Study On Dynamic Mechanical Properties Of Polypropylene Foam Material

The protective helmet cushion is an important part of the combat protective helmet.It is generally composed of foamed polymer materials.It uses its low yield platform stress,large compaction strain and excellent buffer energy absorption performance to realize the impact of explosive waves and high-speed impacts.Attenuation and dissipation of damaging elements such as stress waves,thereby forming effective protection for personnel’s brain tissue.However,the research on the large deformation dynamic mechanical properties and constitutive model of foamed polymers under impact load is still relatively weak.Protective performance such as high-speed impact is far from enough.In this context,this paper mainly conducts the following researches:First,three different densities（23.80kg/m³,35.46 kg/m³ and 63.64 kg/m³）of expanded polypropylene（EPP）were carried out in 10^-5s^-1,10^-4s^-1,10^-3s^-1,10^-2s^-1 and 10^-1s^-1,quasi-static compression tests at 5 strain rates,obtained stress-strain curves and established main mechanical performance parameters such as elastic modulus,yield stress,compaction strain and energy absorption efficiency.And established an empirical equation.The effects of strain rate and relative density on the resilience performance of materials after quasi-static compression are analyzed.A large-strain（maximum engineering strain>80%）SHPB impact test of foamed polypropylene was carried out.The ultra-long SHPB equipment and waveform shaping were designed and processed,and the impact test that single-pulse loading could reach the compaction stage was realized,and the full stress-strain curve,yield platform stress,compaction strain and energy absorption were obtained at a strain rate of 1000s-1.Efficiency and other parameters,an empirical equation that comprehensively considers the effects of strain rate and relative density is established,and a phenomenological constitutive model with a wide strain rate domain(10^-5s^-1-10³s^-1)is established.The constitutive model of foam materials commonly used in DYNA software is analyzed.Combined with experimental research,the material model MAT57（LOW＿DENSITY＿FOAM）is selected as the constitutive model of foamed polypropylene material,and the SHPB impact test simulation is carried out.The simulation results are in good agreement with the test results.Well,the validity of the model is verified.The passive confining pressure SHPB test of foamed polypropylene material was carried out,and the constitutive relation of passive confining pressure was obtained.The research results show that the foamed polypropylene material has a pressure effect under high strain rate,and the confining pressure can effectively improve its axial strength.Numerical simulation of passive confining pressure SHPB test is carried out,and the simulation results also prove this conclusion.Finally,the experimental study on the anti-explosive wave buffer energy absorption of the foamed polypropylene sheet was carried out,and the shock wave pressures of the blasting face and the back blasting face of the foamed polypropylene sheet with different proportional distances were measured,and the foamed polypropylene under one-dimensional strain conditions was obtained.The cushioning and energy-absorbing properties of the material provide a technical reference for the design of explosion-proof helmets.