JP2013120553A - Method for evaluating dent resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate dent resistance at a portion such as a character line where a curvature changes steeply.SOLUTION: A finite element analysis simulation is performed for a panel plate having a surface-shape steep portion in which a curvature changes steeply, using a panel shape condition of the panel plate and a material condition to be applied to the panel plate, so that an applied load in which plastic strain is generated on a plate surface of the surface-shape steep portion is acquired. Dent resistance at the surface-shape steep portion is evaluated based on the applied load.

Description

  The present invention relates to a method for evaluating the dent resistance of an automotive outer panel such as a door panel or a roof panel. In particular, the present invention relates to a technique capable of preliminarily evaluating dent resistance in a region where a steep panel surface curvature change such as a character line occurs in a design stage.

  In recent years, in order to reduce the weight of vehicles such as automobiles, there is an increasing need for thinner and lighter automobile outer parts such as doors and hoods. However, the thinning of the panel parts leads to a decrease in dent resistance and tension rigidity, which has a detrimental effect on the rigidity when touched by a person and the difficulty of being depressed when hit by an object. For this reason, it is a major issue for automobile manufacturers to ensure the rigidity of panel panels and the resistance to dents and to reduce the weight of parts.

  Since the tension stiffness is affected by the elastic deformation behavior, it cannot be solved by increasing the tensile strength of the outer plate (increased material strength). Therefore, in recent years, countermeasures for the entire part, such as a change of the reinforcing part provided inside the panel, are becoming main. On the other hand, since the dent resistance is affected by the difficulty of plastic deformation, a countermeasure is basically taken by increasing the tensile strength (increasing yield strength). Specifically, measures have been taken to apply high tensile strength TS340 MPa grade high tensile strength and bake hardened BH steel plates to the sites where mild steel plates have been used.

  However, when further weight reduction is required in the future, there is a limit to the tension rigidity only with measures against the internal structure of the parts, so the character line (generally having a radius of curvature smaller than the panel surface curvature at the top) Design measures such as providing a linear pattern extending in the front-rear direction) have been considered. However, although the tension rigidity is improved in the portion where the character line is provided, there is a case where a noticeable jump phenomenon called “peking” occurs when a high load is applied. When the jumping phenomenon occurs or before it occurs, the mountain-shaped character line is plastically deformed (collapsed), so that the character line itself is deformed (dents are generated), resulting in a problem that the appearance quality is impaired.

  Such a phenomenon does not occur on a general curved surface having no steep surface shape portion such as a character line, but is a characteristic remarkable jumping phenomenon in a portion having a sharp curvature such as a mountain-shaped character line portion. If the unique remarkable jumping phenomenon and the dent dent generated in the previous stage can be predicted at the drawing design stage, it is possible to reduce the man-hours required for trial and error in new vehicle development.

Examples of methods for predicting and evaluating dent resistance of automobile outer plate parts include methods described in Patent Document 1 and Patent Document 2, for example.
Patent Document 1 describes a dent resistance evaluation method that takes into account the influence of material factors such as plate thickness reduction and work hardening by press molding.
Patent Document 2 discloses a method of calculating a deflection amount from a deflection area that is enlarged around a load point of a component, a curvature of the component, a plate thickness, and a material.

JP 2000-249636 A JP 2007-33067 A

However, in Patent Document 1, since it is an object to select an appropriate material, a study including tension rigidity and dent resistance in a final actual part shape has not been reached. In the technique of Patent Document 2, it is impossible to predict a dent dent that occurs as a permanent deformation after unloading.
In addition, in a portion where the curvature changes sharply such as a character line, the deflection grows in an asymmetric shape and abrupt deflection expansion occurs with jumping. Therefore, in the conventional technique, in the portion where the curvature changes sharply, the initial It is considered difficult to predict the dent from the part shape.

Here, if the dent resistance in the character line portion cannot be predicted in advance, it may be assumed that the occurrence of dent due to the jumping phenomenon becomes clear at the stage of the completed vehicle body. In that case, as a countermeasure, it is difficult to change the character line involved in the car body design, so the man-hours such as changing the material and thickness, adding internal reinforcing parts, thermosetting resin sheet, etc. It is conceivable that there will be disadvantages such as an increase in material costs and a lack of sufficient weight reduction.
The present invention pays attention to the above points, and an object of the present invention is to enable prediction of dent resistance in a portion where the curvature changes sharply such as a character line.

In order to solve the above-mentioned problem, the invention described in claim 1 of the present invention is a method for evaluating dent resistance of a surface shape steep portion in a panel plate having a surface shape steep portion whose curvature changes steeply. Because
By performing a finite element analysis simulation using the panel shape conditions of the panel plate and the material conditions applied to the panel plate, a load load at which plastic strain occurs on the plate surface at the surface shape steep portion is obtained, and the load Based on the load, the dent resistance at the steep surface shape portion is evaluated.
Next, the invention described in claim 2 is directed to the structure described in claim 1, based on a load applied to generate plastic strain on the plate surface on the side where the curvature of the surface shape steep portion is convex. It is characterized in that a load load at the time of occurrence of a dent at a shape steep portion is calculated.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to evaluate accurately the dent generation | occurrence | production in a steep surface curvature change part in panel components containing a steep surface curvature change part (surface shape steep part), such as a character line part.
In particular, since the load that generates plastic strain on the plate surface can be obtained by simulation analysis, it is possible to predict the load at which dent is generated at the design stage of the panel shape.
That is, since dent resistance can be evaluated at the stage of drawing design, for example, trial and error in new vehicle development can be reduced.

It is a cross-sectional schematic diagram explaining the dent generation | occurrence | production in the site | part where the curvature has not changed sharply. It is a cross-sectional schematic diagram explaining dent generation | occurrence | production in a surface shape steep part. It is a figure explaining the analysis model in simulation analysis. It is a figure explaining the board used for experiment, and its restraint. It is a figure which shows the relationship between the amount of plastic strains and a load load. It is a figure which shows the relationship of a load-displacement. It is a figure explaining the processing flow which concerns on embodiment based on this invention. It is a figure explaining the FEM analysis model which concerns on embodiment based on this invention. It is a figure explaining the true stress-true strain data of the material which concerns on embodiment based on this invention.

Next, embodiments of the present invention will be described with reference to the drawings.
First, the validity of the dent prediction method based on this invention is demonstrated.
FIG. 1 is a schematic cross-sectional view for explaining the occurrence of dent at a non-steep portion (a position other than a surface shape steep portion) where the curvature of an outer panel of an automotive outer plate component does not change sharply. FIG. 2 is a schematic cross-sectional view for explaining the occurrence of dent at the surface shape steep portion 2 in the outer panel of the automotive outer plate part.

  As shown in FIG. 1, a non-steep portion that is a different portion from the surface shape steep portion where the curvature sharply changes is targeted, and the panel 1 is plasticized by the indenter in the thickness direction from the convex side surface of the panel 1. When a load is applied until deformation occurs, compressive strain occurs on the front surface 1a of the panel 1 (the surface on the convex side of curvature, the upper side in FIG. 1), and the back surface 1b (the surface on which the curvature is concave), A tensile strain is generated on the lower side in FIG. In many cases, the radius of curvature of the entire profile based on the outer panel shape is relatively loose, such as usually designed in a range of about 500 to 10,000 mm. Moreover, the plate | board thickness of the steel plate used for an outer plate is comparatively thin with 0.6-0.8 mm. For this reason, when a load is applied in the thickness direction, the difference in strain between the front surface 1a and the back surface 1b of the panel 1 is small. There is no problem even if the sex is evaluated.

  On the other hand, as shown in FIG. 2, from the front surface 1a (upper surface in FIG. 2) on the convex side of the character line to the character line portion that becomes the surface shape steep portion 2 where the curvature sharply changes, as in FIG. In addition, when a load is applied around the character line by the indenter, a compressive strain is generated on the front surface 1a and a tensile strain is generated on the back surface 1b as in the non-steep portion described above.

  However, compared with a non-steep portion as shown in FIG. 1, the occurrence of dent in the surface shape steep portion 2 is considered to be a state close to a kind of bending back deformation, so a load sufficient to generate dent (permanent dent) is applied. When a load is applied, it is considered that the strain difference, which is the difference between the strain generated on the front surface 1a of the panel 1 and the strain generated on the back surface 1b, is large. For this reason, the amount of dent in the surface shape steep portion 2 seems to change according to the amount of compressive strain of the front surface 1a and the amount of tensile strain of the back surface 1b. It is estimated that the actual dent generation phenomenon cannot be simulated.

Next, in order to verify the estimation, a simple shape model simulating a character line shown in FIG. 3 was set, and a simulation and experiment by FEM analysis were performed.
First, FEM analysis will be described.
The model is a triangular roof shape model in which two flat plates are combined at an angle of 170 degrees and a curved curved surface shape having a radius of curvature of R = 5 mm is formed at a connecting portion between the two flat plates. Here, the size of the planar portion was 400 mm × 600 mm. The ridge line portion of the triangular roof shape model simulates the character line.

In the FEM analysis, the load indenter was set to a rigid body (size 20 mm width × 60 mm length × 5 mm thickness), and the load load position was set to the center of the panel directly above the character line. In the FEM analysis, as shown in the FEM model in FIG. 8, the mesh size is set to 5 mm (however, the mesh size is set to 2 mm at the indenter contact portion and the vicinity 100 mm square), and the solver is LSTC (Livermore Software Corporation). It was performed by static implicit method using LS-DYNA ver9.71. Further, in order to calculate the jumping phenomenon, analysis was performed by an incremental displacement in which the indenter was pushed at a pitch of 0.01 mm. At this time, as a boundary condition, the four sides of the model were restricted only in translation in the X, Y, and Z directions.
As the material conditions, the true stress-true strain data shown in FIG. 9 obtained from the tensile test results of the steel sheet (yield strength YP 163 MPa, tensile strength TS 293 MPa, elongation El 50%) used in the experiments described below were used. The Young's modulus is 206 GPa and the plate thickness is 0.8 mm.
And in FEM analysis, the plastic strain amount about 20 meshes of the panel part (character line ridge line part) that the indenter contacts was calculated for the plate thickness center part and the plate surface (front side and back side), respectively. .

Next, experiments will be described.
In the experiment, a steel indenter having the same size as the indenter conditions set in the FEM analysis was used. The material has the characteristics described above, and a steel plate (yield strength YP163 MPa, tensile strength TS293 MPa, elongation El50%) of about 400 mm × 600 mm flat plate (plate thickness 0.8 mm) was adopted.
Then, as shown in FIG. 4, after pre-bending the plate center portion of the flat plate, the four sides of the plate on which the ridge line portion (vertical angle 170 degrees) is formed by the pre-bending are constrained by a jig. The same configuration as the model set in the analysis was realized. In addition, it restrained by joining 4 sides of a steel plate to a jig | tool by welding. Then, a load was applied to the ridge line portion formed by the pre-bending from the convex side of the ridge line (upper side in FIG. 4) in the plate thickness direction with the indenter. The load conditions are as follows: load load is increased at 10N pitch, load load, unloading, and measurement of the dent amount after unloading are repeated for each load. The load was the dent generation load. The dent amount was measured using a three-point gauge having a gauge length of 50 mm.

FIG. 5 shows the relationship between the amount of plastic strain and the load applied at the center of the plate thickness and the plate surface (front side and back side) determined by FEM analysis. Moreover, since the dent generation load calculated | required by experiment was 350 N, the numerical value (dent generation load) is also written in FIG.
FIG. 6 shows a load-displacement curve obtained in the experiment at that time. As can be seen from FIG. 6, in this experiment, the jumping load was 470N.
As can be seen from the above results, in the simulation analysis by the FEM analysis, the plate thickness back surface 1b reaches the jumping load (470N) and the plastic strain is generated, but the plate thickness front surface 1a is more than that. It can be seen that plastic strain starts to occur at a low value of about 320N.
Since the dent generation load when the dent was actually generated was 350 N, it was found that the plastic strain of the plate thickness front surface 1a is important in the character line portion.

Furthermore, the curvature radius of the ridge line portion was changed from 5 mm to 100 mm (the angle between the flat plates to be combined was 170 degrees), and other conditions were the same as described above, and simulations and experiments by FEM analysis were performed. In this experiment, the dent generation load was 320 N and the jump load was 460 N. In the same manner as described above, the generation load of plastic strain on the plate thickness front surface 1a by FEM analysis was about 320N, and the plastic strain start load on the plate thickness back surface 1b was about 460N.
From the simulation analysis and experiment as described above, the inventors start to generate plastic strain on the front surface 1a in the simulation analysis in the surface shape steep portion 2 such as the character line portion where the curvature changes sharply. It was found that the load at the time was the load when the dent was generated for the first time.

That is, based on the material conditions and panel shape of the target panel 1, the first load load that is the minimum load load that causes plastic strain on the plate front surface 1 a due to the load on the surface shape steep portion 2 is obtained. The surface shape steep portion 2 was found to generate dent when a load greater than or equal to the first load is applied, and the dent generated load can be predicted at the design stage.
It should be noted that the load generated when the plastic strain on the front surface 1a in the FEM analysis begins to occur may also be used as the dent generation load for portions other than the surface shape steep portion 2, that is, the portion where the curvature does not change sharply.

Next, the dent resistance evaluation method based on this invention is demonstrated.
FIG. 7 is a diagram illustrating a processing procedure for dent resistance prediction.
First, in step S10, an analyst sets a model corresponding to the material conditions of the target panel 1 and the target panel shape. For example, the material conditions are true stress-true strain curve, Young's modulus, plate thickness, indenter information (shape), and panel shape conditions are panel size (length, width) radius of curvature of the panel surface, surface shape The apex radius of curvature and apex angle of the steep part and further constraint conditions (whether translational movement is possible, whether rotational movement is possible) are set.

Next, in step S20, the computer performs a simulation analysis on the model, and when the load is applied to the surface shape steep portion 2 from the surface on which the curvature is convex in the plate thickness direction, The analyst obtains the load applied when the plastic strain starts to occur on the front surface 1a, which is the surface, as the first load load.
For the simulation analysis, for example, FEM analysis using the static implicit method as described above may be employed.

Next, in step S30, the analyst determines whether or not the first load load that is a dent generation load is less than a preset target dent generation load T1.
When the condition of step S30 is satisfied (that is, when the first load load is less than the target dent generation load T1), the target dent resistance cannot be obtained, and the process proceeds to step S40. On the other hand, when the above condition is not satisfied (that is, when the first load load is equal to or greater than the target dent generation load T1), it is determined that the target dent resistance can be obtained, and the process proceeds to step S50.

In step S40, the first load load is displayed as a dent generation load and a jump phenomenon generation load of the surface shape steep portion 2 and the analyst requests a panel condition change, and according to the request After the computer performs a process of acquiring and updating the input of the set panel shape and material condition change information, the process proceeds to step S20, and the computer and the analyst repeat the process. For example, the change information of material conditions is true stress-true strain curve, plate thickness, etc., and the change information of panel shape conditions is the radius of curvature of the panel surface, the radius of curvature of the apex of the steep surface shape, the apex angle, etc input.
In step S50, the first load load is displayed as a dent generation load of the surface shape steep portion 2 and the process ends.
The above processing is performed for each surface shape steep portion 2, but when the surface shape steep portion 2 is continuous, the analyst sets evaluation points at the representative points or preset distance intervals. What is necessary is just to implement for every evaluation point.

As described above, in the present embodiment, in the panel 1 including the steep surface curvature changing portion such as the character line portion, it is possible to accurately predict the occurrence of dent at the steep surface curvature changing portion. Moreover, prediction can be made at the time of simulation analysis.
Then, the design can be changed so that the predicted dent generation load becomes equal to or higher than the target dent generation load at the design stage of the drawing.
At this time, the simulation analysis may be applied to an analysis of the tension rigidity, which is an evaluation value related to the elastic deformation behavior, and an evaluation of the jump phenomenon occurrence load.

1 Panel 1a Front side 1b Back side 2 Surface shape steep part

Claims (2)

In a panel plate having a surface shape steep portion where the curvature changes sharply, the method for evaluating dent resistance of the surface shape steep portion,
By performing a finite element analysis simulation using the panel shape conditions of the panel plate and the material conditions applied to the panel plate, a load load at which plastic strain occurs on the plate surface at the surface shape steep portion is obtained, and the load A dent resistance evaluation method, wherein the dent resistance at a steep portion of the surface shape is evaluated based on a load. 2. The load at the time of occurrence of a dent at the surface shape steep portion is calculated based on a load load at which plastic strain occurs on the surface of the plate having a convex curvature at the surface shape steep portion. Dent resistance evaluation method described in 1.

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