Ramp-Wave Loading Technique Based On Additive Manufacturing Generalized Wave Impedance Gradient Flyer Numerical Simulation Study

Gradient functional materials are a new type of composite material in which two or more materials are composited and the composition and structure are continuously gradient.In the light gas gun experiment,the flying piece made of the wave impedance gradient functional material can generate a compression loading wave with a slowly rising front edge in the target after high-speed collision of the target material,and realize the oblique wave loading on the target material.In the preparation of wave impedance gradient flyers,the additive manufacturing technology uses a layer-by-layer layering of materials,mainly relying on computer-aided design data.Therefore,based on the metal additive manufacturing technology,this paper develops a new generalized wave impedance gradient flyer material through geometric design.The main research results of the thesis are as follows:(1)By performing quasi-static compression and dynamic uniaxial compression experiments on GP1 stainless steel material in MTS810 universal testing machine and SHPB pressure bar,the stress-strain curves at different strain rates are obtained.The constitutive model parameters of the GP1 stainless steel Johnson-Cook constitutive model are fitted to provide a constitutive model for the numerical simulation of generalized wave impedance gradient flyers.(2)Based on the wave propagation characteristics of the variable cross-section bar,the "needle-bed" and "cone-hole" generalized wave impedance gradient flyers are designed.The SPH algorithm in the LS-DYNA simulation software is used for "needle bed shape" and "cone shape".The high-speed target process in the generalized wave impedance gradient flyer is numerically calculated.The key parameters of the structural design and the influence of the collision velocity on the loading waveform are discussed.As the impact speed of the "needle-bed" flyer increases,the rising edge time of the loading wave decreases,and the peak velocity increases.As the height of the quadruple pyramid of the "needle-bed" flyer increases,the rising edge of the loading wave increases.And the peak velocity is reduced;on the contrary,keeping the height of the quadrangular pyramid is constant,only changing the size of the cone angle,as the cone angle increases,the rising edge of the loading wave decreases,and the peak velocity increases;in order to obtain a relatively smooth For quasi-isentropic compression loading conditions,quadrangular frustums need to maintain sharpness.The peak value of the "cone-shaped" flyer loading wave is lower than that of the "needle bed shape",and the oblique wave loading effect is not as good as the "needle bed" flying piece.(3)Based on the numerical calculation results,the laser needle selection sintered metal additive manufacturing technology was used to prepare the "needle bed shape" and "cone hole shape" generalized impedance gradient flyer samples,and the target experiment was carried out on the first stage gas gun.The time-history curve of the free surface velocity of the target plate is presented,and the waveform exhibits the oblique wave loading characteristics.The results are compared with the calculated results.The two trends are basically the same,which verifies the feasibility and numerical simulation of the design of two generalized wave impedance gradient flyers.The reliability of the results.(4)Based on the additive manufacturing technology,a "foam hole shape" generalized wave impedance gradient flyer was designed,and the numerical simulation of the "foam hole shape" flyer was focused on the impact velocity and pore size and porosity of the flyer.And the effect of target thickness on ramp loading.The higher the target speed is,the longer the rising time of the front surface of the target free surface wave array is,and the higher the peak velocity is.The hole diameter is changed only.The larger the aperture is,the smaller the peak velocity of the target surface is,and the wavefront in the target plate is smaller.The rise time of the leading edge is also correspondingly extended;in the range of small aperture,changing the number of holes has little effect on the rise time of the target wavefront and the peak of the free surface velocity.In a certain range of target thickness,the wave-wave impedance gradient flyers hit the target plate and all are oblique wave compression waves,and these waveforms may vary with the thickness of the target plate.These influence laws provide guidance for the design and application of generalized wave impedance gradient flyers.