| Laser peening(LP)technology utilizes the interaction between high power laser beam and material to generate severe plastic deformation,so that stable residual compressive stress distribution and grain refinement are achieved on the surface of component.Thus,LP can delay the initiation of fatigue crack and reduce crack growth rate effectively,then the service life of key components is improved obviously.In order to decrease high temperature fatigue failure of hot end components in aerospace engine,an approach integrating experiment and numerical simulation was adopted to investigate the characteristic of residual stress distribution around hole of IN718 alloy sample subjected to LP,as well as the thermal and mechanical relaxation behaviour of residual stress induced by LP.Eventually,the mechanism of high temperature fatigue improvement by LP was explored for predicting high temperature fatigue life of LPed material reasonably.The main research contents of this paper include the following aspects.(1)The high temperature fatigue failure mechanism was analyzed by considering the effects of creep damage,fatigue damage and oxidation.Based on elastic-plastic mechanics,the residual stress field induced by LP was estimated,and the dynamic response mechanism of materials under high strain rate was analyzed.Additionally,the relaxation behavior of the residual stress induced by LP under thermal and mechanical condition was investigated,and then the estimation model of residual stress relaxation was established.Finally,the high temperature fatigue life estimation formula of LPed component was deduced according to the theory of creep mechanics and fracture mechanics.(2)The numerical simulation and experiment work of LP were conduced to study the characteristic of residual stress distribution on the surface around hole of IN718 alloy sample subjected to LP.Due to the anisotropy of residual stress induced by LP,the residual minimum principal stress was selected to characterize strengthening effect.The generation mechanism of typical “residual compressive stress ring” induced by LP around hole was explored.Further,the position of “residual compressive stress ring” to hole wall with the increase of power density was investigated.(3)Tensile tests were conducted to obtain the mechanical properties of matrix atelevated temperature.According to tensile test results,fatigue tests and simulation work were performed to investigate the effect of LP on fatigue life of specimens at elevated temperature.Then,the functional relationship model between fatigue life of whole specimen and risk nodes was proposed to predict ultimate high temperature fatigue life according to results of experiments and finite element analysis.Moreover,the fatigue fracture mode changes at different temperatures by observing the fatigue fracture. |
PDF Full Text Request