Explanation

A kind of mechanical property test to determine the fatigue curve and fatigue limit of materials. The delayed brittle fracture of materials under the repeated action of alternating load is called fatigue fracture. The level of loading stress (T) is low, and there are many loading cycles before fracture, which is called high cycle fatigue or stress fatigue; The loading stress level is high (near the yield point), and the loading cycles before fracture are few (hundreds to tens of thousands of cycles). It is called low cycle fatigue or strain fatigue. The fatigue test can be used to determine the fatigue curve of materials, i.e. rN curve, and also to determine the fatigue limit of materials, i.e. the maximum bearing stress without fracture after infinite cycles. The fatigue test is to load the specimen with certain shape, size and surface accuracy on the fatigue test machine until fracture. There are rotating bending fatigue testing machine, tension and compression fatigue testing machine, torsional fatigue testing machine and so on depending on the type of alternating load. It should be carried out in accordance with relevant standards and regulations. At least 10 identical specimens are required to start the test at the stress level where the fatigue limit is predicted. Then the lifting method is used, that is, the former sample has fatigue fracture, and the stress level of the latter sample decreases, otherwise, the stress increases, and all samples are made. There are many factors affecting the fatigue test, and the test data are scattered. Statistical methods are usually used for data processing. The test proves that the lognormal distribution function and Weber distribution function are consistent with the results of fatigue test. The fatigue limit measured by rotationally symmetric cyclic loading is the main mechanical parameter for fatigue strength design. fatigue test is time-consuming and laborious, and the results are scattered. Therefore, only those components with fatigue fracture as the main failure form are subject to fatigue test.

Classification