Testing device for evaluating dent resistance and method for evaluating dent resistance

Abstract

To provide a technique that can evaluate the dent resistance more accurately and easily by using a smaller device configuration.SOLUTION: A testing device for evaluating dent resistance of a plate-shaped test material 1 by a measurement object part being a portion for performing the test of the dent resistance includes: an indenter 13 which presses one surface 1A of the measurement object part in the thickness direction of the test material 1; multiple imaging parts which can image the one surface 1A of the measurement object part; a displacement analysis part 18A which refers to each image data of the one surface 1A before pressing by the indenter 13 and after releasing the pressing imaged by the multiple imaging parts and obtains coordinates of the measurement object part and displacement information in the plate thickness direction by means of the digital image correlation method using a computer; and an evaluation part 18B which evaluates the dent resistance from the displacement information obtained by the displacement analysis part 18A.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for evaluating the dent resistance of test materials whose measurement site is in the shape of a plate (panel), such as an outer panel part (panel part) for an automobile body. [Background technology]

[0002] Metal sheets that require dent resistance include, for example, panel parts for automobiles, particularly outer panel parts. In recent years, there has been a trend toward reducing the thickness of the metal plates that make up the body of automobiles to reduce their weight, with the aim of improving fuel efficiency and driving range. However, while thinner metal plates reduce collision safety, this reduction tends to be addressed by using high-strength steel plates.

[0003] Therefore, there is a trend toward higher strength and thinner thickness for exterior panel parts such as doors and hoods. In this regard, design is particularly important for automotive exterior panel parts, and it is desirable for them to have good dent resistance, which is an indicator of appearance quality. However, thinner exterior panel parts result in a decrease in dent resistance. Therefore, the problem of dent resistance is solved by, for example, increasing the strength of exterior panel parts. A "dent" refers to the phenomenon in which a depression (indentation) remains in a plate member (panel material) when a local force is applied to the plate member and then released, and this phenomenon affects the appearance quality of the plate member.

[0004] There are no established standards for the evaluation and testing methods of dent resistance. Generally, dent resistance is evaluated by the following method. That is, in this evaluation method, a highly rigid indenter is pressed against the surface of the plate member to be evaluated under load control or displacement control. Then, the dent resistance is evaluated based on the size of the dent (residual dent) remaining after the pressure from the indenter is released, or by increasing the load in stages until a dent appears.

[0005] The residual dent depth is usually measured using a contact-type dial gauge. However, this measurement method has problems with the accuracy of the measurement, such as the difficulty of accurately measuring the deepest dent using a dial gauge and inconsistent measurements depending on the person taking the measure. In particular, when measuring the dented area from multiple directions using a contact-type dial gauge in order to improve the accuracy of dent resistance evaluation, this becomes a cumbersome task and there is a risk of a significant decrease in measurement accuracy.

[0006] Here, a simple and accurate method for testing dent resistance is described, for example, in Patent Document 1. Patent Document 1 describes a test method in which a test device that reproduces test conditions determined by CAE is used to apply a load to an automobile body using an electric cylinder and non-contact measurement is performed using a displacement sensor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-42030 Summary of the Invention [Problem to be solved by the invention]

[0008] The test method described in Patent Document 1 is a method in which the displacement of a point where a load is applied by a spherical load head (indenter) is measured at a point. Therefore, this test method has the problem that it cannot measure the history of the shape around the loaded point. Furthermore, because this test method measures the displacement of the loaded point at a point, there is a problem in terms of accuracy in whether the most depressed point can be accurately measured. Furthermore, this test method may require large-scale test equipment. Furthermore, because it is necessary to perform CAE analysis in advance to determine the test conditions, the preparation required for the test takes a lot of man-hours, and it cannot be said that the test can be easily performed.

[0009] The present invention has been made in light of the above points, and aims to provide a technique that enables evaluation of dent resistance with simple labor and greater accuracy using a smaller-scale device configuration. [Means for solving the problem]

[0010] In order to solve the problem, one aspect of the present invention is a testing device for evaluating the dent resistance of a plate-shaped test material, where the test subject, which is the part where the dent resistance is tested, is a testing device for evaluating dent resistance, comprising: an indenter that presses one side of the test subject in the thickness direction of the test material; a plurality of imaging units that can image the one side of the test subject; a displacement analysis unit that references each image data of the one side of the test subject, imaged by the plurality of imaging units, before and after pressing by the indenter, and determines the coordinates of the test subject and displacement information in the plate thickness direction by a digital image correlation method using a computer; and an evaluation unit that evaluates the dent resistance from the displacement information determined by the displacement analysis unit.

[0011] Another aspect of the present invention is a method for evaluating dent resistance in which a test piece has a plate-shaped test piece as a measurement portion, which is the part to be tested for dent resistance, and one side of the test piece is pressed in the thickness direction of the test piece with an indenter, and dent resistance is evaluated from the shape of the test piece after the load from the indenter is released. The method comprises: capturing images of the one side of the test piece before and after the load from the indenter is released; referencing the captured image data before and after the load from the indenter, and using a digital image correlation method using a computer to determine coordinates and displacement information in the plate thickness direction at the test piece; and evaluating dent resistance from the determined displacement information. [Effects of the Invention]

[0012] According to this aspect of the present invention, it is possible to easily and accurately detect the depression caused by the load applied by the indenter at the portion pressed by the indenter in the plate-shaped test part and at the outer periphery of the pressed part, and as a result, it is possible to easily and accurately evaluate the dent resistance of the test part. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a conceptual diagram of a test device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the arrangement of the measurement target portion, the placement table, and the pressing tool. [Figure 3] FIG. 2 is a diagram illustrating a configuration of an evaluation control unit. [Figure 4] 1A is a side view showing a blank material before processing, and FIG. 1B is a cross-sectional view showing the shape of the test material after press processing. [Figure 5] FIG. 1 is a diagram illustrating measurement using a conventional three-point gauge type dial gauge. [Figure 6] FIG. 10 is a plan view showing the relationship between the maximum displacement position and the separated position. [Figure 7] FIG. 10 is a diagram showing an example of three-dimensional displacement distribution after unloading. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. (composition) The testing device for evaluating dent resistance of this embodiment is a testing device for evaluating the dent resistance of a test material whose measurement portion, which is the portion where the dent resistance test is performed, is in the form of a plate.

[0015] In this embodiment, dent resistance is evaluated by pressing an indenter against the surface of a plate-shaped test material to apply a load, and then determining whether or not a dent occurs after the load is removed, and the state of the dent that occurs. In this embodiment, a digital image correlation method is used to accurately measure the displacement of the pressing position and its surroundings in three dimensions. As a result, one of the features is that, for example, evaluation information (relative displacement amount) for one dent from multiple directions can be easily and accurately obtained.

[0016] <Test material 1> In this embodiment, as shown in FIG. 4, a flat steel plate (FIG. 4(a)) made of the material to be evaluated was blunt-formed to form a test material 1. Specifically, in this embodiment, as shown in FIG. 4(b), a panel part manufactured by blunt-forming into a truncated cone shape was used as the test material 1. The top plate portion 1A of the truncated cone-shaped panel part was used as the part to be measured. In the test material 1, reference numeral 1B denotes a wall portion, and reference numeral 1C denotes a flange portion. In the test material 1 of this embodiment shown in FIG. 4, the top plate portion 1A has a curved shape that is convex upward with the central portion as the apex, in order to make it easier to evaluate dent resistance.

[0017] The shape of the panel component that serves as the test material 1 is not limited to this. A flat plate itself may also be used as the panel component (test material 1). However, if a wall 1B is formed around the entire periphery, deformation at the outer periphery of the measured part can be minimized when pressed with an indenter. In other words, by forming a wall 1B around the outer periphery of the test material 1, the rigidity at the outer periphery of the test material 1 (measured part) is increased, making it easier to perform measurements on the plate-shaped measured part. Furthermore, by forming the outer periphery of the part to be measured into a circular shape in a plan view, the directionality of deformation in the in-plane direction is suppressed.

[0018] The present disclosure provides a technique suitable for evaluating the dent resistance of outer panel parts for automobiles. Furthermore, although there are no particular limitations on the material of the test material 1, in this embodiment, assuming an automotive panel part, a case will be described in which the test material 1 is a steel plate as an example. The test material 1 targeted by the present disclosure is not limited to a steel plate, but may be other metal plates such as aluminum or copper. Furthermore, the test material 1 targeted by the present disclosure may be made of resin, etc. Note that, in evaluating dent resistance, the final automotive panel part itself does not need to be used as the test material 1; for example, it is sufficient to reproduce a partial area of ​​the final product and evaluate the dent resistance. Furthermore, when evaluating the dent resistance of the plate material itself used, it is not necessary to give the test material 1 the same shape as the plate shape to be given to the final product.

[0019] In this specification, a panel component refers to a component having a panel-like plate-like portion. The panel-like plate-like portion to be measured may be flat or may have a plate shape with a predetermined curvature. In addition, in the present embodiment illustrated in FIG. 4, the entire top panel portion 1A has an upwardly convex curve, but there are no particular limitations on the surface shape of the measured portion, such as a shape with a partial recess. In addition, automotive panel components often have different curvatures in two orthogonal directions.

[0020] In this embodiment, the upper surface (one surface 1A) of the top plate portion 1A, which is the portion to be measured, is used as the measurement surface. In this embodiment, a random pattern for processing by digital image correlation is applied to at least the upper surface of the top plate portion 1A of the test material 1. A known method may be used to apply a random pattern to the surface of the test material 1.

[0021] <Test equipment> The test device for evaluating dent resistance of this embodiment is a device for evaluating the dent resistance of a test material 1, the measurement portion of which is the part to be tested for dent resistance, being a plate-shaped (panel-shaped) test piece. The test device for evaluating dent resistance of this embodiment includes a test material support mechanism, a load applying unit, a camera 17, and an evaluation control unit 18.

[0022] <Test material support mechanism> As shown in FIG. 1, the test material support mechanism supports the outer periphery of the top plate portion 1A (measurement portion) of the test material 1. In the test material support mechanism of this embodiment, the outer periphery of the top plate 1 A is restrained. The restraining position may be the position of the flange, but from the viewpoint of suppressing the influence of deformation of the wall 1 B, it is preferable to restrain the outer periphery of the top plate 1 A.

[0023] As shown in FIG. 1, the test material support mechanism of this embodiment comprises a placement table 10 and a presser 11 arranged opposite each other above and below, and further comprises a clamp 12 for restraint. The upper part of the placement table 10 is made of a frame material that can abut against the outer periphery of the lower surface (other surface 1A) of the top panel 1A. In other words, the placement table 10 does not support the surface inside the outer periphery of the top panel 1A. The upper part of the placement table 10 in this embodiment is configured in a ring-shaped frame shape that can abut along the outer periphery of the top plate portion 1A, as shown in Fig. 2. Note that the frame shape of the upper part of the placement table 10 is not limited to a ring shape, and may be other shapes such as a rectangle.

[0024] The presser 11 of this embodiment is a ring-shaped frame member as shown in FIG. 2, and abuts against the upper surface (one surface 1A) of the outer periphery of the top panel portion 1A. Furthermore, with the outer periphery of the top plate portion 1A sandwiched between the test stand and the retainer 11 from above and below, the retainer 11 is pressed downward toward the placement stand 10 by three or more clamps 12. This restrains the outer periphery of the top plate portion 1A. Here, the test material support mechanism may be composed of only the placement table 10.

[0025] <Load bearing part> The load applying unit is a device that presses the top plate 1A and applies a load from above in the plate thickness direction to a part of the top plate 1A. As shown in FIG. 1, the load applying unit of this embodiment includes an indenter 13, a load measuring instrument 15, and a pressing force applying device 16.

[0026] The indenter 13 is made of steel and has a hemispherical surface that comes into contact with the test material 1. There is no limitation on the shape of the surface that comes into contact with the test material 1. The indenter 13 is connected to a pressing force applying device 16 via a rod-shaped connecting member 14 and can be moved up and down by a movable part of the pressing force applying device 16 . The test piece 1 is also provided with a load measuring instrument 15 that measures the pressing load applied to the test piece 1 by the indenter 13. In this embodiment, the load measuring instrument 15 is configured from a load cell. The load cell is inserted into the connection between the connecting member 14 and the movable part of the pressing force loading device 16, thereby detecting the load applied to the indenter 13. The pressing force of the indenter 13 is set, for example, assuming the force of an adult pressing against a panel component with their hand. The pressing force of the indenter 13 can be set assuming the pressing force when the dent to be evaluated occurs. It is not necessary to use the load measuring device 15. Instead, the pressing force of the indenter 13 may be controlled by the amount of movement of the indenter 13 in the pressing direction.

[0027] In this embodiment, a displacement meter 19 is provided that comes into contact with the underside of the top plate 1A and measures the displacement of the top plate 1A in the up-down direction (thickness direction). This displacement meter 19 is not necessary. For example, the displacement meter 19 can determine whether the amount of pressing by the indenter 13 is excessive, even if the pressing load is within the allowable value.

[0028] <Camera 17 (imaging unit)> This embodiment includes a plurality of cameras 17. By referring to image data from the plurality of cameras 17, displacement in the out-of-plane direction can be detected by digital image correlation. Each camera 17 has the upper surface of the tabletop 1A set as its imaging area, and captures an image of the upper surface of the tabletop 1A. The image data captured by each camera 17 is used by the evaluation control unit 18.

[0029] <Evaluation control unit 18> 3, the evaluation control unit 18 includes a displacement analysis unit 18A and an evaluation unit 18B. The evaluation control unit 18 is configured to execute processing using a computer.

[0030] <Displacement analysis section 18A> The displacement analysis unit 18A refers to the image data of the top surface (one surface 1A) of the top plate 1A captured by each camera 17 before and after the load is applied by the indenter 13. Then, the displacement analysis unit 18A calculates the coordinates of the top plate 1A, which is the part to be measured, and displacement information in the plate thickness direction before and after the load is applied, by a digital image correlation method using a computer.

[0031] The displacement analysis unit 18A of this embodiment inputs image data of the top surface of the tabletop 1A before the indenter 13 presses, and image data of the top surface of the tabletop 1A after the indenter 13 presses and then lifts to release the load from the indenter 13. The displacement analysis unit 18A then applies a digital image correlation method to the input image data to obtain coordinates and displacement information in the plate thickness direction (vertical direction) of the top surface of the tabletop 1A after the pressure from the indenter 13 is released, relative to the top surface of the tabletop 1A before the load. The coordinates and displacement information constitute, for example, information on the three-dimensional displacement distribution on the top surface of the tabletop 1A.

[0032] Here, a marking may be applied to the indenter 13. Then, the camera 17 may continuously or intermittently capture images of the top surface of the top plate 1A, and the displacement analysis unit 18A may acquire image data to be used for processing by the digital image correlation method, provided that the mark on the indenter 13 is not reflected in the image data or the mark does not overlap with the top surface of the top plate 1A.

[0033] <Evaluation section 18B> The evaluation unit 18B evaluates the dent resistance from the displacement information consisting of the distribution information of the displacement obtained by the displacement analysis unit 18A. For example, the evaluation unit 18B determines that a dent will occur when the maximum value of the displacement calculated by the displacement analysis unit 18A is equal to or greater than a preset threshold value. Alternatively, the dent resistance of the test material 1 may be evaluated by using the ratio of the maximum value of the displacement to a preset threshold value as an evaluation value of the dent resistance.

[0034] Here, a dent is a depression that occurs locally due to local pressure, and therefore, it is preferable to judge dent resistance based on the state of local depression occurrence due to pressure. For this reason, in conventional methods, as shown in FIG. 5, for example, the amount of depression at the center of the pressing is measured using a three-point gauge type dial gauge with a position near the center of the pressing (for example, a position 25 mm away) as a reference before and after applying a load with an indenter 13, and dent resistance is evaluated.

[0035] The evaluation unit 18B of this embodiment also preferably processes the displacement distribution information to evaluate dent resistance based on the relative displacement in the thickness direction at the maximum displacement position P relative to the displacement in the thickness direction at one or more positions K1, K2, ..., Kn (see Figure 6) spaced a predetermined distance L from the maximum displacement position P, which is the most displaced in the thickness direction. Here, the maximum displacement position P, which is the most displaced in the thickness direction, is usually located at the center of the pressing part of the indenter 13. However, depending on the test conditions, the maximum displacement position P may be slightly shifted laterally from the center of the pressing part of the indenter 13. The predetermined distance L is, for example, in the range of 20 mm (greater than the radius of the indenter 13) to 50 mm. If the predetermined distance L is set too large, it may be affected by the surface shape of one surface 1A of the measurement target. If the predetermined distance L is set too small, it may be difficult to evaluate the dent depression.

[0036] In this embodiment, the displacement in the plate thickness direction of the surface after pressing and unloading by the indenter 13 relative to the surface before pressing with the indenter 13 is acquired, and the dent depression can be evaluated based on this displacement information. Therefore, in this embodiment, it is possible to easily evaluate dent resistance by taking into account the curvature of the surface before pressing. Furthermore, when the curvature of the surface of the measured portion differs in two directions, it is preferable to evaluate dent resistance using the relative displacement amount from two or more directions. In contrast, in this embodiment, it is possible to obtain the relative displacement amount from multiple directions along the surface with respect to the maximum displacement position P from a single measurement data.

[0037] For example, the evaluation unit 18B of this embodiment determines the maximum displacement position P (maximum displacement point) that is displaced the most in the plate thickness direction from the information on the distribution of displacement after the load by the indenter 13 is removed. Next, in a plan view (seen from the pressing direction of the indenter 13), the displacement at positions on a circle with a radius of a preset distance L and centered on the maximum displacement point is obtained. The positions on this circle are one or more distant positions K that are spaced a preset distance L from the maximum displacement position P.

[0038] The evaluation unit 18B of this embodiment then determines, for example, the relative displacement amount in the thickness direction at the maximum displacement position P (referred to as the first relative displacement amount) relative to the displacement in the thickness direction at the position on the circle where the displacement is maximum (separate position K) as the evaluation value of dent resistance. Alternatively, the evaluation unit 18B of this embodiment determines the relative displacement amount in the thickness direction at the maximum displacement position P (referred to as the second relative displacement amount) relative to the displacement in the thickness direction at the position (separate position K) on the circle where the displacement is minimum, as the evaluation value of dent resistance.

[0039] Moreover, the evaluation unit 18B of this embodiment uses the average value of the first relative displacement amount and the second relative displacement amount or the two relative displacement amounts as an evaluation value of the dent resistance. In addition, the first relative displacement amount and the second relative displacement amount are often the relative displacement amounts in the directions along the largest curvature and the smallest curvature imparted along the first surface before pressing by the indenter 13, respectively.

[0040] The method of determining the relative displacement amount as the evaluation value described above is one example. For example, the relative displacement amount in the thickness direction at the maximum displacement position P to the average value of the displacement amounts at multiple points on a circle may be used as the evaluation value for dent resistance. Furthermore, by imitating the conventional three-point gauge method, the relative displacement amount in the thickness direction at the maximum displacement position P to the average value of the displacements at distant points symmetrically positioned on the left and right sides of the maximum displacement position P may be used as the evaluation value for dent resistance. The ratio of the calculated relative displacement amount to a reference value may also be used as the evaluation value.

[0041] In the above description, the relative displacement amount is used as the evaluation value of dent resistance, but this is not limiting. For example, the gradient (inclination) of a line connecting the maximum displacement position P and the isolated point based on the displacement distribution information may be used as the evaluation value of dent resistance. The evaluation value of dent resistance can also be calculated by taking into account the set distance from the maximum displacement position P to the isolated point in a plan view.

[0042] Furthermore, in this case, since the process is performed by computer, the position of the maximum displacement position P can be determined with high accuracy.

[0043] (Operation etc.) In this embodiment, as in the conventional measurement method, the part to be measured is pressed with an indenter 13 to apply a local load, and the dent resistance is evaluated based on whether or not a dent occurs after the load is applied, and the state of the dent. However, in this embodiment, image data of one surface 1A of the measurement part before pressing (loading) with the indenter 13 and image data after the pressing (loading) is removed are acquired. Then, by referring to the image data, a digital image correlation method using a computer is used to obtain information on three-dimensional displacement distribution, which is made up of coordinates at the measurement part and displacement information in the plate thickness direction.

[0044] This allows for the determination of three-dimensional displacement information in the thickness direction of the surface shape after unloading, relative to the surface shape before loading, through a single computer process. In other words, three-dimensional displacement information can be obtained easily and accurately. As a result, in this embodiment, by referring to the above displacement information data, the maximum displacement position P, which is the position where the displacement is greatest in the plate thickness direction, can be easily and accurately determined, and a highly accurate evaluation value for dent resistance can be obtained.

[0045] Here, since automotive panel parts usually have different curvatures in two orthogonal directions, it is preferable to evaluate dent resistance using information on the degree of depression from these two directions. In contrast, in this embodiment, three-dimensional displacement information is obtained in a single process, so evaluation values ​​for dent resistance in multiple directions along the surface of the measured part can be obtained easily and accurately.

[0046] The above loading and unloading process is performed by applying a load to the test material 1 with the indenter 13, and then driving it in the opposite direction to unload it when a predetermined load is reached. If this loading and unloading is considered one cycle, the testing machine may be set so that the predetermined load is reached in one cycle, or a continuous test may be set so that the predetermined load is reached in several cycles, for example, by loading 50 N and unloading, followed by loading 100 N and unloading.

[0047] The displacement information may be obtained for each cycle, or after multiple cycles have been completed. In this embodiment, image data is acquired for each cycle to be evaluated and processed by a computer, so that the change in the dent, etc., can be easily obtained. Furthermore, if a displacement meter is installed, the amount of displacement of the measurement target relative to the load can also be measured.

[0048] The camera 17 may also be set to take continuous images. In this case, the continuous images are taken after the testing machine is set up and before the test is started. The sampling rate at this time should be such that the deformation behavior of the test material 1 during the test can be smoothly analyzed. The sampling rate may be set according to the moving speed (displacement speed) of the indenter 13.

[0049] In this case, although the deformation of the test material 1 cannot be measured in the area where the indenter 13 is captured in the image during testing, it is possible to measure the deformation behavior of the surrounding test material 1. Furthermore, because the initial and final images were taken with the indenter 13 outside the angle of view, it is possible to pinpoint and evaluate the most depressed area by analyzing the displacement in the load direction, and there is no variation in values ​​depending on the measurer.

[0050] In this case, the deformation behavior of the measured part in response to the pressing load can be obtained. In addition, the 3D shape of the measured surface can be output using finite elements, which has the advantage of making it easy to compare the accuracy with that of CAE analysis. In other words, it can also contribute to improving the accuracy of CAE analysis.

[0051] (others) The present disclosure may also have the following configuration. (1) A test device for evaluating the dent resistance of a plate-shaped test material, the test part being the part where the dent resistance is tested, an indenter that presses one surface of the measurement portion in the thickness direction of the test material; a plurality of imaging units capable of imaging the one surface of the measurement target; a displacement analysis unit that refers to each image data of the one surface before and after pressing by the indenter, which is captured by the plurality of imaging units, and determines the coordinates of the measurement portion and displacement information in the plate thickness direction by a digital image correlation method using a computer; an evaluation unit that evaluates dent resistance based on the displacement information obtained by the displacement analysis unit; A test device for evaluating dent resistance comprising: (2) A restraining portion is provided that restrains the outer periphery of the measurement target portion. (3) A load measuring device is provided to measure the pressing load applied by the indenter. (4) The evaluation unit uses a computer to evaluate the dent resistance based on the displacement information and the relative displacement in the thickness direction at the maximum displacement position relative to the displacement in the thickness direction at one or more positions spaced a predetermined distance from the maximum displacement position where the greatest displacement in the thickness direction occurs. (5) A method for evaluating dent resistance in which a test piece having a plate-shaped test piece as a test piece for which a test piece is to be tested for dent resistance is subjected, the method comprising pressing one surface of the test piece with an indenter in the thickness direction of the test piece, and evaluating the dent resistance from the shape of the test piece after removing the load from the indenter, taking images of the one surface of the measurement part before and after the load is removed by the indenter; The image data taken before and after the load by the indenter is referenced, and the coordinates and displacement information in the plate thickness direction at the measurement portion are obtained by a digital image correlation method using a computer. Evaluating dent resistance from the displacement information obtained above. Method for evaluating dent resistance. (6) Based on the displacement information obtained above, the relative displacement amount in the thickness direction at the maximum displacement position relative to the displacement in the thickness direction at each of one or more positions spaced a predetermined distance from the maximum displacement position where the greatest displacement in the thickness direction due to the load of the indenter occurs is obtained, and the dent resistance is evaluated from the one or more relative displacement amounts. [Example]

[0052] Next, an example of this embodiment will be described. As the plate material for the test material, a BH steel plate having a thickness of 0.50 mm and a tensile strength of 440 MPa class was used. In this example, the above plate material was subjected to truncated cone bulging to produce test material 1. The press forming conditions were set so that the equivalent strain at the punch bottom (the surface to which the indenter 13 applies a load) was 2%. After forming, the material was subjected to a heat treatment simulating an automobile baking line.

[0053] A coating was applied to the top plate portion 1A of the test material 1 to give it a random pattern. In order to make it easier to understand the comparison with the conventional method, in this example, the top plate portion 1A was set to a flat shape before the test. The outer periphery of the top plate 1A of the test material 1 was restrained as in the above embodiment. The loading condition was one cycle of loading and unloading, and a load of 250 N was applied by the indenter 13.

[0054] Example 1 In Example 1, as described in the embodiment, three-dimensional displacement information was obtained by the digital image correlation method from image data before the load was applied by the indenter 13 and image data after the load was removed. An example of the distribution of the displacement is shown in FIG.

[0055] Then, from the displacement information, an evaluation value was calculated using the three-point gauge method. That is, the displacement amounts were calculated at three points before and after the load: the center of the test piece 1 (the point where the indenter 13 applied the load), and points symmetrical about the center of the test piece 1, at a distance of +25 mm and a distance of -25 mm. The relative displacement amount (residual depression amount) at the maximum displacement position P relative to the distance points was calculated to be 0.36 mm. In this example, since the top plate portion 1A had a flat shape before the test, the difference in the relative displacement amount depending on the measurement direction was small.

[0056] Furthermore, the remaining dent depth of the top plate portion 1A after unloading was separately measured using a commercially available three-dimensional shape measuring device with a laser distance meter, and was found to be 0.36 mm. This value is the same as that of Example 1. This result demonstrates that the test method according to the present invention can accurately evaluate dent resistance.

[0057] In this example, since the top plate 1A has a flat shape, the measurements using the laser distance meter match those in Example 1. If the top plate 1A is curved, the measurements will differ depending on the measurement direction even when using a laser distance meter. For this reason, for example, it would be time-consuming to measure the amount of residual depression along the surface direction of the maximum curvature using a laser distance meter. In contrast, the test method according to the present invention allows for simple and accurate determination.

[0058] (Comparative Example) On the other hand, after the load was removed from the top plate portion 1A, three people measured the amount of residual dent using a contact dial gauge, a conventional method, by the three-point gauge method, as shown in Figure 5. The measurement result (residual dent amount) by measurer A was 0.31 mm, the measurement result (residual dent amount) by measurer B was 0.26 mm, and the measurement result (residual dent amount) by measurer C was 0.33 mm. In other words, the measurements were different between the three people, and also different from the measurement results obtained using a commercially available 3D shape measuring device. From these results, it is clear that while the conventional method results in variations in values ​​depending on the measurer, the measurement method according to the present invention makes it possible to measure the amount of residual dent with high accuracy. [Explanation of symbols]

[0059] 1 Test material 1A Top plate 1B Wall section 10 Placement stand 11 Retainer 12 Clamp 13 Indenter 15 Load measuring instrument 16 Pressurized load device 17 Camera 18 Evaluation control section 18A Displacement analysis section 18B Evaluation Section K remote position L distance P Maximum displacement position

Claims

1. A test device for evaluating the dent resistance of a plate-shaped test material, the test part being the part where the dent resistance is tested, an indenter that presses one surface of the measurement portion in the thickness direction of the test material; a plurality of imaging units capable of imaging the one surface of the measurement target; a displacement analysis unit that refers to each image data of the one surface before and after pressing by the indenter, which is captured by the plurality of imaging units, and determines the coordinates of the measurement portion and displacement information in the plate thickness direction by a digital image correlation method using a computer; an evaluation unit that evaluates dent resistance based on the displacement information obtained by the displacement analysis unit; Equipped with The evaluation unit evaluates the dent resistance based on the displacement information, using a computer, based on the relative displacement amount in the plate thickness direction at the maximum displacement position relative to the displacement in the plate thickness direction at one or more positions spaced a predetermined distance from the maximum displacement position where the plate thickness direction is most displaced. A test device for evaluating dent resistance, characterized by:

2. A restraining portion is provided which restrains the outer circumferential side of the measurement target portion.

2. A test device for evaluating dent resistance according to claim 1.

3. a load measuring instrument for measuring the pressing load applied by the indenter; 2. A test device for evaluating dent resistance according to claim 1.

4. A method for evaluating dent resistance in which a test piece has a plate-shaped test piece as a test piece portion to be tested for dent resistance, the method comprises pressing one surface of the test piece portion with an indenter in the thickness direction of the test piece, and evaluating the dent resistance from the shape of the test piece portion after the load imposed by the indenter is removed, taking images of the one surface of the measurement part before and after the load is removed by the indenter; The image data taken before and after the load by the indenter is referenced, and the coordinates and displacement information in the plate thickness direction at the measurement portion are obtained by a digital image correlation method using a computer. Evaluate dent resistance from the displacement information obtained above, Based on the displacement information thus obtained, a relative displacement amount in the thickness direction at the maximum displacement position relative to the displacement in the thickness direction at each of one or two or more positions spaced a predetermined distance from the maximum displacement position where the indenter has displaced the most in the thickness direction due to the load of the indenter is obtained, and dent resistance is evaluated from the one or more relative displacement amounts. A method for evaluating dent resistance, comprising:

Images