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What is a Tensile Strength Tester? Principle | Structure | Function | Classification

Tensile strength tester machine is also called universal material testing machine. Mainly used for a variety of materials for static load, tensile, compression, bending, shear, tear, peel and other mechanical properties of the test machine, suitable for plastic plates, tubes, profiles, plastic film, rubber, steel, fabric and other materials of various mechanical properties test. It is an indispensable testing machine for material development, physical properties tests, teaching research, quality control, etc. The tensile strength machine fixture is an important part of the instrument, and different materials require different fixtures, which is an important factor in the smooth conduct of the test and the accuracy of the test results.

★ The two principles of tensile strength tester

1 Hydraulic type tensile strength tester

The hydraulic type tensile testing machine is driven by hydraulic cylinders moving up and down to move the fixture up and down to achieve the various functions of the pulling machine. The advantage is that it can do higher strength tensile testing, the disadvantage is that the control precision is not high and not very hygienic. It is mainly applied to metal materials, bridge bearings, large plates, construction materials, composite materials and other industries. Its load is generally above 300KN (30T).

Working principle: the motor drives the oil pump to rotate, oil pump suction oil, converting mechanical energy into hydraulic oil pressure energy. The hydraulic valve realises the direction, pressure, flow regulation by the integrated block, through the external pipeline transmission to the hydraulic machinery cylinder or oil motor, so as to control the hydraulic machine direction change, the size of force and speed, to promote the hydraulic machinery to do work.

2 Mechanical tensile strength tester

Mechanical tensile strength machine is mainly driven by the motor spiral screw rotation, the screw rotation drives the fixture up and down to achieve the tensile strength machine tensile, compression peel, tear, shear, three-point bending resistance and other functions, the advantage is the high precision control.

Mechanical tensile strength tester

Mechanical tensile strength machine mainframe for single rod structure or door structure, mainly suitable for rubber, plastic, textile, geotextile, waterproof material, wire and cable, net rope, metal wire, metal bar, metal plate and other materials tensile test, increase the attachment can do bending, tearing, peeling and other tests.

★ Structure and function of tensile strength tester

The tensile strength tester is a large precision test instrument combining modern electronic technology with mechanical transmission technology, giving full play to the special features of electromechanical integration, with a wide measuring range, high precision and fast response. The tensile strength machine works reliably and efficiently, and can display and record and print test data in real time. It consists of a measuring system, a driving system, a control system and a computer structure.

1 Measuring systems for tensile strength tester

1.1 Measurement of force values

Force is measured by means of the load cell, amplifiers and data processing systems. The most commonly used load cell is the strain gauge sensor.

load cell

A strain gauge sensor is a device that consists of a strain gauge, an elastic element and certain accessories (compensation elements, shields, wiring sockets, loading parts) that can turn a certain mechanical quantity into an electrical output. There are many types of strain gauge sensors, mainly barrel force sensors, spoke force sensors, S-double-linked hole type sensors, cross beam sensors and other types.

It is known from the mechanics of materials that the strain Ɛ at a certain point of an elastic element is proportional to the force applied to the elastic element and to the deformation of the elasticity under conditions of small deformation. For example, when a sensor is subjected to a pulling force P, the strain gauge is attached to the surface of the elastic element because the strain on the elastic element is proportional to the magnitude of the external force P, therefore, the strain gauges are connected to the measurement circuit and the output voltage can be measured to determine the force.

For force sensor, a differential full bridge measurement is generally used, where the strain gauges are attached to form a bridge circuit. In simple terms, the external force P causes the deformation of the strain gauges in the transducer, resulting in an unbalanced bridge, which causes a change in the output voltage of the transducer.

Generally speaking, the output signal of the sensor is very weak, usually only a few millivolt, if we measure this signal directly, it is very difficult and can not meet the requirements of high precision measurement. This weak signal must therefore be amplified by means of an amplifier, which amplifies the signal voltage up to 10V. At this point the signal is analogue, this analogue signal is transformed into a digital signal by means of a multiplex switch and an A/D converter chip, and then the data processing is carried out, at which point the force measurement comes to an end.

1.2 Measurement of deformation

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

The device has two collets which are connected by a series of drives to an optical encoder mounted on the top of the measuring device. When the distance between the two holders changes, the shaft of the photoelectric encoder is rotated and a pulse signal is output from the photoelectric encoder. This signal is then processed by a microcontroller to give the amount of deformation of the specimen.

1.3 Measurement of cross-beam displacement

The principle is the same as for the deformation measurement, the displacement of the beam is obtained by measuring the number of pulses at the output of the optical encoder.

2 Drive system of tensile strength tester

It is mainly used for the movement of the beam of the universal material testing machine. Its working principle is to control the motor by the servo system, and the motor drives the rotation of the screw through a series of transmission mechanisms such as reduction box, so as to control the movement of the beam. By changing the speed of the motor, the movement speed of the beam can be changed.

3 Control system of tensile strength tester

As the name suggests, it is the system that controls the operation of the computer servo system of universal material testing machine, people can control the operation of the test machine through the console, know the status and the test parameters of the test machine through the display. If the machine is equipped with a computer, it is also possible to realise various functions and 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 communication, which is carried out through the serial port (COM number) on the back of the computer, which is a mature, reliable and easy to use technology.

4 Computer of tensile strength tester

The computer is used to collect and analyse data. After entering the test interface, the computer will continuously collect various test data, draw test curves in real time, automatically derive each test parameter and output reports.

★ Classification of tensile strength tester

1 According to the degree of automation can be divided into …

1.1 Pointer type tensile strength tester: This traditional type of tensile strength tester has been largely eliminated by the digital display type tensile strength tester due to its low testing accuracy and low cost performance. But in the small force range, is our common tensile strength meter, often used by factories for simple force testing of small products, because of its low price, quite popular.

1.2 Digital display type tensile strength tester, also known as microcomputer type tensile strength tester: the test data is directly displayed on the LCD screen, the test items are relatively single, commonly used in factories for quality control.

1.3 Computerised system tensile strength tester: the most versatile tensile strength tester, as the test data is collected through the computer and then processed by the software program to produce the final data desired by the user, and can be printed out by way of a report. Commonly used in scientific research units, testing institutions, new product development, etc.

2 According to the control system can be divided into …

2.1 Frequency conversion system tensile testing machine: using frequency conversion motor control system, the speed of stretching and compression is controlled by frequency conversion speed regulator.

2.2 Servo system tensile testing machine: using servo motor control system, the speed of tensile and compression, displacement control more accurate. A servo control system, using intelligent feedback type operation, can be fixed speed test, cycle test, programming test, etc.

2.3 Other drive mode tensile testing machine: through the DC motor control, the drive mode tensile testing machine due to low cost performance, has been gradually eliminated.

3 According to the industry and functional characteristics can be divided into …

3.1 Metal tensile strength tester: metal materials with high tensile strength and small elongation, need to be equipped with a metal point elongation gauge.

3.2 Rubber tensile strength tester: rubber or elastomer elongation is relatively large, need to be accompanied by a large mark point elongation device, while the fixture design should be considered suitable for the characteristics of rubber, not slippery. Can be equipped with O-ring fixture, tyre industry with fixture, etc.

3.3 Plastic tensile strength tester: the tensile strength of plastic than rubber, elongation has a large and small, and often need to test the three-point bending test.

3.4 Fabric tensile strength tester: the textile industry needs to test fabric peeling, puncture, tearing, single yarn stretching and other tests, fixtures and software is special.

3.5 Paper tensile strength tester: paper needs to test tensile strength, ring strength, vertical compression, flat compression, edge compression, peel strength, etc., with many fixtures.

3.6 Leather tensile strength tester: Leather needs to test tensile strength, tearing strength, etc. The testing items are relatively simple.

 

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