Study On Shock Resistance Of Star Negative Poisson Ratio Structure

Foamed metal structure has important application value in the field of impact protection because of its excellent mechanical properties,good capacity of energy absorption and lightweight characteristics.In this paper,the mechanical properties of foamed metal structure with star structure under quasi-static compression,in-plane impact load and local impact load were studied by numerical simulation and experiment methods.The main research contents are as follows:(1)The static mechanical properties of star-honeycomb structural materials were studied.The finite element model of star-honeycomb structure under quasi-static compression was established.Considering the geometrical nonlinearity of star-honeycomb structure,the equivalent elastic modulus and Poisson's ratio of star-honeycomb structure under quasi-static compression were derived.It was found that the equivalent modulus of elasticity and the equivalent Poisson's ratio vary linearly with the equivalent strain.,the empirical coefficients was proposed and the functional expression of the equivalent Poisson's ratio for the equivalent strain was given.Finally,the effects of cell geometric parameters on the equivalent elastic modulus and Poisson's ratio of star-honeycomb structures were analyzed.(2)The dynamic mechanical behavior and influence law of star-honeycomb structure materials under in-plane impact were studied.The finite element model of star-honeycomb structure under in-plane impact was established,and the influences of impact velocity,thickness gradient and angle gradient on the deformation mode and energy absorption of star-honeycomb structure were analyzed.The simulation results showed that the deformation modes of the star-honeycomb structurecould be divided by the impact velocity,and the star-honeycomb structure with different thickness gradient and angle gradient has different deformation modes;the stress-strain curve of the star-honeycomb structure could be divided into four stages: elastic-zone,platform-zone,stress enhancement-zone and compact-zone.platform stress and the peak value of initial stress was affected by thickness gradient,angle gradient and impact velocity,in which the influence of the impact velocity was dominant,and the peak value of platform stress and initial stress changed linearly related to the square of impact velocity.(3)The impact dynamic characteristics of star-honeycomb structural members were studied.The impact of foam aluminum bullet on a sandwich beam was simulated by simulating the impact load at high velocity.The impact of foam core on the sandwich beam was studied.The influence of the thickness of core layer on the dynamic impact performance of sandwich structure was analyzed.The deformation process of foam aluminum bullet impacting sandwich beam was recorded by high-speed photography,and the deformation process of backplane was recorded by DIC.The experimental results show that there were different failure modes of the sandwich beam panel,core layer and backplane.The thickness of the core layer has a significant effect on the deformation of the sandwich beam structure,and the deflection of the sandwich beam has a linear relationship with the initial velocity of the aluminum foam.(4)The numerical simulation method was used for the research on the influenses factors of star-honeycomb structure under impact load.The effects of initial velocity,core thickness and thickness of aluminum foam on the deformation and energy absorption of star shaped sandwich beams were analyzed.The results show that the deflection of the sandwich beam has a linear relationship with the initial velocity of the foam aluminum bullet and the thickness of the core layer;The deflection of the sandwich backing-plate would be affected by the thickness distribution of the panel and the backing plate;the energy absorption of the sandwich beam structure was linearly related to the square of the initial velocity of the aluminum foam projectile;The energy absorption of the sandwich beam structure was suppressed by the thickness of the panel and the thickness of the core layer.