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The reason why the tensile testing machine has the title universal is that it can be used for a variety of mechanical performance tests, and each test corresponds to a jig, so the jig is an indispensable part of the tensile testing machine is . According to the different testing methods, jigs can be roughly divided into: pulling jigs, pushing jigs, bending jigs, stripping jigs, shearing jigs, etc., with the pulling jigs accounting for about 80% of the whole jigs.
1, fixture type selection
In order to test the mechanical properties of materials, it is necessary to apply a loading force to the specimen by clamping the specimen with a fixture. Therefore, the test load that the fixture can bear is an important indicator of the fixture, which determines the strength of the jig, the size of the structure and the labor intensity of the jig operation.
The sample materials for mechanical performance tests include metal, plastic, rubber, wood, composite materials, polymeric materials, etc. and the include sample shapesn Plate, pipe and rod, wire and other categories. The test force that the sample can bear can be ≤ 0.1N (such as spandex wire for textiles) or ≥ 300kN (such as ordinary steel, etc .), and the size of the sample is as follows, as small as a gold wire with a diameter of φ0.006mm and as large as a PVC pipe with a diameter of 1m, etc. This requires the selection and design of various jigs according to different testing forces and sample shapes and sizes, and some special materials even require special custom fixtures.
2. Choice of fastening materials
(1) For general metallic and non-metallic specimens, the fixture jaws have directcontact with the sample. Generally high quality structural alloy steel, high carbon alloy steel (or low carbon alloy steel), cold work steel, etc. are used through appropriate heat treatment processes (quenching and tempering, carburizing and quenching, etc.) to increase its strength and wear resistance, sometimes special steel is used on the cheek piece or gold steel grit is sprayed onto the cheek surface.
(2) For some low test force devices, the surface in contact with the sample is made of soft rubber, etc. (for example: the clamping surface of the sample, such as plastic film, fiber filament, etc.)
(3) The clamp body is generally made of high quality medium carbon steel and alloy structural steel, and its mechanical properties are improved by appropriate heat treatment processes. Non-ferrous metals and special metals such as aluminum alloys are used in part used to reduce weight, sometimes cast constructions (cast steel, cast aluminum, etc.) are also used.
