Study On The Difference Of Fatigue Life Under Laser Shock Peening Of Different Detail Structures

There are many details in the structural components of the aircraft,such as rounded corners,fastening holes etc.These details are prone to fatigue fracture during service.The fatigue effect of the laser shock effect of different detail structures is great.Therefore,studying on the difference of residual stress under various laser vibrations can help predict the fatigue performance and provide reference for the parameter selection of laser shock processing.Based on theoretical research and numerical analysis,this paper combined with the experimental verification to verify the fatigue difference of laser shock with different detail structures.The main research contents are as follows:(1)The formation mechanism of residual stress of laser impact target was discussed,and the influence of geometric features of detail structure on laser shock effect was analyzed based on stress intensity factor theory.The results showed that the influence of radius of curvature on stress intensity factor is mainly in stress concentration and laser shock effect.The stress concentration and laser shock effect increase with the increase of curvature;the thickness of the hole wall has little effect on the stress concentration of the hole wall.The crack initiation interval of the wall increases with the increase of the pore wall thickness.(2)Based on ABAQUS software,the residual stresses of different radius fillets,different thickness small hole parts,different diameter round bars and different curvatures under laser shock peening were simulated.The results showed that the residual compressive stress of the fillet structure increased with peak pressure and pulse width increase,and the residual stress distribution of the rounded corner R3 is better than the rounded corner R6;the thickness of the hole wall has almost no effect on the stress distribution at the hole angle,and the inner tensile stress interval of the hole wall increase with the increase of the thickness of the hole wall.Different thickness of the small hole parts have different laser energy requirements,due to the different stress penetrating forces;The surface residual compressive stress and the residual tensile stress of the different round bars increase with the decrease of the diameter,and the internal tensile stress fluctuates greatly;The relationship between the residual compressive stress and the depth of the compressive layer of different curvature structures is: the residual compressive stress and the compressive stress layer depth increase with the increase of curvature.(3)Based on ABAQUS software to simulate the stress concentration level of each detail structure and calculate its actual stress level,the results showed that the stress concentration level of the round corner R3 is larger than the round corner R6,and the difference between the two is reduced after laser shock peening;The stress concentration level of the hole wall is not much different,but the actual stress level in the wall of the small hole under laser shock peening increases with the increase of the thickness of the hole wall;The stress concentration level of the round bar structure increases with the decrease of the diameter,but the actual stress level inside treated round bar is greatly increased.Finally,based on the numerical analysis results,the appropriate laser shock test parameters were selected and the fatigue gain of each detail structure were predicted.(4)The laser shock and fatigue tests were carried out on the TC4-DT titanium alloy double specimens with detailed structure.The results showed that the fatigue gain of the R3 and R6 specimens with laser impact is good,but the fatigue gain of rounded corner R3 is greater than R6,and the fatigue source is transferred from the root of the fillet to the depth direction.The fatigue gain of the small hole sample with different thickness is better after laser shock,and the fatigue gain of the thin plate small hole is slightly better than that of the thick plate.The fatigue sources are transferred from the hole angle to the hole wall;The tensile fatigue gain of bar samples after laser shock peening is negative,and the fatigue source is transferred to the inside,but the fatigue gain of the bending fatigue test is larger.It was found that the residual tensile stress of the rounded structure(open structure)after laser shock peening is very small.The residual tensile stress of the bar structure(fully closed structure)after laser shock peening cannot be diffused,and form a large residual tensile stress on the axis.The tensile fatigue properties of the open structure after laser shock are superior,but the residual tensile stress formed by the laser shock after the closed structure increases the effective stress level and has a certain negative impact on the tensile fatigue performance.