Investigation On The Behaviors Of Metal Tube Forming And Fracture Induced By Laser Shock Wave

Laser shock tube bulging is a novel tube forming technology,which uses laser to irradiate on absorption layer attached to the mandrel inside the tube.The absorption layer is vaporized almost simultaneously,and the high pressure plasma is generated in an ultra-short time.The high pressure plasma absorbs subsequent energy and expand rapidly to induce shock waves,which then causes plastic deformation of the metal tube.In order to used widely this technology,it is necessary to research on the bulging process and fracture failure.In this paper,the bulging process and fracture of copper tube under laser shock are studied by combining numerical simulation and experimental study.The main work and conclusions of this paper are as follows:Firstly,the failure of sheet metal forming and two common failure forms are introduced,and the fracture mechanism of sheet metal under laser shock is described.The research status of bulging and fracture of tube fittings at home and abroad is further summarized,and the research progress of explosion fracture of cylindrical tube is introduced.Then the principle of laser shock tube bulging is described.Then,STAR-CCM+ and ABAQUS software were used to simulate the fluidstructure coupling of laser shock tube bulging to explore the expansion and diffusion of plasma in the tube.And the pressure curve of the tube wall in the process of tube bulging was obtained,which laid the foundation for the simulation of tube bulging fracture.In the structural field simulation,it is found that the maximum deformation of copper tube with outer diameter of 3 mm and wall thickness of 0.2 mm is about 0.53 mm under initial pressure of 3GPa,and the whole deformation region has a certain asymmetry.The maximum thinning rate of tube wall thickness is 28.5%,slightly less than the extreme value of the maximum thinning rate,and the tube is basically in the forming limit range at this time.With the increase of initial pressure,the greater the deformation of tube,the greater the thickness thinning rate.When the initial pressure is3.5 GPa,the thickness reduction rate is about 33.0%,and the tube has failed.With the increase of mandrel angle,the deformation of tube is smaller and the thickness thinning rate decreases,but the bulging profile asymmetry of tube becomes more serious.Under the same initial pressure,the maximum thinning rate decreases with the increase of tube wall thickness.Next,combined with the fluid simulation in the early stage,the simulation analysis of tube fracture is carried out,and multiple cracks appeared in the tube.It can be seen from the simulation results that the tensile hoop stress increases gradually from inside to outside.Since the maximum tensile stress is located on the outer surface,the outer surface cracks first due to hoop stress.The dynamic hoop stress develops towards the inner surface as the crack develops on the outer surface.When the crack extends along the shear zone at an angle of about 45 degrees from the radial direction and eventually penetrates the entire tube wall,the shear oblique fracture surface is formed.Finally,relevant laser impact experiments were carried out.The three-dimensional morphology of the bulging tube was measured and compared with the finite element simulation results,which verify the accuracy and reliability of the fluid-structure coupling simulation.The fracture samples obtained by the experiment are basically consistent with the simulation.The following conclusions were obtained by SEM observation of fractured tube: the bulging of tube during laser shock is the result of mechanical action;the crack section is about 45 degrees in radial diameter direction of the tube;and the crack extends from the outer wall to the inner wall.