Tensile Tester: The Complete Guide

 This will be the most comprehensive guide on the subject of the tensile tester. In this guide, you will learn about the classification of the tensile tester, the principles of construction, the factors affecting performance and accuracy, and how to buy a tensile tester.

Introduction of Tensile Tester

1 What is a tensile tester?

tensile 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 test, teaching research, quality control, etc. The tensile tester 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.

2 Tensile tester drive method

2.1 Hydraulic type tensile tester

The hydraulic type tensile tester 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.

• Hydraulic tensile tester, limited by the configuration of the oil source, the test speed is low.
• Compared with the tensile tester, the small tonnage (<300kN) comprehensive cost performance is low and scalability is poor.
• The servo valve requires high filtration precision for the hydraulic oil of the oil source, and the hydraulic oil needs to be replaced regularly.
• The hydraulic connection lines and joints are prone to oil leakage and the oil source is relatively noisy.
• Hydraulic oil source needs to be equipped with a cooling system (air-cooled or water-cooled), high energy consumption.
• Hydraulic tensile tester on the foundation requirements are very high, especially the large force value of the machine, the foundation needs to be prepared in accordance with the drawings provided by the testing machine manufacturer, the whole machine occupies a large space.
• Hydraulic drive, strong power, more reliable and stable when doing large tonnage material mechanics test.

2.2 Mechanical tensile tester

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

Mechanical tensile tester 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.

• Servo motor drive, compact structure, high efficiency of energy use, easy to use and maintain, low noise, stable and reliable.
• Three closed-loop controls for load control, strain control and displacement control can be achieved.
• Wide range of force measurement, between 0.4% and 100% of the full range, the accuracy of force measurement can reach 0.5 grade.
• Test speed range can be adjusted, test speed can be 0.001mm/min-1000mm/min, test stroke can be determined according to needs, more flexible.
• Flexible test methods: test fixtures can be freely selected and replaced for models with a test range below 300kN, and external sensors and corresponding fixtures can be extended to meet different types of material mechanics tests (e.g. tensile, compression, bending, peeling, tearing, shearing, pulling and twisting tests).
• High temperature ovens, high and low temperature chambers or other environmental chambers can be added for environmental simulation tests.
• Large tonnage is more costly to manufacture.

3 Classification of the tensile tester

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

Pointer type tensile tester: This traditional type of tensile tester has been largely eliminated by the digital display type tensile 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.

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

Computerised system tensile tester: the most versatile tensile 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.

3.2 According to the control system can be divided into …

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

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

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

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

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

Rubber tensile 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.

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

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

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

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

Factors Influencing Performance and Accuracy of Tensile tester

The tensile 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 tester 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 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 strain gauge sensor.

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 the 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.

The quality of the sensor determines the accuracy and stability of the tensile tester, the current market tensile tester with sensor, small force values generally use S-type sensors, large force values generally use the spoke type sensor. The internal sensor is generally resistive strain gauge type, if the strain gauge accuracy is not high or fixed strain gauge with bad ageing resistance ability of the adhesive, or the sensor material is not good, these will affect the accuracy and service life of the sensor. tensile tester of TESTEX uses well-known sensors, which are highly accurate, linear and very stable, and will not change for decades.

2 Measurement of deformation and cross-beam displacement

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 an output from the photoelectric encoder. This signal is then processed by a microcontroller to give the amount of deformation of the specimen.

The principle of measuring the displacement of the cross-beam is roughly the same as that of deformation measurement, which is obtained by measuring the number of pulses output from the photoelectric encoder to obtain the displacement of the crossbeam.

The transmission is mainly done by the screw, if there is a gap in the screw, the tension test will directly affect the maximum test deformation and elongation after break. At present, some of the tensile tester on the market are with T-shaped ordinary screw, so that the gap is relatively large, and the friction is relatively large, resulting in short life. The screw used in the tensile tester of TESTEX is a high-precision backlash-free ball screw with high surface quenching and hardness, and the service life can reach decades, and ensure the same accuracy.

3 Drive system of the tensile tester

The drive system 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.

Currently on the market, some tensile tester use ordinary three-phase motors or frequency motors, such motors use analog signal control, slow control response, inaccurate positioning, general speed range is narrow, there is a high speed without low speed or low speed without high speed, and speed control is not accurate. The motor used by TEXTEX tensile tester is a full digital AC servo motor, the control method uses full digital pulse control, speed range is wide, up to 0.01-1000mm/min, control positioning accurate, fast response, the motor can ensure full range speed control accurate, and long service life, can reach decades.

4 Control system of the tensile 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.

Most of the current market, the measurement and control system of tensile tester using 8-bit microcontroller control, low sampling rate, and poor anti-interference ability, in addition, if the number of bits of the AD converter is also low resolution, then the measurement will not be accurate.

How to Choose Tensile Tester?

Now there are many brands of tensile tester on the market, with many types of tests and varying prices and quality. So as a buyer or business owner, how should we go about choosing a tensile tester? How to determine which brand of the tensile tester is good? What is the reference basis? Below I will do a detailed analysis for you.

When buying a tensile tester, you will probably follow three principles: testing needs, machine performance and manufacturer service. Firstly, choose a tensile tester with the appropriate specification parameters according to the type of test. In addition, the tensile tester have high requirements for both hardware and software, so choose the right manufacturer based on service and quality. Here are the details.

1 Determine what tests need to be done?

Determine what tests to do in order to determine what instruments we need to buy. First of all we must make sure that we choose the right machine to prevent the machine that buying back is not what we thought it would be, because in some industries some tests are dedicated to special machines.

For example, the spring tensile fatigue test, in theory, the tensile tester can also do, but the best test instrument is not a tensile tester, but a spring fatigue test machine, which is a professionally built machine for the spring test. Another example is the rubber tensile tester. We all know that rubber products need to be tested for tensile damage in order to test their mechanical properties such as tensile strength and extension. But because the deformation of rubber is very large in the stretching, especially latex products, elongation may be as high as 1000% or more. So before the rubber specimen breaks, it is necessary to ensure that the effective stroke of the tensile tester is large enough, it is necessary to use it in conjunction with the use of a large deformation extensometer. Therefore, it is more important to choose the right one than a good one.

2 Determine the maximum test force of the material?

Determine the maximum destructive force will be able to determine the range of the tensile tester, because it is based on the range of the sensor to distinguish the model of tensile tester. First of all, different ranges of the machine sensor is different, in addition, the screw, motor, gearbox and other accessories of tensile tester are different, and finally, the structure of the tensile tester will also be different, for example: 0-500kg range are single-column type tensile tester, 1-20T range are double-column type electronic tensile tester, more than 30T range are hydraulic multi-column type electronic tensile tester.

3 Determine whether the function meets the requirements?

Determine what tests the tensile tester can do: computer-type tensile tester can generally achieve tensile, compression, bending, peel, tear, shear, puncture, low fatigue and other tests, but some simple digital display type tensile tester can not test the peel, fatigue, shear and other functions.

4 Determine whether the test stroke and test speed are consistent?

Test stroke is based on the characteristics of the material to determine, the stroke of metal and other hard materials is usually not very large, the standard testing machine can meet. But some soft packaging film, rubber, silica gel and other materials, the test stroke is very large, some may need to increase the stroke of the tensile tester to meet the measurement. Test speed is also an important parameter of the tensile tester, the general tensile tester in 0.1-500mm/min, this speed range has been able to meet the majority of test requirements, some special products may require 1000mm/min or even greater test speed, these are required to determine in advance.

5 Determine the brand of the core spare parts of the machine?

We all know that the core parts of the tensile tester are: sensors, screw, motor, gearbox and even including the controller, etc. Domestic and foreign manufacturers of tensile tester, none of the accessories used 100% of their own production, so some of the core accessories are outsourced, which also involves the brand of these accessories. A good brand not only precision, quality convenience better, for the overall performance of the machine, stability, reliability also has an important impact. Therefore, the core accessories are also used as an important basis for comparative reference.

6 Determine whether the accuracy of the machine meets the requirements?

The accuracy standard of common tensile tester is 1 level, that is, the accuracy of the machine within ±1%; of course, there is a higher 0.5 level, the measurement accuracy error within ±0.5%. Just choose according to your actual needs when selecting.

7 Determine whether the brand is directly sold by the manufacturer and whether the after-sales service is guaranteed?

As a tensile tester for their own use, we have to determine whether the supplier is a factory direct sales, after-sales service is guaranteed, after all, there are many electronic products of the tensile tester, there may be all kinds of failure, so the choice of what kind of supplier is equally important.

8 Compare prices and choose a brand with a good reputation

After the above is no problem, the last is to examine the price, after all, the price is still very important. On price advice: according to your company’s budget to choose a brand, not the blind pursuit of big brands, but definitely not to buy far below the normal market price, unless you buy just use to see.

Brand Recommendations of Electronic Universal Tensile Tester

In addition to assessing the brand from the quality of the tensile tester, we can also assess them by after-sales service, compliance with testing standards, simplicity of operation and price. Here is a brief list of some of the better brands to meet different purchasing needs.

Japan Shimadzu tensile tester. Japan’s electronic technology has been very well developed, its Panasonic AC servo motor in various industries can be seen, and Japan’s NTS sensor is also a well-known sensor worldwide.

Germany ZWICK tensile tester. German industrial manufacturing is indeed the heritage of the times, exquisite craftsmanship dedication plus Schneider series brand accessories, so that ZWICK tensile tester wears the top title.

MTS tensile tester from the USA. The United States MTS tensile tester is famous for its stability, no matter what, its quality is guaranteed, is a hundred-year tradition of the old brand.

American Instron tensile tester, 1946 to the present well-known historical brand, belongs to the quality is still good instrument.

Taiwan Gotech tensile tester, Taiwan has always been known for quality and dedication, but also a world-renowned brand.

Guangdong TESTEX tensile tester, test stable, specifically for rubber, plastic, fibers and other organic polymer materials, more professional.