JP7415960B2 - test jig - Google Patents

Description

The present invention relates to a test jig that can convert a uniaxial load into a multiaxial load.

Tests that apply a load to a test piece and measure its physical properties (mechanical properties) are essential in product development (particularly material development), quality control, etc. Such tests are usually performed using a dedicated testing machine or test jig that is appropriate for the physical property value to be measured. Among these, the most commonly performed material test is a uniaxial tensile test (a test in which a uniaxial tensile load is applied to a test piece) using a material testing machine.

By the way, optimal design that balances performance/function (characteristics), weight and compactness, etc. at a high level is being advanced, and in addition to isotropic materials, anisotropic materials whose characteristics differ depending on the direction are also frequently used. Furthermore, even isotropic materials can be subjected to different loads from multiple directions when actually used.

In order to conduct evaluation tests in line with such actual circumstances, for example, in a general material testing machine, the load in one axis direction (referred to as "uniaxial load") is converted to the load in two axial directions (referred to as "biaxial load"). ) has been proposed. Descriptions related to this can be found, for example, in the following documents.

Development of a biaxial tensile test method for hard aluminum alloy plates for cans, Yasuhiro Hanabusa, Tokyo University of Agriculture and Technology, dissertation (2014)

The test jig described in the above document has one driving link and four driven links rotatably attached to a rotating disk. When a uniaxial load is applied to the drive link, each driven link is interlocked, and a biaxial load is applied to the cross-shaped test piece attached to the other end of the driven link. By changing the mounting position and length of the driven link, it is also possible to adjust the load ratio (displacement ratio) in each direction.

However, the test jig has 11 connection points (rotation center/permanent center) for each link (joint), and a slider that directly moves the attachment part of the test piece provided on each link (total four). Such test jigs are complex and have many links (nodes, elements) and connection points.

The present invention has been made in view of these circumstances, and an object of the present invention is to provide a test jig, etc. with a new structure (link mechanism) different from the conventional one.

As a result of intensive research to solve this problem, the present inventor conceived and implemented a test jig that utilizes a toggle mechanism. By developing this result, we have completed the present invention described below.

《Test jig》
(1) The present invention is a test jig that is mounted on a testing machine that includes an upper mounting body and a lower mounting body that move relative to each other in the vertical direction, the upper base mounted on the upper mounting body, and the lower mounting body that A lower base to be attached to the body, an upper left link having one end pivoted to the left side of the upper base, an upper right link having one end pivoted to the right side of the upper base, and one end to the left side of the lower base. A lower left link whose side is pivoted, a lower right link whose one end is pivoted to the right side of the lower base, an upper chuck that holds the upper part of the test specimen in conjunction with the upper base, and an upper chuck that is coupled with the lower base. a lower chuck that holds the lower part of the test piece; a left chuck that holds the left side of the test piece while the other end side of the upper left link and the other end side of the lower left link are pivotally supported; This test jig includes a right chuck to which the other end of the upper right link and the other end of the lower right link are pivotally supported and which holds the right part of the test piece.

(2) According to the test jig of the present invention, it is possible to perform measurements while applying loads in at least two directions to a test piece while using a testing machine that can apply loads in one direction. Further, the test jig of the present invention has a relatively small number of links (nodes, elements) and connection points, and can simplify the structure. Therefore, it is excellent in ease of handling, maintainability (for example, management of connection point clearance and friction, etc.), stability of measurement accuracy, etc. Note that by adjusting the length of each link, the attachment angle, etc., it is also possible to adjust the load ratio in each direction (for example, left-right direction, up-down direction) applied to the test piece.

Further, according to the test jig of the present invention, for example, the front and back sides can be opened while holding a test piece. In this case, it becomes possible to perform multidimensional damage analysis by simultaneously measuring full-field deformation and strain using the image correlation method and measuring dissipated energy using active thermography.

(3) In addition to each link and each chuck disposed in the left-right direction, the test jig of the present invention has similar links and Each chuck may further be provided. For example, the test jig of the present invention further includes an upper front link having one end pivotally supported on the front side of the upper base, an upper rear link having one end pivotally supporting on the rear side of the upper base, and the lower base. a lower front link with one end pivotally supported on the front side of the lower base; a lower rear link with one end pivotally supported on the rear side of the lower base; the other end of the upper front link and the other end of the lower front link with a front chuck that is supported and holds the front part of the test piece; a rear chuck that supports the other end side of the upper and rear links and the other end side of the lower rear link and holds the rear part of the test piece; may be provided. This makes it possible to perform measurements by applying loads in three directions to the test piece, while using a testing machine that can apply loads in one direction.

The test jig of the present invention preferably has a structure that is substantially symmetrical with respect to at least one direction (or each direction) of the up-down direction, the left-right direction, or the front-back direction. This makes it possible to efficiently analyze measurement results and design and manufacture jigs.

"Test method"
The present invention can also be understood as various test methods using the test jig described above. The test jig may be used for, for example, compression tests, bending tests, etc. in addition to tensile tests.

"others"
(1) The load direction (axial direction) applied via the test jig does not necessarily have to be in the direction of orthogonal axes (x-axis, y-axis, z-axis). Further, the test piece may have any shape as long as it can apply a load in each axial direction, and does not necessarily have to be in the shape of a planar four-sided cross or a three-dimensional six-sided cross. The load is not limited to a tensile load, but may be a compressive load. The object to be measured is not limited to load (stress), but may also be displacement (strain) or the like.

(2) The shape (plate, rod, tube, straight, curved, etc.), size, material, etc. of the links, bases, chucks, etc., as long as they have enough rigidity and strength to ensure the desired measurement accuracy. No questions asked. The type and model of the testing machine equipped with the test jig does not matter as long as it can apply a uniaxial load.

(3) In this specification, "upper/lower", "left/right", and "front/rear" are names for convenience of explanation, and do not necessarily have to be along the vertical direction. For example, the up-down direction may be a horizontal direction, and the left-right direction may be a vertical direction.

The "end side" (one end side, the other end side) used in this specification is also a name for convenience of explanation, and does not necessarily have to be the end of the link. Any region (part) that can be connected or interlocked with other elements may be used. The same applies to "left side", "right side", "left part", "right part", "front side", "rear side", "front part", "rear part", etc.

(4) Unless otherwise specified, "x to y" as used herein includes a lower limit x and an upper limit y. A new range such as "a to b" can be established by setting any numerical value included in the various numerical values or numerical ranges described herein as a new lower limit or upper limit.

FIG. 2 is a plan view schematically showing a test jig (one example). This is a group of mathematical formulas that calculate the balance of forces, elongation, and load acting on the test piece attached to the test jig. It is a graph showing the relationship between the angle formed by the link and the load ratio in the test jig. It is a photograph showing an example of strain in each direction that occurs when a tensile load is applied to a test piece using the test jig. It is a graph showing an example of the relationship between the tensile load and strain in each direction.

The content described in this specification may apply not only to a test jig but also to a test method using the same. One or more components arbitrarily selected from the present specification may be added to the components of the present invention described above. Which embodiment is best depends on the object, required performance, etc.

《Test jig》
By adjusting the length of each link, the angle between the links, etc., it is possible to adjust the direction of the load applied to the test piece, the ratio of the load (simply referred to as "load ratio"), etc. The load and direction acting on the test piece are determined mechanistically.

For example, the left external angle (α) is the angle between the upper left link and the lower left link toward the outside, and the right angle is the angle between the upper right link and the lower right link toward the outside. If the external angle (β) is within 180°, tensile loads can be applied to the test piece in two directions.

Conversely, for example, if both the left outer angle and the right outer angle are made larger than 180°, it is possible to apply a tensile load to one direction of the test piece while applying a compressive load to the other direction of the test piece. In addition, even at a mechanistic point of consideration (for example, when the left external angle and right external angle are 180°), if we consider the Poisson's ratio (ν) of the material that makes up the test piece, the test piece has the following characteristics in at least two directions: Load can be applied stably. For example, when a vertical tensile load is applied to a test piece held by upper and lower chucks, even when both the left and right outer angles are 180°, the test piece held by left and right chucks will be affected in the left and right direction due to the Poisson effect. A tensile load of (when ν>0) can act.

However, the left external angle (α) and/or the right external angle (β) may be, for example, 70° to 160°, 80° to 150°, or even 90° to 140°. This makes it possible to measure the ratio of the load between the left and right chucks to the load between the upper and lower chucks (simply referred to as "load ratio") within a predetermined range. In this specification, when α=β, the half angle is appropriately referred to as θ (that is, α=β=2θ).

"Test pieces"
The material and characteristics of the test piece to be tested do not matter. Further, the form (shape, size) of the test piece does not matter as long as it can be held by the left and right and upper and lower chucks. The test piece may have a parallel portion having a constant width, thickness, diameter, etc. along each direction in which a load is applied, but the shape may be different in each direction. For example, if a tensile test is performed by applying a load in orthogonal biaxial directions, a test piece having at least a substantially cross-shaped central portion may be used.

The present invention will be specifically explained by showing an example of a test jig and a measurement example using the test jig.

《Test jig》
A test jig S (simply referred to as "jig S") which is an embodiment of the present invention is schematically shown in FIG. Note that the directions shown by arrows in FIG. 1 are the up-down direction (Y-axis direction) and the left-right direction (X-axis direction).

(1) Configuration Jig S has a symmetrical structure in the vertical and horizontal directions, and is installed between the crosshead (fixed side) and piston (movable side) of a material testing machine that can apply a uniaxial load. Ru.
The specific configuration of the jig S is as follows.

The jig S is provided with an upper base 11 that is removable from a crosshead (upper mounting body), a lower base 12 that is removable from a piston (lower mounting body), and between the upper base 11 and the lower base 12. Four upper left links 211, lower left links 221, upper right links 212, and lower right links 222,
It includes 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. In addition, the bases 11 and 12 are collectively referred to as "base 1," the links 211, 221, 212, and 222 are collectively referred to as "link 2," the chucks 31 and 32 are collectively referred to as "chuck 3," and the chucks 41 and 42 are collectively referred to as "link 2."It's called "Chuck 4". Attachment and detachment (fixation) of the base 1, gripping (fixation) of the test piece by each chuck, etc. are performed by fastening bolts b.

One end of the upper left link 211 is rotatably connected (pivotally supported) to the left end of the upper base 11 by a pivot 511, and the other end is pivotally supported to the upper part of the left chuck 41 by a pivot 611. One end of the lower left link 221 is pivotally supported by the left end of the lower base 12 and a pivot 521, and the other end is pivotally supported by the lower part of the left chuck 41 and a pivot 621.

One end of the upper right link 212 is pivotally supported by the right end of the upper base 11 and a pivot 512, and the other end is pivotally supported by the upper part of the right chuck 42 and a pivot 612. One end of the lower left link 222 is pivotally supported to the right end of the lower base 12 by a pivot 522, and the other end is pivotally supported to the lower part of the right chuck 42 by a pivot 622.

(2) Operation When the test machine is operated and the lower base 12 is moved relative to the upper base 11 (relative movement in the vertical direction away from each other), the upper chuck 31 fixed to the upper base 11 and the lower base 12 A tensile load in the vertical direction (Y-axis direction) acts on the test piece T held by the fixed lower chuck 32. In conjunction with this, the test held by the left chuck 41 which is pivotally supported by the upper left link 211 and the lower left link 221, and the right chuck 42 which is pivotally supported by the upper right link 212 and the lower right link 222. A tensile load in the left-right direction (X-axis direction) also acts on the piece T.

(3) Load Ratio Each link 2 has the same distance (L) between its pivot points, and is pivoted to the base 1 and the chucks 3 and 4 in vertically and horizontally symmetrical positions. Further, the testing machine applies a tensile load (P0) in the vertical direction (uniaxial direction) on the center between the left and right pivot points of the base 1. Let the angle between each link 1 and the left-right direction (horizontal direction) be θ (half-exterior angle), and the tension acting along each link 1 be Pθ. The angle that the upper left link 211 and the lower left link 221 make outward (left outer angle: α) and the angle that the upper right link 212 and the lower right link 222 make outward (left outer angle: β) are 2θ. expressed.

In the case of such a symmetrical jig S, the tensile load (Py) that acts between the chucks 3 and the tensile load (Px) that acts between the chucks 4 are expressed by the equation (11) shown in Fig. 2 from the balance of forces. , (12). From both equations, the relationship between the tensile loads P0, Px, and Py is expressed by equation (13).

When applying a tensile load P0 to Gx, Gy, which changes the stiffness of the specimen T in the left-right direction (x direction) and up-down direction (y direction), the change from the initial half external angle (θ) of each link is Δθ shall be. At this time, the elongations δx and δy in each direction are expressed as equations (21) and (22) shown in FIG. 2.

Here, assuming that the rigidity of the test piece T is isotropic in the left-right direction and the up-down direction (Gx=Gy), the load ratio (Px/Py) is expressed by equation (31) shown in FIG. 2. Note that from equation (31) and equation (13), for example, the relationship between the tensile loads P0 and Py can be found as shown in equation (32).

Although it depends on the material of the test piece T, the measurement range, etc., if Δθ is sufficiently small (θ≒0), the tensile loads Px and Py are calculated as the tensile load P0 and P0 from equations (31) and (32), respectively. Using the half external angle θ, it is expressed as equations (41) and (42) shown in FIG.

From equations (41) and (42), the relationship between Px/P0, Py/P0, and Px/Py and the semi-external angle θ (α/2=β/2) is plotted as shown in FIG. 3. As can be seen from Fig. 3, for example, when θ = 45° to 80°, or even 45° to 75° (external angle 2θ = 90° to 160°, or even 90° to 150°), the specimen T is It can be seen that the applied load is within a reasonable range.

《Test example》
(1) As a test piece T, a sample was prepared in which tapes (referred to as "UD tape") made of resin reinforced in one direction with carbon fibers (referred to as "UD tape") were laminated in a cross shape. The shape of this test piece T was symmetrical with respect to the left and right and the top and bottom.

(2) The upper and lower parts and left and right parts of this test piece T were gripped with chucks 3 and 4 of a jig S attached to an electro-hydraulic material testing machine. At this time, the external angle (α, β=2θ) was 127°. Note that a marker was attached in advance to the center part (cross-crossing part) of the test piece T.

The material testing machine was operated to apply a uniaxial tensile load (P0) to the jig S. An image taken of the surface (marker) of the test piece T was analyzed using image correlation software to determine vertical strain (eyy) and horizontal strain (exx).

FIG. 4 shows the state of the test piece T on which tensile loads are applied in each direction. Moreover, the relationship between the load (P0) and each strain (exx, eyy) is shown in FIG. From FIG. 5, it was confirmed that each strain (exx, eyy) in the biaxial direction was approximately directly proportional to the load (P0) measured by the material testing machine. From this, it was also found that the loads (Px, Py) in the biaxial directions were also approximately directly proportional to the load (P0) measured by the material testing machine.

As described above, it was confirmed that according to the test jig of the present invention, it is possible to perform measurements while applying loads in at least two directions to a test piece, even though a testing machine capable of applying loads in one direction is used.

S Test jig T Test piece 11, 12 Base 211-222 Link 31, 32 Chuck 41, 42 Chuck

Claims (4)

A test jig attached to a testing machine comprising an upper mounting body and a lower mounting body that move relative to each other in the vertical direction,
an upper base attached to the upper mounting body;
a lower base attached to the lower mounting body;
an upper left link having one end pivoted to the left side of the upper base;
an upper right link having one end pivoted to the right side of the upper base;
a lower left link having one end pivoted to the left side of the lower base;
a lower right link having one end pivoted to the right side of the lower base;
an upper chuck that holds the upper part of the test piece in conjunction with the upper base;
a lower chuck that interlocks with the lower base to hold the lower part of the test piece;
a left chuck on which the other end side of the upper left link and the other end side of the lower left link are pivotally supported, and which holds the left side of the test piece;
a right chuck to which the other end side of the upper right link and the other end side of the lower right link are pivotally supported and which holds the right side of the test piece ;
The left outer angle, which is the angle formed by the upper left link and the lower left link outward, and the right outer angle, which is the angle formed outward by the upper right link and the lower right link, are within 180°. Test jig. The test jig according to claim 1 , wherein the left outer angle and/or the right outer angle are 70° to 160°. The test jig according to claim 1 or 2, which has a substantially symmetrical structure in the vertical and horizontal directions. The test jig according to claim 3 , further having a substantially symmetrical structure in the front-back direction.

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