JP2006308569A - Impact analysis method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact analysis method, capable of accurately realizing impact analysis on complex deformation processes of resin parts. <P>SOLUTION: In the impact analysis method, physical property values indicating mechanical properties of resin materials are set in an analysis program, to evaluate the impact characteristics of resin molded bodies and their failure behaviors. As a failure determination method for determining failure of the resin molded bodies, a ductile failure conditional expression is used to determine the failure. A ductile failure conditional expression, in which stress multi-axiality can be taken into consideration, may be used. Deformation speed dependence may be taken into consideration, in the ductile failure conditional expression for dealing with viscoelasticity characteristics to resins. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an impact analysis method used for predicting a deformation behavior of a resin molded body under an impact load.

  For example, when designing resin interior parts for automobiles, it is desirable to use an impact analysis method using a computer instead of a labor-intensive field test. However, resin interior parts for automobiles have a complicated shape such as a rib structure. Further, in a collision test or the like, the resin interior parts are greatly deformed to absorb impact energy and partially break down. In addition, unlike a metal material, a resin material has viscoelastic properties, and thus the physical property value is affected by the strain rate. Therefore, it has been difficult to set physical property values that can accurately realize impact analysis of complicated deformation processes of resin parts.

  The technique of Patent Document 1 proposed as a method for analyzing the impact characteristics in the impact test as described above is based on an actual test using a resin molded body having a predetermined shape for each speed condition, and an impact with changed fracture plastic strain. Analysis and comparing the actual test result and the impact analysis result to determine the breaking plastic strain for each speed condition. Thereby, the fracture determination of the rib portion corresponding to the strain rate becomes possible. However, a complicated fracture behavior in which the rib portion and the substrate portion of the resin molded body are integrated and the rib portion and the substrate portion both break can not be reproduced by impact analysis.

  In addition, as a technique for analyzing impact characteristics in a collision test, there is a technique in which fracture determination is performed based on the relationship between strain rate and fracture strain obtained from various tensile tests as disclosed in Patent Document 2.

  On the other hand, for metals, attempts have been made to quantitatively grasp the deformation behavior using a ductile fracture conditional expression. Further, in Patent Document 3, considering the equivalent plastic strain-stress multiaxiality relationship of the elastoplastic body (metal material), the crack generation condition for each element is updated while the external force given as the boundary condition is updated up and down. Is satisfied, and crack growth is predicted.

Japanese Patent Laid-Open No. 2003-279456 JP-A-2005-337784 JP 2004-069638 A Manabu Goto “Conditions for Ductile Fracture” Plasticity and Processing (Journal of the Japan Society for Technology of Plasticity) Vol.38, No.434, March 1997, P200-205 Moriya Oyane “Conditions for Ductile Fracture” Journal of the Japan Society of Mechanical Engineers Vol. 75, No. 639 April 1972 P596-601

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an impact analysis method for accurately realizing impact analysis of a complicated deformation process of a resin molded body.

  That is, the present invention sets a physical property value indicating the mechanical properties of a resin material in an analysis program, and in the impact analysis method for evaluating the impact properties and fracture behavior of a resin molded body, As a determination method, it is an impact analysis method characterized by performing a fracture determination using a ductile fracture conditional expression.

  Further, the present invention provides a ductile fracture for each element of a finite element model in an impact analysis method for setting a physical property value indicating a mechanical characteristic of a resin material in an analysis program and evaluating an impact characteristic and a fracture behavior of a resin molded body. A first step of calculating a fracture judgment value related to the conditional formula, a fracture judgment reference value related to the ductile fracture conditional formula, a fracture judgment value related to the ductile fracture conditional formula obtained in the first step, and a fracture judgment related to the ductile fracture conditional formula It is an impact analysis method characterized by having the 2nd process of comparing with a standard value and performing destruction judgment.

  According to the impact analysis method of the present invention, impact analysis of a complicated deformation process of a resin molded body can be realized with high accuracy.

  According to the first aspect of the present invention, in the impact analysis method for setting the physical property value indicating the mechanical characteristics of the resin material in the analysis program and evaluating the impact characteristics and the fracture behavior of the resin molded body, the fracture of the resin molded body is determined. As a failure determination method, an impact analysis method characterized by performing a failure determination using a ductile failure conditional expression.

  The ductile fracture condition is a means that has been developed to quantitatively understand the fracture behavior of metals. Ductile fracture is different from other fracture modes such as brittle fracture in that fracture occurs after a predetermined amount of deformation. In general, in ductile fracture, (1) a void is generated at a high triaxial tensile field in the material, (2) the void grows and merges with new generation, and (3) the material eventually breaks. Is the mechanism.

The ductile fracture condition formula has been developed mainly for the purpose of preventing fracture during plastic working. Ductile fracture conditional expressions are intended to model and formulate the above-described ductile fracture process, and many are proposed as described in Non-Patent Document 1. For example, in Non-Patent Document 2, Oyane approximates the process in which void defects are generated, coalesced, and grows with a porous body and tracks the volume change history by assuming a volume change due to plastic deformation. The following formula (1) was proposed on the assumption that the fracture condition formula can be obtained.

  The inventors have considered that such a ductile fracture conditional expression can be applied to the fracture of a resin molded body, and have reached the present invention. This is because the resin molded body is considered to be ductilely broken depending on conditions. Of course, there are significant differences between metals and resins. For example, the resin already has many voids in the initial state, and is different from a metal that is an elastic body in that it has viscoelasticity.

However, for the former, for example, Equation (1) is modeled on a porous body that originally has void defects, so it is considered that there is basically no problem. Among the ductile fracture conditional expressions, analysis can be performed with higher accuracy by using an expression that takes into account the multiaxiality of stress that is considered necessary for handling three-dimensional deformation, such as Expression (1). .

In order to consider the viscoelasticity of the resin, it is preferable to use a formula that takes into account the strain rate dependency. For example, as shown in Formula (2-1) or Formula (2-2), analysis can be performed with higher accuracy by adding a factor depending on the strain rate to the right side of Formula (1). In formula (2-1) and formula (2-2), the logarithm is the left side and the strain rate on the right side is the logarithm. In the uniaxial tensile test, the relationship between the breaking strain and the strain rate can be linearly approximated on both logarithms. Because. Further, since the resin is in a glass state at a certain strain rate or higher, the right side is set to a certain value.

In order to express the viscoelastic properties of the resin and the fact that it becomes a glass state when the strain rate is large, for example, Equation (2-1) and Equation (2-2) are shown. Other ductile fracture condition formulas may be used. For example, a modification of Oya's equation (1) so that only the strain rate on the right side is a logarithm may be effective in some cases.

  When the resin molded body to which the impact analysis method of the present invention is applied is a resin molded body having a rib portion and a substrate portion, a ductile fracture conditional expression is used as a fracture determination method for determining the fracture of the entire resin molded body. However, since the direction of the impact is different between the rib part and the board part of the resin molded body, the impact analysis should be performed using different fracture judgment methods for the rib part and the board part. Is preferred. In a resin molded body having a rib portion and a substrate portion, an impact force acts in a direction perpendicular to the plate surface at the substrate portion, whereas an impact force acts substantially along the plate surface at the rib portion. Therefore, since the process leading to the rupture is different, it is preferable to use a different rupture determination method for each. In particular, it is preferable to perform the fracture determination using the ductile fracture direction formula described above for the substrate portion and to use a different fracture determination method for the rib portion.

  For example, if the resin molded product has a rib part, as a method for determining the fracture of the rib part, conduct a plurality of field tests using a resin molded body of a predetermined shape and impact analysis with different fracture plastic strains. It is preferable to use a fracture plastic strain determined by comparing impact analysis results.

  In addition, when the resin molded product has a rib portion, it is also preferable to use the relationship between the breaking strain and the strain rate obtained by conducting a uniaxial tensile test at various tensile speeds as a method for determining the fracture of the rib portion.

  According to another aspect of the present invention, in the impact analysis method for setting the physical property value indicating the mechanical characteristics of the resin material in the analysis program and evaluating the impact characteristics and fracture behavior of the resin molded body, each element of the finite element model For the ductile fracture condition formula (the left side of formula (2-1) or formula (2-2)) and the fracture criterion value for the ductile fracture condition formula (formula (2-1) or formula (2-2) ) On the right side) and the fracture determination value (the left side of formula (2-1) or formula (2-2)) and the ductile fracture condition formula regarding the ductile fracture condition formula obtained in the first step. A destruction determination reference value (the right side of Expression (2-1) or Expression (2-2)) is compared with the second step of performing the destruction determination.

  Hereinafter, preferred embodiments of the invention will be described in more detail with reference to the drawings. In this embodiment, the impact characteristics and deformation behavior of a resin molded body as shown in FIG. 1 are predicted by an impact analysis method using an analysis program. In FIG. 1, the shape of a resin molded body 10 as an object of impact analysis as viewed from the front is drawn using computer graphics. The resin molded body 10 includes a rib portion 12 and a flat substrate portion 14. The rib portion 12 is configured such that a plurality of rib plates having a constant thickness extend from the substrate portion 14 so as to be orthogonal to the plate portion 14 to form a regular lattice. The arrangement of the lattice is 3 × 9 in the width direction × length direction, the lattice interval is 30 mm, and the height of the rib is 25 mm. The rib portion 12 is formed with a taper for die cutting, and the plate thickness is 1.12 mm on the base end side (substrate side) and 0.69 mm on the tip end side. The substrate part 14 has a width of 150 mm, a length of 310 mm, and a plate thickness of 2 mm. When creating an analysis model, it is desirable to use a shell element for the rib portion and a solid element for the substrate portion.

  With respect to the resin molded body 10, physical property values indicating the mechanical characteristics of the resin material are set, and the impact characteristics and deformation behavior in the collision test as shown in FIG. 2 are analyzed using an analysis program. In this test, the front end side of the molded body is opposed to the barrier (solid barrier) 16 and the dart 18 is advanced from the base end side at 5.7 m / s and 4.5 m / s to collide with the molded body. At that time, the deformation of the molded body and the applied load are measured. The dirt 18 is a hemispherical impactor having a mass of 6.8 kg and a diameter of 165 mm.

  The physical property values indicating the mechanical properties of the resin material include elastic modulus, Poisson's ratio, density, yield stress, strain hardening degree, and material constants of the ductile fracture condition formula. Among these physical property values, the yield stress can be determined by carrying out a uniaxial tensile test at various tensile speeds. In the resin material, the yield stress is usually significantly dependent on the strain rate, and generally the yield stress increases as the strain rate increases.

  Regarding the strain hardening degree, stress multiaxiality can be considered. The degree of strain hardening is 0 when the true stress after yielding is constant, and 1 when the true stress follows the true stress of the uniaxial tensile test result.

As described above, the ductile fracture conditional expression uses the expression (2-1) and the expression (2-2) obtained by modifying the Oyane expression (1).

Among the above physical property values, as a method for determining the material constant of the ductile fracture condition formula, for example, the following method can be adopted.

Since the elements of the analysis model cannot be made infinitely small, the stress and strain generated at the crack tip during the test cannot be reproduced in the analysis. Therefore, even if the starting point of the crack can be reproduced, the propagation of the crack may not be reproduced. In that case, the calculation may be performed by setting the area around the destroyed element so that the destruction is likely to occur. For example, when the destruction determination of the elements around the destroyed element is performed, the value on the left side of the equation (2-1) or the equation (2-2) is weighted so as to facilitate destruction.

Further, when one solid element of the substrate portion is destroyed, the calculation may be performed by setting so as to delete all the solid elements in the thickness direction of the substrate portion of the element.

Hereinafter, the steps of the impact analysis method of this embodiment will be described with reference to the flowchart of FIG.
First, in Step 1, a finite element model is created, static property value data, yield stress strain rate data, strain hardening stress multiaxiality data, and ductile fracture condition material constants. Input and start calculation with the general-purpose finite element program LS-DYNA. Next, in step 2, when a certain time t is less than or equal to the end time, the time is advanced for each time increment Δt determined in each time step. Then, in step 3, the displacement of the node is calculated by the general-purpose finite element program LS-DYNA. In step 4, the elements at time t are sequentially selected. In step 5, the failure determination of the stress and the ductile fracture conditional expression is performed for the element. Calculate the value and failure criterion.

  Next, in Step 6, it is determined whether or not the value obtained in Step 5 satisfies Expression (2-1) and Expression (2-2). If the destruction judgment value is greater than or equal to the destruction criterion value, the element is deleted in step 7, and if the destruction judgment value is smaller than the destruction criterion value, the process returns to step 4 and uncalculated elements remain. As long as this is the case, in step 5, the stress for the next element, the fracture judgment value of the ductile fracture condition formula, and the fracture reference value are calculated. In this way, steps 3 to 7 are repeated until the end time.

FIG. 4 is a flowchart for making it easy to break around the broken element. In this method, after calculating the stress, the fracture determination value of the ductile fracture condition formula and the fracture reference value for the element in step 5, it is determined in step 6 whether the element in contact with the element is broken. If it is destroyed, the destruction determination value is weighted in step 7, and if it is not destroyed, it is left as it is, and in step 8, it is determined whether the destruction conditional expression is satisfied. If the destruction determination value is greater than or equal to the destruction reference value, the element is deleted in step 9. Other steps are the same as in the previous case.

When one solid element of the substrate part is destroyed, when all solid elements in the thickness direction of the substrate part of the element are deleted, when the destruction conditional expression is not satisfied in step 8, as shown by a broken line in the figure, In step 10, it is determined whether an element in the same thickness direction of the substrate portion is destroyed. If the element is destroyed, the process returns to step 9 to delete the element.

An impact analysis method for evaluating impact properties and fracture behavior when Noblen AZ864E4 manufactured by Sumitomo Chemical Co., Ltd. is used as the material of the resin molding is shown below.
(1) Software analysis software used for analysis: LS-DYNA version 9.70 (Livermore
Software Technology Corporation)
(2) Discretization of analysis method space: Finite element method Time integration: Explicit solution based on center difference Material model: LS-DYNA physical property type 44 (user-defined physical property)
(3) Physical property values
The following values were used as physical properties of AZ864E4.
Elastic modulus: 1000MPa
Yield stress: 22.8 MPa
Poisson's ratio: 0.40
Specific gravity: 0.90
True stress-true plastic strain curve: FIG.
Yield stress-strain rate: FIG.
Strain hardening-stress multiaxiality: FIG.
Material constants of the ductile fracture condition formula: C ₁ = 0.970, C ₂ = 67.2,
C ₃ = −0.128, C ₄ = 0.168,
C ₅ = 1.51 × 10 ¹⁴ , C ₆ = −1.65
The material constants of the ductile fracture conditional expressions (2-1) and (2-2) are determined as shown in the example of the material constant determination method.

Considering that the elements of the analysis model are large enough to reproduce the propagation of cracks in the substrate part, the surroundings of the broken elements were easily broken.
The weighting factor was set to W = 3.0.
Further, when the solid element of the substrate portion was destroyed, the calculation was performed so as to delete all the solid elements in the thickness direction of the substrate portion of the element.

The molded object 10 of the analysis target model shown in FIGS. 1 and 2 was actually created, and a field test was performed at collision speeds of 5.7 m / s and 4.5 m / s. Next, the analysis model shown in FIG. 2 was analyzed by the impact analysis method of the present invention at the collision speeds of 5.7 m / s and 4.5 m / s using the above physical property values for the resin molded body 10 ( Example). Specifically, if the strain rate is _{C 5} below formula (2-1), if more than _{C 5} using the equation (2-2).

  As a comparative example, LS-DYNA physical property type 24 (multiple types) was used at the collision speeds of 5.7 m / s and 4.5 m / s using the above physical property values for the molded resin 10 in the analysis model shown in FIG. Analysis was performed using a linear approximate isotropic elasto-plastic body. In the physical property type 24, the strain rate dependence of the yield stress can be considered, and the fracture plastic strain is a model that is constant regardless of the strain rate. The data of fracture plastic strain was 0.56 in Comparative Example 1 and 0.57 in Comparative Example 2.

A load-displacement curve as a result of the field test, the example, and the comparative examples 1 and 2 is shown in FIG. In FIG. 8, (a) shows the result of the speed 5.7 m / s, and (b) shows the result of the speed 4.5 m / s.
FIGS. 9A, 9B, and 9C show the shapes of the molded object 10 of the analysis target model after the impact analysis results of Comparative Examples 1 and 2. FIG.
FIG. 10 and FIG. 11 show the destruction state of the substrate portion at a speed of 5.7 m / s and a speed of 4.5 m / s. 10 and 11, (a) shows the results of the field test, (b) shows the results of analysis by the method of the example, (c) shows the results of Comparative Example 1, and (d) shows the results of Comparative Example 2.

From these results, in the method of the comparative example, it was not possible to determine whether the substrate portion was broken or not broken depending on the speed, but in the method of the example, it was possible to make a determination. It can also be seen that the load-displacement curves in FIG.

This is a resin molded body to be subjected to impact analysis. It is a conceptual diagram which shows the outline of a structure of an impact test. It is a flowchart which shows the process of the impact analysis method of this embodiment. It is a flowchart which shows the process of the impact analysis method of this embodiment. It is the true stress-true plastic strain curve of the test material of a resin molding. It is a yield stress-strain rate curve of the test material of a resin molding. It is a strain hardening degree-stress multiaxial degree curve of the test material of a resin molding. It is a load-displacement curve for evaluating the impact characteristic of a resin molding. It is a figure which shows the destruction condition of a resin molding. It is a figure which shows the destruction condition of the board | substrate part of the resin molding in the impact test at a speed of 5.7 m / s. It is a figure which shows the destruction condition of the board | substrate part of the resin molding in the impact test at a speed of 4.5 m / s.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Resin molding 12 Rib part 14 Substrate part 16 Barrier (solid barrier)
18 Dirt

Claims (7)

Set physical properties that indicate the mechanical properties of the resin material in the analysis program,
In the impact analysis method to evaluate the impact characteristics and fracture behavior of resin moldings,
An impact analysis method comprising performing a failure determination using a ductile failure conditional expression as a failure determination method for determining the failure of a resin molded body.   The impact analysis method according to claim 1, wherein a ductile fracture conditional expression capable of considering multiaxiality of stress is used as the ductile fracture conditional expression.   The impact analysis method according to claim 1 or 2, wherein a strain rate dependency is considered in the ductile fracture conditional expression.   The resin molded body has a rib portion and a substrate portion, the substrate portion is subjected to failure determination using a ductile fracture conditional expression, and a different failure determination method is used for the rib portion. The impact analysis method according to claim 3.   Rupture plasticity determined by comparing the actual test results and impact analysis results by conducting multiple tests using a resin molded body of a predetermined shape and impact analysis with different fracture plastic strains when determining the fracture of the rib part. The impact analysis method according to claim 4, wherein strain is used.   5. The impact analysis method according to claim 4, wherein a relationship between a fracture strain and a strain rate obtained by performing a uniaxial tensile test at various tensile speeds is used when determining the fracture of the rib portion. Set physical properties that indicate the mechanical properties of the resin material in the analysis program,
In the impact analysis method to evaluate the impact characteristics and fracture behavior of resin moldings,
For each element of the finite element model, a first step of calculating a fracture determination value related to the ductile fracture conditional expression and a fracture determination reference value related to the ductile fracture conditional expression;
An impact analysis method comprising a second step of performing a fracture determination by comparing a fracture determination value related to a ductile fracture conditional expression obtained in the first step and a fracture determination reference value related to a ductile fracture conditional expression.

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