JPH05149848A - Tensile tester - Google Patents

Abstract

PURPOSE:To obtain a smooth continuous curve by eliminating such a problem that a stress-strain curve (S-S curve) becomes discontinuous when valve holding control is changed over to stroke control in such a case that a metal material is conducted by a tensile tester. CONSTITUTION:In a tensile tester capable of performing stress speed control controlling the change speed of stress during a tensile test, valve holding control holding the liquid pressure valve for applying load to a predetermined opening and closing degree and stroke control controlling a stroke speed deforming a test piece, a stroke speed measuring means measuring a stroke speed during valve holding control at the time of the transfer from the valve holding control to the stroke control, a calculation means calculating the difference between a preset stroke speed and the stroke speed measured by the measuring means to divide the same into a plurality of stages and a speed control means changing a stroke speed at every stages to finally allow the same to coincide with a set speed are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tensile tester for performing a tensile test on a test piece such as a metallic material.

[0002]

2. Description of the Related Art Stress rate control for controlling the rate of change of stress during a tensile test, valve holding control for holding a hydraulic valve for load application at a predetermined opening / closing degree, and stroke speed for deforming a test piece are known. A tensile tester capable of controlling stroke control is used as a tensile tester for metallic materials.

[0003]

When performing a tensile test on a metal material with the above-described conventional tensile tester, stress rate control is performed at the first stage, and after the stress rate control, the valve angular opening at that point is set. It is general to perform valve holding control to hold the valve, and after detecting the characteristic value, switch to the stroke speed control to pull at high speed and perform the test.However, the valve holding control is changed to the stroke control. When switching, stress-
There is a problem that the distortion curve (SS curve) becomes discontinuous. Therefore, it is an object of the present invention to provide a tensile testing machine that can obtain a stress-strain curve as a smooth continuous curve when the above control switching is performed.

[0004]

In order to solve the above problems, the present invention employs the following configurations. That is,
The tensile testing machine according to the present invention includes a stress rate control for controlling a rate of change of stress during a tensile test, a valve holding control for holding a hydraulic valve for load application at a predetermined opening / closing degree, and a strobe for deforming a test piece. -Stroke to control the speed-
In a tensile tester capable of controlling each of the stroke control, a stroke speed measuring means for measuring the stroke speed during the valve holding control when the valve holding control is changed to the stroke control is preset. The difference between the stroke speed and the stroke speed measured by the measuring means is calculated, and the difference between the stroke speed and the stroke speed is calculated in a plurality of steps. It is characterized by comprising a speed control means for changing the speed and finally matching the set speed.

[0005]

In the transition from the valve holding control to the stroke control, the difference between the stroke speed during the valve holding control measured by the stroke speed measuring means and the preset stroke speed is It is calculated and this difference is divided into stages. Then, at each stage, the stroke speed is switched so as to approach the set speed, and finally the set speed is matched. Even if there is a difference between the stroke speed and the set speed during the valve holding control, the difference is eliminated stepwise, so that a smoothly continuous SS curve can be obtained.

[0006]

Embodiments of the present invention shown in the drawings will be described below. FIG. 1 shows an embodiment of a tensile tester according to the present invention. The tensile tester 1 includes an upper crosshead 3 which is moved up and down by a hydraulic actuator 2 and a lower crosshead 4 whose vertical position can be adjusted. The test piece 7 is gripped by the grippers 5 and 5 respectively attached to the test pieces 7, and a tensile load is applied by the hydraulic actuator. The displacement of the upper crosshead is detected by the ram stroke detector 9, the load is detected by the load cell 10, and the strain of the test piece is detected by the strain gauge 11. These detection signals are input to a control device 13 having a computer 12 as a calculation means, and a test is controlled. The output of the hydraulic actuator is adjusted by the opening degree of the servo hydraulic valve 14.

FIG. 2 schematically shows the state of control of this tensile tester. From the start of the test until the stress limit P indicating the proportional limit is reached, stress rate control is performed to keep the stress change constant. After reaching the stress limit, control is performed by maintaining the valve opening angle at that time. At this time, the measurement of the stroke value to be the next control target and the calculation of the stroke speed obtained from the value are simultaneously performed.

After the characteristic values such as the upper yield point and the lower yield point are detected, the stroke control for pulling the test piece at high speed is switched to. When this switching command is issued from the control device,
The control is switched to the stroke speed measured at that time, but at the moment of this switching, only the control is switched, and the measured stroke speed is set and maintained. No discontinuity occurs.

At the same time, the difference between the set stroke speed and the actual stroke speed at that time is calculated, and the difference is divided into preset division numbers. Then, the stroke speed as expressed by the following equation is output, and the actual stroke speed is output.
The speed is switched to this speed. Stroke speed V1 = (Vs-Vo) / n + Vo Here, V1: Stroke speed to be set Vs: Preset stroke speed after control switching Vo: Stroke speed at control switching n: Division number

Further, V1 = (Vs-Vo) m / n + Vo
Speed (m = 2 ... n), and finally m = n
The control is performed when the set speed is reached. In this way, since the stroke speed is gradually approached to the set speed, a discontinuity as shown in FIG. 3 has been conventionally generated, but in the present invention, a continuous speed as shown in FIG. 4 is obtained. The curve came to be obtained. It should be noted that the division number n may be an appropriate number so that a smooth curve can be obtained according to the test conditions.

[0011]

As is apparent from the above description, the tensile tester according to the present invention has a continuous smooth SS curve when the control is switched from the valve holding control to the stroke speed control. Has come to be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of the present invention.

FIG. 2 is a graph schematically showing control.

FIG. 3 is a graph showing a part of a conventional SS curve.

FIG. 4 is an enlarged view of a main part of an SS curve obtained by the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tensile tester 2 Hydraulic actuator 5 Grip 7 Test piece 13 Controller

Claims (1)

[Claims] 1. A stress rate control for controlling a rate of change of stress during a tensile test, a valve holding control for holding a hydraulic valve for load application at a predetermined opening / closing degree, and a stroke speed for deforming a test piece. In a tensile tester capable of controlling each stroke control, the stroke speed measuring means for measuring the stroke speed during the valve holding control at the time of transition from the valve holding control to the stroke control. , A calculating means for calculating a difference between the preset stroke speed and the stroke speed measured by the measuring means, and dividing the difference into a plurality of steps, and a stroke for each of the divided steps. A tensile tester, which comprises a speed control means for changing the speed and finally matching the set speed.