A New High-Cycle Fatigue Model Under Multiaxial Loading

With the rapid development in technology and economy, a higher level requirement on the service life of the aircraft and ships are proposed by countries in the world. In this situation the deformation of most force-bearing components of the aircraft and ships under the fatigue loading are predominantly elastic deformation(defined as high-cycle fatigue), but the loading paths are often non-proportional. In addition, the presence of notches or weld in these components generates stress concentration, which leads to complex multi-axial stress field even when the externally applied load is uniaxial. However, the multi-axial high-cycle fatigue failure mechanism is not yet systematically established domestic and abroad up to now, and multi-axial high-cycle failure analysis under the complex multi-axial stress field as well as fatigue life prediction have not come to perfection. Therefore, the in-depth study of multi-axial high-cycle fatigue behavior under complex loading plays an important part in developing advanced aircraft structural design theory.The method of the combination of theoretical research and the experiment is adopted and the mechanism of fatigue failure is analyzed. Based on the latest strain energy theory, a new kind of plastic strain energy of multi-axial high cycle fatigue life prediction model is proposed. The established multi-axial fatigue life prediction formula contains three material parameters, and is determined by uniaxial fatigue experiment data. Preliminary research indicates that the model can predict the referenced multi-axial fatigue test data well.Secondly, an estimation method for the fatigue life of notched specimen is proposed. This method takes into account the stress gradient of the notch. The combination of the critical distance method and a new type of high cycle fatigue life prediction model predicts the life of notched specimen. The reliability of the devised method was systematically checked by using experimental results. Our method was seen to give successful predictions.Last, an estimation method for the fatigue life of welded structure is proposed. Critical distance method can accurately reflect the actual situation of welded structure fatigue damage, to obtain the equivalent stress of welding structure. The accuracy of the method was further verified by using several data sets taken from the literature. Our method was seen to give successful predictions.