be applied to each beam unit of a bolt center unit.
In particular, in practical cases, the bolts are usually mounted with a corresponding mounting moment. The method of operation in the analysis software LS-dyan is that, depending on the different friction coefficients of the bolt mounting surface, a moment-to-AXIAL FORCE should be applied to each BEAM unit generated in the bolt model modeling step by an initial_axis_force_beam key.
Further, in the bolt preload adding step, after the axial force is applied to each beam unit of the bolt center unit, dynamic release is performed before the actual calculation operation starts, and the preload is stably applied to the bolt model.
That is, the operation method in the analysis software LS-dyan is that, after the addition of the preload is completed, the control_dynamic_ RELAXATION key is added before the actual calculation condition starts to dynamically release, and the preload is stably applied to the bolt model.
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in an embodiment of the present invention, in the step of connecting a bolt model with a nut model, a node of an upper portion of the bolt model beyond an upper surface of the nut model and a node of an uppermost surface of the nut model are connected by a rigid unit to rigidly connect the bolt model with the nut model.
In particular, the threaded portion of the bolt beyond the height of the nut is generally considered not loaded, where the model can be simplified to handle the load on the entire bolt model. The connection between the bolt model and the nut model can be specifically realized by connecting a node of the upper part of the bolt model exceeding the upper surface of the nut model with a node of the uppermost surface of the nut model through a rigid unit (rigidbody).
According to another embodiment of the present invention, a finite element modeling method for simulating a bolt collision fracture failure is disclosed in an embodiment of the present invention, in the step of connecting a bolt model and a nut model, a nut shell unit on an upper surface of the nut model is made into a first rigid body unit, a bolt shell unit of an upper portion of the bolt model beyond a nut portion is made into a second rigid body unit, and the first rigid body unit and the second rigid body unit are rigidly connected to rigidly connect the bolt model and the nut model.
In particular, the threaded portion of the bolt beyond the height of the nut is generally considered to be unloaded, where the model process can be simplified and the entire bolt model is not affected by loading. The operation method in the analysis software LS-dyan is that the nut shell unit on the upper surface of the nut model is made into one rigid body, the bolt shell unit on the upper part of the bolt model, which exceeds the nut model part, is made into the other rigid body, and the two rigid bodies are rigidly connected through the keyword CONSTRAINED _ RIGID _ BODIES.
According to another specific embodiment of the present invention, a finite element modeling method for simulating bolt impact fracture failure is disclosed in the embodiment of the present invention, and the unit dimensions of a beam unit, a bolt housing unit, a nut housing unit and a rigid unit all satisfy the conditions: the characteristic degree of the three-dimensional solid unit is not less than 3.5mm, the characteristic length of the two-dimensional shell unit is not less than 3mm, and the characteristic length of the one-dimensional unit is not less than 2mm.
Specifically, the cell size is a very important factor affecting the crash simulation modeling, and the following mainly describes the impact of the cell size on the crash simulation of the whole vehicle, thereby also affecting the bolt modeling manner. In order to fully express the conditions of bolt morphology, preload, contact and the like, if full solid grid modeling is adopted, relatively fine characteristics such as threaded screws and the like are involved, so that a plurality of fine grids are generated. According to the foregoing, too small a unit in the prior art will cause additional mass increase, affecting the model simulation accuracy.
In the existing whole car collision simulation process, the number of units in the finite element simulation model is far more than one million because of the whole car, and the parts are numerous. Collision simulation typically employs a central difference algorithm, so that there is a definition of the time step when the model is calculated. The smaller the time step, the more accurate the algorithm, the more stable the model, and the higher the accuracy, however, the total calculation time will also increase correspondingly, and the development period will need to be prolonged correspondingly.
Typically, the calculation time steps are taken in the general model to be 5E-4ms to 7E-4ms each for the calculation accuracy and the calculation total time length. The calculation time step is proportional to the cell size and inversely proportional to the material density. When the cell size is too small to meet the time step requirement, the computer will make its time step meet the calculation requirement by amplifying the material density of the cell.
Density amplification means an increase in mass which in dynamics means an increase in energy. The unreasonable energy increase and mass change can change the motion gesture and stress condition of parts, thereby directly causing the distortion of the whole car collision simulation result.
Therefore, all units in the whole vehicle model have reasonable unit sizes. The definition of corresponding whole vehicle time step is that the preferable unit size requirements are that the three-dimensional entity unit feature degree is not less than 3.5mm, the two-dimensional shell unit feature length is not less than 3mm, and the one-dimensional unit feature length is not less than 2mm. In addition, most models of connecting bolts for passenger cars are generally between M8 and M16, namely, the large diameter of threads is 8mm to 16mm, and the connecting bolts can be selected by a person skilled in the art according to actual needs.
According to another specific embodiment of the invention, the embodiment of the invention discloses a finite element modeling method for simulating bolt collision fracture failure, wherein MAT9 materials are given to a bolt shell unit and a nut shell unit in a bolt model modeling step and a nut model modeling step; and, a MAT No. 100 material is given to the beam unit generated in the bolt modeling step.
Specifically, the MAT9 material is endowed, and the main function is to bear all contact with the outside, and the rigidity and the strength are not provided. In MAT100 material, the parameters NRR/MRR represent axial tension/torsion moment limits which can be born by bolts, and the parameters NRS/MSS and NRT/MTT represent transverse shearing force/bending moment limits which can be born by bolts.
According to another embodiment of the invention, the finite element modeling method for simulating the collision fracture failure of the bolt is disclosed in the embodiment of the invention, the size of a beam unit is not smaller than 2mm, and the size of a bolt shell unit is 3mm.
And establishing a bolt center unit by using a beam unit, arranging a bolt shell unit on the periphery of the bolt center unit, giving material parameters, enabling the bolt center unit to correspond to nodes of the bolt shell unit one by one, and arranging rigid connection between the corresponding nodes.
According to another embodiment of the present invention, a finite element modeling method for simulating bolt impact fracture failure is disclosed in the embodiment of the present invention, in which, in the external contact setting step, when the actual nut is a weld nut, the nut model is set as a weld-simulated connection.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a further detailed description of the invention with reference to specific embodiments, and it is not intended to limit the practice of the invention to those descriptions. Various changes in form and detail may be made therein by those skilled in the art, including a few simple inferences or alternatives, without departing from the spirit and scope of the present invention.
Claims (10)
1. A finite element modeling method for simulating bolt impact fracture failure, comprising the steps of:
modeling a bolt model: setting points and using a beam unit to establish a bolt center unit, arranging a bolt shell unit on the periphery of the bolt center unit, and giving material parameters to the bolt shell unit; the bolt center units are in one-to-one correspondence with the nodes of the bolt shell units, and rigid connection is arranged between the corresponding nodes of the bolt shell units and the bolt center units;
modeling a nut model: establishing a nut model, and dividing the outer surface of the nut model into nut shell units; and material parameters are given to the nut shell unit, and nut quality is given to the centroid of the nut model;
And connecting the bolt model and the nut model: establishing a rigid connection between corresponding nodes of the bolt shell unit and the nut shell unit;
An external contact setting step: adding the bolt housing unit and the nut housing unit to contact with an external part to bring the bolt housing unit and the nut housing unit into contact with an external part model;
the method comprises the following steps of: providing a preload on each of the beam units generated in the bolt modeling step;
bolt failure criterion setting: and (3) endowing the beam unit in the bolt modeling step with material parameters, and adding corresponding failure force and failure moment limit values to the material parameters.
2. The finite element modeling method for simulating bolt impact fracture failure according to claim 1, wherein,
In the bolt modeling step, two circle centers of a bolt head plane and a screw head plane are respectively distributed, at least one beam unit is used for connecting the two circle centers and establishing a bolt center unit, a layer of bolt shell unit is arranged on the outer surface of the bolt center unit, and each node of the bolt shell unit is connected with a corresponding node of the bolt center unit through a rigid unit; wherein the method comprises the steps of
The bolt center unit is respectively defined into a threaded part and a non-threaded part according to the section diameter; and
The cross-sectional diameter of the threaded portion is the diameter at the thread root and the cross-sectional diameter of the unthreaded portion is the true diameter of the screw.
3. The finite element modeling method for simulating a bolt impact fracture failure according to claim 2, wherein in the bolt preload adding step, a friction coefficient between a bolt and the external part is determined based on actual material properties of the bolt and the external part, and a mounting moment calculated based on the friction coefficient is converted into an axial force to be applied to each of the beam units of the bolt center unit.
4. A finite element modeling method for simulating a bolt impact fracture failure according to claim 3, wherein in the bolt preload adding step, after the axial force is applied to each of the beam units of the bolt center unit, dynamic release is performed before actual calculation starts, and preload is stably applied to the bolt model.
5. A finite element modeling method for simulating a bolt impact fracture failure according to claim 3, wherein in the step of connecting the bolt model with the nut model, a node of an upper portion of the bolt model beyond an upper surface of the nut model and a node of an uppermost surface of the nut model are connected by a rigid unit to rigidly connect the bolt model with the nut model.
6. A finite element modeling method for simulating a bolt collision fracture failure according to claim 3, wherein in the step of connecting the bolt model and the nut model, the nut shell unit on the upper surface of the nut model is made into a first rigid body unit, the bolt shell unit on the upper portion of the bolt model which exceeds the nut portion is made into a second rigid body unit, and the first rigid body unit and the second rigid body unit are rigidly connected to rigidly connect the bolt model and the nut model.
7. The finite element modeling method for simulating bolt impact fracture failure according to any one of claims 2-6, wherein cell sizes of the beam cell, the bolt housing cell, the nut housing cell, and the rigid cell all satisfy a condition:
The characteristic degree of the three-dimensional solid unit is not less than 3.5mm, the characteristic length of the two-dimensional shell unit is not less than 3mm, and the characteristic length of the one-dimensional unit is not less than 2mm.
8. The finite element modeling method for simulating a bolt impact fracture failure according to claim 7, wherein in the bolt model modeling step and the nut model modeling step, math No. 9 material is given to the bolt housing unit and the nut housing unit; and
And (3) giving MAT No. 100 material to the beam unit generated in the bolt modeling step.
9. The finite element modeling method for simulating a bolt impact fracture failure according to claim 8, wherein the size of the beam unit is not less than 2mm, and the size of the bolt housing unit is 3mm.
10. The finite element modeling method for simulating bolt impact fracture failure according to claim 9, wherein in the external contact setting step, when the actual nut is a weld nut, the nut model is set as a weld simulated connection.
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| CN111400948A (en) * | 2020-03-16 | 2020-07-10 | 中国航天空气动力技术研究院 | Finite element calculation method for stress borne by stress release bolt |
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