JP5093005B2 - Material testing equipment - Google Patents

Description

  The present invention relates to a material testing apparatus that performs a material test by an unloading compliance method.

Generally in the J _1C test by unloading compliance method, giving a tensile test force to the test piece formed in advance cracks performs unloading of, for example, about 10% each time reaches the predetermined load point displacement, during the unloading Detect test force and aperture displacement. Then, the crack growth length Δa is calculated from the compliance obtained from these detected values, a J-Δa curve is formed by the J integral value of the unloading point and the Δa, and the J _1C value is obtained (see, for example, Patent Document 1). ).

JP 2001-337015 A

In this type of test apparatus, the unloading point is set according to a predetermined load step width. However, when the unloading point increases, the test time becomes longer and the test efficiency is poor. On the other hand, if there are too few unloading points, the number of data recommended by the standard cannot be satisfied, and an effective _J1C value cannot be obtained.

Material testing apparatus according to the present invention, tensile while loading a tensile test force to advance the crack has been formed test piece, and load means for unloading the test force at the target unloading point, it is loaded into the test piece Test Determining the compliance at the target unloading point based on the detection results of the test force detecting means for detecting force, the displacement detecting means for detecting the opening displacement of the test piece, and the test force detecting means and the displacement detecting means. While calculating the crack growth length of the test piece, calculating means for calculating a J integral value that is a parameter of crack growth at the target unloading point, and calculating the crack growth length and the J integrated value calculated by the calculating means The unloading point for setting the target unloading point so that the number of calculated data is equal to or greater than a predetermined target number in a predetermined region on the J-Δa curve representing the relationship between the crack growth length and the J integral value. And a constant section, the unloading point setting means, and the difference between the target unloading point of previous target unload point and the time before last, and the crack propagation length in the previous target unloading points calculated by said calculation means The target unloading point is calculated and set based on the difference from the crack propagation length at the target unloading point two times before .

  According to the present invention, the target unloading point is set so that the number of crack growth length and J integral value calculation data is equal to or greater than a predetermined target number in a predetermined region on the J-Δa curve. It is possible to prevent taking too many unloading points as described above, and the test can be performed efficiently.

Hereinafter, with reference to FIGS. 1-6, one Embodiment in the case of performing the _J1C test by the unloading compliance method with the material test apparatus by this invention is described.
FIG. 1 is a diagram illustrating a schematic configuration of a material testing apparatus according to the present embodiment, and FIG. 2 is a diagram illustrating a shape of a test piece TP loaded by the material testing apparatus.

  As shown in FIG. 2, the test piece TP is a substantially rectangular flat plate, and a substantially U-shaped notch 11 is formed at an intermediate portion of one end surface of the test piece TP. Through holes 12 and 13 penetrating in the thickness direction of the test piece TP are opened at positions facing the notch 11. A jig (not shown) is inserted into the through holes 12 and 13, and a tensile test force P is applied to the test piece TP in the direction of the arrow through the jig. This test force P causes a crack 14 to occur at the tip of the notch 11.

  As shown in FIG. 1, the material testing apparatus includes a load mechanism 1 that applies a tensile test force P to a test piece TP, a load cell 2 that detects the test force P applied to the test piece TP, and a cutout of the test piece TP. A clip gauge 3 for detecting a displacement of 11 width (opening displacement v), a controller 4 for controlling the load mechanism 1, an operation panel 5 for a user to input test conditions, a test start command, etc., test results and test conditions And a display monitor 6 for displaying various types of information. The load mechanism 1 has, for example, a double-acting hydraulic cylinder, and loads the test force P to the test piece TP by driving the hydraulic cylinder.

The controller 4 includes an arithmetic processing unit having an A / D converter, an amplifier, a CPU, a ROM, a RAM, and other peripheral circuits. When performing the _J1C test by the unloading compliance method, after outputting a control signal from the controller 4 to the load mechanism 1 (control valve for driving the hydraulic cylinder) to give a predetermined tensile test force to the test piece TP, For example, the test force is unloaded about 10%. The test force P and the opening displacement v at this time are detected by the load cell 2 and the clip gauge 3, respectively, and the controller 4 obtains a load curve from the detection result.

  FIG. 3A is a diagram showing an example of a load curve, and FIG. 3B is an enlarged view of a portion b in FIG. In FIG. 3B, the tensile test force P is loaded from the point p1 to the point p2, and the test force P is unloaded from the point p2 to the point p3. Further, the tensile test force P is loaded from the point p3 to the point p4, and the test force P is unloaded from the point p4 to the point p5. Such loading and unloading of the test force are repeated to obtain a load curve. A load amount (for example, a change amount of the opening displacement v) from the point p1 to the point p2 and from the point p3 to the point p4 is referred to as a load step width Δv.

  The controller 4 calculates the compliance from the slope of each load curve at the time of unloading (for example, p2 to p3, p4 to p5), and calculates the crack propagation length Δa at each unloading point (point p2 or point p4). To do. Further, a J-integral value that is a parameter of crack propagation is calculated at each unloading point, and a J-Δa curve that is an approximate curve of these J-Δa data is obtained.

FIG. 4 is a diagram illustrating an example of a J-Δa curve (also referred to as an R curve). In the figure, the points plotted with J-Δa data, the blunting line passing through the origin, and the blunting line are offset by 0.15mm, 0.2mm, 0.5mm, 1.0mm, 1.5mm, 0.15mm boundary line, 0.2mm boundary line, 0.5 The mm boundary line, 1.0 mm boundary line, and 1.5 mm boundary line are also shown. The controller 4 calculates the J value at the intersection of the R curve and the 0.2 mm boundary as a J _1C value (elastic-plastic fracture toughness value).

Here, the region between the 0.15 mm boundary line and the 0.5 mm boundary line is the region A, the region between the 0.5 mm boundary line and the 1.0 mm boundary line is the region B, and the region between the 1.0 mm boundary line and the 1.5 mm boundary line. Is region C. In order for the J _1C value to be effective, the number of J-Δa data in each of the areas A to C needs to satisfy the standard. For example, according to the JIS standard (JIS Z 2284), the number of data in the area A is 1 point or more, the area B is 5 points or more, and the area C is 1 point or more. Further, according to the ASTM standard (ASTM E813), the number of data in the area A is 1 point or more, the area B is 4 points or more, and the area C is 1 point or more.

In this case, if the load step width Δv (for example, the width of p1 to p2 and p3 to p4 in FIG. 3) for loading the test piece TP is reduced to increase the number of unloading points as much as possible, the number of J-Δa data increases. Can meet the standards. However, this increases the test time and the test efficiency is poor. On the other hand, if the load step width Δv is too large, the unloading points are insufficient and the standard cannot be satisfied, and an effective J _1C value cannot be obtained. Therefore, in the present embodiment, the minimum number of unloading points satisfying the standard is calculated as follows, and this is set as the target unloading point for testing.

  FIG. 5 is a flowchart illustrating an example of processing executed by the CPU of the controller 4. The process shown in this flowchart is started when the controller 4 is turned on. In step S1, it is determined whether or not the setting of test conditions has been completed. Test conditions to be set include the test piece shape, the elastic modulus E of the test piece TP, the initial load step width Δv0, the load speed, the unloading amount (%), the unloading time, and the like. Note that the initial load step width Δv0 is set to a value at which the initial test data (J-Δa data) is at least a region smaller than the region A in FIG. As a test condition, a standard (JIS standard or ASTM standard) applied at the time of the test is also set. In the following description, it is assumed that the JIS standard is set.

  If step S1 is affirmed, the process proceeds to step S2 to determine whether or not a load start command is input. The load start command is input, for example, when the user turns on a load start switch of the operation panel 5. When step S2 is input, the process proceeds to step S3, and a control signal is output to the load mechanism 1 according to a predetermined test condition. Thereby, after applying the tensile test force P to the test piece TP with the initial load step width Δv0, the test force P is unloaded by a predetermined amount (for example, 10%).

  In step S4, a control signal is output to the display monitor 6, a load curve (FIG. 3) is displayed on the display monitor 6 based on the signals from the load cell 2 and the clip gauge 3, and the crack propagation length Δa at the unloading point is displayed. The J integral value is calculated, and the J-Δa data is plotted and displayed on the J-Δa graph. In step S5, it is determined whether or not the plotted J-Δa data is within the area A in FIG. If step S5 is negative, the process returns to step S2 and the same processing is repeated. As a result, the crack growth length Δa gradually increases.

  If step S5 is affirmed, the process proceeds to step S6, and the target step width Δva is calculated. The target step width Δva is such a step width that a number of data satisfying the standard can be obtained in each of the areas A to C on the J-Δa graph. Here, since the necessary number (1) of area A data is obtained, first, the target step width Δva for obtaining the necessary number (4) of area B data is calculated, and then the data of area C is obtained. A target step width Δva for obtaining the required number (one) is calculated.

  This point will be described more specifically. For example, it is assumed that calculated points q0 to q6 on the J-Δa graph shown in FIG. 6B are obtained corresponding to the unloading points p0 to p6 on the load curve shown in FIG. The opening displacements of the points p0 to p6 are v0 to v6, and the crack propagation lengths of the calculation points q0 to q6 are Δa0 to Δa6, respectively. In FIG. 6B, the J-Δa curve connecting the calculation points q0 to q6 is indicated by a broken line. At this time, since the point q1 is included in the region A, when the data of the point q1 is obtained, in step S6, first, the target step width for obtaining the data of the point q2 in the region B, that is, as shown in FIG. An increment Δva1 (= v2−v1) of the opening displacement v from the unloading point p1 to p2 is calculated.

  The target step width Δva1 is obtained, for example, by calculating the ratio between the previous load step width Δva0 (= v1−v0) and the change amount sa0 (= Δa1−Δa0) of the previous crack growth length, It is obtained by multiplying the target change amount. Similarly, the target step width Δva2 (= v3-v2) for obtaining the data of the point q3 in the region B is the previous load step width Δva1 (= v2-v1) and the change amount sa1 of the previous crack length. It is obtained by obtaining a ratio with (Δa2−Δa1) and multiplying this by the target change amount of the crack growth length.

  Here, as the target change amount of the crack progress length, the target value of the crack progress length in the region B of 4 points (target points of q2 to q5) is 20%, 40%, 60%, 80 of the region B in advance. % Target value of the crack growth length in the region C (q6 target point) is set to a value of 50% of the region C, and the target point and the current crack growth length Δa It is a difference. For example, the target change amount when obtaining the target load step width Δva1 is the difference between the target point corresponding to 20% of the region B and the crack propagation length Δa1 at that time, and the target when obtaining the target load step width Δva2 The amount of change is the difference between the target point corresponding to 40% of the region B and the crack propagation length Δa2 at that time.

  When the target step width Δva is calculated as described above, the process proceeds to step S7, where the data is horizontally shifted on the load curve by the unloading point corresponding to the target step width Δva, for example, the target load step width Δva. Is displayed on the display monitor 6. The target unloading point displayed on the monitor may be changeable by the user by operating the operation panel 5.

  In step S8, it is determined whether or not a load start command is input by turning on the load start switch of the operation panel 5. If step S8 is affirmed, the process proceeds to step S9, a control signal is output to the load mechanism 1, the test specimen P is loaded with the tensile test force P with the target step width Δva of step S6, and then the test force P is unloaded. .

  In step S10, a control signal is output to the display monitor 6, a load curve (FIG. 3) is displayed on the display monitor 6 based on the signals from the load cell 2 and the clip gauge 3, and the crack propagation length Δa at the unloading point is displayed. The J integral value is calculated, and the J-Δa data is plotted and displayed on the J-Δa graph. In step S11, it is determined whether or not the necessary number of data satisfying the standard has been acquired, that is, whether or not J-Δa data of points q2 to q6 has been acquired. If step S11 is negative, the process returns to step S6, and the same processing is repeated until the required number of data is acquired.

If step S11 is affirmed, it will progress to step S12 and will process test result data. For example, a J-Δa curve that is an approximate curve of J-Δa data is displayed, or a J _1C value of the test piece TP is calculated and displayed on the display monitor 6. These processes may be performed after the user gives a command by operating the operation panel 5. Whether or not to end the test is displayed after the process of step S11. If the user selects the test end by operating the operation panel 5, the process proceeds to step S12. If the test end is not selected, the test is further continued. May be. In this case, the test may be continued with the load step width Δva instructed by the user.

  The above test procedure is summarized as follows. First, after setting the test piece TP in the tester main body, the user sets various test conditions by operating the operation panel 5 and instructs the load start. Thereby, after the tensile test force P is loaded on the test piece TP with the predetermined initial load step width Δv0, the test force is unloaded (step S3). The loading and unloading of the test force with the initial load step width Δv0 is repeated until the J-Δa data is included in the region A.

  When the data of the point q1 in FIG. 6B is obtained, the controller 4 calculates the target step width Δva1 corresponding to the point q2 (step S6). In this case, the ratio between the previous load step width Δva0 (= v1−v0) and the change amount sa0 (= Δa1−Δa0) of the previous crack growth length is obtained, and this corresponds to the 20% point in the region B. Multiply by the target change in crack growth length. When the load start is commanded in this state, the test force is loaded and unloaded with the target step width Δva1 (step S9). Thereby, the data of the point q2 is obtained in the vicinity of 20% in the region B on the J-Δa graph.

  Next, the controller 4 calculates a target step width Δva2 corresponding to the point q3 in FIG. In this case, a ratio between the previous load step width Δva1 (= v2−v1) and the change amount sa1 (Δa2−Δa1) of the previous crack growth length is obtained, and this corresponds to a point of 40% in the region B. Multiply the target change in crack growth length. By loading and unloading the test force with this target step width Δva2, the data of the point q3 is obtained in the vicinity of 40% in the region B on the J-Δa graph. Similarly, data of the point q4 is obtained in the vicinity of 60% in the area B, data of the point q5 is obtained in the vicinity of 80%, and data of the point q6 is obtained in the vicinity of 50% in the area C.

Through the above processing, the minimum necessary J-Δa data defined in the standard can be obtained, and the test time can be shortened. After the test is completed, the J-Δa curve is displayed on the display monitor, and the J _1C value is calculated (step S12). In this case, since the points q2 to q6 are obtained as equal points, the J-Δa curve can be accurately calculated with a small number of points.

According to the present embodiment, the following operational effects can be achieved.
(1) Based on the signals from the load cell 2 and the clip gauge 3, the compliance at each of the unloading points p0 to p6 is obtained to calculate the crack propagation length Δa of the test piece TP, and the J integral value is calculated. The target step width Δva was calculated so that the unloading point was set so that the number of data of Δa became the target number determined by the standard in each of the areas A to C on the J-Δa curve. That is, the difference Δva (previous target step width) between the previous unloading point and the previous unloading point, the crack propagation length Δa at the previous target unloading point, and the crack propagation length Δa at the previous target unloading point. The target step width Δva is calculated based on the difference sa (the amount of change in the previous crack growth length) and the unloading point is set. Thereby, the unloading point at the time of the test can be suppressed to a necessary minimum, and the crack growth test can be efficiently performed.

(2) Since the load step width Δva is obtained by setting the target value of the crack growth length (target points of q2 to q6) equally in the regions B and C, the J-Δa curve can be obtained accurately with a small number of points. Can be calculated.
(3) Since the unloading point corresponding to the target step width Δva is displayed on the display monitor 6 (step S7), the user can easily recognize the next measurement point of the crack propagation length Δa.

  In the above embodiment, the elastic modulus E of the test piece TP is input as the test condition. However, the elastic modulus E varies, and if the input elastic modulus E is different from the actually measured value, after the test is completed. There is a deviation between the actually measured crack growth length and the calculated crack growth length Δa. As a result, the number of J-Δa data may not satisfy the standard as a result. In consideration of this point, the target step width Δva may be calculated in step S6 as follows.

In this case, for example, in addition to the set elastic modulus E0, the upper limit elastic modulus E1 obtained by increasing the elastic modulus by a predetermined amount (for example, 5%) from the set elastic modulus E0, and the elastic modulus by a predetermined amount (for example, 5%) from the set elastic modulus E0. %) The reduced lower limit elastic modulus E2 is set in the controller, and J-Δa data at each unloading point is calculated using each elastic modulus E0, E1, E2. That is, the data of q1 to q6 in FIG. 6B is obtained for each elastic modulus. At this time, if there are three types of elastic modulus E, three values of the target step width Δva are also calculated, and the minimum value among them is set as the target step width Δva. As a result, the number of J-Δa data calculated by the respective elastic moduli is at least one point in the region A, four points or more in the region B, and one point or more in the region C. For this reason, even when the elastic modulus E is set to an incorrect value, the number of J-Δa data may satisfy the standard if the elastic modulus E is within the range of the upper limit elastic modulus E1 and the lower limit elastic modulus E2. The _J1C value can be obtained with high accuracy.

  If the target unloading point is set so that the number of J-Δa data obtained for each elastic modulus is equal to or greater than the target number, the number of elastic modulus E is not limited to three, but two. Or it is good also as four or more. The user may set the elastic modulus E to an arbitrary value, and the elastic modulus setting means is not limited to that described above.

  In the above embodiment, when it is determined that the data of J−Δa is in the area A, the target step width Δva is calculated so that the number of data in the area B and the area C becomes a value satisfying the standard. Although the target unloading point is set, the target unloading point may be set using the data immediately before the region A so that the number of data in the region A becomes a value satisfying the standard. Although the target unloading point is set so that the number of J-Δa data is the minimum necessary number that satisfies the standard, the number of data may be increased from the minimum necessary number. That is, if the target unloading point is set so that the number of J-Δa data is equal to or more than the predetermined target number in the predetermined areas A to C on the J-Δa curve, The configuration of the controller 4 is not limited to that described above.

  As long as the tensile test force P is applied to the test piece TP in which a crack is formed in advance and the test force is unloaded at the target unloading point, any load mechanism 1 as a loading means may be used. Although the test force loaded on the test piece TP is detected by the load cell 2, the test force detection means is not limited to this. Although the opening displacement v of the test piece TP is detected by the clip gauge 3, the displacement detection means is not limited to this. As long as the compliance at the target unloading point is obtained based on these detection results to calculate the crack propagation length Δa of the test piece TP and the J integral value is calculated, any configuration of the controller 4 as the calculation means can be used. Good.

  In the above embodiment, the difference (previous load step width Δva) between the previous target unloading point and the previous unloading point, the crack progress length Δa at the previous target unloading point, and the previous unloading target unloading point. The target unloading point is calculated based on the difference from the crack propagation length Δa at the point (the amount of change in the previous crack growth length), but the calculation of the target unloading point is not limited to this. Instead of using the opening displacement v as the load step width, the test force P may be used as the load step width. Alternatively, the load step width of the opening displacement and the load step width of the test force may be combined. Although the set target unloading point is displayed on the display monitor 6 (step S7), the configuration of the display means is not limited to this. In the above embodiment, after the target step width Δva is calculated, the load is applied to the test piece TP by the user inputting the load start command. However, the user automatically enters the load start command without inputting the load start command. A load may be applied. That is, as long as the features and functions of the present invention can be realized, the present invention is not limited to the material testing apparatus according to the embodiment.

The figure which shows the whole structure of the material test apparatus which concerns on embodiment of this invention. The figure which shows the shape of a test piece. The figure which shows the relationship between opening displacement and test force. The figure which shows the relationship between crack progress length (DELTA) a and J integral value. The flowchart which shows an example of the process in the controller of FIG. The figure for demonstrating the calculation method of the target step width | variety of FIG.

Explanation of symbols

1 Load mechanism 2 Load cell 3 Clip gauge 4 Controller 5 Operation panel 6 Display monitor

Claims (3)

Loading means for applying a tensile test force to a test piece in which a crack has been formed in advance and unloading the test force at a target unloading point;
A test force detecting means for detecting a tensile test force applied to the test piece;
Displacement detecting means for detecting an opening displacement of the test piece;
Based on the detection results of the test force detection means and the displacement detection means, the compliance at the target unloading point is obtained to calculate the crack growth length of the test piece, and the crack growth parameters at the target unloading point A computing means for calculating a certain J integral value;
The number of pieces of crack growth length and J integral value calculation data calculated by the computing means is greater than or equal to a predetermined target number in a predetermined region on the J-Δa curve representing the relationship between the crack growth length and the J integral value. Unloading point setting means for setting the target unloading point so as to become ,
The unloading point setting means includes the difference between the previous target unloading point and the previous target unloading point, the crack propagation length at the previous target unloading point calculated by the computing means, and the previous unloading target unloading point. A material testing apparatus characterized in that the target unloading point is calculated and set based on a difference from a crack propagation length in . The material testing apparatus according to claim 1 , wherein
Comprising elastic modulus setting means for setting a plurality of elastic modulus of the test piece,
The unloading point setting means sets the target unloading point so that the number of pieces of calculation data of crack growth length and J integral value obtained for each elastic modulus is equal to or more than the target number, respectively. Material testing equipment. In the material testing apparatus according to claim 1 or 2 ,
A material testing apparatus further comprising display means for displaying a target unloading point set by the unloading point setting means.

Images