Study On Impact Mechanical Response And Failure Mechanism Of High-strength Closed Cell Aluminum Foam

Closed cell aluminum foam highlights its excellent energy absorption characteristics and lightweight structure,so as to been taken as good structural protections from collision and shock,and applied already in some fields.In view of its severe working conditions and performance requirements,it is studied for the dynamic mechanical response of a high-strength aluminum foam directly prepared by the low-cost foaming method,as well as the one of its composites.The mechanical properties of closed cell aluminum and its sandwich composite under low speed and high speed are studied by using separate Hopkinson pressure bar,high-speed camera system and drop hammer tester,the failure mechanism and energy dissipation mechanism under different working conditions were revealed,and the residual strength of closed cell aluminum foam after low speed impact was predicted.The main results are as follows:（1）Under high-speed impact,closed cell aluminum foam shows obvious strain hardening and strain rate strengthening effects,but both weaken with the increase of strain rate.The closed cell aluminum foam not only has strain rate effect,but also has obvious temperature softening effect.The strain rate effect and temperature softening effect synergistically affect the mechanical properties of aluminum foam.（2）In the range of 150 s^-1～650 s^-1strain rate,the deformation mode of closed cell aluminum foam goes through three different stages:quasi-static deformation mode,transition deformation mode and dynamic deformation mode.The degree of localization of deformation increases successively,which is the reason for the material exhibits structural brittleness and the main reason why the strain rate effect weakens with the increase of strain rate.（3）The energy absorption of closed cell aluminum foam increases with the increase of strain rate in the range of 150 s^-1to 650 s^-1.But its energy absorption efficiency is basically independent of strain rate.The deformation of its meso-structure also breaks through the loading condition of uniaxial compression and presents a multi-directional plastic deformation mode,resulting in multi-point fracture in the structure and providing more mesoscopic mechanism for energy absorption.（4）Under low velocity impact,the overall damage degree of closed cell aluminum foam has a positive linear correlation with impact energy.At the same time,the deformation of aluminum foam is obviously localized,showing a layer by layer collapse mode.Residual strength after damage is negatively correlated with impact energy.The critical condition of material complete failure can be predicted by using two-parameter Weibull distribution function.（5）Aluminum foam sandwich composite,showing a certain strain rate strengthening effect;The energy absorption mechanism is mainly due to the deformation and fracture of aluminum foam sandwich layer,and the plastic deformation of back plate also contributes to the energy absorption.The average residual strength decreases with the increase of impact energy.