Investigation Of Laser Shock And Core Rod Extrusion Composite Reinforcement Method And Fatigue Characteristics Of Fastener Hole Component

The hole is one of the parts where the fatigue fracture is easily occurred on the structural parts.There are considerable numbers of hole structures in the aircraft.In order to improve the fatigue life,the laser shock processing technology and the cold extrusion strengthening technology are more effective methods.This article attempts to combine the two methods to achieve a new composite strengthening.Through theoretical analysis and numerical calculation method,this article studied the effects of composite and non-composite strengthening methods on the stress distribution and fatigue life of the structure.The mechanical properties of traditional mandrel extrusion process with the assistance of ultrasonic vibration were also investigated,and the experiment of composite extrusion strengthening was carried out.The main research work and purpose were as follows:(1)It theoretically analyzes the mechanism and influencing factors of laser shock strengthening and cold extrusion strengthening.The distribution of residual stress after strengthening treatment and its influence on fatigue life are analyzed.It was proposed to use composite strengthening to realize the complementary of laser shocking and mandrel extrusion strengthening.The effect of composite strengthening on the inhibition of fatigue crack was also analyzed.(2)Based on ABAQUS software which is used for numerical simulation of composite and non-composite strengthening,the influence of different process parameters on the residual stress distribution was analyzed.The results showed that the peak pressure is high with the laser shock processing,the effect time is long,and the strengthening effect is good.The stress distribution of the squeezing end and the extruded end is not consistent for cold extrusion strengthening,and 3% ~ 4% of the amount of extrusion is more reasonable.In the process of composite strengthening,the effect of the laser shock processing,which is produced by the strengthening of mandrel after laser shock processing,is completely covered by Mandrel extrusion strengthening,but the strengthening effect is slightly better than that of the single core rod extrusion strengthening.The order of laser shock processing after cold extrusion can effectively improve the difference between the squeezing head and extruded end caused by the cold extrusion.It can effectively solve the problem of residual tensile stress caused by laser shock processing.It also realizes the mutual complement of laser shock processing and mandrel extrusion strengthening.The experimental results show that the fatigue life of the 7050-T7451 specimen is greatly improved after the composite strengthening.(3)Mandrel extrusion strengthening applies the assistance of ultrasonic vibration,reducing the drawing force,effectively preventing the broken mandrel.A comparative study of ultrasonic respiratory vibration and longitudinal vibration modes,indicates that the effect is better with the use of breathing Ultrasonic vibration extrusion process.Ultrasonic vibration can be practically used in engineering;with the increase of ultrasonic frequency,the drawing force decreases obviously under different extrusion.In the process of composite strengthening,the deformation resistance of the hole angle can be reduced effectively by adding the anti-deformation mandrel.