KR102317640B1 - Specimen fixation apparatus for shear testing device - Google Patents

Abstract

A specimen holding device for a simple shear test includes a first wedge grip coupled to a first end of a specimen, and a second wedge grip coupled to a second end opposite to the first end in the specimen, wherein the first and Each of the second wedge grips includes a first grip including a groove portion in which the first end or the second end of the specimen is mounted, and the specimen is fixed to the groove portion by coupling to the groove portion while the specimen is mounted in the groove portion. It may include a second grip including a protrusion.

Description

Specimen holding device for simple shear testing equipment

An embodiment of the present invention relates to a specimen holding device, and more particularly, to a specimen holding device for a simple shear test device of ultra-high strength steel sheet.

Recently, in the automobile industry, the demand for light and rigid ultra-high-strength steel sheet is increasing due to various environmental and safety regulations. For example, a giga-class ultra-high-strength steel sheet having a tensile strength of 1 GPa or more is used as a frame for protecting the vehicle from external impact by forming the frame of the vehicle.

In the case of giga-class ultra-high strength steel sheet, a large amount of springback occurs during bending and drawing processing. Therefore, in order to apply such giga-class ultra-high-strength steel sheet as an actual product, various trials and errors are required through process equipment. However, these trials and errors performed while replacing equipment are inevitably costly and time-consuming. Accordingly, many automobile companies are solving the problems related to the forming of ultra-high-strength steel sheets by predicting the formability of ultra-high-strength steel sheets through a simulation method called finite element analysis and configuring facilities accordingly.

A simple shear testing device is a testing device mainly used to obtain the values of physical properties required for the simulation, and is a device that contributes to improving the accuracy of molding simulation. The simple shear test is a test to obtain simple shear stress and strain values from the deformation region of the specimen by fixing both sides of a rectangular specimen to the grip part and then applying a downward or upward deformation of one grip part in the longitudinal direction of the specimen. The simple shear stress and strain values obtained in the deformation region of the specimen through the simple shear test are used to obtain material property values, and the obtained property values can be input to the simulation to improve the molding prediction accuracy.

On the other hand, in the case of 1 GPa class ultra-high strength steel sheet, since the yield strength and tensile strength of the steel are very high, the force of the specimen grip part of the simple shear test apparatus may be insufficient. In this case, there is a problem in that a reliable shear-stress strain value cannot be secured because slip occurs in the grip part of the specimen during a simple shear test.

An object to be solved through an embodiment of the present invention is to provide a specimen fixing device capable of preventing the specimen from slipping during a simple shear test.

A specimen fixing device for a simple shear test according to an embodiment of the present invention for solving the above problems, a first wedge grip coupled to a first end of a specimen, and a second end opposite to the first end in the specimen and a second wedge grip, wherein the first and second wedge grips each include a first grip including a groove portion in which the first end or the second end of the specimen is mounted, and the specimen is placed in the groove portion. It may include a second grip including a protrusion for fixing the specimen by being coupled to the groove in the mounted state.

The groove portion may have a shape in which a first direction opposite to the first end or the second end of the specimen and a second direction opposite to the protrusion are opened.

The groove portion may include a bottom surface in contact with the first surface of the specimen, and a plurality of sidewalls in contact with the first end or the second end of the specimen.

The protrusion may be in contact with the second surface of the specimen.

The specimen has first and second grip regions to which the first and second wedge grips are respectively coupled, and a deformable region positioned between the first and second grip regions, the length (L) of the specimen and The width W may satisfy Equation 1 below.

[Equation 1]

2 ≤ L/W ≤ 3.2

The width h of the deformation region may satisfy Equation 2 below.

[Equation 2]

12 ≤ L/h ≤ 16

The thickness t of the specimen may satisfy Equation 3 below.

[Equation 3]

0.8mm ≤ t ≤ 2mm

The height (a) of the protrusion may satisfy Equation 4 below.

[Equation 4]

(c-t) × 1.1 ≤ a ≤ (c-t) × 1.2

Here, c is the depth of the groove and has a fixed value.

The length D of the groove may satisfy Equation 5 below.

[Equation 5]

L × 1.008 ≤ D ≤ L × 1.01

The width of the groove portion may satisfy Equation 6 below.

[Equation 6]

W × 1.008 ≤ V ≤ W × 1.01

Here, V is the sum of the width v1 of the groove portion in the first wedge grip, the width v2 of the groove portion in the second wedge grip, and the width h of the deformation region.

The length B of the protrusion may satisfy Equation 7 below.

[Equation 7]

D × 0.96 ≤ B ≤ D × 0.98

According to an embodiment of the present invention, the slip of the specimen is prevented during the simple shear test, thereby improving the reliability of the simple shear test.

1 schematically shows a specimen fixing device for a simple shear test according to an embodiment of the present invention.
2A and 2B are perspective views schematically illustrating wedge grips coupled to both ends of a specimen in the specimen holding device according to an embodiment of the present invention.
3 is a view for explaining a coupling structure between the wedge grips and the specimen of the specimen fixing device according to an embodiment of the present invention.
4 is a view for explaining the dimensions of the specimen of the simple shear test apparatus to which the specimen fixing apparatus according to an embodiment of the present invention is applied.
5 is a plan view of the lower grips of the specimen holding device according to an embodiment of the present invention as viewed from above.
6 is a side view of the wedge grip of the specimen fixing device according to an embodiment of the present invention as viewed from the specimen insertion direction.
7 illustrates a relationship between the thickness of the specimen and the height of the protrusion for fixing the specimen in a simple shear test using the specimen fixing device according to an embodiment of the present invention.
8 is a view showing the performance comparison results of the simple shear test apparatus to which the specimen fixing apparatus according to an embodiment of the present invention is applied and the conventional simple shear test apparatus.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in several different forms and is not limited to the embodiments described herein. In addition, since the size and thickness of each component shown in the drawings are arbitrarily indicated for convenience of description, the present invention is not necessarily limited to the bar shown in the drawings, and the thickness is enlarged to clearly express various parts and modes. It was.

In order to clearly describe the embodiment of the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar elements throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "electrically connected" with another element interposed therebetween. .

Hereinafter, a specimen fixing device for a simple shear test according to an embodiment of the present invention will be described in detail with reference to the necessary drawings.

1 schematically shows a specimen fixing device for a simple shear test according to an embodiment of the present invention.

1, the specimen fixing device 10 for a simple shear test according to an embodiment of the present invention has two wedge grips (wedge grips, 11a, 11b) for fixing both sides of the specimen 20 may include.

In the simple shear test, both ends (edges, 21, 22) of the specimen 20 (hereinafter, used interchangeably with “grip region” for convenience of description) are fixed to wedge grips 11a and 11b. In , it is a test to obtain simple shear stress and strain values of the specimen 20 by applying an external force in a specific direction (eg, the longitudinal direction of the specimen 20 (y-direction in FIG. 1 )).

In one embodiment of the present invention, in order to prevent slipping of the specimen during a simple shear test of a 1 GPa class ultra-high strength steel sheet, groove portions (reference numerals 112a and 112a and 112b) is formed, and both ends 21 and 22 of the specimen 20 are respectively positioned and fixed in the respective grooves 112a and 112b.

Hereinafter, a specimen fixing structure of the specimen holding apparatus 10 according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 to 3 .

2A and 2B are perspective views schematically illustrating wedge grips 11a and 11b coupled to both ends 21 and 22 of the specimen 20 in the specimen holding device 10 according to an embodiment of the present invention. admit. Also, FIG. 3 is a view for explaining a coupling structure between the wedge grips 11a and 11b of the specimen fixing device 10 and the specimen 20 according to an embodiment of the present invention.

2A and 2B , each of the wedge grips 11a and 11b of the specimen holding device 10 includes lower grips 110a and 110b and upper grips 120a and 120b.

Each lower grip (110a, 110b), the body (111a, 111b), is formed in the body (111a, 111b) to the corresponding end (21, 22) of the specimen 20 is inserted into the specimen fixing groove portion 112a, 112b).

The specimen fixing grooves 112a and 112b are opened in a direction opposite to the ends 21 and 22 of the specimen 20 so that the corresponding ends 21 and 22 of the specimen 20 may be inserted therein. In addition, the specimen fixing grooves 112a and 112b are opened in a direction opposite to the specimen fixing protrusions 122a and 122b of the upper grips 120a and 120b, and the corresponding upper grips 120a and 120b are fixed to the specimen. For protrusions (122a, 122b) may be inserted and coupled.

In addition, each of the specimen fixing grooves 112a and 112b may be closed in directions other than the aforementioned opening direction to contact the corresponding ends 21 and 22 of the specimen 20 . That is, each of the specimen fixing grooves 112a and 112b has a bottom surface in contact with the lower surface of the specimen 20 and a corresponding end 21 of the specimen 20 in the remaining directions except for the direction corresponding to the specimen 20. 22) surrounding the plurality of sidewalls (eg, three sidewalls). These bottom surfaces and sidewalls fix the positions of the corresponding ends 21 and 22 of the specimen 20, thereby preventing the specimen 20 from sliding during a simple shear test.

Each upper grip (120a, 120b) is formed to protrude from the body (121a, 121b) and the corresponding specimen fixing groove (112a, 112b) from the body (121a, 121b), the corresponding specimen fixing groove (112a) , 112b) may include protrusions (122a, 122b) for fixing the specimen to be inserted.

Each of the specimen fixing protrusions 122a and 122b is formed in a shape that can be inserted into the corresponding specimen fixing grooves 112a and 112b, and the end of the specimen 20 mounted in the corresponding specimen fixing grooves 112a and 112b. (21, 22) can be fixed in close contact with the specimen fixing groove (112a, 112b). Accordingly, the protrusions 122a and 122b for fixing the specimen may be in contact with the upper surface of the specimen 20 .

As shown in FIG. 3 , the specimen holding device 10 having the above structure is provided at both ends 21 and 22 of the specimen 20 in the specimen fixing grooves 112a and 112b of the lower grips 110a and 110b. ) in the mounted state, the specimen fixing protrusions 122a and 122b of each of the upper grips 120a and 120b are coupled to the specimen fixing grooves 112a and 112b, and then to the fixing means such as bolts (not shown). Accordingly, the lower grips 110a and 110b and the upper grips 120a and 120b corresponding to each other are fixed to each other to restrain the specimen 20 .

The above-described specimen fixing device 10 is included in the simple shear test device, and may be used for fixing the rectangular-shaped specimen 20 to the simple shear testing device.

On the other hand, when the above-described specimen fixing device 10 is applied to a simple shear test device for applying an ultra-high strength steel sheet with a maximum tensile strength of 1 GPa, each wedge grip 11a, 11b) and the dimensions of the specimen 20 may be limited.

4 illustrates the dimensions of the specimen 20 that can be used in the simple shear testing device when the specimen fixing device 10 according to an embodiment of the present invention is applied to the simple shear testing device for an ultra-high strength steel sheet. It is a drawing for 5 is a plan view of the lower grips 110a and 110b of the specimen holding device 10 according to an embodiment of the present invention as viewed from above, and FIG. 6 is a specimen holding device 10 according to an embodiment of the present invention. It is a side view of the wedge grips 11a and 11b viewed from the insertion direction of the specimen 20. In addition, FIG. 7 shows the relationship between the thickness of the specimen 20 and the height of the specimen fixing protrusions 122a and 122b in a simple shear test using the specimen fixing device 10 according to an embodiment of the present invention.

Table 1 below shows that, when performing a simple shear test by applying the specimen fixing device 10 according to an embodiment of the present invention to a simple shear testing apparatus for an ultra-high strength steel sheet, the dimensions of the specimen 20 are changed while The results of the simple shear test are shown.

Table 1. Simple shear test results (specimen dimension change) L/W 1.9 2 2.2 2.4 2.6 2.8 3 3.2 3.3 Whether a boundary line break occurs ○ × × × × × × × ○ L/h 10 11 12 13 14 15 16 17 18 Whether the strain difference is less than ±1% × × ○ ○ ○ ○ ○ × × Specimen thickness t (mm) 0.6 0.7 0.8 One 1.2 1.4 1.8 2.0 2.1 Whether buckling occurs in the width direction ○ ○ × × × × × × ○

In Table 1 above, the occurrence of boundary line breakage indicates whether breakage has occurred at the boundary line between the deformation region 23 and the grip regions 21 and 22, and is indicated by “○” when a breakage occurs, and “○” when a breakage does not occur. x". In addition, whether the strain difference is less than ±1% indicates whether the strain in the deformation region 23 satisfies the condition of less than ±1%, and when satisfied, “○” is indicated, and when unsatisfactory, “x” is indicated. In addition, the occurrence of buckling in the width direction indicates whether or not buckling in the width direction occurs in the specimen 20, and is indicated by "○" when buckling occurs, and "x" when buckling does not occur. Referring to Table 1 above, in order to secure the reliability of a simple shear test targeting an ultra-high strength steel sheet, regardless of the size of the specimen 20, the width (refer to reference numeral W in FIG. 4) and length of the specimen 20 the ratio (L/W) between (reference numeral L in FIG. 4 ), the ratio (L/h) between the width (refer to reference numeral h in FIG. 4 ) and the length (L) of the deformation region 23 of the specimen 20, and The thickness of the specimen 20 (see reference numeral t in FIG. 4 ) must satisfy Equations 1 to 3 below.

[Equation 1]

2 ≤ L/W ≤ 3.2

[Equation 2]

12 ≤ L/h ≤ 16

[Equation 3]

0.8mm ≤ t ≤ 2mm

When the L/W ratio of the specimen 20 is too large, it is difficult for simple shear deformation to occur completely in the deformation region 23 of the specimen 20, and when the L/W ratio is too small, the grip region 21 of the specimen 20 , 22) is concentrated, and fracture may occur at the boundary line between the grip regions 21 and 22 and the deformation region 23 . Therefore, based on Table 1 above, the L/W ratio at which no fracture occurs at the boundary line between the grip regions 21 and 22 and the deformation region 23 was derived as shown in Equation 1 above.

In the simple shear test, the L/h ratio of the specimen 20 is an important factor in determining the difference in the simple shear deformation of the deformation region 23 . That is, the difference in simple shear deformation of the deformation region of the specimen 20 is small or large according to the L/h ratio of the specimen 20 . Therefore, based on Table 1 above, the L/h ratio satisfying the shear strain difference of less than ±1% in the deformation region 23 of the specimen 20 was derived as in Equation 2 above.

In the case of a simple shear test, if the thickness t of the specimen 20 is too thick, a sliding phenomenon may occur in the specimen holding device 10 due to the design of the shear test device, and the thickness t of the specimen 20 may be too thin. In this case, buckling may occur in the width direction of the specimen 20 . Therefore, based on Table 1 above, the thickness t of the specimen 20 in which the buckling in the width direction does not occur was derived as shown in Equation 3 above.

The dimensions of the specimen fixing device 10 according to an embodiment of the present invention may be determined based on the aforementioned dimensions of the specimen 20 .

In an embodiment of the present invention, when the depth (refer to reference numeral c in FIG. 6) of the specimen fixing grooves 112a, 112b is set to a specific value (eg, the thickness of the specimen 20 is set to 2mm at most 3mm) The height of the specimen fixing protrusions 122a and 122b of the upper grips 120a and 120b based on the thickness t of the specimen 20 (reference numeral a in FIG. 6 ) in a state fixed to the depth c) reference) was set as in Equation 4 below.

[Equation 4]

(c-t) × 1.1 ≤ a ≤ (c-t) × 1.2

Equation 4 above is based on the relationship between the thickness (t) of the specimen 20 of FIG. 7 and the height (a) of the specimen fixing protrusions 122a and 122b obtained through a simple shear test, the boundary line breaking and sliding was derived so that it does not occur. That is, when the height a of the specimen fixing protrusions 122a and 122b does not satisfy Equation 4 above, the specimen 20 slides during the simple shear test or the deformation region 23 and the grip of the specimen 20 A fracture may occur at the boundary line between the regions 21 and 22 . At this time, whether the specimen 20 slips, it can be determined that the slip occurs when the elastic shear modulus value obtained through the simple shear test is out of the range of 71.43 to 78.95 GPa.

Length (refer to reference numeral D in FIGS. 5 and 6) and width (refer to reference numerals v1 and v2 in FIG. 5) of the groove portions 112a and 112b for fixing the specimen in the specimen fixing device 10 according to an embodiment of the present invention ) may be formed differently depending on the size of the specimen 20 . When the length (D) or width (v1, v2) of the specimen fixing grooves (112a, 112b) matches the length (L) or width (W) of the specimen 20, the specimen 20 is the specimen fixing groove portion It may not be stably fixed to (112a, 112b), or breakage may occur at the boundary line between the specimen fixing grooves (112a, 112b) and the specimen 20 during a shear test. On the other hand, when the length (D) or width (v1, v2) of the specimen fixing grooves (112a, 112b) and the length (L) or width (W) of the specimen 20 have a large dimensional difference, the specimen during the shear test The specimen 20 may slide inside the fixing grooves 112a and 112b.

Table 2 below shows, when performing a simple shear test by applying the specimen fixing device 10 according to an embodiment of the present invention to a simple shear testing device for an ultra-high strength steel sheet, groove parts 112a and 112b for fixing the specimen. ) shows the results of a simple shear test while changing the dimensions.

Table 2. Simple shear test results (changed the dimensions of the groove for fixing the specimen) Length of groove for specimen fixing (D) 1.006L 1.007L 1.008L 1.009L 1.01L 1.011L 1.012L 1.013L Whether the specimen slips or breaks the boundary line ○ ○ × × × ○ ○ ○

Table 3 below shows, when a simple shear test is performed by applying the specimen fixing device 10 according to an embodiment of the present invention to a simple shear testing apparatus for an ultra-high strength steel sheet, the specimen fixing protrusions 122a, 122b ) shows the results of a simple shear test while changing the dimensions.

Table 3. Simple shear test results (changed the dimension of the protrusion for holding the specimen) Length of the protrusion for holding the specimen (B) 0.94D 0.95D 0.96D 0.97D 0.098D 0.099D Whether the specimen slips or breaks the boundary line ○ ○ × × × ○

In Tables 2 and 3 above, the case where boundary line breakage or slippage of the specimen 20 occurred is indicated by “○”, and when neither boundary line breakage nor slippage of the specimen 20 occurred, it was indicated by “×”. . In an embodiment of the present invention, with reference to Tables 2 and 3 above, the length (D) and width (v1, v2) of the grooves (112a, 112b) for fixing the specimen, and the length of the protrusions (122a, 122b) for fixing the specimen ( B) was set as in Equations 5 to 7 below.

[Equation 5]

L × 1.008 ≤ D ≤ L × 1.01

[Equation 6]

W × 1.008 ≤ V ≤ W × 1.01

[Equation 7]

D × 0.96 ≤ B ≤ D × 0.98

In Equation 6 above, V is the width (v1, v2) of the specimen fixing grooves (112a, 112b) of the two lower grips (110a, 110b) and the width (h) of the deformation region 23 of the specimen 20 represents the sum of

According to an embodiment of the present invention described above, groove portions 112a and 112b and protrusions 122a and 122b for fixing the specimen are formed in the wedge grips 11a and 11b for fixing the specimen 20, and between them. By inserting and fixing the specimen 20, slippage of the specimen 20 can be prevented during a simple shear test of an ultra-high strength steel sheet.

8 shows the performance comparison results of a simple shear test apparatus to which the specimen fixing apparatus 10 according to an embodiment of the present invention is applied and a conventional simple shear test apparatus, and the shear elasticity for a maximum tensile strength of 1 GPa class ultra-high strength steel sheet The results obtained by the coefficients are compared.

Since the elastic modulus (E) of general steel has a value of 190~210GPa, the shear modulus (G) of ultra-high strength steel should have a value of 71.43~78.95GPa by the relational expression G=E/2(1+ν). However, when a 1GPa-class ultra-high strength steel sheet is tested with the conventional simple shear test device, the shear modulus is 41.75GPa, which is a very low value, which means that the specimen slips.

On the other hand, when a simple shear test is performed on an ultra-high strength steel sheet using a simple shear test device to which the specimen fixing device 10 according to an embodiment of the present invention is applied, the shear modulus obtained is 75.44 GPa, which is a very reasonable value. this can be obtained.

The drawings and the detailed description of the described invention referenced so far are merely exemplary of the present invention, which are only used for the purpose of describing the present invention, and are used to limit the meaning or the scope of the present invention described in the claims. it is not Therefore, those of ordinary skill in the art can easily select from it and replace it. In addition, those skilled in the art may omit some of the components described herein without degrading performance or add components to improve performance. In addition, those skilled in the art may change the order of the method steps described herein according to the process environment or equipment. Accordingly, the scope of the present invention should be determined by the claims and their equivalents rather than the described embodiments.

10: specimen holding device
11a, 11b: wedge grip
20: Psalm
21, 22: grip area (end of specimen)
23: deformation area
110a, 110b: lower grip
111a, 111b: lower grip body
112a: 112b: groove for fixing the specimen
120a, 120b: upper grip
121a, 121b: upper grip body
122a, 122b: protrusions for fixing the specimen

Claims (8)

In the specimen fixing device for simple shear test,
a first wedge grip engaging the first end of the specimen; and
a second wedge grip coupled to a second end opposite to the first end in the specimen;
Each of the first and second wedge grips includes a first grip including a groove portion in which the first end or the second end of the specimen is mounted, and the specimen is coupled to the groove portion in a state in which the specimen is mounted in the groove portion. and a second grip including a protrusion for fixing the specimen;
The groove portion includes a bottom surface in contact with the first surface of the specimen, and three portions surrounding the first end or the second end in a direction other than a direction in which the first end or the second end of the specimen is inserted. comprising a sidewall;
The protrusion is coupled to the groove portion so as to be in contact with a second surface of the specimen opposite to the first surface of the specimen,
The length (D) of the groove portion satisfies Equation 5 below, and the width of the groove portion satisfies Equation 6 below.
[Equation 5]
L × 1.008 ≤ D ≤ L × 1.01
[Equation 6]
W × 1.008 ≤ V ≤ W × 1.01
(In Equation 5, L is the length of the specimen, in Equation 6 W is the width of the specimen, V is the width v1 of the groove portion in the first wedge grip and the second wedge grip is the sum of the width (v2) of the groove portion and the width (h) of the deformation region of the specimen.) delete delete delete According to claim 1,
The height (a) of the protrusion is a specimen holding device, characterized in that it satisfies Equation 4 below.
[Equation 4]
(ct) × 1.1 ≤ a ≤ (ct) × 1.2
Here, t is the thickness of the specimen, and c is the depth of the groove and has a fixed value. delete delete According to claim 1,
The length (B) of the protrusion is a specimen holding device, characterized in that it satisfies Equation 7 below.
[Equation 7]
D × 0.96 ≤ B ≤ D × 0.98

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