Research On Fatigue Crack Propagation Behavior And Life Prediction Of Laser Shot Peening 2524 Aluminum Alloy

Compared with the traditional surface treatment technology,laser shot peening can introduce deeper residual compressive stress,and has a weaker impact on surface roughness.Therefore,it is used to improve the fatigue life of important components.However,the effect of loading form on the life extension of laser peening process is not clear.In this paper,the effects of different loading forms on laser peening process of aviation high-strength 2524 aluminum alloy are studied experimentally.The analytical model based on fracture mechanics and machine learning algorithm are used to predict the fatigue life.The main research contents are as follows:(1)The fatigue crack propagation experiments of 2524 aluminum alloy were carried out under different laser shot peening loading ratios.The results show that the life prolonging effect decreases with the increase of loading ratio.The crack closure model is used to normalize the crack growth rate data of shot peened and un-shot peened samples.The results show that the residual stress has a great influence on the accuracy of the crack closure model.(2)The fracture morphology under different loading ratios is analyzed.The macro fracture under low loading ratio shows that the shot peened sample will have torsional entanglement at the crack tip and more Z-shaped deflection in the process of crack propagation.SEM fracture shows that it shows obvious brittle fracture characteristics at low loading ratio,while it shows obvious ductile fracture characteristics at high loading ratio.(3)The fatigue crack growth life of shot peened and un-shot peened specimens under equal amplitude load is predicted by crack closure model and two parameter model.In contrast,FCGR data are used to train ANN model and SVR model based on particle swarm optimization algorithm.The prediction results show that the artificial neural network model has higher prediction accuracy than the SVR model.And the model based on intelligent algorithm is better than the traditional model.(4)The fatigue crack propagation behavior of laser shot peening2524 aluminum alloy under single peak overload is studied.The results show that laser shot peening can reduce the hysteresis caused by overload.The effect of the order of loading ratio on the fatigue crack growth behavior of laser shot peened 2524 aluminum alloy is studied.The results show that the crack growth rate under the subsequent loading ratio will be affected by the previously applied loading ratio.The effect of amplitude sequence on the fatigue crack growth behavior of laser shot peened 2524 aluminum alloy under a given loading ratio is studied.The results show that the amplitude sequence has little effect on the fatigue life of shot peened and un-shot peened samples.(5)The Wheeler model is used to predict the fatigue life under overload.The results show that it can well describe the hysteresis effect caused by overload.The improved walker model is used to predict the effect of loading ratio order on fatigue life.The results show that the improved walker model can describe the interaction between loads caused by the change of loading ratio.