Test fixture

Abstract

The present invention provides a test fixture that can be attached to a uniaxial testing machine to accurately apply loads in at least two axial directions to a test specimen. [Solution] The test fixture (S) of the present invention comprises an upper base (11), a lower base (12), a left base (43), and a right base (44), an upper left link (211), an upper right link (212), a lower left link (221), and a lower right link (222) connecting them, and a suppression means (R1, R2, 431, 432) for suppressing abnormal loads that may occur on the test specimen (T). The suppression means is, for example, a horizontal mechanism (R1) that restricts the relative movement of the chuck that grips the test specimen in the horizontal direction, and a vertical mechanism (R2) that restricts it in the vertical direction. The suppression means may also be balance weights (431, 432) that adjust the center of gravity of the fixture.

Description

Technical Field

[0001] The present invention relates to a test jig capable of converting a uniaxial load into a multiaxial load.

Background Art

[0002] A test for applying a load to a test piece and measuring its physical properties (mechanical properties) is essential in product development (especially material development), quality control, etc. Such a test is usually performed using a dedicated testing machine or test jig suitable for the physical property value to be measured. A typical example is a uniaxial tensile test (a test in which a unidirectional tensile load is statically applied to a test piece) using a universal testing machine (tensile testing machine).

[0003] However, in a real member, stresses in multiple directions can act in a complex manner. Therefore, the material strength, etc. cannot always be accurately evaluated by only a uniaxial tensile test. For example, in the shell wall (circumferential side wall) constituting a cylindrical pressure vessel, stresses in the longitudinal direction, circumferential direction, and thickness direction act in a complex manner. Also, due to the optimal design of members, anisotropic materials are used instead of isotropic materials. In order to evaluate the properties of such materials, it is desirable to simultaneously apply loads in multiple directions to a test piece while ensuring the degree of freedom of adjustment.

[0004] Therefore, a test jig (method) that can reproduce a stress state close to that of a real member in a test piece while using a universal testing machine has been proposed. Descriptions related to this are, for example, in the following documents.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0006] Both testing fixtures are excellent in that they can apply multi-axial loads to the test specimen while using general-purpose universal testing machines. However, it has recently been discovered that when performing fatigue tests that apply dynamic, cyclic loads, not just static tensile tests, conventional testing fixtures can produce errors in the measurement results of fatigue characteristics (lifespan, strength, etc.).

[0007] This invention was made in view of these circumstances, and aims to provide a new test fixture, etc., that can properly perform not only simple tensile tests but also fatigue tests. [Means for solving the problem]

[0008] As a result of diligent research, the inventor conceived and successfully realized a new testing jig that restricts the application of loads in unexpected directions to a test specimen when repeated loads are applied to the specimen. By further developing this result, the present invention described below was completed.

[0009] Test fixtures (1) The present invention relates to a test fixture to be mounted on a testing machine having an upper mounting body and a lower mounting body that move relative to each other in the vertical direction, comprising: an upper base mounted on the upper mounting body; a lower base mounted on the lower mounting body; an upper left link with one end pivotally supported on the left side of the upper base; an upper right link with one end pivotally supported on the right side of the upper base; a lower left link with one end pivotally supported on the left side of the lower base; a lower right link with one end pivotally supported on the right side of the lower base; and the other end of the upper left link and the other end of the lower left link The test fixture comprises a pivoted left base, a right base pivoted to the other end of the upper right link and the other end of the lower right link, an upper chuck that holds the upper part of the test piece and is linked to the upper base, a lower chuck that holds the lower part of the test piece and is linked to the lower base, a left chuck that holds the left part of the test piece and is linked to the left base, a right chuck that holds the right part of the test piece and is linked to the right base, and a suppression means for suppressing abnormal loads that may occur on the test piece.

[0010] (2) According to the test fixture of the present invention, multiaxial loads can be applied to the test piece while using a testing machine that applies a uniaxial load, and accurate measurement tests can be performed not only in simple tensile tests but also in fatigue tests in which loads are repeatedly applied.

[0011] Furthermore, the test fixture of the present invention has a relatively small number of links (joints, components) and connecting points, resulting in a simplified structure. This makes it easy to handle and maintain, and the load applied to the test piece can be adjusted in each direction by adjusting the length and angle of each link.

[0012] In this specification, "abnormal load" refers to a load (including moments) that differs from the intended load (steady load / intended load) to be applied. For example, it refers to a load or moment acting on a test specimen held by opposing chucks along its axis, in a direction deviating from that axis. In fatigue tests, for example, the more repeatedly a fluctuating load is applied, the greater the influence of abnormal loads on the measurement results can become.

[0013] 《Examination Method》 The present invention can also be understood as various testing methods using the test fixtures described above. The type of test is not limited to fatigue testing, but may also be simple (static) tensile tests, bending tests, compression tests, etc.

[0014] "others" (1) In this specification, "left / right," "up / down," and "front / back" are terms used for convenience of explanation. Unless otherwise specified, the left-right direction is the horizontal direction, the up-down direction is the vertical direction, and the front-back direction is the direction perpendicular to them (the horizontal direction perpendicular to the left-right direction). In this specification, the left-right direction is referred to as the X (axis) direction, the up-down direction as the Y (axis) direction, and the front-back direction as the Z (axis) direction.

[0015] In this specification, the terms "end side" (one end, other end) are merely convenient designations, and any region (part) that can be connected, linked, or interlocked with other components does not need to be a strictly defined end. The same applies to terms such as "left side," "right side," "left section," "right section," "front side," "rear side," "front section," and "rear."

[0016] The "pivot point" means the connecting part (couple, rotation axis) of the rotating link, regardless of its form. The "point" (similarly, the "center of gravity") referred to in this specification does not have to be a geometric point, but may be a part, axis, or region within a realistic range.

[0017] (2) The links, bases, chucks, etc. that make up the mechanism, as long as they have the rigidity, strength, etc. required for the test, can be of any shape (plate-like, rod-like, tubular, straight, curved, etc.), size, material, etc. The testing machine to which the test fixture is attached only needs to be able to apply a load in one direction, regardless of its type, model, etc.

[0018] (3) Unless otherwise specified, "x~y" referred to in this specification includes the lower limit value x and the upper limit value y. Any numerical value included in the various numerical values or numerical ranges described in this specification can be used as a new lower limit value or upper limit value to newly set a range such as "a~b".

Brief Description of the Drawings

[0019] [Figure 1] It is a perspective view showing a test fixture (first embodiment). [Figure 2] It is a perspective view showing a guide mechanism (an example). [Figure 3] It is a plan view and a rear view showing a base, a chuck, and a balance weight provided in the horizontal direction (left-right direction). [Figure 4] It is a perspective view showing a test fixture (second embodiment). [Figure 5] It is a perspective view showing a pressing mechanism (an example). [Figure 6A] It is a sectional view taken along the line A-A of the test fixture. [Figure 6B] It is a sectional view taken along the line B-B of the test fixture. [Figure 7] It is a schematic view showing an adjustment mechanism for the pivot point (an example). [Figure 8A] It is a schematic view of a link mechanism for converting a uniaxial load into a biaxial load. [Figure 8B] It is a group of mathematical formulas for mechanical calculations related to the link mechanism. [Figure 9] This graph shows the relationship between εy and εx measured at different link angles. [Modes for carrying out the invention]

[0020] The contents described herein may apply not only to test fixtures but also to test methods using them. One or more components arbitrarily selected from this specification may be added to the components of the present invention described above. Which embodiment is best depends on the subject, required performance, etc. Furthermore, the entire content (full text) disclosed in the prior applications (JP 2022-107955, JP 2024-8330) which form the basis of this invention is included in this specification, and components that can be extracted therefrom may be incorporated into the present invention as appropriate.

[0021] 《Suppression means》 (1) Abnormal loads can be suppressed, for example, by positioning the center of gravity of the holder, including the base and chuck, between the pivot points of the links. Specifically, for example, to suppress abnormal loads that may occur when a horizontal load is applied to a test specimen, a left balance weight may be provided, which positions the center of gravity of the left holder, including the left base and left chuck, approximately midway between the pivot point on the other end of the upper left link and the pivot point on the other end of the lower left link, and a right balance weight may be provided, which positions the center of gravity of the right holder, including the right base and right chuck, approximately midway between the pivot point on the other end of the upper right link and the pivot point on the other end of the lower right link. When the center of gravity of each holder is approximately midway between the pivot points of the links, the rotation of the tip of the chuck (so-called "bow") is restricted, making it easier to hold the holder horizontally, and abnormal loads acting on the test specimen are also suppressed.

[0022] The centers of gravity of the left and right support bodies only need to be equilibrium points in the horizontal direction, and do not necessarily need to be equilibrium points in the vertical direction (or even the front-to-back direction). The centers of gravity should be approximately midway between the pivot points, but it is preferable that they be (or near) the center between the pivot points.

[0023] In this specification, the balance weight (counterweight) may be a separate component from the base, chuck, etc., or it may be a part of the base, chuck, etc. (a part integrated with the base, chuck, etc.).

[0024] The components of the test fixture should be shaped and arranged such that the axis of action (the axis through which the load is applied) passes through the center of the test specimen. Furthermore, if the center of gravity of each component or group of components lies on its line of action, oscillation in directions different from that line of action will be suppressed, and consequently, abnormal loads will also be suppressed. In addition, the test fixture should be symmetrical with respect to at least two planes (cross-sections) passing through its center (or the center of the test specimen).

[0025] (2) The restraining means may be, for example, a horizontal mechanism that restricts the relative movement of the left chuck and the right chuck in the horizontal direction, or a vertical mechanism that restricts the relative movement of the upper chuck and the lower chuck in the vertical direction. The horizontal mechanism and the vertical mechanism force the movement of opposing chucks to be in a direction along a single axis (line of action). In other words, the chucks are prevented from swinging or moving in a direction that deviates from that direction. Depending on the specific configuration of the test fixture and the specifications of the test, both a horizontal mechanism and a vertical mechanism may be provided, or only one of them may be provided.

[0026] Horizontal and vertical mechanisms consist of, for example, a slider mounted on a base or chuck, and a guide on which the slider moves (slid). The guide is, for example, a straight rail or bar extending in the horizontal or vertical direction.

[0027] Pressing mechanism The test fixture may include a pressing mechanism for pressing the test specimen in the front-rear direction. The pressing mechanism is realized, for example, by an upper link pivotally supported at one end and connected to an upper base, a lower link pivotally supported at one end and connected to a lower base, a front base pivotally supported at the other end of the upper link and the other end of the lower link, and a pressurizing body that moves the test specimen in conjunction with the front base. One end of the upper link and the lower link may be directly pivotally supported to the upper base and the lower base, respectively, or they may be pivotally supported to another base (upper front base and lower front base) attached to the upper base and the lower base.

[0028] If the pressing mechanism consists of a parallel crank mechanism, the pressurizing body can be stably pressed in the front-rear direction. Furthermore, if the front base and the pressurizing body are connected via an elastic body, the load applied to the test piece can be easily adjusted by adjusting the spring constant (modulus of elasticity), natural length, and set length of the elastic body (spring, etc.).

[0029] The pressing mechanism can be a vertical type that links the upper and lower bases, or a horizontal type that links the left and right bases. Such a pressing mechanism can also serve as the vertical or horizontal mechanism described above, as it restricts the range of motion of each base to which one end of each link is pivotally supported.

[0030] The test fixture may be configured such that the center of gravity in the front-to-back direction, including the pressing mechanism, is approximately in the center of the test specimen. This may involve adjusting the shape and weight of each component, or providing front-to-back balance weights. By adjusting the center of gravity in this way, oscillation and vibration of the test fixture, at least in the front-to-back direction, can be reduced, and abnormal loads can also be suppressed.

[0031] 《Load ratio》 By adjusting the length (pivot length) and angle of the link (including the base), the ratio of the load applied to the test specimen (load ratio) can be adjusted.

[0032] For example, if the left exterior angle (α) is the angle between the upper left link and the lower left link pointing outwards, and the right exterior angle (β) is the angle between the upper right link and the right left link pointing outwards, then the left exterior angle (α) and / or the right exterior angle (β) should be, for example, between 70° and 160°, 80° and 150°, or even between 90° and 140°.

[0033] The load ratio can be determined kinematically (logically) from the configuration of the link mechanism, but in reality, some error may occur compared to the theoretical value. Such errors can be reduced or eliminated, for example, by slightly displacing the pivot point of the link and correcting the angle of the link relative to the base (called the link angle). Therefore, the test fixture should be equipped with, for example, an upper adjustment mechanism that can displace (adjust the position) the pivot point on one end of the upper left link or upper right link relative to the upper base, and a lower adjustment mechanism that can displace (adjust the position) the pivot point on one end of the lower left link or lower right link relative to the lower base.

[0034] Test specimen The form (shape, size) and material of the test specimen can be adjusted as appropriate according to the purpose of the test, and may be isotropic or anisotropic. By using the test fixture of the present invention, fatigue tests and the like can be properly performed even on low-rigidity test specimens by suppressing the effect of abnormal loads. Examples of such test specimens include flexible, thin, plate-shaped specimens (e.g., cross-shaped) made of fiber-reinforced resin (FRP) sheets or laminates thereof.

[0035] By using the test fixture of the present invention, which is equipped with a pressing mechanism, tensile stress and bending stress can be applied to the test specimen in a superimposed manner. For this reason, fatigue tests of materials (such as FRP) that constitute the shell wall (circumferential side wall) of a pressure vessel can be appropriately performed. [Examples]

[0036] The present invention will be specifically explained with reference to examples of test fixture configurations and measurement examples using them.

[0037] [First Embodiment] "composition" Figure 1 shows an overall perspective view of the test fixture S1 (simply referred to as "fixture S1"), which is the first embodiment of the present invention.

[0038] (1) The jig S1 is mounted between the crosshead (fixed side) and the piston (movable side) of a material testing machine capable of applying a uniaxial load. The jig S1 includes a link mechanism L1 (first link mechanism) that applies loads to the test piece in the left-right direction (X-axis direction) and the up-down direction (Y-axis direction), and guide mechanisms R1 and R2 (restraining means) that stabilize the direction of action of these loads. A schematic overview of the link mechanism L1 is also shown in Figure 8A. In this specification, reference numerals are mainly used for representative members and drawings.

[0039] The link mechanism L1 follows the relative movement of the crosshead and piston, and has an overall symmetrical structure with respect to the vertical and horizontal directions. The specific structure is as follows:

[0040] (2) The link mechanism L1 comprises an upper base 11 that is detachable from the crosshead (upper mounting body), a lower base 12 that is detachable from the piston (lower mounting body), four upper left links 211, lower left links 221, upper right links 212 and lower right links 222 disposed between the upper base 11 and the lower base 12, four upper chucks 31, lower chucks 32, left chucks 41 and right chucks 42 that grip the upper, lower, left and right parts of the test piece T respectively, a left base 43 that follows the upper left links 211 and lower left links 221 and holds the left chuck 41, and a right base 44 that follows the upper right links 212 and lower right links 222 and holds the right chuck 42. The attachment and detachment (fixing) of each component, gripping (fixing) of the test piece, etc. are done by fastening a plurality of bolts b.

[0041] One end of the upper left link 211 is pivotally connected (supported) to the left end of the upper base 11 by pivot 511, and the other end is pivotally supported to the upper part of the left base 43 by pivot 611. One end of the lower left link 221 is pivotally supported to the left end of the lower base 12 by pivot 521, and the other end is pivotally supported to the lower part of the left base 43 by pivot 621.

[0042] One end of the upper right link 212 is pivotally supported by pivot 512 to the right end of the upper base 11, and the other end is pivotally supported by pivot 612 to the upper part of the right base 44. One end of the lower right link 222 is pivotally supported by pivot 522 to the right end of the lower base 12, and the other end is pivotally supported by pivot 622 to the lower part of the right base 44.

[0043] When the testing machine is activated and the lower base 12 is moved relative to the upper base 11 (relative movement in the vertical direction away from it), a tensile load in the vertical direction (Y-axis direction) acts on the test specimen T held by the upper chuck 31 fixed to the upper base 11 and the lower chuck 32 fixed to the lower base 12. In conjunction with this, the left base 43, pivotally supported by the upper left link 211 and the lower left link 221, and the right base 44, pivotally supported by the upper right link 212 and the lower right link 222, move away from each other in the horizontal direction. As a result, a tensile load in the horizontal direction (X-axis direction) also acts on the test specimen T held by the left chuck 41 fixed to the left base 43 and the right chuck 42 fixed to the right base 44. Conversely, when the lower base 12 is moved relative to the upper base 11, the vertical and horizontal tensile loads acting on the test specimen T are removed. In fatigue testing, a predetermined load is repeatedly applied and removed.

[0044] (3) As shown in Figure 2, the guide mechanism R1 includes a roughly L-shaped left front base 45 fixed to the left base 43 near the center (right end) and protruding forward, a roughly L-shaped right front base 46 fixed to the right base 44 near the center (left end) and protruding forward, a straight rod-shaped guide bar 47 communicating with the left front base 45 and the right front base 46 and extending in the left-right direction, and coil springs 481 and 482 fitted into the left and right ends of the guide bar 47 and elastically held between the left side of the left front base 45 and the right side of the right front base 46.

[0045] The guide mechanism R1 allows the left chuck 41, fixed to the left base 43, and the right chuck 42, fixed to the right base 44, to reciprocate stably only in the horizontal direction along the guide bar 47, suppressing vertical and horizontal wobble (oscillation, twisting, etc.).

[0046] Guide mechanism R2 has substantially the same structure as guide mechanism R1. Specifically, it comprises a substantially L-shaped upper front base 15 fixed to the center of the upper base 11 and protruding forward, a substantially L-shaped lower front base 16 fixed to the center of the lower base 12 and protruding forward, a straight rod-shaped guide bar 17 communicating with the upper front base 15 and the lower front base 16 and extending in the vertical direction, and coil springs 181 and 182 fitted into the left and right ends of the guide bar 17 and elastically held between the upper surface of the upper front base 15 and the lower surface of the lower front base 16.

[0047] Guide mechanism R2 is provided with a guide bar 17 extending vertically inside (rear) guide mechanism R1, where guide bar 47 extends horizontally. Guide mechanism R2 allows the upper chuck 31 fixed to the upper base 11 and the lower chuck 32 fixed to the lower base 12 to reciprocate stably only in the vertical direction along guide bar 17, suppressing wobble in the left-right and front-back directions.

[0048] (4) Figure 3 shows an enlarged rear view and a plan view of the left holder H1, which consists of the left chuck 41 and the left base 43, as viewed from the rear. The left base 43 has balance weights 431 and 432 (restraining means) that extend to the opposite side of the left chuck 41 with respect to the pivots 611 and 621.

[0049] The form (shape (length, etc.) and weight) of the balance weights 431 and 432 is set considering the weights of the left chuck 41, left base 43, left front base 45, guide bar 47, coil spring 481, fixing bolt b, etc., so that their center of gravity G1 (referred to as "center of gravity G1 of the left holder H1") is between the center (axis) O11 of the pivot 611 and the center O12 of the pivot 621 (axis) (the midpoint in this embodiment).

[0050] The balance weights 431 and 432 maintain equilibrium (horizontal balance) of the left holder H1 with respect to the pivots 611 and 621 connected to links 211 and 221, thereby suppressing the downward sagging (so-called "bowing") of the heavy left chuck 41. The same applies to the right holder H2, which consists of the right chuck 42 and the right base 44.

[0051] The test specimen T, gripped by the left chuck 41 and right chuck 42 of the left holder H1 and right holder H2, which are arranged symmetrically, is less susceptible to loads deviating from the horizontal direction (abnormal loads), and a tensile load can be stably applied in the left-right direction.

[0052] Although Figure 3 shows the balance weights 431 and 432 integrated into the left base 43, they may be separate components. Using separate balance weights 431 and 432 may increase the freedom of placement (center of gravity adjustment) and form, or reduce manufacturing costs.

[0053] [Second Example] Figure 4 shows a perspective view of a test jig S2 (simply referred to as "jig S2"), which is a second embodiment of the present invention. Jig S2 is a modification of jig S1 in which the guide mechanism R2 is replaced with a link mechanism L2 (second link mechanism). Figure 5 shows an enlarged perspective view of the link mechanism L2. Figures 6A and 6B show cross-sectional views AA and BB of Figure 4, respectively. Components and mechanisms similar to those of jig S1 are denoted by the same reference numerals, and their descriptions have been omitted where appropriate.

[0054] The link mechanism L2 comprises an upper front base 711, a lower front base 712, a front base 713, a pressurizing body 72, an upper link 81, a lower link 82, and a biasing mechanism 9.

[0055] The upper front base 711 is fixed to the center of the upper base 11, and the lower front base 712 is fixed to the center of the lower base 12. One end of the upper link 81 is rotatably connected (pivoted) to the upper front base 711 by a pivot 751, and the other end is pivotally supported by a pivot 761 located on the left front of the front base 713. Similarly, one end of the lower link 82 is rotatably connected (pivoted) to the lower front base 712 by a pivot 752 (details omitted), and the other end is pivotally supported by a pivot 762 (details omitted) located on the front base 713.

[0056] The upper link 81 and the lower link 82 each consist of two parallel links arranged vertically. The upper link 81, the upper front base 711, and the front base 713 constitute a parallel crank mechanism. Similarly, the lower link 82, the lower front base 712, and the front base 713 also constitute a parallel crank mechanism.

[0057] The biasing mechanism 9 comprises a base 91, a left guide 921 and a right guide 922 made of hexagonal bolts, and a left spring 941 and a right spring 942 made of coil springs. The left guide 921 and the right guide 922 are loosely fitted to the base 91 and the front base 713 from the rear and are held in place by an upper nut 931 and a lower nut 932 on the front side of the front base 713. The left spring 941 and the right spring 942 are inserted through the left guide 921 and the right guide 922, respectively, and are elastically held between the base 91 and the front base 713.

[0058] The front base 713, which follows the upper link 81 and lower link 82, moves back and forth along the left guide 921 and right guide 922. For example, when the front base 713 moves backward, the left spring 941 and right spring 942 contract, biasing the base 91 backward. The pressing force exerted on the base 91 by the left spring 941 and right spring 942 is transmitted to the pressurizing body 72. As a result, the pressurizing body 72, with a pad 722 at its rear end, contacts the central front surface of the test piece, applying a load (pressure) in the front-rear direction to the test piece.

[0059] The relationship between the amount of movement of the front base 713 and the load applied to the test specimen by the pressurizing body 72 is adjusted by the spring constants of the left spring 941 and the right spring 942 and their preset loads. The spring constants are adjusted by changing the coil springs. The preset loads are adjusted, for example, by the tightening amount of the upper nut 931 and the lower nut 932.

[0060] In both fixture S1 and S2, the form (weight, shape) and arrangement of the components (base, chuck, link, balance weight, etc.) that make up each mechanism (link mechanism L1, guide mechanism R1, guide mechanism R2 or link mechanism L1) are adjusted so that the center of gravity G3 in the front-to-back direction lies on a plane passing through the center (center of gravity) Ct of the test piece T.

[0061] Furthermore, as shown in Figure 7, both fixtures S1 and S2 allow for stepless or multi-step adjustment of the mounting positions (pivot points) of the pivots 511, 512, 521, and 522 (upper adjustment mechanism, lower adjustment mechanism). This makes it possible to adjust the link angle (θ), and to change or correct the ratio (load ratio: Px / Py) of the lateral load (Px) and the vertical load (Py) acting on the test piece T (see Figure 9).

[0062] 《Analysis example》 Figure 8B shows an example of the analysis of the load applied to the test specimen by the link mechanism L1 (see Figure 8A). Specifically, it is as follows:

[0063] Links 211, 221, 212, and 222 (collectively referred to as "Link 2") are all pivotally supported by bases 11 and 12 (collectively referred to as "Base 1") and chucks 31 and 32 (collectively referred to as "Chuck 3") or bases 43 and 44 (collectively referred to as "Base 4") in symmetrical positions with respect to the vertical and horizontal directions, with equal distance (L) between pivot points.

[0064] Furthermore, the testing machine applies a tensile load (P0) in the vertical direction (uniaxial direction) above the center between the left and right pivot points of base 1. The angle between link 2 and the left-right direction (horizontal direction) (referred to as the "link angle") is θ (half-external angle), and the tension acting along link 2 is Pθ. The angle between the upper left link 211 and the lower left link 221 (left external angle: α) and the angle between the upper right link 212 and the lower right link 222 (left external angle: β) are expressed as 2θ.

[0065] In the case of a symmetrical fixture, the tensile load (Py) acting between chucks 3 and the tensile load (Px) acting between chucks 4 are given by equations (11) and (12) in Figure 8B, based on the balance of forces. From both equations, the relationship between the tensile loads P0, Px, and Py is given by equation (13).

[0066] Let Gx and Gy be the stiffnesses of the specimen T in the left-right direction (x direction) and the up-down direction (y direction), respectively, and let Δθ be the change in the half-external angle (θ) of each link from the initial state when a tensile load P0 is applied. In this case, the elongations δx and δy in each direction are expressed as shown in equations (21) and (22) in Figure 8B.

[0067] Here, assuming that the stiffness of the specimen T is isotropic in the left-right and up-down directions (Gx=Gy), the load ratio (Px / Py) is given by equation (31) shown in Figure 8B. From equations (31) and (13), for example, the relationship between tensile loads P0 and Py can be found as shown in equation (32).

[0068] Depending on the material of the test specimen T and the measurement range, if Δθ is sufficiently small (θ≈0), the tensile loads Px and Py can be expressed using equations (31) and (32), respectively, with respect to the tensile load P0 and the link angle θ, as shown in equations (41) and (42) in Figure 8B.

[0069] From equations (41) and (42), the relationship between Px / P0, Py / P0, and Px / Py and the link angle θ (α / 2 = β / 2) is such that, for example, when θ = 45° to 80° and even 45° to 75° (exterior angle 2θ = 90° to 160° and even 90° to 150°), the load acting on the test specimen T from two directions falls within a reasonable range.

[0070] [Example Test] (1) A test specimen T was prepared by laminating a tape made of carbon fiber reinforced polymer (CFRP) (referred to as "UD tape") in a cross shape. The test specimen T was symmetrical in terms of left-right and top-bottom.

[0071] (2) The upper and lower ends and the left and right ends of the test specimen T were gripped by chucks 3 and 4 of a fixture S attached to an electrohydraulic material testing machine. A marker was pre-applied to the center of the test specimen T (the cross intersection).

[0072] The material testing machine was activated to apply a uniaxial tensile load (P0) to the fixture S, and then the load was removed. Images of the surface (marker) of the test specimen T were taken and analyzed using image correlation software to determine the strain in the vertical direction (Y direction) (εy) and the strain in the horizontal direction (X direction) (εx).

[0073] Based on the theoretical formula (31) shown in Figure 8B, biaxial tensile tests were performed on specimen T under two conditions: assuming Px / Py=1 with a link angle θ=45°, and assuming Px / Py=2 with a link angle θ=63.4°. The relationship between εy and εx obtained at this time is shown in Figure 9. As is clear from Figure 9, for each link angle θ, measured values ​​close to the assumed values ​​(εy / εx=1 or 2) were obtained.

[0074] From the above, it has been confirmed that, according to the test fixture of the present invention, it is possible to accurately apply loads in at least two axial directions to the test piece while using a uniaxial testing machine. [Explanation of Symbols]

[0075] S1, S2 Test Fixtures T Test specimen L1, L2 linkage mechanism R1, R2 Guide mechanism (suppression means) 431, 432 Balance weights (suppression means) 11, 12, 43, 44 Bass Links 211-222 31, 32, 41, 42 Chuck

Claims

1. A test fixture to be mounted on a testing machine having an upper mounting body and a lower mounting body that move relative to each other in the vertical direction, An upper base that is attached to the upper mounting body, A lower base attached to the lower mounting body, An upper left link, with one end pivotally supported on the left side of the upper base, An upper right link, with one end pivotally supported on the right side of the upper base, A lower left link, with one end pivotally supported on the left side of the lower base, A lower right link, with one end pivotally supported on the right side of the lower base, The left base is pivotally supported on the other end of the upper left link and the other end of the lower left link, The right base is pivotally supported on the other end of the upper right link and the other end of the lower right link, An upper chuck that holds the upper part of the test specimen and is in conjunction with the upper base, A lower chuck that holds the lower part of the test piece and is in conjunction with the lower base, A left chuck that holds the left portion of the test piece and is linked to the left base, A right chuck that holds the right portion of the test piece and is linked to the right base, A means for suppressing abnormal loads that may occur on the test specimen, A test fixture equipped with the following features.

2. The suppression means includes a left balance weight that positions the center of gravity of the left holder, including the left base and the left chuck, approximately midway between the pivot point on the other end of the upper left link and the pivot point on the other end of the lower left link, A right balance weight is provided, which positions the center of gravity of the right retainer, including the right base and the right chuck, approximately midway between the pivot point on the other end of the upper right link and the pivot point on the other end of the lower right link. A test fixture according to claim 1, comprising the following components.

3. The test fixture according to claim 1, wherein the restraining means comprises at least one of a horizontal mechanism that restricts the relative movement of the left chuck and the right chuck in the horizontal direction, and a vertical mechanism that restricts the relative movement of the upper chuck and the lower chuck in the vertical direction.

4. Furthermore, the test fixture according to claim 1, further comprising a pressing mechanism that presses the test piece in the front-rear direction in conjunction with the upper base and the lower base.

5. The test fixture according to claim 3 or 4, wherein the center of gravity in at least the front-to-back direction is located approximately in the center of the test piece.

6. The upper left link and the upper right link can move their pivot points relative to the upper base. The test fixture according to claim 1, wherein the lower left link and the lower right link are capable of moving their pivot points relative to the lower base.

7. The test fixture according to claim 1, wherein the test specimen is made of a fiber-reinforced resin sheet.

Images