Fatigue Life Prediction Of High Strength Steel Welds Under Prestrain Based On Energy Method And Its Application

High-strength steel welded joints are widely used in construction machinery,aerospace,rail transportation,automobiles,marine platforms and other equipment.With the development of machinery towards highspeed,heavy-duty and intelligent,welded structures in equipment often generate pre-strain due to overload,and the introduction of pre-strain can cause changes in the fatigue performance of the structure,causing potential problems for the reliability and safety of the structure.In the study of failure fracture of high-strength steel welded joints,the consideration on the effect of pre-strain is still insufficient,especially the fatigue life prediction method of welded joints under pre-strain is far from perfect.The general fatigue life prediction method is difficult to adapt to the fatigue life prediction of welded joints under pre-strain,so this thesis takes the welded joints of high-strength steel as the object of study and investigates the fatigue behavior of high-strength steel welded joints under pre-strain.At the same time,the method is applied to the fatigue life assessment of mining dump truck rear axle shell under preload,and the fatigue-resistant optimized design is carried out.The main research contents of this thesis are as follows.1.Fatigue life test study of high-strength steel welded joints under pre-strain.Mechanical property parameters of high-strength steel welds were obtained through monotonic tensile tests,and on the basis of straincontrolled fatigue life tests of high-strength steel welded joints under prestrain,the strain fatigue life curves of welded joints under different prestrain levels were obtained,laying the foundation for the study of fatigue life prediction methods of high-strength steel welded joints under prestrain.2.A fatigue life prediction method under pre-strain is proposed.In view of the actual cracking of welds under pre-strain,it is considered that fatigue life prediction using strain as its damage parameter is not accurate enough.By comparing several methods for fatigue life assessment of welds,the strain energy density is proposed as a parameter to measure fatigue damage of welds under pre-strain.Based on the calculated elastic strain energy density and plastic strain energy density at different pre-strain levels,the relationship curves with the pre-strain are fitted,and a fatigue life prediction model for the weld under pre-strain is proposed.The fatigue life behavior parameters of high-strength steel welds under pre-strain are obtained based on the results of strain-controlled fatigue life tests of welds under pre-strain.3.Fatigue-resistant optimization design of the rear axle shell of mining dump truck based on energy method.A finite element model of the rear axle shell containing the weld element is established,and the finite element model of the rear axle shell is verified by stress testing.The multistep nonlinear finite element analysis of the rear axle shell under equivalent load is conducted,and the stress-strain response of the rear axle shell at the danger point is calculated.The proposed strain energy density fatigue life prediction model is also used to predict the fatigue life of the danger points on the rear axle shell.The plate thicknesses of the rear axle shell at different parts are used as design variables,and the fatigue life is used as the optimization objective to carry out the fatigue resistance optimization design of the rear axle shell.The response surface model of different plate thicknesses and fatigue life of the rear axle shell is constructed by using the second-order response surface method,and then the global optimal solution is solved based on the multi-island genetic algorithm.The fatigue life of the optimized rear axle shell was improved by 102.8%.In summary,this thesis is a more detailed study of the fatigue life prediction method of welded joints under the action of pre-strain and its application,which provides a new way of thinking for the exploration of related research and has a certain reference value for the systematic development of fatigue-resistant optimization design of the rear axle shell structure of dump trucks.