Indirect tensile tester capable of observing cracks

Abstract

The utility model discloses an indirect tensile tester capable of observing cracks, belongs to the technical field of test devices, and aims to overcome the defects that the conventional indirect tensile tester is troublesome to operate and high in cost when used for testing test pieces with different specifications. The tester comprises a top plate, a bottom plate and guide rails, the top plate and the bottom plate are connected through the guide rails so that the top plate can move relative to the bottom plate, a test space is formed between the top plate and the bottom plate, the top plate and the bottom plate are each provided with a middle hollowed-out part, the two middle hollowed-out parts are each provided with a loading strip, and each loading strip is provided with a first arc-shaped surface and a second arc-shaped surface; the radians of the first arc-shaped surface and the second arc-shaped surface are different, and one of the first arc-shaped surface and the second arc-shaped surface is propped against the test piece. The arc-shaped surfaces with different sizes are arranged on the same loading strip to adapt to test pieces with different sizes, so that on the premise of effectively transmitting vertical load, the operation convenience of the tester is improved, the application range of a single loading strip is enlarged, the number of parts required to be equipped for the tester is reduced, and the cost is reduced.

Description

Technical Field

[0001] The utility model belongs to the technical field of test devices and relates to an indirect tensile tester capable of observing cracks. Background Art

[0002] The essence of fatigue cracking is the physical process of microcrack initiation and evolution of materials under external cyclic loads. At present, in the study of fatigue cracking, based on the principles of mechanical equilibrium and strain energy balance, a more direct damage evaluation index, damage density, is defined using fatigue crack length, which can more accurately evaluate the degree of damage.

[0003] Digital speckle correlation technology is usually used to measure crack length. This measurement method is costly, the measuring instrument is cumbersome to operate, the data processing is complex and requires the assistance of professionals. Digital speckle technology has advantages in measuring crack width and small deformation. However, in fatigue cracking research, the main focus is on crack length rather than crack width. Therefore, using common optical cameras to capture crack length is more suitable in terms of measurement accuracy, ease of operation, and cost control.

[0004] The current indirect tensile test device focuses on measuring the mechanical properties of the material, and there is no indirect tensile test instrument that can directly observe the cracking of the test piece. The guide rail of the existing instrument blocks the main cracking area. If the loading bar is directly rotated to make it 90° with the beam, although the blockage can be avoided, the contact area between the loading bar and the beam is small. Due to the instability of the loading bar during the loading process, the applied fatigue load deviates, which in turn causes local stress concentration.

[0005] In order to ensure that the loading bar of the indirect tensile test device fits the concave arc surface of the specimen, there are two common specifications, namely 12.70mm width, 100mm diameter and 18.75mm width, 150mm diameter. In daily use, it is not only cumbersome to frequently replace the bar, but also requires customized molds according to the test specifications. Summary of the invention

[0006] The utility model proposes an indirect tensile tester capable of observing cracks in view of the problems existing in the prior art, aiming to overcome the defects of the prior indirect tensile tester that is troublesome to operate and has high cost in testing specimens of different specifications.

[0007] The utility model is achieved in this way:

[0008] An indirect tensile tester capable of observing cracks comprises a top plate, a bottom plate and a guide rail, wherein the top plate and the bottom plate are connected by a guide rail so that the top plate can move relative to the bottom plate, and a test space is provided between the top plate and the bottom plate, the top plate and the bottom plate both have a middle hollow portion, and both of the middle hollow portions are provided with a loading bar, the loading bar having a first arcuate surface and a second arcuate surface, the first arcuate surface and the second arcuate surface have different curvatures, and one of the first arcuate surface and the second arcuate surface is selectively abutted against a specimen.

[0009] When in use, the tester is used in conjunction with a universal testing machine or a multifunctional hydraulic servo pavement material dynamic testing system. For example, when using a universal testing machine, according to the size of the specimen, the appropriate arc surface of the loading bar is facing inward for abutment with the specimen. The specimen is placed between the top plate and the bottom plate, abutting against the loading bar on the top plate and the loading bar on the bottom plate. The universal testing machine applies force to the top plate and the bottom plate, and the vertical pressure on the specimen creates a tensile effect in the lateral direction.

[0010] The loading bar is rotatably mounted on the hollow middle portion, and the top plate and the bottom plate are provided with fixings that cooperate with the loading bar to prevent the loading bar from rotating. The fixings are operated to disengage the fixings from the loading bar, so that the loading bar can rotate relative to the top plate and the bottom plate, thereby adjusting the first arc surface or the second arc surface to face inward for contact with the specimen. After the adjustment is completed, the fixings are operated to fix the loading bar on the top plate or the bottom plate and prevent it from rotating.

[0011] The top plate and the bottom plate have a support platform protruding inward, the middle hollow vertically penetrates the support platform, the two end walls of the support platform are provided with a first shaft hole, the loading bar is provided with a second shaft hole, and the first shaft hole and the second shaft hole are inserted with a rotating shaft so that the loading bar can be rotatably connected to the support platform. When the constraint of the fixing part on the loading bar is released, the loading bar can rotate around the rotating shaft, so that the loading bar switches between the first arc surface facing inward and the second arc surface facing inward.

[0012] The second axial hole is a blind hole at both ends of the loading bar, or the second axial hole passes through the loading bar.

[0013] The width of the first arc-shaped surface is 12.7 mm, and the radius is 50 mm; the width of the second arc-shaped surface is 18.75 mm, and the radius is 75 mm.

[0014] The first curved surface and the second curved surface of the loading strip on the top plate have a force-applying groove in the middle of the plane opposite to the side; and / or the first curved surface and the second curved surface of the loading strip on the bottom plate have a force-applying groove in the middle of the plane opposite to the side. The universal testing machine has a loading head, and the loading head is inserted into the force-applying groove to apply a load to the loading strip.

[0015] The two ends of the side wall of the loading bar have symmetrically distributed straight through holes, the distance between the two straight through holes is greater than the thickness of the test piece, and the fixing member is a pin, which passes through the support platform and penetrates into the straight through hole.

[0016] The top plate and the bottom plate have wing-shaped protrusions at their four corners, the wing-shaped protrusions have guide holes, the guide rails are passed through the guide holes, and the spacing between adjacent guide rails is greater than the thickness and diameter of the test piece. The wing-shaped protrusions are conducive to the lightweight design of the tester.

[0017] The wing-shaped protrusion is provided with a guide flange, and the guide rail is a cylinder passing through the guide flange. A ball is provided in the guide flange, and the ball contacts the guide rail, thereby reducing the friction between the top plate and the guide rail.

[0018] The indirect tensile tester capable of observing cracks provided by the utility model has the following beneficial effects:

[0019] Arc surfaces of different sizes are set on the same loading bar to accommodate specimens of different sizes. Under the premise of effectively transmitting vertical loads, the operating convenience of the tester is improved, the application scope of a single loading bar is increased, the number of parts required for the tester is reduced, and the cost is reduced.

[0020] While conducting mechanical tests, research objectives such as observation of cracks and specimen deformation were also taken into account. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the structural diagram of the tester;

[0022] Figure 2 It is a schematic diagram of the cross-sectional structure of the tester;

[0023] Figure 3 A schematic diagram of the structure of the top plate or the bottom plate;

[0024] Figure 4 A schematic diagram of the loading bar structure.

[0025] Explanation of the accompanying drawings: 100, top plate; 200, bottom plate; 300, guide rail; 410, hollow in the middle; 420, base; 421, round hole; 422, first axial hole; 430, wing-shaped protrusion; 431, guide hole; 432, guide flange; 500, loading bar; 510, first arcuate surface; 520, second arcuate surface; 530, second axial hole; 540, through hole; 550, force groove; 600, loading head; 700, test piece. DETAILED DESCRIPTION

[0026] The following will further describe the specific implementation of the utility model in combination with the accompanying drawings of the embodiments, so that the technical solution of the utility model is easier to understand and grasp. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not used to limit the utility model.

[0027] This embodiment provides an indirect tensile tester capable of observing cracks, such as Figure 1-4 As shown, it includes a top plate 100, a bottom plate 200 and a guide rail 300, the top plate 100 and the bottom plate 200 are connected by the guide rail 300 so that the top plate 100 can move relative to the bottom plate 200, and there is a test space between the top plate 100 and the bottom plate 200, the top plate 100 and the bottom plate 200 both have a middle hollow 410, and the two middle hollows 410 are both equipped with a loading bar 500, the loading bar 500 has a first curved surface 510 and a second curved surface 520, the first curved surface 510 and the second curved surface 520 have different curvatures, and the first curved surface 510 and the second curved surface 520 are selectively abutted against the test piece 700.

[0028] The tester is a hollow structure formed by a top plate 100 and a bottom plate 200 which are symmetrical in upper and lower directions and connected by a guide rail 300. The first curved surface 510 and the second curved surface 520 of the loading bar 500 on the top plate 100 are symmetrically arranged with the first curved surface 510 and the second curved surface 520 of the loading bar 500 on the bottom plate 200, respectively, to meet the test requirements of specimens 700 of different sizes. When in use, the tester is used in conjunction with a universal testing machine or a multifunctional hydraulic servo pavement material dynamic testing system (DTS-30). For example, a universal testing machine is used. According to the size of the specimen 700, the appropriate arc surface of the loading bar 500 is facing inward for abutting against the specimen 700. The specimen 700 is placed between the top plate 100 and the bottom plate 200, abutting against the loading bar 500 on the top plate 100 and the loading bar 500 on the bottom plate 200. The universal testing machine applies force to the top plate 100 and the bottom plate 200, and the vertical pressure on the specimen 700 creates a tensile effect in the lateral direction.

[0029] The loading bar 500 is rotatably mounted on the middle hollow 410. The top plate 100 and the bottom plate 200 are provided with fixings that cooperate with the loading bar 500 to prevent the loading bar 500 from rotating. The middle hollow 410 provides a reasonable space for the rotation of the loading bar 500. The fixings are operated to disengage the fixings from the loading bar 500, so that the loading bar 500 can rotate relative to the top plate 100 and the bottom plate 200, thereby adjusting the first arc surface 510 or the second arc surface 520 to face inward for contact with the test piece 700, thereby simplifying the adjustment steps of the loading bar 500 corresponding to test pieces 700 of different sizes. After the adjustment is completed, the fixings are operated to fix the loading bar 500 on the top plate 100 or the bottom plate 200 and prevent it from rotating. The length of the middle hollow 410 is 182 mm, and a gap of 1 mm is reserved between the two end walls and the end of the loading bar 500 in the length direction. The width of the middle hollow 410 is 24 mm, which is slightly larger than the width of the loading bar 500. At this time, the maximum width of the loading bar 500 is 22.6 mm, providing sufficient space for the loading bar 500 to rotate.

[0030] The top plate 100 and the bottom plate 200 have a support platform 420 protruding inward, the middle hollow 410 vertically penetrates the support platform 420, the two end walls of the support platform 420 are provided with a first shaft hole 422, the loading bar 500 is provided with a second shaft hole 530, and the first shaft hole 422 and the second shaft hole 530 are inserted with a rotating shaft so that the loading bar 500 can be rotatably connected with the support platform 420. When the constraint of the fixing member on the loading bar 500 is released, the loading bar 500 can rotate around the rotating shaft, so that the loading bar 500 switches between the first arc surface 510 facing inward and the second arc surface 520 facing inward. The loading bar 500 transfers the load to the test piece 700 through the rotating shaft and the fixing member. The support platform 420 is integrally formed with the main structure of the top plate 100 and the bottom plate 200. The protruding height of the support platform 420 is preferably 8mm. The loading bar 500 protrudes inward relative to the support platform 420 to prevent the support platform 420 from affecting the transmission of load to the specimen 700.

[0031] The second shaft hole 530 is a blind hole at both ends of the loading bar 500. The two blind holes correspond to two rotation axes. The diameter of the blind hole can be 3 mm and the hole depth can be 6 mm. In other optional embodiments, the second shaft hole 530 passes through the loading bar 500, and the rotation connection between the loading bar 500 and the support platform 420 can be completed by a rotation axis passing through the second shaft hole 530.

[0032] The width of the first arc surface 510 is 12.7 mm and the radius is 50 mm; the width of the second arc surface 520 is 18.75 mm and the radius is 75 mm. When the thickness of the cylindrical asphalt mixture specimen 700 is 50 mm and the diameter is 100 mm, the first arc surface 510 is used to fit and abut the specimen 700, the fatigue load size is 3 kN, the frequency is 5 Hz, and the fatigue crack length in the middle of the specimen 700 is measured to increase with the increase of the number of cyclic loading. When the thickness of the specimen 700 is 80 mm and the diameter is 150 mm, the fixing piece is pulled out and the polygonal loading bar 500 is rotated 90°, so that the second arc surface 520 is fitted and abutted against the specimen 700, the fatigue load size is 10 kN, the frequency is 5 Hz, and the fatigue crack length in the middle of the specimen 700 is measured to increase with the increase of the number of cyclic loading.

[0033] A force-applying groove 550 is provided in the middle of the opposite plane of the first curved surface 510 and the second curved surface 520 of the loading bar 500 on the top plate 100; meanwhile, a force-applying groove 550 is provided in the middle of the opposite plane of the first curved surface 510 and the second curved surface 520 of the loading bar 500 on the bottom plate 200. The universal testing machine is provided with a loading head 600, and the loading head 600 is inserted into the force-applying groove 550 to apply a load to the loading bar 500. The force-applying groove 550 is a bowl-shaped semicircular groove, which matches the curvature of the end of the loading head 600 of the universal testing machine. In this embodiment, a load is only applied to the loading bar 500 on the top plate 100. In other optional embodiments, a load may also be applied to the loading bars 500 of the top plate 100 and the bottom plate 200 at the same time, or a load may be applied only to the loading bar 500 of the bottom plate 200. In other optional embodiments, the force-applying groove 550 may also be provided only on the loading bar 500 on the top plate 100,

[0034] The two ends of the side wall of the loading bar 500 have symmetrically distributed straight holes 540, the spacing between the two straight holes 540 is greater than the thickness of the test piece 700, and the spacing between the two straight holes 540 is preferably 160 mm. The fixing member is a pin, which passes through the support 420 and penetrates into the straight hole 540. The support 420 has a circular hole 421, through which the pin passes, and the diameter of the circular hole 421 is preferably 4 mm, and the distance from the center of the circular hole 421 to the main body inner surface of the top plate 100 or the bottom plate 200 is 3 mm. The inner side of the top plate 100 and the bottom plate 200 described in this embodiment refers to the side facing the test piece 700, that is, the lower side of the top plate 100 and the upper side of the bottom plate 200.

[0035] The top plate 100 and the bottom plate 200 have wing-shaped protrusions 430 at the four corners, and the wing-shaped protrusions 430 have guide holes 431. The guide rails 300 are arranged on the guide holes 431, and the spacing between adjacent guide rails 300 is greater than the thickness and diameter of the test piece 700. The wing-shaped protrusions 430 are conducive to the lightweight design of the tester. The main body thickness of the top plate 100 and the bottom plate 200 is 10mm, the outer contour side length is 250mm, the side is a concave curved surface with a radius of 80mm. The larger spacing between the guide rails 300 is conducive to providing sufficient space for observing the test phenomenon. Preferably, the diameter of the guide hole 431 is 8mm, and the spacing between adjacent guide holes 431 is 200mm. The length of the guide rail 300 is preferably 250mm, and the diameter is preferably 7.8mm. The guide rail 300 is preferably made of high-strength steel, and the surface is smoothed to reduce friction.

[0036] like Figure 1 , 2 As shown, a guide flange 432 is provided on the wing-shaped protrusion 430, and the guide rail 300 is a cylinder passing through the guide flange 432. A ball is provided in the guide flange 432, and the ball contacts the guide rail 300, thereby reducing the friction between the top plate 100 and the guide rail 300.

[0037] In the description of the present invention, it should be understood that the terms "center", "lateral", "thickness", "up", "down", "vertical", "horizontal", "top", "bottom", "inside", "outside", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In the present utility model, unless otherwise clearly specified and defined, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection, or integrated; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to the specific circumstances.

Claims

1. An indirect tensile tester capable of observing cracks, comprising a top plate (100), a bottom plate (200) and a guide rail (300), It is characterized in that The top plate (100) and the bottom plate (200) are connected by a guide rail (300) so that the top plate (100) can move relative to the bottom plate (200), and a test space is provided between the top plate (100) and the bottom plate (200). Both the top plate (100) and the bottom plate (200) have a central hollow (410), and both central hollows (410) are provided with a loading bar (500). The loading bar (500) has a first curved surface (510) and a second curved surface (520), and the first curved surface (510) and the second curved surface (520) have different curvatures, and one of the first curved surface (510) and the second curved surface (520) is selectively contacted with the test piece (700).

2. An indirect tensile tester capable of observing cracks according to claim 1, It is characterized in that The loading bar (500) is rotatably mounted on the middle hollow (410), and fixing parts are provided on the top plate (100) and the bottom plate (200) to cooperate with the loading bar (500) to prevent the loading bar (500) from rotating.

3. An indirect tensile tester capable of observing cracks according to claim 2, It is characterized in that The top plate (100) and the bottom plate (200) have a support platform (420) protruding inwardly, the central hollow (410) vertically penetrates the support platform (420), and the two end walls of the support platform (420) are provided with a first shaft hole (422), and the loading bar (500) is provided with a second shaft hole (530), and the first shaft hole (422) and the second shaft hole (530) are inserted with a rotating shaft so that the loading bar (500) and the support platform (420) can be rotatably connected.

4. An indirect tensile tester capable of observing cracks according to claim 3, It is characterized in that The second axial hole (530) is a blind hole at both ends of the loading bar (500), or the second axial hole (530) passes through the loading bar (500).

5. The indirect tensile tester capable of observing cracks according to claim 1, It is characterized in that The width of the first arc-shaped surface (510) is 12.7 mm and the radius is 50 mm; the width of the second arc-shaped surface (520) is 18.75 mm and the radius is 75 mm.

6. An indirect tensile tester capable of observing cracks according to claim 1, It is characterized in that A force-applying groove (550) is provided in the middle of the opposite side planes of the first curved surface (510) and the second curved surface (520) of the loading bar (500) on the top plate (100); and / or a force-applying groove (550) is provided in the middle of the opposite side planes of the first curved surface (510) and the second curved surface (520) of the loading bar (500) on the bottom plate (200).

7. An indirect tensile tester capable of observing cracks according to claim 3, It is characterized in that The two ends of the side wall of the loading bar (500) have symmetrically distributed straight through holes (540), the distance between the two straight through holes (540) is greater than the thickness of the test piece (700), and the fixing member is a pin, which passes through the support platform (420) and penetrates into the straight through hole (540).

8. An indirect tensile tester capable of observing cracks according to claim 1, It is characterized in that The top plate (100) and the bottom plate (200) have wing-shaped protrusions (430) at their four corners, the wing-shaped protrusions (430) have guide holes (431), the guide rails (300) are passed through the guide holes (431), and the spacing between adjacent guide rails (300) is greater than the thickness and diameter of the test piece (700).

9. An indirect tensile tester capable of observing cracks according to claim 8, It is characterized in that A guide flange (432) is provided on the wing-shaped protrusion (430), and the guide rail (300) is a cylinder passing through the guide flange (432).

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