Study On The Forming Mechanism Of 316L Stainless Steel 4D Printing Stimulated By Laser Thermal Stress

4D printing refers to the structure printed by 3D technology that can achieve targeted changes in shape,performance or function under external stimulation,and it can realize self-assembly,multi-function and self-repair of materials.It is a material preparation technology with predictable functions,and has broad application prospects in biomedical,aerospace,robotics and other fields.so as to meet the application needs in various fields,including biomedical,aerospace,robot,etc.The smart materials used in 4D printing mainly include shape memory polymers/alloys、hydrogels and liquid crystal elastomers.At present,the limited availability of 4D printing materials limits the application of complex self-deformable structures in the engineering field.Therefore,it is very meaningful to break through the limitations of materials on 4D printing.In the metal laser 3D printing system,the laser will produce locally concentrated energy input,temperature gradient mechanism and subsequent plasticity,this usually leads to local residual stress in metal parts.Inspired by the deformation ability of thermal stress,combining thermal stress with 4D printing,studies the 4D printing method of structural transformation by thermal stress,and defines it as metallic 4D printing stimulated by laser thermal stress.The specific research contents of this paper are as follows:(1)Based on the macroscopic deformation characterization finite element simulation analysis of the sample,the relationship between the support distribution,laser scanning strategy,thermal stress distribution and the warping deformation of the sample was studied,and a metallic 4D printing method based on the laser thermal stress stimulate was developed.The influence mechanism of laser parameters(laser power,scanning speed,printing angle),support parameters(laser power,scanning speed,support thickness),and sample geometry(length,width,angle)on the shape changes of 4D printed metal samples stimulated by thermal stress was revealed.(2)Based on the support distribution design and the programming of laser scanning strategy,a 3D deformable structure design method based on 2D precursor model was proposed.so that the printed 2D precursor can be transformed into the expected 3D structure.Through the combination design of support distribution and laser scanning strategy,a 3D systems with various geometric structures was constructed,including bioinspired structures(flower,mimosa,butterfly,frog,etc.),regular geometric structures(rectangle,triangle,ring,etc.)and special structures(vortex,spiral,JLU,etc.).Finally,based on the finite element analysis software,the structural transformation process of the designed 3D structure from 2D to 3D in metallic 4D printing was analyzed and simulated,and the forming mechanism of the 2D to 3D structural transformation by laser stimulation was revealed.(3)By strategically inducing thermal stress in the manufacturing process,the biomimetic frog tongue structure was 4D printed and its structural transformation process from 2D to 3D was filmed using a high-speed camera,so as to make the specific process of laser thermal stress stimulating 3D deformation clearer.The application prospects of the technology in the field of mechanical processing were propose,including manufacturing manipulators that can generate bending behavior by laser stimulation and controlling the 3D shape of parts on demand by laser stimulation.(4)The influence of different specific laser scanning strategies on the structural transformation effect of 2D sample precursors in metallic 4D printing stimulated by laser thermal stress was studied.The influence mechanism of structural transformation effects of different laser scanning degrees,scanning sequences and scanning positions on the sample(Different bending degrees,bending sequences and bending postures generated by structures such as palms/mimosa)were revealed.Based on the analysis of the above three scanning strategies,the mechanism of the combination of scanning strategies(scanning degree + scanning sequence,scanning degree + scanning position,scanning sequence + scanning position,scanning degree + scanning sequence +scanning position)on the structural transformation of the sample was studied.The structural transformation effect of repeated scanning on the sample was studied,and its application prospects in the engineering field were explored.Finally,the influence of specific laser scanning strategies(scanning degree,scanning part)on the mechanical properties of 4D printed samples was studied.