Impact Mechanical Behavior Research Of UHMWPE/Aluminum Foam Sandwich Composites

With the design requirements for high survivability of structures and the concept of antiwar wound design,more and more attention has been paid to the development and impact resistance research of new emergency protective materials instead of traditional solid protective materials,and the optimization design of multi-material and multi-level innovative functional component structure has gradually become the pursuit goal of researchers.Aluminum foam is a brand-new strategic functional structural material with many excellent characteristics such as light weight,energy absorption and damping.It is widely used in engineering protection module to reduce the shock wave strength due to the long platform stress after initial failure when subjected to strong dynamic impact loads,but the load-bearing capacity of aluminum foam is limited to relatively low peak strength.Ultra-high molecular weight polyethylene(UHWMPE)fiber is as light as paper and hard as steel.It is an ideal bulletproof and anti-impact safety protection material which has strong energy absorption capacity and outstanding local impact resistance.Therefore,this paper proposes to combine the two materials into a special protective functional structure,which can exhibit excellent protective efficiency when it is subjected to impact loads to achieve the purpose of protecting the safety of buildings and personnel beyond a certain distance.Sandwich composite structure is generally composed of two layers of high-strength facesheets that bear bending loads and light-weight core materials that bear shear loads.It has typical characteristics of low weight,high stiffness and high strength.Therefore,in this paper,the sandwich composites with porous aluminum foam as core material and UHWMPE fiber reinforced composite as the facesheet were prepared by molding process.The effects of material parameters and impact parameters on the mechanical behavior of UHWMPE/aluminum foam sandwich composites under low-velocity impact and split Hopkinson pressure bar(SHPB)impact were investigated.The response characteristics and deformation failure mechanism of the sandwich composites under different dynamic impact loads are obtained,which provided the necessary experimental basis and design reference for the engineering application of the sandwich composites in the field of explosion impact protection.The research work of this paper mainly involves the following points:First,the types of adhesive used to prepare UHWMPE/aluminum foam sandwich composites were determined.The results of peel strength test show that the failure mode of the sample bonded by thermosetting adhesive is the failure of the bonding interface,while the sample bonded by hot melt adhesive exhibits typical adhesive cohesive failure,and its peel strength is much greater than the bonding strength of the thermosetting adhesive film.Therefore,it is recommended to use hot-melt adhesive film between the facesheet and the core material to prepare UHWMPE/aluminum foam sandwich composites taking into account the facesheet layup angle,core material ratio and front-to-back facesheet thickness ratio under a certain thickness.Second,on the basis of quasi-static compression test,the low-velocity impact properties of UHWMPE/aluminum foam sandwich composites were studied.Through the drop-impact test,it is found that the sandwich composites have undergone significant plastic deformation.The main energy absorption modes are local indentation,plastic deformation and delamination of the facesheet,densification and cracking of the core material,and debonding of the edge interface between the facesheet and the core material.The test results within the design parameters show that the anisotropic degree of the facesheet directly affects the mechanical response and damage propagation of the sandwich composites.The high core material ratio does not mean the improvement of the energy absorption ability and the extension of the impact response time of the sandwich composites,but the increase of the front-to-back facesheet thickness ratio can improve the maximum contact load of the sandwich composites and affect the cracking mode of the core material.The increase of impact energy makes the sandwich composites prone to produce peak force and rebound displacement with high growth rate.Third,the SHPB impact properties of UHWMPE/aluminum foam sandwich composites were studied.Under high strain rate impact,core compression is the main damage form of UHMWPE/aluminum foam sandwich composites,and the resulting non-uniform extrusion band corresponds to the oscillation phenomenon on the stress-strain curve.The test results within the design parameters show that the anisotropic degree of the facesheet affects the strain softening phenomenon of the sandwich composites.When the front-to-back facesheet thickness ratio is the lowest,it has the maximum peak stress,while with the increase of ratio,the deformation of sandwich composite is more uniform.The effect of core material ratio on the energy absorption capacity of sandwich composite is consistent with the conclusion of lowvelocity impact test,that is,the energy absorption capacity of sandwich composites with facesheet layup of [0/45/-45/90]s,core material ratio of 60% and front-to-back facesheet ratio of 1 is the strongest at the same strain rate,but far lower than the theoretical energy absorption limit value.The strain hardening behavior of sandwich composites is also observed only at the highest strain rate in the measurement range.By analyzing the strain rate effect,it is concluded that UHWMPE/aluminum foam sandwich composite is a rate-dependent material with moderate strain rate sensitivity.