JP2015014544A - Compression test method and compression test device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compression test method and a compression test device capable of reliably obtaining compressive strength of an object material without causing an explosive fracture on the object material.SOLUTION: A compression test method includes: loading and unloading a test load on an object material after an initial load; and a first repetition step for repeating a second loading step, a second unloading step, and a test load comparison step until deterioration of the test load immediately after a peak load point which is equal to or below the test load of the previous peak load point is detected.

Description

  The present invention relates to a test method and apparatus for measuring the compressive strength of a material such as concrete.

  In order to confirm whether the strength of a material such as concrete is appropriate, a compression test is performed on a specimen of the material, and the compression strength of each material is obtained. Here, the “compressive strength” refers to a stress value obtained by dividing the maximum loaded load detected in the compression test by the cross-sectional area perpendicular to the loading direction of the specimen. In a compression test of a concrete specimen, if a load is continuously applied to the concrete specimen after the maximum load load has appeared, a fracture phenomenon called `` explosion '' occurs in which the concrete specimen suddenly breaks and fragments are scattered around. May occur. Since the explosion has an unfavorable effect on the surroundings, such as danger to the tester and breakage of the test and measurement equipment, the compression test of the concrete specimen must be performed without exploding the concrete specimen. Patent Documents 1 to 3 are examples of conventional devices aimed at enabling a compression test without exploding a concrete specimen.

  Patent Document 1 describes a compression test apparatus that performs both a compression test and a measurement of lateral strain generated during the compression test.

  Patent Document 2 describes a material testing machine that stretches an expansion spring in a direction opposite to the loading direction of the loading mechanism to prevent overshoot after a decrease in loading force.

  Patent Document 3 describes a material testing machine that adjusts a loading force reduction rate for detecting breakage according to a set predicted compressive strength.

  Here, in the conventional compression test apparatus including Patent Documents 1, 2, and 3, it may be difficult to perform a compression test without causing explosion and to detect the compression strength correctly. Will be described with reference to FIG.

  FIG. 1A shows a loading table displacement δ in a conventional compression test apparatus when the compression strength of the specimen is small and the rigidity of the test apparatus frame is sufficiently large (hereinafter referred to as “first case”). It is the example of the graph shown about the relationship with the test load P which acts on a test body. In the case of the first case, if a displacement control system loading method in which the displacement δ increases at a constant speed is adopted, a compression test can be easily realized in which the compressive strength can be reliably confirmed without causing the specimen to explode. it can. The compression test apparatus of Patent Document 1 is an example of a testing machine that aims to make it possible to more easily carry out such a compression test of a displacement control system by using both the measurement of displacement δ and the measurement of lateral strain. It is.

  On the other hand, FIG. 1B shows a case where the compression strength of the specimen is high or the rigidity of the test apparatus frame is insufficient (hereinafter referred to as “second case”) in the conventional compression test apparatus. 5 is an example of a graph showing the relationship between the loading table displacement δ and the test load P.

  In the case of the second case, even if a displacement control system in which the displacement δ increases at a constant speed is adopted, the pressure load (test load P) of the specimen rapidly decreases at a point Pz that exceeds the maximum load point Pmax. Thus, the deformation energy that has been stored on the frame side of the compression test apparatus until then is kicked back to the specimen side, which causes the specimen to break down and explode in an instant. Therefore, in the case of the second case, the conventional compression test apparatus adopts a load control system loading method in which the test load P is adjusted and loaded in order to prevent explosion. In such a load control system loading method, the test load P decreases after the maximum load point Pmax, and the test load P is unloaded by shifting the loading table to a rapid descent before reaching the point Pz. Therefore, the compressive strength is confirmed without exploding the specimen.

  The compression test apparatus of Patent Literature 2 and Patent Literature 3 is an example of a testing machine that enables a compression test of such a load control system. Note that the loading method of the load control system as described above is effective in preventing explosion even in the case of the first case shown in FIG.

Japanese Patent Laid-Open No. 8-17881 (published July 12, 1996) JP 2003-65918 A (published March 5, 2003) JP 2003-307476 A (published October 31, 2003)

  However, in the compression test, as shown in FIG. 2A, before reaching the maximum load point Pmax, the test load P has a peak load point Pa indicating a temporary decrease (hereinafter referred to as “third”. "Case"). 2 (a) and 2 (b) show the relationship between the loading table displacement δ of the conventional compression test apparatus and the test load P acting on the specimen, before the test load P reaches the maximum load point. It is an example of the graph which showed the case where it has a load drop point. FIG. 2A shows the relationship between the actual loading table displacement δ and the test load P acting on the specimen. FIG. 2B shows the relationship between the loading table displacement δ when erroneously recognized and the test load P acting on the specimen. The decrease in the test load P immediately after the maximum load point Pmax is caused by the fact that the scale is large and a fatal crack has occurred for the entire specimen. On the other hand, the temporary decrease in the test load P immediately after the peak load point Pa is caused by the occurrence of local cracks in the specimen while the test load P is being loaded. Such a temporary decrease in the test load P immediately after the peak load point Pa is considered to occur regardless of the material characteristics such as the compressive strength of the specimen. In addition, it is difficult to distinguish between a decrease in the test load P immediately after the peak load point Pa and a decrease in the test load P immediately after the maximum load point Pmax.

  In particular, when the specimen has a high compressive strength, the load control system loading method as described above needs to detect the decrease in the test load P more sensitively in order not to explode the specimen. For this reason, a decrease in the test load P immediately after the peak load point Pa is often mistakenly recognized as a decrease in the test load P immediately after the maximum load point Pmax. If the peak load point Pa is mistakenly recognized as the maximum load point Pmax, the maximum load point Pmax is originally measured from the relationship between the displacement δ and the test load P as shown in FIG. However, the relationship between the displacement δ and the test load P is erroneously measured as shown by the arrow in FIG. Therefore, there is a problem that correct compressive strength cannot be measured.

  Therefore, the present invention provides a compression that can correctly detect the maximum load point Pmax and the compressive strength without causing the specimen to explode in any of the first case, the second case, and the third case. It is an object of the present invention to provide a test method and a compression test apparatus that can implement the test method.

  In order to solve the above-described problems, the compression test method according to the present invention includes a first loading step of loading the target material while increasing the test load until the first load decrease at which the test load first decreases after the initial load. And a first unloading step of unloading while reducing the test load loaded on the target material when the first load is reduced, and before the test load loaded on the target material becomes the initial load. After the first unloading step is finished, the second loading step of loading the target material while increasing the test load until the second load reduction where the test load is reduced, and when the second load is reduced Then, the second unloading step of unloading while reducing the test load loaded on the target material, the first test load loaded on the target material at the peak load point immediately before the first load drop, Peak load just before the second load drop A test load comparison step for comparing the second test load loaded on the target material at a point, and if the second test load is greater than the first test load, the test load is equal to or less than the test load at the previous peak load point And a first repetition step of repeating the second loading step, the second unloading step, and the test load comparison step until a decrease in the test load immediately after the peak load point is detected. .

  In addition, a compression test apparatus used in the compression test method according to the present invention includes a test load loading unit that loads or unloads a test load on the target material, and a test load that compares the test loads loaded on the target material. A determination unit, and the test load loading unit performs a first loading on the target material while increasing the test load until the first load is reduced, and when the first load is reduced, the target material is loaded. The first unloading is performed while reducing the test load loaded on the target material, and the first unloading is terminated before the test load loaded on the target material reaches the initial load. The second loading is performed while increasing the test load on the target material until the load is decreased by 2 and when the second load is decreased, the second load is decreased while reducing the test load loaded on the target material. Unloading, the test load judgment part When the first test load and the second test load are compared, and the second test load is greater than the first test load, immediately after the peak load point that is equal to or less than the test load of the previous peak load point The second loading, the second unloading, and the comparison are repeated until a decrease in the test load is detected.

  With the above configuration, even in a specimen having a peak load point other than the maximum load point Pmax, the maximum load point Pmax can be correctly detected by confirming the test load at the subsequent peak load point. Therefore, the compressive strength of the specimen can be reliably obtained without causing the specimen to explode.

  In the compression test method according to the present invention, in the test load comparison step, the second loading step and the second unloading step are repeated when the second test load is not more than the first test load. It is preferable that it is further included.

  With the above configuration, specimen characteristics (relationship between the test load P and the displacement δ) after the point at which the specimen has exploded in the conventional loading method, which could not be obtained by the conventional loading methods, can be obtained.

  The present invention has an effect that the compressive strength of the specimen can be obtained with certainty without causing the specimen to explode.

It is the example of the graph shown about the relationship between the loading table displacement (delta) of the conventional compression test apparatus, and the test load P which acts on a test body. (A) shows the case where the compressive strength of the specimen is small and the rigidity of the test apparatus frame is sufficiently large. (B) The case where the compressive strength of the specimen is high or the rigidity of the test apparatus frame is insufficient is shown. Regarding the relationship between the loading table displacement δ of the conventional compression test apparatus and the test load P acting on the specimen, a graph showing a case where the test load P has a temporary load drop point before reaching the maximum load point. It is an example. (A) shows the relationship between the actual loading table displacement δ and the test load P acting on the specimen. (B) shows the relationship between the loading table displacement δ when erroneously recognized and the test load P acting on the specimen. BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the compression test apparatus which concerns on one Embodiment of this invention, and is the figure which writes and shows along with the schematic longitudinal cross-sectional view showing a mechanical principal part structure, and the block diagram showing an electrical principal part structure. FIG. 5 is a graph showing that the compressive strength can be detected correctly without causing a test specimen to explode, regarding the relationship between the loading table displacement δ of the compression test apparatus according to an embodiment of the present invention and the test load P acting on the test specimen. It is an example. Regarding the relationship between the loading table displacement δ of the compression test apparatus according to an embodiment of the present invention and the test load P acting on the specimen, even when a temporary load drop point is reached before reaching the maximum load point, It is an example of the graph which showed that compressive strength was correctly detectable, without causing a specimen to explode. Regarding the relationship between the loading table displacement δ of the compression test apparatus according to another embodiment of the present invention and the test load P acting on the specimen, after passing the maximum load point, until the test load P becomes sufficiently small, It is an example of the graph which showed that the relationship between displacement (delta) and the test load P was detectable.

Embodiment 1
Embodiments of the present invention will be described below with reference to FIGS. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[Compression test device 1]
First, the configuration of the compression test apparatus 1 will be described with reference to FIG. FIG. 3 is a configuration diagram of a compression test apparatus according to an embodiment of the present invention, and is a diagram illustrating a schematic longitudinal sectional view showing a mechanical main part configuration and a block diagram showing an electrical main part configuration. The compression test apparatus 1 includes a hydraulic cylinder 4, a loading ram 5, a loading table 6, and a spherical seat 7 inside the test apparatus frame 3. A spherical seat 7 is installed on the upper part of the test apparatus frame 3 (upward in FIG. 3), and a hydraulic cylinder 4 fixed to the lower part of the test apparatus frame 3 is placed below the spherical seat 7 via a loading ram 5. A loading table 6 that moves up and down is installed. The specimen 2 (target material) is disposed between the spherical seat 7 and the loading table 6. The test load P is loaded or unloaded on the specimen 2 by driving the hydraulic cylinder 4 and moving the loading table 6 up and down in the state arranged as described above. Further, the rigidity of the test apparatus frame 3 is very large and can be regarded as δ≈the amount of compressive deformation of the specimen 2 itself.

  The compression test apparatus 1 further includes a control unit 10. The control unit 10 includes a test load loading unit 11, a test load detection unit 12, and a test load determination unit 13. The test load loading unit 11 drives the hydraulic cylinder 4 with the test load P detected by the test load detection unit 12 to load or unload the test load P on the specimen 2. The test load detector 12 detects a test load P acting on the specimen 2. The test load determination unit 13 compares the magnitude of the test load P at the peak load point immediately before the test load P detected by the test load detection unit 12 decreases and the peak load point next to the peak load point. Further, the test load P detected by the test load detector 12 is used to measure the distance between the loading table 6 of the compression test apparatus 1 and the lower surface of the spherical seat 7, that is, the height of the specimen 2 by some method, If the amount of change is represented by displacement δ, a graph of the relationship between test load P and displacement δ can be obtained.

[Compression test method]
The test load P is loaded by a load control system loading method. First, the case where compressive strength is so large that the specimen 2 shows the graph shape as shown in FIG. 2A will be described with reference to FIGS. FIG. 4 shows that the compressive strength can be detected correctly without causing the specimen to explode, regarding the relationship between the loading table displacement δ of the compression testing apparatus according to one embodiment of the present invention and the test load P acting on the specimen. It is an example of the shown graph. FIG. 5 shows that the relationship between the displacement δ and the test load P can correctly detect the compressive strength without causing the specimen to explode even when the load has a temporary load drop point before reaching the maximum load point. It is an example of the graph which showed. First, from the initial load state until the test load P first decreases (first load decrease A1), the test load loading unit 11 drives the hydraulic cylinder 4 to raise the loading table 6, and the test load P is applied to the specimen 2. (1st loading process). Next, when the first load reduction A1 is performed, the test load loading unit 11 lowers the loading table 6 and unloads while reducing the test load P loaded on the specimen 2 (first unloading step). Further, the test load loading section 11 finishes the first unloading before the test load P loaded on the specimen 2 reaches the initial load, and then the second load decrease A2 in which the test load P decreases. Until then, the test specimen 2 is loaded while increasing the test load P (second loading step). Further, when the second load reduction A2 is performed, the test load loading unit 11 lowers the loading table 6 and unloads while reducing the test load P loaded on the specimen 2 (second unloading step). Here, the test load determination unit 13 performs the second test load loaded on the specimen 2 at the peak load point (second peak load point P2) immediately before the second load drop A2, and immediately before the first load drop A1. The first test load loaded on the specimen 2 at the peak load point (first peak load point P1) is compared (test load comparison step). If the second test load is equal to or less than the first test load, the test load loading unit 11 unloads the test load P loaded on the specimen 2 as it is and ends the test.

  Moreover, as shown in FIG. 5, when the 2nd test load is larger than the 1st test load, it can be judged that the 1st peak load point P1 is not what detected the maximum load point Pmax of the test body 2. FIG. Therefore, in the above case, after the second unloading step, the test load loading unit 11 finishes the second unloading before the test load P loaded on the specimen 2 reaches the initial load, and then The test load 2 is loaded while increasing the test load P until the third load drop A3 at which the test load P decreases (second loading step). When the third load drop A3 is performed, the test load P loaded on the specimen 2 is unloaded (second unloading step). The test load determination unit 13 compares the third test load loaded on the specimen 2 at the third peak load point P3 that is the third peak load point with the second test load (test load comparison step). ). If the third test load is equal to or less than the second test load, the test load loading unit 11 unloads the test load P loaded on the specimen 2 as it is and ends the test. If the third test load is larger than the second test load, the first test load is detected until a decrease in the test load immediately after the peak load point that is equal to or less than the test load loaded on the specimen 2 at the previous peak load point is detected. 2 loading processes, the said 2nd unloading process, and the said test load comparison process are performed repeatedly (1st repetition process).

  With the above configuration, even in a specimen having a peak load point other than the maximum load point Pmax, the maximum load point Pmax can be correctly detected by confirming the test load P at the peak load point next to the peak load point. it can. Therefore, it is possible to correctly measure the compressive strength of the target material.

  In the present embodiment, the test method for the case where the comparison of the test loads P is completed in three times is described, but the comparison may be four times or five times or more. That is, as an essential condition for the end of the test, in the reloading subsequent to the unloading of the test load P after the decrease in the test load P, the test load becomes equal to or less than the test load at the peak load point immediately before the decrease in the test load P. This is to detect a decrease in the test load P immediately after the peak load point next to the decrease in the test load P.

  Moreover, in order to avoid explosion, it is necessary to detect a decrease in the test load by a sufficiently sensitive detection capability of the test load detector 12. The detection capability may be set in advance by a tester in the range of, for example, 1/1000 to 1/10000 of the compression tester loading capacity in consideration of the detection accuracy of the loading load. The loading method as described above is named “second peak loading method”.

  In addition, the compression test method when the compressive strength of the specimen 2 is small is carried out for the purpose of avoiding the explosion of the specimen in a manually controlled compression test performed in a general concrete quality control laboratory. It can be realized in the same manner as the “dimension test”.

[Embodiment 2]
Further, in the case of the second case and the third case, the displacement δ and the range until the test load P becomes sufficiently small after passing the maximum load point Pmax, which could not be obtained by the conventional compression test apparatus or test method. There is a need for a compression test method that can detect the relationship with the test load P and a compression test apparatus that can implement the compression test method.

  Hereinafter, a material testing method according to another embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows the relationship between the loading table displacement δ of the compression test apparatus according to another embodiment of the present invention and the test load P acting on the specimen, and the test load P becomes sufficiently small after passing the maximum load point. It is an example of a graph showing that the relationship between the displacement δ and the test load P can be detected up to a range.

  The test method according to the present embodiment detects a decrease in the test load P immediately after the peak load point after the maximum load point Pmax is confirmed, that is, immediately after the peak load point that is equal to or less than the test load of the previous peak load point. After that, it is the same as the second peak test until the transition to the unloading process. However, the test method according to the present embodiment does not end the test by completely unloading the test load P there. After confirming the peak load point next to the maximum load point Pmax, the test load loading unit 11 unloads while reducing the test load P loaded on the specimen 2 (second unloading step). Further, the test load loading section 11 finishes the unloading before the test load P loaded on the specimen 2 reaches the initial load, and then applies the test load P to the specimen 2 until the test load P decreases. (2nd loading process). Moreover, the test load loading part 11 unloads the test load P loaded on the specimen 2 when the test load decreases (second unloading step). In the test method according to the present embodiment, after the peak load point next to the maximum load point Pmax is confirmed, the second unloading step and the second loading step are repeatedly performed as described above (second repeating step). The above loading method is named “post-peak loading method”.

  When the compression test is performed by the post-peak loading method, if the amount of change of the specimen 2 is measured by some method and expressed as the displacement δ, the relationship between the test load P and the displacement δ draws a curve as shown in FIG. The curve drawn by the displacement δ shown in FIG. 6 shows the test load P indicated by a broken line after the point Pz in FIG. 2A that could not be obtained by the conventional loading method if the envelope of the peak load point Pn is taken. And the relationship of displacement δ. Obtaining such a relationship between the peak load point Pn and the displacement δ in the compression test of the material is significant technical information in conducting quality control and research on the material properties of the specimen.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used for a compression test performed by loading a test load.

  DESCRIPTION OF SYMBOLS 1 Compression test apparatus, 2 Specimen (target material), 3 Test apparatus frame, 4 Hydraulic cylinder, 5 Loading ram, 6 Loading table, 7 Spherical seat, 11 Test load loading part, 13 Test load determination part, A1, A2, A3 Load drop, Pz point, Pa, P1, P2, P3, Pn peak load point, Pmax maximum load point

Claims (3)

A first loading step of loading while increasing the test load on the target material until the first load drop where the test load first decreases after the initial load;
A first unloading step of unloading while reducing the test load loaded on the target material when the first load is reduced;
After the first unloading step is completed before the test load loaded on the target material becomes the initial load, the test load is increased on the target material until a second load decrease where the test load decreases. A second loading step of loading while
A second unloading step of unloading while reducing the test load loaded on the target material when the second load is reduced;
A first test load loaded on the target material at a peak load point immediately before the first load drop, and a second test load loaded on the target material at a peak load point immediately before the second load drop. A test load comparison process to be compared;
If the second test load is greater than the first test load, the second loading step until a decrease in the test load immediately after the peak load point that is equal to or less than the test load of the previous peak load point is detected; A compression test method comprising: a second repetition step of repeating the second unloading step and the test load comparison step.   The test load comparing step further includes a second repetition step of repeating the second loading step and the second unloading step when the second test load is equal to or less than the first test load. The compression test method described in 1. In the compression test apparatus used for the compression test method according to claim 1,
A test load loading section for loading or unloading the test load on the target material;
A test load determination unit for comparing test loads loaded on the target material,
The test load loading part is
Until the first load is reduced, the first loading is performed while increasing the test load on the target material,
When the first load is reduced, the first unloading is performed while reducing the test load loaded on the target material,
After the first unloading is finished before the test load loaded on the target material becomes the initial load, the second load is loaded while increasing the test load on the target material until the second load is reduced. And
When the second load is reduced, the second unloading is performed to unload while reducing the test load loaded on the target material,
When the test load determination unit compares the first test load and the second test load, and the second test load is larger than the first test load, the test load is equal to or less than the test load at the previous peak load point. The compression test apparatus, wherein the second loading, the second unloading, and the comparison are repeated until a decrease in the test load immediately after the peak load point is detected.

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