Electronic universal testing The machine is a frequently used testing instrument in material mechanics. It is mainly used to measure the mechanical performance parameters of different types of materials. It is suitable for mechanical performance tests such as tension, compression, bending and shearing of metal and non-metallic materials. Due to various factors such as the design, processing, assembly and use of the upper and lower specimen clamps in the production process of the electronic testing machine, there will inevitably be a coaxiality positioning error. Influenced by the positioning error of coaxiality, in tensile testing of materials, additional stress will be generated by bending when the specimen bears normal stress, such as B. Bend normal chipvoltage and flexural shear stress, etc., affecting the accuracy of the test results sex.
1、Expression of the coaxiality positioning error of a universal electronic testing machine
(1) The axes of the upper and lower probe heads are parallel and the center of the shaft shoulder section is non-concentric, i. H. the upper and lower probe heads produce a parallel displacement, and the measuring part of the sample is twisted in an S shape;
(2) The center of the shaft shoulder section is concentric but there is an included anglel between the axes of the upper and lower probe heads. The portion of the gauge length of the sample is twisted in an S shape;
(3) lowering the probe head There is some angular adjustability, but the upper and lower axes do not coincide, so the center of the shaft shoulder section is not concentric, and the gauge length part of the probe is curved.
2, coaxiality detection method
Due to the influence of the positioning error of the coaxiality, the accuracy of the test results of the electronic universal testing machine is also specified in the national standard JJG475-2008 Inspection Regulations for Electronic Universal Testing Machines.laid. The detection method and technical requirements, the coaxiality detection method of the universal electronic testing machine can be summarized into the following two types
(1) Method for detecting geometric quantities. Includes dial gauge measurement method and cone weight measurement method.
(2) Strain detection method. Use an automated coax tester (or other fairly accurate meter) to measure.
Reminder: The universal electronic test set produced by regular manufacturers performs a coaxiality calibration before leaving the factory to ensurethat the coax positioning error is within national regulations .within reach. For small manufacturers with insufficient technical strength, there may be obvious problems with the testing machine coaxiality, and they may be asked to replace the host, repair or return the product.