JPH0820345B2 - Method of detecting break point of specimen - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a breaking point of a specimen in a material test such as tension and bending.

[0002]

2. Description of the Related Art A load such as a compressive force or a tensile force is applied to a specimen, the load and displacement at that time are measured, and a load-displacement curve (SS curve) is recorded based on the measured data.
A material testing machine is known that is designed to determine the mechanical properties and characteristics of a test piece. Conventionally, in such a material testing machine, when detecting the breaking point of the specimen, for example, by calculating the load and elongation data detected by the load meter and the extensometer in the data processing unit, the load per unit time The point at which the amount of decrease in () was significantly changed (which was empirically determined) was determined, and this point was regarded as the breaking point.

[0003]

By the way, the material test,
For example, when performing a tensile test, a tensile load that continuously increases is applied to the test piece, the elongation of the test piece is measured simultaneously with the load, and the load-elongation curve (SS curve) is recorded.
The S-curve depends on the material of the tested specimen.

FIG. 6 is an SS curve of a test piece made of a material such as mild steel when subjected to a tensile test. As is clear from FIG. 6, when the yield point P1 is passed and the maximum load M1 point is passed, the test piece breaks at P2 point and the load sharply decreases.
On the other hand, S, which is a ductile material such as plastic, is used.
As shown in FIG. 7, the −S curve is a curve in which the load gradually decreases even after the maximum load M2 point and the P3 point enters the fracture region.

Therefore, even if an attempt is made to detect the break point of the specimen having the SS curve as shown in FIG. 7 by the above-mentioned conventional method (method of detecting by the load reduction rate), the actual break point P3 is detected. However, there is a problem that the point P4 at which the load becomes zero is erroneously detected as a break point.

It is an object of the present invention to provide a method for detecting a break point of a test piece, which is capable of accurately detecting the break point of the test piece made of a material having a high ductility in which the load in the break region gradually decreases. It is in.

[0007]

SUMMARY OF THE INVENTION The method of the present invention comprises the steps of tracing a recorded load-displacement curve in reverse of its recording,
The gradient of the load-displacement is sequentially calculated from the current-previous load-displacement of each measurement point on the load-displacement curve, and the angle difference between the sequentially-obtained current and previous slopes is calculated. At that time, the above object can be achieved by determining the measurement point as a break point.

[0008]

[Function] By tracing the load-displacement curve in the opposite direction to the recording, the load-displacement data at each measurement point is sequentially captured,
As a result, the load-displacement gradient between each measurement point this time and the previous time is obtained. Then, the calculated angle difference between the present and previous gradients is compared with the set value, and the measurement point detected when the gradient is equal to or larger than the set value is detected as the break point.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a block diagram showing the configuration of the entire material testing machine to which the method for detecting the breaking point of the specimen according to the present invention is applied. Here, the material testing machine grips the test piece through a pair of upper and lower gripping tools, for example, between the ascending and descending crosshead and the fixed table, and lifts the crosshead to load the test piece. The load meter 11 detects a load such as a tensile force or a compressive force applied to a test piece (not shown) and outputs a corresponding load signal. The extensometer 12 detects the elongation between the reference points of the sample and outputs a corresponding elongation signal. Load cell 11
The load signal and the extension signal output from the and extensometer 12 are amplified by the amplifiers 13 and 14, respectively, further converted into digital signals by the AD converters 15 and 16 and sent to the control circuit 17. .

The control circuit 17 controls and manages the whole, a central processing unit (hereinafter referred to as CPU) 171, a read-on memory (hereinafter referred to as ROM) 172, a random access memory (hereinafter referred to as RAM) 173, and an input interface 174. And an output interface 175,
These are connected to the CPU 171 via the bus 176. The ROM 172 stores a program or the like for detecting a breaking point corresponding to FIGS.
A calculation result of the CPU 151, input data from the outside, and the like are stored in 73. Input interface 174
Are connected to A-D converters 15 and 16. A printer 19 is connected to the output interface 175 via the DA converter 18, and a display device 20 such as a CRT is further connected. The printer 19 draws the load-elongation curve shown in FIG. 6 or 7 from the load data W and the elongation data δ processed by the control circuit 17, and records and outputs the maximum yield load, the minimum yield load, the proof stress, etc. as numerical values. . Further, the display device 20 displays the same data as that of the printer 19, and also displays a processing program and the like.

Next, the fracture detecting operation of the specimen will be described with reference to the flow charts shown in FIGS. When the tensile test on the sample is started, the fracture detection processing program shown in FIGS. 3 and 4 is started. First, when a continuously increasing tensile load is applied to the sample, the load applied to the sample is detected by the load meter 11, and the elongation of the sample is detected by the extensometer 12. These load signals and extension signals are amplified by the respective amplifiers 13 and 14 and then amplified by the respective A / D converters 15 and 16.
By inputting to, the signal is sampled at a predetermined cycle and converted into a digital signal. The sampled load data W and elongation data δ are sequentially loaded into the ROM 173 of the control circuit 17 in step S1.

[0012] In the next step S2, the current load data Wn taken into the control circuit 17, which from the sampling to the previous (measured before the unit time t) the load data Wn - reading _one and. In the next step S3, (Wn
_-1 ) -Wn = Δw calculation, load change per unit time (sampling cycle) (amount of decrease in load)
Calculate Δw. Then, in the next step S4, the reference load change amount w per unit time, which is regarded as the fracture of the test piece, is compared with Δw, and it is determined whether w <Δw. w <Δ
When it is determined to be w, it is determined that the test piece is broken, the process proceeds to step S6, and the material testing machine is stopped. When it is determined that w <Δw is not satisfied, the process proceeds to step S5 and it is determined whether the current load data Wn = 0. That is, it is determined whether the load change amount Δw does not reach the reference change amount w or more and the load becomes near zero, even though the specimen has reached the fracture region. Here, when it is determined that Wn = 0 is not satisfied, the process returns to step S2, and the processes from step S2 onward are repeated. When it is determined that Wn = 0, the process proceeds to step S6, the material testing machine is stopped, and the process shown in FIG. 4 is performed. The load-elongation curve of the test piece when the process proceeds from step S5 to step S6 corresponds to the graph shown in FIG.

In FIG. 4, the slope due to load-elongation is obtained by tracing the SS curve shown in FIG. 7 or FIG. 6 in the opposite direction to that at the time of data recording, and the point where this slope change exceeds the set value. Is a processing flow having a break point. In FIG. 4, in step S7, the contents of the software-configured counter in the control circuit 17 are reset. Then, in step S8, the current (finally captured) load data Wn and the corresponding elongation data δn, and the immediately preceding load data (Wn ₋₁ ) and the corresponding elongation data ( The gradient (αn _-c ) is obtained from δn _-1 ). That is, the load is shown in Figure 1 - elongation and intersection Pn of the load data Wn and elongation data .DELTA.n on the curve, an intersection Pn _-1 and data elongation and load data (Wn _-1) (δn _-1)
The gradient (αn- _c ) of the line segment Ln connecting to and is calculated.

In the next step S9, the previous load data [Wn- ( ₁ + c)] and the corresponding elongation data [δ
n− ( ₁ + c)], and load data [Wn−
( ₂ + c)] and the corresponding elongation data [δn- ( ₂ +
c)], the gradient [αn + ( ₁ + c)] is obtained. That is, the gradient [αn- ( ₁ + c)] of the line segment Ln- ₁ connecting the intersection points Pn- ₁ and Pn- ₂ on the load-elongation curve shown in FIG.
To calculate. Then, in the next step S10, it is determined whether or not the angular difference between the gradient [αn-c] and the gradient [αn- ( ₁ + c)] is larger than the reference angular difference Δα of the gradient regarded as the breaking point. Here, the angle difference between the two gradients is the reference angle difference Δα.
If it is determined that it is larger, the process proceeds to step S11,
The breaking point P of the test piece is Pn _-1, and the load (Wn
_-1 ) is detected.

On the other hand, if the result in step S10 is negative, the process proceeds to step S12 and the counter is incremented by +1. Then, in the next step S13, the number of times of detection x is preset (x <n, n:
It is determined whether or not the total number of detections by the test). When the result is negative, the process returns to step S9, and the gradient obtained from the load data and the elongation data before the intersection point Pn _-2 on the load-elongation curve shown in FIG. 1 is sequentially compared with the reference angle difference Δα to detect the fracture point. To do. In addition, even if the number of times of detection reaches the set value x, if the slope regarded as the break point cannot be detected,
In step S14, the breaking point P is set to Pn, and the load Wn is detected. FIG. 5 is a load curve in this case.

As described above, in this embodiment, a load which continuously increases is applied to the test piece, and the load and the elongation at this time are measured by the load meter and the extensometer until the rupture region is reached, and the load-elongation curve is obtained. By recording and then tracing the load-elongation curve in the reverse direction of the recording, the gradient of load-elongation is sequentially obtained from the current and previous load and elongation data of each measurement point on the load-elongation curve, and this sequence Since the breaking point can be detected by determining whether the required angle difference between the present and previous gradients is greater than or equal to the reference angle difference, even if the specimen is made of a ductile material with a gradually decreasing load, the fracture The point can be detected reliably and easily, and if the point is applied to the specimen having the load-elongation curve shown in FIG. 7, the break point can be detected more accurately. Further, the breaking point P2 of the test piece having the load-elongation curve as shown in FIG. 6 can be similarly detected by the processing of FIGS. Furthermore, in the above-mentioned examples, although the tensile test was described, the bending test (load-
It can also be applied to bending test, compression test (load-strain) and the like.

[0017]

As described above, according to the present invention, the load applied to the test piece and the displacement of the test piece due to the load are measured until breaking, and the load-displacement curve is recorded.
By tracing the displacement curve in the reverse direction of the record, the load-displacement gradient is sequentially obtained from the current and previous load and displacement at each measurement point on the load-displacement curve, and the angle of this and previous gradient that is sequentially obtained Since the measurement point is determined as the break point when the difference is equal to or more than the set value, even if the test piece is made of a material whose load in the break region gradually decreases,
The breaking point can be detected accurately and easily.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a fracture point detection method according to the present invention.

FIG. 2 is a block diagram showing an overall configuration of a test-point breaking point detection system according to the method of the present invention.

FIG. 3 is a flowchart showing a procedure of detecting a break point in the present embodiment.

FIG. 4 is a flowchart showing a procedure for detecting a break point in the present embodiment.

FIG. 5: Load when no steep slope is found −
It is a graph which shows an elongation curve.

FIG. 6 is a graph showing an example of a load-elongation curve of a material testing machine.

FIG. 7 is a graph showing another example of the load-elongation curve of the material testing machine.

[Explanation of symbols]

 11 load meter 12 extensometer 15 and 16 AD converter 17 control circuit

Claims (1)

[Claims] 1. A load applied to a specimen and a displacement of the specimen are respectively detected, and the detected load and displacement are measured until breakage, a load-displacement curve is recorded, and a fracture is made from this load-displacement curve. In the breaking point detection method for detecting points,
By tracing the load-displacement curve in the reverse direction of the recording, the gradient of the load-displacement is sequentially obtained from the present-time and previous load-displacement of each measurement point on the load-displacement curve, and the sequentially-obtained current and previous A method for detecting a break point of a specimen, wherein an angle difference between gradients is calculated, and the measurement point is determined as a break point when the angle difference is equal to or larger than a set value.