Fatigue Study Of 16MnR Steel Based On Ubiquitiform Theory

According to the requirements of scientific research and industrial production,16MnR steel is widely used in various structures which are damaged by various loading methods.Fatigue damage is a common failure accident.Although the damage surface is confirmed to have fractal features,the physical dimension of the object in fractal theory loses its physical meaning.In this paper,the fatigue failure of 16MnR steel is studied based on the ubiquitiform theory,which fundamentally solves the essential defects of fractal application and provides a new idea for fatigue research of 16MnR steel.In the first place,by applying the ubiquitiform theory,the complexity of the fracture morphology and the minimum threshold had been obtained based on the experimental data,and then the crack length of the ubiquitiform theory is verified.Crack propagation model of ubiquitiform theory was established and the formula of crack growth rate of ubiquitiform theory was deduced.In the second place,16RnM steel fatigue test was carried out.The loading stress is a certain stress ratio with varying mean stress,certain loading amplitude with varying average stress,and a certain mean stress with varying loading amplitude,respectively.The effects of different loading conditions on fatigue life and fatigue crack length were discussed.Fracture surface data were measured by CSM.The trend of the complexity of the fracture morphology and the effect of cyclic loading on the complexity of fracture morphology had been discussed.By distinguishing the boundary between fatigue fracture and tensile fracture generated under cyclic loading,fatigue crack length was obtained.Finally,from the macro,fine and micro perspective,the crystal structure,fracture morphology and crack growth rate of 16MnR steel are combined.The influence of crystal structure on the fracture morphology was discussed.The fatigue fracture process was simulated based on the experimental data,the material fatigue constants of various cyclic loads were obtained,and the crack growth rate of the ubiquitiform theory was calculated.The results show that the change of crack growth rate with the ubiquitiform theory is related to the crack length.Furthmore,the relationship between fatigue crack length and fatigue life of ubiquitiform theory are also calculated and the fatigue life of 16MnR steel is accurately predicted.