JP2002296163A - Impact analysis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an impact analysis method capable of nicely reproducing a destroy behavior which can not be reproduced by the prior impact analysis method for a resin molding. SOLUTION: The impact analysis method is the impact analysis method for the molding composed of a resin material using a finite element method, and reduces a destroy decision condition to 10%-80% about the element neighboring the element reached to the destroy decision condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impact analysis method used to predict a deformation behavior of a resin molded product under an impact load.

[0002]

2. Description of the Related Art For example, in order to improve the safety of passenger cars, molded articles (resin molded articles) made of a resin material for the purpose of absorbing and reinforcing impact are used in various parts of a vehicle body. Such a molded product needs to exhibit the required performance within the conditions such as the volume and shape of the storage space and the weight. In order to save labor in designing such molded products, it is necessary to input physical properties such as the mechanical properties of the material into a computer and predict the behavior when a load or impact is applied by an impact analysis method. Have been done. The mechanical properties of the material have been measured using an injection molded test product having a shape specified by ASTM, JIS, ISO, and the like.

[0003] By using such a method, it is possible to save the trouble of molding and testing on the ground and to easily optimize the structure. Therefore, it is possible to shorten the development period and cost of the structural component.

[0004]

In such a method for analyzing the impact of a resin molded article, which part of the molded article is destroyed by impact or the like, and how the destruction spreads,
Also, it is important to reproduce the load and displacement generated in the molded product due to impact or the like. However, there have been cases where it has been difficult to reproduce such a destructive behavior in a well-known impact analysis method. The problem to be solved by the present invention is to provide an impact analysis method that can successfully reproduce a fracture behavior that cannot be reproduced by a conventional impact analysis method for a resin molded product.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is an impact analysis method for a molded article made of a resin material using a finite element method. This is an impact analysis method for reducing the destruction judgment condition to 10% to 80% for an element adjacent to the reached element.

According to this analysis method, the destructive behavior of a resin molded product that cannot be reproduced by the conventional impact analysis method (for example, the destructive behavior of an anisotropic resin molded product having a property of easily cracking in the fiber orientation direction) is described. Highly accurate analysis results can be obtained by simple means. The analysis method usually uses a method in which the interaction between individual elements is analyzed by discretizing the space and this is integrated in the time element, and the finite element method can obtain highly accurate results. It is suitable.

As an analysis method for reducing the fracture judgment condition of an element adjacent to the element which has reached the fracture judgment condition, for example, a composite material model based on the Chang fracture condition can be mentioned.
It is preferable that the destruction judgment condition of the element adjacent to the element that has reached the destruction judgment condition is reduced to 10% to 80%, and 1
More preferably, it is reduced to 5% to 50%, and 15% to
More preferably, it is reduced to 35%. If the fracture judgment conditions are too low, the analytical breaking load will be underestimated compared to the actual test results, and if the amount of the fracture judgment conditions is too small, the analytical breaking loads will not be the actual test results. This is not preferable because it is overestimated as compared with.

As the resin material, a thermoplastic resin is preferable. Specifically, polypropylene, polyamide,
A mixture thereof, a resin composition containing these as a main component, or a liquid crystal polymer is preferably used. Particularly, a resin molded product using polypropylene is excellent in workability and cost and is suitable.

The impact analysis method of the present invention is preferably used for a molded article having anisotropic mechanical properties such as a fiber reinforced resin. Such a fiber-reinforced resin is obtained by reinforcing the thermoplastic resin with reinforcing fibers. Glass fiber, inorganic fiber such as carbon fiber, silicon fiber, silicon titanium titanium carbon fiber, boron fiber, iron, metal fiber such as titanium, etc.
Known materials such as organic synthetic fibers such as aramid fibers, polyester fibers, polyamide fibers, and vinylon, and natural fibers such as silk, cotton, and hemp can be widely used. These may be used alone or in combination of two or more, and glass fibers are preferred from the viewpoint of reinforcing effect and availability.

[0010] As glass fiber, E glass (Electric
al glass), C glass (Chemical glass), A glass (Alkali glass), S glass (High strength glass)
And glass obtained by melt-spinning glass such as alkali-resistant glass into filamentous fibers.

Although there is no particular limitation on the actual method of manufacturing a molded article made of the resin material, a resin pellet is manufactured, and injection molding, injection compression molding, gas injection injection molding, or foam injection molding is performed using the resin pellet. Can be used.

The method for producing the resin pellets of the fiber-reinforced resin is not particularly limited. For example, a method of impregnating a roving of the reinforcing fibers with a molten propylene polymer using a crosshead die is used. A pellet production method in which the temperature at which the propylene polymer is melted is set to 250 to 350 ° C. is exemplified.

As a condition for judging fracture, it is preferable to form a test flat plate from the resin material and set a tensile yield strength or a tensile breaking strength in a direction in which an angle formed with a resin flow direction at the time of molding is 60 ° to 120 °. The direction perpendicular to the resin flow direction is more preferable. When the resin material is a fiber-reinforced resin, the fibers tend to be oriented by the resin flow, which is considered to be a major cause of the anisotropy in the mechanical properties of the molded article. In fiber reinforced resin, the strength of the molded product is
This is because the direction orthogonal to the fiber orientation is the weakest, and fracture is considered to occur in the direction orthogonal to the fiber orientation. If the tensile yield strength or the tensile rupture strength whose angle with the resin flow direction is not in this range is used as the condition for judging fracture, the breaking load in the analysis is undesirably overestimated. From such a background, the method of the present invention is particularly effective when a fiber-reinforced resin is used as the resin material.

The use of the molded article made of the resin material handled in the impact analysis method of the present invention is not particularly limited, and examples thereof include automobile parts.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. Fig. 1
Analysis results by the analysis method of the present invention when an impact test involving destruction is performed on the shock absorbing member 10 having a channel-shaped cross section as shown in (a) and (b),
The test results of actual molded products were compared. Furthermore, the analysis results using the conventional analysis method are also shown.

(1) Molded Product FIG. 1A shows a shape of a resin molded product 10 of a shock absorbing member as a model for analysis, as viewed from the front, and a dirt (collision body) 12 for performing an impact test. Is drawn using computer graphics. This resin molded product 1
Reference numeral 0 denotes a channel shape having two-step grooves.
As shown in (b), reinforcing ribs 14 extending in the width direction are formed at equal intervals in the length direction inside the groove. In this example, the resin molded product has a width of 115 mm, a length of 500 mm,
The central groove depth is set to 30 mm, and the total depth is set to 70 mm. The wall thickness is uniform and 3.0 mm as a whole, and the reinforcing rib 14 is formed with a taper for die cutting. The material of the resin molded product of this example is Sumitomo Chemical Co., Ltd. glass reinforced fiber reinforced polypropylene, Smith Tran (trademark)
PG4003 (glass content: 40%) and molded under the following conditions. <Injection molding machine> IS650E manufactured by Toshiba Machine Co., Ltd. (clamping force: 650 t, screw diameter: 90 mm, screw L
/ D: 20, screw type: full flight) <Mold for injection molding> Molded product: 115 mm x 500 mm x 70 mm, channel shape Gate: Dub gate (center) <Injection molding conditions> Cylinder temperature: 220 ° C, mold temperature: 50 ℃

(2) Impact Test In order to test the impact absorption characteristics of the resin molded product 10, FIG.
A collision test was performed as shown in FIG. That is, the front of the molded product is opposed to the barrier (fixed barrier) 16 and the dirt 12 is moved forward from the rear surface at a constant speed to collide the molded product with the barrier. Was measured. In this example, a piece of wood 18 is attached to the barrier surface to prevent dart damage when bottomed. The dirt 12 has a trapezoidal cross section with a short side (collision surface) of 65 mm, a long side (opposite side of the collision surface) 180 mm, and a height of 60 mm, and is made to collide perpendicularly with the sample molded product 10. Can be In this example, the test conditions are a dirt mass of 20 kg and a collision speed of 3.0 m / s. FIG. 3 shows a displacement-load curve as a result of the test performed twice. The average value of the maximum load was 5.4 kN, and the average value of the deformation amount was 33 mm.

[Example 1] (1) Software used Analysis software: LS-DYNA version 9.40 (Livermor
e Software TechnologyCorporation)

(2) Analysis method Discretization of space: Finite element method Time integration: Explicit method based on central difference Material model: LS-DYNA physical property type 54 (composite material by Chang fracture condition) Failure judgment condition: Resin flow of test piece Tensile rupture strength in the direction perpendicular to the direction For elements adjacent to the element that has reached the fracture criterion, the rupture criterion was reduced to 25% of the tensile rupture strength in the direction perpendicular to the resin flow direction of the test piece. After the analysis, each of the broken elements and the surrounding elements was divided into four parts and analyzed again to obtain results.

(3) Physical property values The physical property values required for this analysis are elastic modulus, tensile strength at break, Poisson's ratio, and specific gravity. A test plate was prepared and measured.

(4) Test Plate In order to obtain the same physical properties as the molded product, the test plate is preferably the same as the molded product. However, if the same molded article is molded under the same conditions, it is overturned. Molding was performed using a test plate mold having a plate-shaped cavity. Fig. 5
As shown in Table 2, two test pieces having different directions were cut out. The first direction is a direction in which the resin material flowing from the gate flows, and the second direction is a direction (TD) orthogonal to the direction. <Injection molding machine> Injection molding machine manufactured by Sumitomo Heavy Industries, Ltd. (mold clamping force: 180 t, screw diameter: 45 mm, screw L / D: 12, screw type: for deep groove long fiber) <Injection molding die> Molded product: 150 mm x 150 mm x 3 mm, flat gate: Edge gate (having a thickness distribution such that the flow of the molten resin in the cavity is parallel) Land (width 150 mm, thickness 3 mm, length 3 mm) <Injection molding conditions > Cylinder temperature: 250 ° C., mold temperature: 50 ° C., screw rotation speed: 150 rpm, back pressure: 8 MPa

(5) Calculation of Physical Properties Each test was performed on these test pieces, and the elastic modulus and tensile strength were measured. The specific gravity and Poisson's ratio had little influence on the analysis of the impact characteristics, and were measured for one test piece and used for the analysis. The measuring method is as follows. a) Elastic modulus: Measured according to the method specified in JIS-K-7203. b) Tensile rupture strength: Measured according to the method specified in ASTM D638. c) Specific gravity: Measured based on the method specified in JIS-K-7112. d) Poisson's ratio: Calculated from longitudinal strain and transverse strain measured from strain gauges attached in the tensile direction and the direction perpendicular to the tensile direction of the test piece. Test piece shape: 150 mm x 15 mm x 3 mm Tensile speed: 1 mm / min

Table 1 shows the obtained physical properties.

[Table 1] In this table, the average value (5180 MPa) as the elastic modulus
As the tensile strength at break in the TD direction (54.8MP
Computer analysis was performed using a).

(6) Analysis Results The analysis results are shown in Table 2, and the displacement-load curves are shown in FIG.

Comparative Example 1 Example 1 was the same as Example 1 except that the material model was changed to LS-DYNA physical property type 19 (strain-rate-dependent elastoplastic body) and the fracture criterion was changed to 0.1%. Analysis was performed by the same analysis method. The analysis result is shown in Table 2, and the displacement-load curve is shown in FIG.

[0026]

[Table 2]

From these results, while the displacement-load curve in the conventional analysis method is significantly different from that in the actual test, the displacement-load curve in the analysis method of the present invention almost matches, and the maximum load, Both the maximum displacements agreed well. Therefore, it was found that the analysis accuracy can be significantly improved by using the analysis method of the present invention.

By improving the precision in this way, the impact analysis method can be put to practical use even for a resin molded product having anisotropy such as fiber reinforced resin. In comparison, the advantages of the analysis method that the structure can be easily optimized and the period of development of structural parts and the cost can be reduced can be exhibited.

In order to maintain the analysis accuracy, it is necessary that the degree of coincidence between the physical property value data obtained using the test piece and the physical property value of the actual product is high. For a material having anisotropy such as a fiber reinforced resin, there is a possibility that the sampling method of the test piece varies greatly, and it may not be possible to obtain a physical property value close to a product value. That problem has been overcome by the present invention.

As a second problem in the fiber reinforced resin,
The problem of the dispersion state of the fibers, especially the dispersion of the fiber length remains. In the molding step, the fibers in the raw material pellets are separated by a shearing force of a screw in a cylinder of an injection molding machine. Therefore, when the molding conditions are different, the fiber length in the molded article varies even with the same material, and the fiber length in the test piece and the actual fiber length in the molded article may be different. In addition, differences in resin flow conditions due to differences in the shape and dimensions of the test mold and the molded product mold may also cause physical property value errors between the test specimen and the actual molded product. . Therefore, in order to secure the analysis accuracy, it is preferable that the thickness of the test flat molded product and the average fiber length and the thickness of the resin molded product and the average residual fiber length are close to each other.

[0031]

As described above, according to the present invention, a highly accurate impact analysis of a resin molded product can be performed by a simple method without complicating the analysis method. Therefore, even if the mechanical properties of the molded article have anisotropic properties such as fiber reinforced resin, even if it is difficult to reproduce using the conventional analysis method, the analysis using a computer can be put to practical use. This makes it possible to easily optimize the structure without the labor of molding and testing, thereby shortening the development period of structural components and reducing costs.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a computer-analyzed model showing a resin molded product sample and dart, and FIG. 1B is a computer-based analytical model drawing of a resin molded product sample viewed from the back.

2A is a conceptual diagram schematically showing the overall configuration of a collision test, and FIG. 2B is a plan view showing the shape of a dart.

FIG. 3 is a drawing of a displacement-load curve obtained by an actual collision test.

FIG. 4 is an analysis model drawing of a collision test by a computer.

FIG. 5 is a view for explaining how to cut out a test piece for measuring physical property values.

FIG. 6 is a graph showing a comparison between an analysis result according to Example 1 and an actual test result.

FIG. 7 is a graph showing a comparison between an analysis result according to Comparative Example 1 and an actual test result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Resin molding 12 Dirt 16 Barrier

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G061 AA14 AB04 BA04 CA10 CB03 DA11 EA02 EC02 5B046 AA04 JA07

Claims (6)

[Claims] 1. A method for analyzing the impact of a molded article made of a resin material using a finite element method, wherein a breaking judgment condition is set to 10% to 80% for an element adjacent to an element which has reached a breaking judgment condition.
% Impact analysis method. 2. The impact analysis method according to claim 1, wherein the molded article made of the resin material exhibits anisotropy in mechanical properties. 3. A physical property value indicating mechanical properties obtained from a test flat molded product of the resin material as a condition for judging destruction.
The impact analysis method according to claim 1 or 2, wherein a tensile yield strength or a tensile rupture strength in a direction at an angle of 60 ° to 120 ° with the resin flow direction is used. 4. The impact analysis method according to claim 1, wherein said resin material is a fiber reinforced resin. 5. The reinforcing fiber contained in the fiber-reinforced resin,
The impact analysis method according to claim 4, wherein the impact analysis method is glass fiber. 6. An impact analysis of a molded article made of a resin material is performed by the method according to any one of claims 1 to 5, and as a result, the element which satisfies the destruction judging condition is subdivided and reclaimed. Item 6. An impact analysis method for performing the impact analysis method according to any one of Items 1 to 5.