Structure and performance of tensile testing machine fixture

Structure of tensile testing machine fixture
The tensile tester fixture itself is a locking mechanism. The fixture for tensile testing machine has no fixed structure. According to different samples and test forces, there are great differences in structure. Samples with large test forces generally adopt a sloped clamping structure. As the test force increases, the clamping force increases accordingly. Shoulder samples adopt a suspended structure, etc. If the fixtures are divided according to the structure, they can be divided into wedge-shaped fixtures (referring to fixtures using the inclined locking principle), clamping fixtures (referring to fixtures using the single-sided or double-sided threaded top tightening principle), winding fixtures (referring to fixtures using the specimen through winding), eccentric fixtures refer to (referring to fixtures using the eccentric locking principle), lever clamps (referring to fixtures using the lever force amplification principle), shoulder clamps (referring to fixtures suitable for shoulder specimens), bolt clamps (referring to fixtures suitable for bolts, screws, studs and other test thread strength), 90° peeling fixtures (referring to fixtures suitable for two samples for hanging and straight peeling), etc. We know that mechanical locking structures include: yarn (i.e. threads, screws, nuts), bevels, eccentrics, levers, etc. The fixture is a combination of these structures. The structures of these fixtures have their own advantages and disadvantages. For example, wedge-shaped fixtures, the initial clamping force is small, and increases with the test force. The clamping force increases accordingly. For clamping fixtures, the initial clamping force is large and increases with the test force. The clamping force decreases accordingly
The tensile tester fixture itself does not have a fixed structure (such as metal wires can be clamped by winding, or two flat plates can be clamped by wedge-shaped clamping, or clamping clamping can be clamped by thin metal plate samples). This is obviously different from the host machine. The main machine of the tester is similar to the domestic and foreign ones, while the different fixtures are very different from the domestic ones, and there are also big differences between different companies. This mainly depends on the overall level of the company and the accumulation of experience of the designers. Foreign fixtures, such as INSTRON, MTS, ZWICK and other companies, are generally meticulous in workmanship and high reliability, but are at a high price, and are in the high-end market. Domestic fixtures, such as Guangzhou Aoke Testing Instrument Co., Ltd., have a wide range of industries and a large domestic market share, and can replace foreign fixtures to a certain extent, but there is still a lot of difference with foreign precision.

Performance and requirements of tensile testing machine fixture
Requirements for fixture structure. The design of the fixture is mainly based on the test standards of the material and the shape and material of the sample (specifically referred to as finished and semi-finished products). The above test standards refer to ISO, ASTM, DIN, GB, BS, JIS, etc., as well as enterprise standards, industry standards, etc. These standards generally have strict regulations on sample preparation and test methods. We can design different fixtures according to the different samples and test methods. For fixtures used for special samples (finished and semi-finished products), fixtures are mainly designed based on the shape and material of the sample.
Fixture strength requirements:
The test force of the sample (or product) is applied to clamp the sample by clamping the sample. The test force that the clamp can withstand is a very important indicator of the fixture. It determines the size of the fixture structure and the labor intensity of the fixture operation. The sample materials are divided into metal and non-metal, and the shapes are divided into various materials. The test force that the sample can withstand is as small as a few dozen centimeters (such as spandex wire for textiles), to dozens of tons, such as ordinary steel. The domestic electronic universal testing machine has a test force of 1000KN, a level 1 machine, the sample size is as small as gold wire with a diameter of φ0.005mm, and PVC pipe with a diameter of 1.5m, etc. This requires the selection and design of different fixtures according to different test forces and the shape of the sample.
Requirements for fixture material.
For general metal and non-metallic specimens, the jaws of the fixture are in direct contact with the specimens. Generally, high-quality alloy structural steel, alloy high-carbon steel or low-carbon alloy steel, cold-work mold steel, etc. are used to increase their strength and wear resistance through appropriate heat treatment processes. Sometimes special steel is also installed at the jaws, or gold steel sand is sprayed on the surface of the jaws (suitable to clamp harder metal materials, such as steel strands, etc.).
For some fixtures with small test force, the surfaces in contact with the sample are made of soft rubber. (For example: the clamping surface of plastic film, fiber wire and other samples,)
The specific clamps generally use high-quality medium-carbon steel and alloy structural steel to increase their mechanical properties through appropriate heat treatment processes. Sometimes, non-ferrous metals such as aluminum alloys and special metals are used in order to reduce weight. Sometimes cast steel, cast aluminum, etc. are also used