Theoreticaland Experimental Research On Stress Field Within The Metallic Sheets Induced By Laser Shock Forming

Laser shock forming is an emerging metal forming technology.It not only has the advantages of non-contact,no mold,high flexibility and controllability,but also can improve the fatigue resistance,wear resistance and corrosion resistance of the metal material.Therefore,laser shock forming technology has received extensive attention.However,the relationship between the stress distribution and the deformation mode which is conductive to guiding the engineering applications has not yet been clarified.Therefore,in this paper,we researched the stress-strain field distribution in the sheet after laser shock forming and visually verified the deformation mechanism of the laser shock forming and the related technological rules by numerical simulation and experiment.The main work and conclusions are as follows:(1)Numerical research on the internal stress field and strain field distribution characteristics of the sheet after laser shock forming.Based on ABAQUS finite element simulation software,a three-dimensional simulation model of laser shock forming 2024 aluminum alloy sheet was established.We studied the internal stress distribution characteristics of laser-impacted curved sheet metal,and by observing the results of numerical simulation,the deformation mechanism of Convex and Concave proposed by Hu was visually verified.The residual stress distributions obtained through the experiment and simulation were compared and analyzed.The results show that: when the metal sheet is convexly deformed,the stress distribution along the thickness direction is roughly divided into three regions: the near surface layer,the intermediate layer and the bottom layer.For the convex deformation,the shock wave effect does not “penetrate” the sheet material,and a stress gradient is induced along the depth direction of the sheet.Then under the action of this stress gradient,the sheet material undergoes the convex macroscopic deformation.When the metal sheet is concavely deformed,the stress distribution along the thickness direction is divided into two regions: the surface tensile stress zone and the lower compressive stress zone.The shock wave effect penetrates the sheet material,causing the overall tensiledeformation of the sheet material,and finally causes the sheet material to undergo deep plastic deformation.(2)The experimental research of the technological rules of laser shock forming.The effects of different laser parameters and impact modes on the deformation mode and deformation of 2024 aluminum alloy sheet were studied.When the energy is the same,Concave deformation occurs when the thickness of the sheet is small;Convex deformation occurs when the thickness of the sheet is large;and the deformation amount is proportional to the energy.When the shock area of the laser is increased,the deformation of the sheet will increase,but the deformation of the sheet will not change.By changing the coverage rate and not change the number of spots,the deformation of the plate basically remains unchanged.The deformation laws of the plates obtained by experiments and simulations are basically the same,which proves the accuracy of the simulation method.(3)The influence of thickness variation of the plate on the transmission law of shock waves.The reflection law of the laser induced shock wave at the interface is similar to the reflection law of light,the shock wave reflected by the oblique bottom surface propagates symmetrically with the incident shock wave along the "normal" axis of the oblique bottom surface.The transmission law makes the impact deformation mechanism,deformation mode and deformation quantity law of unequal thickness plates different from that of equal thickness plates.