The fatigue testing machine is used to measure the fatigue characteristics, fatigue life, prefabricated cracks and crack growth tests of metal, alloy materials and their components (such as operating joints, fasteners, spiral moving parts, etc.) under tensile, compressive or tension-compression alternating load at room temperature. After the high-frequency fatigue tester is equipped with corresponding test fixture, it can carry out three-point bending test, four-point bending test, sheet tensile test, thick plate tensile test, tensile test of reinforced steel bar, chain tensile test, fastener test, connecting rod test, torsion fatigue test, bending-torsion composite fatigue test, interactive bending fatigue test, CT test, CCT test, gear fatigue test, etc. under sinusoidal load.
Fatigue test refers to the determination of metal materials through metal material test σ- 1. Draw the S-N curve of the material, then observe the fatigue failure phenomenon and fracture characteristics, and then learn the method to determine the fatigue limit of metal materials under symmetrical cycles. The testing equipment generally includes fatigue testing machine and vernier caliper.
Under the action of sufficiently large alternating stress, micro-cracks may be caused by large stress concentration in the parts of metal components with sudden shape changes or surface nicks or internal defects.
The dispersed micro-cracks will form macro-cracks through aggregation and communication. The formed macro cracks gradually and slowly expand, and the cross section of the component gradually weakens. When reaching a certain limit, the component will suddenly break. The above failure phenomenon of metal due to alternating stress is called metal fatigue.
Materials with good plastic properties under static load of fatigue testing machine, when subjected to alternating stress, often break suddenly when the stress is lower than the yield limit without obvious plastic deformation. The fatigue fracture surface is obviously divided into two areas: the relatively smooth crack growth area and the relatively rough fracture area.
After the crack is formed, the alternating stress causes the two sides of the crack to open and close, squeeze and grind each other repeatedly, and the smooth zone is formed in this way. The discontinuity and size change of the load leave many cracks along the front of the smooth zone.
As for the rough fracture zone of the fatigue testing machine, it is finally formed by sudden fracture. Statistics show that about 70% of the failures of mechanical parts are caused by fatigue, and most of the accidents are catastrophic. Therefore, it is of practical significance to study the fatigue resistance of metal materials through experiments.
