JP3668837B2 - Strength analysis method for products made by vibration welding resin molded products reinforced with fibers - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a strength analysis method for resin products obtained by vibration welding of resin molded products reinforced with fibers such as glass fibers.
[0002]
[Prior art]
With the progress of resins used for resin molded products, molding technology, reinforcing fibers, and technologies for welding resin molded products together, the application range of resin products is expanding. For example, an engine intake pipe can be a resin product.
As the application range of resin products expands, the need to analyze the strength of resin products is increasing. For example, when the engine intake pipe is made of a resin product, it is required to analyze in advance whether the resin intake pipe can withstand even if backfire occurs.
The usefulness of the finite element method for strength analysis of structures has already been widely verified. However, even if the finite element method is applied to resin products in which resin molded products reinforced with fibers are vibration-welded, only a calculation result that is far from the actual measurement value is obtained, which is almost unreliable. At the present time, there is no method that can analyze the strength of resin products obtained by vibration welding of resin molded products reinforced with fibers, and relies solely on actual measurement.
[0003]
[Problems to be solved by the invention]
Therefore, the present invention proposes a method capable of analyzing the strength of resin products obtained by vibration welding of resin molded products reinforced with fibers to a reliable level.
For this purpose, the present inventors studied current problems. As a result, it was confirmed that there are the following reasons why reliable results cannot be obtained.
(1) When analyzing whether a resin product can withstand, it cannot be assumed that the material is deformed within the elastic range. That is, it must be premised that the “stress-strain” relationship of the material is non-linear. At the current level, if the “stress-strain” relationship is allowed to be non-linear, it must be assumed that the material is isotropic. In other words, a finite element method in which the material is anisotropic and the “stress-strain” relationship is non-linear has not been put into practical use. Thus, the strength of the resin molded product reinforced with fibers cannot be analyzed to a reliable level.
(2) Applying the “resin flow and fiber orientation” model to resin molded products, calculating the distribution within the resin molded product in the fiber main orientation direction, and molding the resin with Young's modulus in the fiber main orientation direction and the direction perpendicular thereto It is possible to calculate the internal distribution. Using this result, it seems that the anisotropy of the resin molded product can be easily realized in the model. However, the value that can be calculated by the “resin flow and fiber orientation” model is Young's modulus, and this cannot cope with the nonlinear relationship of “stress-strain”.
(3) If resin molded products reinforced with fibers are vibration welded together, the fiber main orientation direction is expected to change at the welded portion, but at present, calculations that incorporate this problem cannot be made.
The present inventors proceeded with research based on the above awareness of the problem, and finally came to obtain an analysis method capable of obtaining a reliable analysis result.
[0004]
[Means, actions and effects for solving problems]
In the method of the present invention, as shown in FIG. 1, the following steps are executed.
S1: Using the test piece 4 of the resin molded product reinforced with the fiber 2, the measured stress diagram information 6 of “stress-strain” is obtained for each of the representative angles θ1, θ2,.
S2: The “resin flow and fiber orientation” model is applied to each resin molded product 8 to calculate the distribution in the resin molded product 8 in the fiber main orientation direction 10, and the Young's modulus in the fiber main orientation direction 10 and the direction perpendicular thereto. The distribution in the resin molded product 8 of E1 and E2 is calculated. Usually, the resin molded product 8 is partitioned into a fine lattice shape, and Young's modulus E1, E2 is calculated for each partition.
S3: From the Young's moduli E1 and E2 obtained in the Young's modulus distribution calculation step S2 and the measured diagram information 6 of “stress-strain” obtained for each representative angle, “ Estimated diagram information 12 and 14 of “stress-strain” is obtained. In this step, estimated diagram information 12 and 14 is obtained for each section for which the Young's modulus is calculated.
S4: Measured diagram information 18 and 20 of “stress-strain” at the vibration weld 16 is obtained.
S5: Since a model related to the material of the resin product is obtained as described above, external force information applied to the resin product 22, diagram information of “stress-strain” estimated for each part in the resin molded product in step S3, The finite element method is executed using the measured diagram information of “stress-strain” at the vibration welded part 16 obtained in step S4.
As a result of the actual measurement, the diagram information 20 and 18 of the “stress-strain” in the vibration direction and the direction orthogonal to the vibration direction in the vibration welded portion are the “stress in the fiber main orientation direction measured in step S1 and the direction orthogonal thereto. Since it was confirmed that it was approximated to the measured line information of “distortion”, this approximation can also be utilized. A method using this approximation is described in claim 2. In the invention of claim 2, the main fiber orientation direction at the vibration welded portion is estimated as the direction along the vibration. For this reason, in the method of claim 2, in step S <b> 1, actual measurement diagram information of “stress-strain” is obtained at a representative angle including the main fiber orientation direction and the direction orthogonal thereto. In step S3, the “stress-strain” diagram at the vibration welded portion is obtained from the fiber main orientation direction estimated as described above and the “stress-strain” measured diagram information 6 measured in step 1. get information. For other parts, “stress-strain” diagram information is estimated by the same method as in the method of claim 1.
[0005]
According to these methods, (1) in the resin molded product, the fibers are oriented in a specific direction and are not oriented in the same direction. (2) Therefore, the material constituting the resin molded product is not isotropic. It must be treated as an anisotropic material, (3) The material constituting the resin molded product is deformed beyond the elastic limit, and it cannot be approximated unless the "stress-strain" relationship is treated as non-linear, (4) In the welded part, it was possible to perform an analysis that included everything that must be handled separately from other parts of the resin molded product, and a reliable analysis result could be obtained for the first time.
[0006]
This method was applied to a plastic intake pipe, and the case where a hydrostatic pressure was applied to the inside of the intake pipe was analyzed. Here, it has been confirmed that when the finite element method is repeatedly executed while increasing the hydrostatic pressure, the stress value calculated by the finite element method does not increase even if the hydrostatic pressure is increased. The hydrostatic pressure at this time can be the pressure resistance of the intake pipe.
[0007]
According to the above method, when the plastic air pipe begins to deform greatly as the hydrostatic pressure increases (starting to deform greatly corresponds to reaching the use limit of the resin air intake pipe, The hydrostatic pressure (corresponding to the fact that the stress does not increase above) is calculated. When this was compared with the actual measurement value, the actual measurement value and the calculated value agreed with an error within 10%.
Without greatly changing the shape of the resin intake pipe, it is possible to increase the pressure resistance by about 10%, for example, by adding a reinforcing rib. Therefore, if the pressure resistance calculated by this method can satisfy the requirements, the analysis can be relied upon to start making a mold for the resin intake pipe. If the error is within 10%, the mold can be corrected even in the worst case, and the mold is not wasted.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the main features of the embodiments described below are listed.
(Embodiment 1) A test piece is obtained by injecting a resin mixed with fibers into a thin plate-like right-sided quadrilateral cavity from gates arranged at the left and right target positions to obtain measured stress-strain diagram information. create. According to this test piece, it is possible to easily obtain actual measurement diagram information of “stress-strain” for each angle with respect to the main fiber orientation direction.
(Mode 2) A micro-strain gauge is attached to the side surface of the vibration welded portion to obtain measured diagram information of “stress-strain” at the vibration welded portion. According to this method, it is possible to obtain actual measurement diagram information of “stress-strain” at an extremely thin welded portion, usually about 200 microns.
(Mode 3) In the analysis method according to claim 2, the portion where the stress value becomes the maximum stress value that does not increase any more is displayed. According to this, the part that is the upper limit of the pressure resistance, that is, the part that needs improvement is immediately identified.
[0009]
【Example】
Next, examples will be described.
[0010]
(Analyzed resin products)
The analyzed resin product is an intake pipe made by vibration welding resin molded products reinforced with fibers. FIG. 2 shows a mesh model of a resin intake pipe used in the finite element method. In the figure, reference numeral 30 denotes a welded portion between the resin molded products. Details of the resin of the resin molded product, the reinforcing fiber, and the welding technique are described in JP-A-10-274115.
[0011]
(Test piece of resin molded product reinforced with fiber)
A test piece was prepared by injecting a resin mixed with fibers into a 3 mm thick square cavity. The material and molding conditions are the same as those when molding the intake pipe. As shown in FIG. 3, the gate position and the gate direction are symmetrical, and the fibers 32 are mainly oriented in the vertical direction in FIG. 3 at the center of the test piece.
[0012]
(Measurement of “stress-strain” diagram information for each representative angle with respect to the fiber orientation direction)
As shown in FIG. 4, a test piece 44 for a uniaxial tensile test was cut out while changing the angle of the test piece with respect to the left-right symmetric axis 42. Four test pieces shown in (B) to (E) were obtained. The main fiber orientation directions in the test pieces are different. Here, 0 degrees, 30 degrees, 60 degrees, and 90 degrees were adopted as representative angles with respect to the fiber main orientation direction.
This test piece was set in a uniaxial tensile tester, and the “stress-strain” diagram information was actually measured. The obtained actual measurement diagram is shown in FIG. The vertical axis represents stress (MPa) and the horizontal axis represents strain (%). As expected, it was confirmed that the fiber was not easily distorted in the main fiber orientation direction and was easily distorted in the perpendicular direction.
[0013]
(Application of resin flow and fiber orientation model)
Software that models resin flow and fiber orientation is commercially available, and software called “MOLDFLOW” was used here. In addition, various kinds of software such as “C-MOLD” and “PLANETS” that are widely used in this field have this calculation function. There are no particular restrictions on the type of software used.
With these software, the main orientation direction and orientation ratio of the fiber are calculated for each minute region obtained by finely dividing the resin molded product shown in FIG. 6A and 6C show the calculation results at two locations in the resin molded product, and θA and θC indicate the fiber main orientation directions. The f-axis in the figure indicates the orientation rate, and the larger the value, the better the orientation. (B) and (D) show photographs of the calculated locations, and confirm that reliable values are calculated in both the main orientation direction and the orientation ratio.
[0014]
Each of the software described above has a function of further calculating the Young's modulus in the fiber main orientation direction and the direction orthogonal thereto, from the calculation results of the fiber main orientation direction and the orientation rate exemplified in FIG. . By this function, the Young's modulus distribution in the resin molded product in the fiber main orientation direction and the direction orthogonal thereto is calculated.
[0015]
("Stress-strain" is estimated from the Young's modulus and the measured diagram information of "stress-strain")
As described above, the distribution of the Young's modulus in the resin molded product in the fiber main orientation direction and the direction orthogonal thereto can be calculated by software modeling the resin flow and fiber orientation. However, in order to analyze the strength of a resin product by the finite element method, a reliable result cannot be obtained if it is assumed that the material is deformed within the elastic limit. In order to obtain reliable analysis results, the case where the material deforms beyond the elastic limit must be taken into account.
The broken line in FIG. 7 is actual measurement diagram information of “stress-strain” shown in FIG. A straight line 72 is a diagram when the Young's modulus is valid regardless of the degree of distortion. Obviously, the diagram 72 cannot be adopted. Here, even if the strain has a large Young's modulus in a small range, a “stress-strain” diagram of a material having a Young's modulus of E is estimated with reference to an actual measurement diagram that approaches the horizontal when the strain increases.
As shown in FIG. 8, the simplest estimation method is to obtain two Young's moduli Eθ1 and Eθ2 from an actual measurement diagram (broken line) sandwiching the calculated Young's modulus E, and both of the calculated Young's moduli E Eθ1 and Eθ2 The ratio (a: b) of the proportional distribution with respect to is obtained, and an estimated diagram (solid line) is obtained between the two actually measured diagrams with the obtained distribution ratio. An estimated diagram can be obtained using various other mathematical techniques. The present invention is not tied to a specific estimation method.
[0016]
As described above, the fiber main orientation direction, the Young's modulus in that direction, and the Young's modulus in the direction perpendicular to the direction are calculated for each minute region in which the resin molded product is finely divided in three dimensions. By using this estimation method, it is possible to calculate an estimated diagram of “stress-strain” in the main fiber orientation direction and the direction orthogonal thereto for each minute region in which the resin molded product is finely divided in three dimensions. Suppose that the Z axis is taken in the fiber main orientation direction. Then, the Z-axis azimuth is calculated for each minute region in which the resin molded product is finely divided in three dimensions. Also, the Young's modulus in the Z-axis direction is calculated. Furthermore, the Young's modulus in the X-axis and Y-axis directions orthogonal to the Z-axis is also calculated. Here, it can be assumed that the X-axis and Y-axis directions are isotropic.
[0017]
(Measured diagram information of “stress-strain” at the vibration weld)
9A shows a state in which the resin molded product 91 is vibrated and welded to the resin molded product 92 by applying pressure in the vertical direction while vibrating the resin molded product 91 in the horizontal direction. FIG. 9B shows the welded portion 93 in an enlarged manner, and it has been found that the welded portion 93 has a thickness of about 200 microns, and the reinforcing fiber has a vibration direction in the entire welded portion 93. It was confirmed to reorientate strongly. Apparently, it is different from the main orientation direction in the resin molded product outside the welded portion. Therefore, it is expected that the relationship between the stress and strain at the welded portion 93 is greatly different from other portions.
Therefore, a sample including the welded portion 93 was cut out and a minute strain gauge 94 was attached to the welded portion. The micro gauge 94 used is KFR-015-120-D19-23N10C2 manufactured by Kyowa Denki, and the length is 150 microns. The pasting work was carried out while observing with a microscope manufactured by Keyence Co., Ltd., and could be pasted in the welded portion 93. This sample was subjected to a uniaxial tensile tester to obtain a stress and strain diagram.
[0018]
The resulting diagram 100 is shown in FIG. In FIG. 10, the diagrams at θ = 90 degrees in FIG. 5 are superimposed and displayed. From this measurement, it was confirmed that when the welded portion 93 was pulled in the direction orthogonal to the vibration, the line drawing was almost the same as that pulled in the direction orthogonal to the fiber main orientation direction, and was slightly distorted.
It has also been found that the “stress-strain” diagram along the vibration direction of the welded portion 93 can be estimated from FIG. 10 to be almost the same diagram as when pulled along the fiber main orientation direction. Therefore, in this example, the “stress-strain” diagram along the vibration direction of the welded portion 93 is the same diagram as that when pulling along the fiber main orientation direction. Reflecting that the graph 100 is slightly more distorted than the graph at θ = 90 degrees, the “stress-strain” diagram in the direction along the vibration direction of the welded portion 93 is θ = 0 degrees in FIG. It may be approximated to a graph that is slightly less distorted than the graph in FIG. Alternatively, a “stress-strain” diagram may be measured along the vibration direction at the welded portion 93.
At the weld, the “stress-strain” diagram measured in the direction orthogonal to the vibration or the “stress-strain” diagram measured by pulling perpendicular to the fiber main orientation direction is applied isotropically. You may assume that. In the welded portion, bending due to bending is often the main factor causing fracture, so the anisotropy is not expected to have a significant effect.
[0019]
As described above, a “stress-strain” diagram for each part of the resin product obtained by vibration welding the resin molded products reinforced with fibers was obtained. Then, the finite element method was executed next. Here, software of a finite element method called “ABAQUS” was used. In addition, “NASTRAN” can be used, and the finite element method software to be used is not particularly limited. Here, as an external force applied to the resin product, a hydrostatic pressure is applied to the hollow resin product from the inside. Each micro area was calculated as distorted according to the “stress-strain” diagram information estimated for each part in the resin molded product and the “stress-strain” measured diagram information at the vibration weld.
In the execution stage of the finite element method, the finite element method was repeatedly executed while increasing the hydrostatic pressure. In FIG. 11, the horizontal axis represents the hydrostatic pressure, and the vertical axis represents the maximum stress appearing on the resin product. Apparently, the maximum principal stress was saturated when the hydrostatic pressure was P, and the result did not increase any more.
This indicates that when the hydrostatic pressure exceeds P, the resin product suddenly begins to deform greatly, and as a result, the maximum stress is saturated and does not increase any more. Therefore, the hydrostatic pressure at this time was taken as the pressure resistance.
[0020]
When the breakdown voltage calculated in this way was compared with the actual measurement value, the average of the actual measurement value was 1.0 MPa, whereas the calculated value was 1.1 MPa, and the difference was 10%.
Further, when comparing the greatly distorted part, the calculated part and the actually distorted part agreed well. It was confirmed that a calculation that closely approximates the actual phenomenon can be performed by the method of this embodiment.
[0021]
When the finite element method is executed with the conventional concept of isotropicity, the calculated withstand voltage differs by 59% from the actual measurement value, and cannot be trusted at all. On the other hand, in the method of this embodiment, the error is suppressed to 10%, and this can be reliable.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram schematically showing the method of the present invention.
FIG. 2 is a diagram showing a mesh model used in the finite element method.
FIG. 3 is a view for explaining a method for forming a test piece.
FIG. 4 is a diagram showing a state in which a tensile test sample is adjusted from a test piece.
FIG. 5 is a stress-strain diagram obtained by actually measuring the sample of FIG. 4. FIG. 6 is a diagram showing the calculated fiber main orientation direction, orientation ratio, and actual orientation.
FIG. 7 is a diagram showing an actually measured stress-strain diagram and an estimated stress-strain diagram.
FIG. 8 is a diagram showing a process of obtaining a stress-strain diagram estimated from an actually measured stress-strain diagram.
FIG. 9 is a view for explaining characteristics of a vibration welded portion.
FIG. 10 is a stress-strain diagram measured at the vibration weld.
FIG. 11 is a diagram showing the relationship between the maximum stress calculated by the finite element method and the applied hydrostatic pressure.
[Explanation of symbols]
S1: A process of obtaining measured stress diagram information 6 of “stress-strain” using a test piece 4 of a resin molded product reinforced with fibers 2.
S2: Applying the “resin flow and fiber orientation” model to each resin molded product 8 to calculate the distribution in the resin molded product 8 in the fiber main orientation direction 10, and the Young's modulus in the fiber main orientation direction 10 and the direction perpendicular thereto A step of calculating the distribution in the resin molded product 8 of E1 and E2.
S3: From the Young's moduli E1 and E2 obtained in the Young's modulus distribution calculation step S2 and the measured diagram information 6 of “stress-strain” obtained for each representative angle, “ Step of obtaining estimated diagram information 12 and 14 of “stress-strain”.
S4: A step of obtaining actually measured diagram information 18 and 20 of “stress-strain” at the vibration welding portion 16.
S5: Finite element using external force information applied to resin product 22, "stress-strain" diagram information estimated in step S3, and "stress-strain" measured diagram information obtained in step S4 The process of performing the law.

Claims (3)

It is a strength analysis method for resin products in which resin molded products reinforced with fibers are vibration welded together.
Using a test piece of a resin-molded product reinforced with fibers to obtain measured diagram information of "stress-strain" for each representative angle with respect to the main fiber orientation direction,
Applying the "resin flow and fiber orientation" model to each resin molded product, calculating the distribution in the resin molded product in the fiber main orientation direction, and in the resin molded product of Young's modulus in the fiber main orientation direction and the direction perpendicular to it. Calculating the distribution,
Based on the Young's modulus obtained in the Young's modulus distribution calculation step and the measured diagram information of “stress-strain” obtained for each of the representative angles, “stress-strain” for each part in the resin molded product. Obtaining estimated diagram information of
A process for obtaining information on the actual measurement of "stress-strain" at the vibration weld,
Finite using external force information applied to resin products, "stress-strain" diagram information estimated for each part in the resin molded product, and "stress-strain" measured diagram information at vibration welds Performing the element method,
To analyze the strength of resin products. It is a strength analysis method for resin products in which resin molded products reinforced with fibers are vibration welded together.
Using a test piece of a resin-molded product reinforced with fibers to obtain measured stress-strain diagram information for each representative angle (including the main fiber orientation direction and the direction perpendicular thereto) with respect to the main fiber orientation direction ,
Applying the "resin flow and fiber orientation" model to each resin molded product, calculating the distribution in the resin molded product in the fiber main orientation direction, and in the resin molded product of Young's modulus in the fiber main orientation direction and the direction perpendicular to it. Calculating the distribution,
A step of estimating the fiber main orientation direction at the vibration welded portion as the direction along the vibration;
Based on the Young's modulus obtained in the Young's modulus distribution calculation step and the measured diagram information of “stress-strain” obtained for each of the representative angles, “stress-strain” for each part in the resin molded product. Obtaining estimated diagram information of
A step of executing a finite element method using external force information applied to a resin product and diagram information of “stress-strain” estimated for each part in the resin molded product,
To analyze the strength of resin products. 3. The resin product according to claim 1, wherein the resin product is an intake pipe, and the external force is a hydrostatic pressure applied to the inside of the intake pipe, and when the finite element method is repeatedly executed while increasing the hydrostatic pressure, In contrast, a method of calculating the pressure resistance of the intake pipe that specifies the hydrostatic pressure when the stress value calculated by the finite element method does not increase.

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