Tensile machine, also known as universal material testing machine, is a mechanical testing machine for mechanical load testing of various materials for static load, tensile, compression, bending, shearing, tearing, peeling, etc. Various physical and mechanical properties tests for plastic sheets, pipes, profiles, plastic films and rubber, wire and cable, steel, glass fiber and other materials are developed for materials, and are indispensable testing equipment for physical property testing, teaching research, quality control and so on.

The tension machine is a combination of modern electronic technology and mechanical transmission technology. It is a large-scale precision test instrument that fully utilizes the special features of electromechanical. It has the characteristics of wide measuring range, high precision and fast response. Reliable work, high efficiency, real-time display and printing of test data.

The tension machine is composed of a measurement system, a drive system, a control system, and a computer.

First, the tensile machine measurement system

(a) Measurement of force value

Measurements are made with load cells, amplifiers and data processing systems. The most commonly used load cell is the strain gauge sensor.

The so-called strain gauge sensor is a device that can change a certain mechanical quantity into a power output by strain gauges, elastic components and some accessories (compensating components, protective covers, wiring sockets, and loading components).

Strain gauge type pull and pressure sensors are available at home and abroad, mainly including cylindrical force sensors, spoke-type force sensors, S double-connected sensors, and cross-beam sensors.

It is known from the material mechanics that under small deformation conditions, the strain ε at a certain point of an elastic element is proportional to the force received by the elastic element and also proportional to the elastic deformation. Taking the S-type sensor as an example, when the sensor is subjected to the pulling force P, since the strain gauge is attached to the surface of the elastic member, since the strain of the elastic member is proportional to the magnitude of the external force P, the strain gauge is connected to the measuring circuit. The magnitude of the force is measured by measuring its output voltage.

For the sensor, the differential full bridge measurement is generally adopted, that is, the strain gauge attached is composed of a bridge. In short, the external force P causes deformation of the strain gauge in the sensor, resulting in imbalance of the bridge, thereby causing a change in the output voltage of the sensor. We can know the magnitude of the force by measuring the change in the output voltage.

In general, the output signal of the sensor is very weak, usually only a few mV. If we measure this signal directly, it is very difficult and can not meet the high-precision measurement requirements. Therefore, the weak signal must be amplified by the amplifier, and the amplified signal voltage can reach 10V. The signal at this time is an analog signal, and the analog signal is converted into a digital signal by the multiplex switch and the A/D conversion chip, and then the data is processed. At this point, the measurement of force came to an end.

(b) Measurement of deformation

It is measured by a deformation measuring device, which is used to measure the deformation of the sample during the test.

The device has two chucks connected to the photoelectric encoder mounted on the top of the measuring device through a series of transmission mechanisms. When the distance between the two chucks changes, the shaft of the photoelectric encoder is rotated, and the photoelectric encoder is driven. There will be a pulse signal output. Then, the signal is processed by the single chip microcomputer, and the deformation amount of the sample can be obtained.

(c) Measurement of transverse displacement

The principle is almost the same as the deformation measurement, and the displacement of the beam is obtained by measuring the number of output pulses of the photoelectric encoder.

Second, the tensile machine drive system

It is mainly used for the beam movement of the universal material testing machine. Its working principle is that the motor is controlled by the servo system, and the motor drives the screw to rotate through a series of transmission mechanisms such as a reduction gear box, thereby achieving the purpose of controlling the movement of the beam. By changing the speed of the motor, the moving speed of the beam can be changed.

Third, the tension machine control system

As the name suggests, it is the system that controls the operation of the universal testing machine for computer servo systems. People can control the operation of the testing machine through the console. The status of the testing machine and various test parameters can be obtained through the display. If the machine has a computer, Various functions can be realized by the computer and data processing analysis and test result printing can be performed. The communication between the test machine and the computer is generally RS232 serial communication. It communicates through the serial port (COM number) on the back of the computer. This technology is mature, reliable and easy to use.

Fourth, the rally computer

Used to collect and analyze data, after entering the test interface, the computer will continuously collect various test data, draw test curves in real time, and automatically find each test parameter and output report.