Experiment And Numerical Simulation On Laser Shock Forming Of Pure Titanium Strip

Traditional plastic forming technology of mental sheet gradually can not meet the requirement of rapid update of products now,the development of new mental sheet plastic forming technology is of great significance.Laser shock forming(LSF)is a new plastic forming technology with forming and strengthening effects,which is characterized by high pressure,high speed and precision forming.It has certain advantages for the production of new products with small batch,multi-variety and complex shape,and long-term development prospects.Pure titanium is widely used in the fields of aerospace,automobile industry and medical field because of its low density,high specificity,corrosion resistance and good biocompatibility.The application of laser shock forming technology to plastic forming of pure titanium is of great significance for the research of new plastic forming technology about pure titanium and promotion of pure titanium application.The target material of this paper is cross-rolled TA1 pure titanium strip,the study about multiple impacts of LSF was conducted with different laser power densities.Through experimental research and numerical simulation technology,the forming properties were studied,the changes of microstructure were analyzed.The main work and conclusions are as follow:The shock of laser form a circular pit on surface of titanium strip,and the thinning amount and forming depth in the center are the maximum.With the increase of laser power density and impact times,both the thinning amount and forming depth increased.Effected by heat of laser,different levels of material ablation were gained on surface,and surface roughness increased correspondingly.Hardness of titanium strip was improved after LSF.Hardness increasing and strengthening of surface of titanium strip are the results of multiple impacts.Titanium strip was destroyed after more than ten times of impacts,and the fracture was located in the center.The fracture was characterized by ductile fracture,and where dimples,tearing ridges,and spallation were gained inside.The fracture mechanisms of titanium strip after laser shock include thinning mechanism and spallation mechanism,the thinning behavior lead to necking and a large number of dimples,and spallation is the result of loading of laser in the form of pulse.The plastic deformation mechanism of titanium strip was in the ways of slipping and twinning,then a large amount of parallel deformed twins,high density dislocations,and slipping bands were gained,the improvement of hardness was the result of work hardening behavior.Periodic corrugated structure generated on surface of impact.Results of numerical simulation indicated that high amplitude residual compressive stress was gained on the surface of titanium strip,which was in the distribution shape of “W”.The value of residual compressive stress increased with the improving of laser power density,but increased first and then decreased with impact times.Residual tensile stress generated in the central zone after multiple impacts gradually.Both the forming depth and thinning amount increased with the increase of laser power density and shock times.Titanium strip reached the forming limit and then was destroyed after fifteen impacts with laser power density of 6.11GW/cm2,the fracture located in the center.The maximum forming depth and thinning ratio,and fracture location were compared between experimental and simulation results,simulation results were in good agreement with experimental results.