The Research On Low Cycle Fatigue Fracture Properties Of 304 Stainless Steel Undertensile And Compressive Loading

304 stainless steel's the low cycle fatigue fracture properties and fracture characteristics were mainly studied through the experiments in this article. In the experiments, the loading mode used controlling stress by which fatigue experiments specimens was done in Shimadzu (SHIMADZU) EHF-EM100kN servo frequency fatigue testing machine. The specimen is divided into smooth specimens and notched specimens. The length of the testing machine sample is in accordance with the requirements and standards of countries. But the notch depth, angle and notch tip radius is processed according to the experimental purposes and processing incision on the specimen is mainly consider the notch depth's effect of the specimen's life. Through Hitachi S-3400N scanning electron microscope observed the fatigue fracture surfaces and analyzed the crack source, crack propagation area and the instantaneous fault zone's basic characteristics, stress level and load size on the fatigue fracture characteristics.In this article, through experiments on 304 stainless steel fatigue fracture to analyze:(1) The basic fatigue test of material, in the stress ratio R =-1, the symmetry under the control of constant amplitude cyclic loading, we get The S-N curve of 304 stainless steel by experiments. It can be obtained when the stress isσ≥250MPa , the reduction of material life with the stress is more slow; when the stress is 236MPa≤σ≤250MPa, the reduction of material life with the stress is more fast. Fourth more, stress of life tend to double on a straight line. After analyzing the experimental data, the 304 stainless steel fatigue limit Sf was gotten. Strain and strain energy are increasing with the loading times. When it comes to a certain extent, they have tended to be stable.(2) Cut the gap at different depths on the smooth specimen,when the stress ratio R =-1, the symmetry under the control of constant amplitude cyclic loading, the fatigue tests of axial tension and compression was done. After testing,we get a S-N curve of different depth of the gap, which have a common trend when the gaps are different. At the same time, when the stress is increased, the life time is reduced ; In addition, the deeper the gap, the shorter life of the specimen. The results also show that the specimen notch depth and life is approximately a relationship of linear.(3) Having macro-and micro-fracture analysis of fatigue fracture of 304 stainless steel to study the mechanism. The crack can be obtained by analyzing: the greater the load of the source, the more fatigue source, then the faster fracture, the more rough sources; the greater load of the crack extension the greater the fatigue spacing , the greater the fatigue striations coarser etc; the stress of load have small impact of instantaneous, generally it was lacerated.The research get the data by experiments and analyze data and fatigue rupture characteristics of 304 stainless steel. It can provide data to engineering application and structural fatigue design, and reduce the unnecessary losses in economic.