Selection criteria for tensile tester fixtures
First, the characteristics of the tensile machine fixture:
(1) The clamping is reliable and there is no slipping phenomenon.
(2) During the test, the sample breaks well. Data dispersion is small. (ie, the sample is constantly clamped, inside the jaws, parallel segments or outside the gauge length)
(3) Whether the fixture is convenient and safe to use.
Second, there are several special situations that need attention:
1. For materials with large deformation, the deformation is too large, so the clamping is difficult, and the design of the fixture is also a difficult point.
2, for the test that needs to be done in a high temperature environment, the requirements of the fixture are also very high, both high temperature resistance, no deformation, and small volume, so the general test machine manufacturers are also difficult to get things done.
3, steel wire, steel strand due to the high hardness of the sample, the internal structure is relatively loose, the force is not uniform during the tensile test, the jaws of the clamped sample are easy to wear and so on, the fixture has not been well resolved. In the past, it was made of aluminum foil, and it took four pieces of aluminum foil in one test, which was too much waste. Now using the tensile testing machine clamp of the sprayed diamond, the slipping problem is solved, but the fracture position is always unsatisfactory, and 10 samples can only be about half successful.
4. For large-volume, high-frequency tests, fully automatic clamping is widely used abroad, which is still a new topic for domestic testing machine manufacturers.
5. For the inspection of finished products and semi-finished products, the required fixtures are varied. How to personalize the requirements of customers is a challenge for all test machine manufacturers.
6, commonly used fixture names are: universal universal fixture, wire tension clamp, rubber tensile clamp, spring tension clamp, sewing thread special fixture, terminal special fixture, etc.
Third, we must pay attention to the material of the fixture. The material requirements must meet the following standards:
1. For general metal and non-metal samples, the jaws of the fixture are directly in contact with the sample. Generally, high-quality alloy structural steel, alloy high carbon steel (or low carbon alloy steel), cold work die steel, etc. are used. The heat treatment process (quenching tempering, carburizing and quenching, etc.) increases its strength and wear resistance. Sometimes it is also equipped with special steel at the jaws, or gold steel sand on the surface of the jaws.
2. For some small test force fixtures, the surface in contact with the sample is made of soft rubber. (For example, the clamp holding surface of a sample such as a plastic film or a fiber yarn.)
The 3 clips are generally made of high quality medium carbon steel and alloy structural steel, and their mechanical properties are increased by a suitable heat treatment process. In order to reduce the weight, non-ferrous metals such as aluminum alloys and special metals are sometimes used. Casting structures (cast steel, cast aluminum, etc.) are sometimes used.
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