Stress-strain Analysis And Life Prediction For Notched Specimens Under Tensile And Torsional Cyclic Loading

The mechanical structures in practical application mostly work under cyclic loading. The loading mode may be uniaxial cyclic loading, or likely to be multiaxial cyclic loading, One of the main form of failure is the fatigue fracture. The traditional uniaxial fatigue theory can not meet the strength and life design needs of high-technology products. Thus in recent years the international fatigue community turns to more realistic study of multiaxial fatigue, and pay more attention to it which becomes a hot research spot. How to improve the mutiaxial fatigue theory and predict the fatigue life accurately is one of the important problems which the scientists and engineers try to solve.In this paper, the stress-strain analysis and life prediction for the notched shaft of the forged aluminum alloy LD5 were carried out under the tensile and torsional cyclic loading. The main research work and results are as follows:(1) In the tensile-torsional proportional or non-proportional loading with constant amplitudes or variable amplitudes cases, the 3D elastic-plastic finite element method was uesd to calculate the stresses and strain of the notched specimens under different loading cases. So the FEM method provided the reliable parameters for the theoretical analysis, calculation and life prediction. Compared with the previous methods to access these parameters, The FEM method is more convenient, fast, intuitive and accurate. Therefore it is feasible to investigate the fatigue behavior of the notched specimens under multiaxial loadings by the 3D elastic-plastic finite element method.(2) In the tensile-torsional proportional loading with constant amplitude cases, the Neuber method, ESED method and H-S method were used to calculate the stresses and strain at the notch root of the LD5 shaft. And a modified formula was proposed to calculate the stresses and strain of the same specimen. It proved that the proposed modified formula is available and practicable by the comparative analysis of the calculation results.(3) Through the analysis of the stress-strain on the critical plane of the multiaxial fatigue damage, an unified multiaxial fatigue damage parameter and a life prediction formula were presented. Accordingly, the life prediction formula and the accumulative damage theory were used to predict the fatigue life of the LD5 notched specimens. Then the prediction results were compared with the actual life in the document. The comparison of the results showed that the the life prediction model can predict the life of the notched specimens well under the tensile-torsional proportional or non-proportional loading cases with constant amplitudes or variable amplitudes.