Residual Stress Control And Equal Fatigue Life Design Of Typical Damaged Aircraft Component By Laser Shock Peening

Aircraft beam and rib structural components are usually served in a harsh corrosive environment.Under the action of long-term corrosive environment,aircraft structural components are prone to corrosion damage,which will seriously threaten the airworthiness and navigation safety of aircraft.The aircraft structural component with slight corrosion damage can be repaired by surface strengthening methods such as laser shock peening after grinding,and then put into use again.The grinding operation to remove the corrosive materials will make the corrosion damaged component form complex geometric shapes composed of plane,convex arc surface,inclined plane,concave arc surface and so on.These shapes and edge effects may have adverse effects on the repair quality of laser shock peening(residual stress,fatigue life,surface integrity,etc.).Therefore,in the laser shock peening repair of damaged aircraft component,it is necessary to adjust and control the laser shock peening according to the geometry and loading conditions of the damaged component,and obtain the repair component with equal fatigue life,which is the core scientific problem to be solved in order to realize the intelligent and efficient repair of damaged aircraft component.In this research,the typical 7075-T6 aluminum alloy aircraft damage component were taken as the research object,and the effects of surface shape and edge effect on the residual stress distribution and fatigue life in the process of laser shock peening were mainly studied.According to the corrosion damage characteristics of aircraft structural component,the grinding specification was analyzed,and the typical geometric model of typical aircraft damaged component after grinding was established.On this basis,the shock wave pressure peak value,spatial distribution and time distribution of laser shock peening shock wave were analyzed,and the pressure model of laser shock peening shock wave based on Fabbro theory was established.The accurate loading of shock wave on the damaged component was realized by using VDLOAD subroutine programming of ABAQUS.Johnson-Cook material model parameters of 7075-T6 aluminum alloy were obtained to ensure the accuracy of stress and strain during the FE simulation of laser shock peening.Based on the geometric model,shock wave pressure model and material model,the laser shock peening finite element model of7075-T6 aircraft damaged component was established,which provides a reliable basis for laser shock peening residual stress control and equal fatigue life design of aircraft damaged components;The average error between the residual stress simulation results and the experimental results is 4.8 %,and the maximum error is 7.6 %,which verifies the reliability of the model.Focus on the influence of complex surface shape on residual stress after laser shock peening repair,the shape of grinding area characterizing was analyzed.Three geometric parameters,namely grinding depth,fillet radius of transition area and length of transition area,were proposed to characterize grinding area for the first time;Based on the finite element simulation,the influence of the characterization parameters of the damaged component grinding area on the residual stress distribution after laser shock peening was studied,and the reasonable shape parameter range of the damaged component grinding area was determined.Based on the reasonable grinding parameter range of the damaged component,aiming at the problem of abnormal residual stress caused by the impact of the edge area which is difficult to avoid in the process of laser shock peening,the definition of sample edge effect was proposed and its influence range is studied.The results show that the influence range of edge effect on residual stress distribution is about 70% of the spot diameter.Combined with the influence of geometric parameters on the residual stress,a laser shock peening residual stress control method based on non-uniform overlap ratio was proposed for the first time,which realizes the accurate control of the residual stress field of laser shock peening repair,and the relative error between the control stress field and the expected stress field is ±6%。A method to solve the problem of residual tensile stress on the side caused by the edge effect of the specimen and the unreasonable distribution of residual stress caused by the surface shape of the specimen were proposed;So as to realize the fatigue design of damaged aircraft component such as laser shock peening.Firstly,the influence of edge effect on residual stress and fatigue life after laser shock peening was studied.The elimination method of edge effect such as multi surface laser shock peening,non edge area laser shock peening and laser spot path sequence method were analyzed and compared.The solution of edge effect based on multi surface laser shock peening was determined.Based on the method of non-uniform overlap ratio,the residual stress of damaged aircraft component under load was adjusted to solve the problem of unreasonable distribution of residual stress.Based on the solution of edge effect and the control of residual stress,the equal fatigue design of damaged aircraft component was realized,and its accuracy was verified by fatigue test.The experimental platform of laser shock peening was built,and the surface integrity indexes such as surface morphology,surface hardness,surface roughness and average grain size were studied.The results show that,after laser shock peening,with the increase of laser energy,overlap ratio and shock times,the surface hardness of the impact area gradually increases and tends to saturation(the maximum increase rate of surface hardness is 19.49%).With the increase of laser incidence angle,the surface hardness of the specimen increases,but the increasing range decreases gradually.Under the same laser shock peening parameters,the microhardness of different areas of damaged component is different,which is reflected as concave arc surface > plane > convex arc surface.The surface roughness of the shock region tends to a certain range.The effect of laser shock peening is to make the rough specimen smooth and to make the smooth specimen rough.Under the experimental conditions in this paper,the range is Ra 0.2μm～Ra 0.5μm.With the increase of laser shock peening parameters,the surface grain of the material is refined gradually.The conclusion has high theoretical and engineering application value,which lays a good foundation for the practical application of laser shocl peening repair of aircraft damaged parts.