Factors Affecting the Performance and Accuracy of Tensile Testing Machine

A tensile testing machine is a large-scale precision testing instrument combining modern electronic technology and mechanical transmission technology. It gives full play to the characteristics of mechatronics and has the characteristics of a wide measurement range, high precision, and fast response.

The uniaxial tensile test machine works reliably and efficiently and can display, record, and print test data in real-time. It consists of the measuring system, driving system, control system, and computer structure.

Measurement of force value

The force is measured by a load cell, amplifier, and data processing system. The most commonly used load cell is the strain gauge sensor.

A strain gauge sensor is a device composed of a strain gauge, elastic element, and some accessories, which can convert a certain mechanical quantity into electrical output. There are many kinds of strain sensors, mainly including barrel force sensor, spoke force sensor, s-double hole sensor, beam sensor, and so on.

For force sensors, differential full bridge measurement is usually used, in which strain gauges are connected to form a bridge circuit. In short, the external force P deforms the strain gauge in the transducer, resulting in the imbalance of the bridge, resulting in the change of the output voltage of the transducer.

The quality of the sensor determines the accuracy and stability of the tensile testing machine. At present, the uniaxial tensile test machine with the sensor in the market generally adopts an S-type sensor for those with small force value and a spokes sensor for those with large force value. Internal sensors are generally resistive strain plates. If the strain gauge's accuracy is not high or the fixed strain gauge, the adhesive's anti-aging ability is poor, or the sensor material is not good, these will affect the accuracy and the service life of the sensor.

Measurement of deformation and beam displacement

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

The device has two chucks, which are connected to the optical encoder installed on the top of the measuring device through a series of drivers. When the distance between the two supports changes, the shaft of the photoelectric encoder rotates and the photoelectric encoder outputs a pulse signal. The signal is then processed by the microcontroller to give the deformation of the sample.

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

The transmission is mainly completed by the screw. If the screw has clearance, the uniaxial tensile test machine will directly affect the maximum test deformation and elongation at break. At present, some tensile pull test machine metals on the market use T-type ordinary screws, which have large clearance and large friction, resulting in short service life.

Driving system of tensile testing machine

The driving system is mainly used for the movement of the beam of the universal material testing machine. Its working principle is to control the motor through the servo system, and the motor drives the lead screw to rotate through a series of transmission mechanisms such as a reducer, to control the movement of the beam. By changing the speed of the motor, the moving speed of the beam can be changed.

At present, some tensile pull test machine metal in the market uses ordinary three-phase motors or variable-frequency motors, which are controlled by analog signals, with slow control response, inaccurate positioning, narrow general speed range, high or low speed or low speed without fast speed, and inaccurate speed control.

Control system of tensile testing machine

As its name suggests, it is a system that controls the operation of the computer servo system of the universal material testing machine. People can control the operation of the testing machine through the console and understand the state and test parameters of the testing machine through the console exhibition. If the machine is equipped with a computer, it can also realize various functions, carry out data processing and analysis, and print test results.

The communication between the tester and the computer is generally in the form of RS232 serial port communication, which is carried out through the serial port (COM number) on the back of the computer. It is a mature, reliable, and easy-to-use technology.

At present, the measurement and control system of tensile testing machines in the market is mostly controlled by an 8-bit single-chip microcomputer, which has a low sampling rate and poor anti-interference ability. In addition, if the digit resolution of the AD converter is also low, the measurement will be inaccurate.

We are the universal testing machine manufacturer, any interests, welcome to contact us.