Impact Resistance Of Aluminum Foam Sandwich Structure

Aluminum foam sandwich structure is characterized by light weight,high specific strength,high specific stiffness.Moreover,it has superior shock wave scattering capability since it undergoes large strain with nearly constant stress when subjected to quasi-static or dynamic compression.The superior shock mitigation capacity of aluminum foam sandwich structure allows it used as energy absorption components in fields such as transportation,aerospace and military.Therefore,it is significant to study mechanical behaviors of aluminum foam sandwich structure subjected to impacts.However,researches on mechanical properties of aluminum foam sandwich structure is mainly focused on static or low-velocity impact while few studies on the performance of aluminum foam sandwich under high-velocity impact are available.Thus,this paper concerns the performance of aluminum foam sandwich structure inmedium and high velocity impacts.In this work,impact tests on aluminum foam sandwich structures with impact velocity in 200?500m/s was conducted using a one stage gas gun system modified from hopkinson pressure bar.To qualitatively characterize the stress attenuation capacity of aluminum foam,PVDF(Polyvinylidene Fluoride)transducers were introduced.The effects of panel thickness,panel material and impact velocity were discussed in terms of the PVDF results and deformation/failure modes of the targets.The main results are as follows:(1)Stress histories were obtained using PVDF transducers,verifying the feasibility of PVDF transducers used to measure stress in medium and high velocity impacts.(2)Effects of panel thickness,panel material and impact velocity on the impact resistance of aluminum foam sandwich structure were investigated.The results showed that both increasing panel thickness and choosing panel material with higher strength can contribute to expanding the damage area and make more foams beneath the panel participate in energy dissipation.Higher impact velocity can also benefit energy absorption owing to the strain rate effect of aluminum foam used in this work.(3)In aluminum foam sandwich structure,the acoustic impedance mismatch between the panel and foam significantly reduced shock waves transmitted into foam.within the aluminum foam,foams at different position possessed different energy absorption mechanisms,such as compressive bending,brittle fracture,cell wall cracking/shearing and friction between fracture walls.Besides,aluminum foam is usually regarded as a composite of the aluminum matrix and gas.Thus,shock waves transmitted into foams also go through reflections on interface between aluminum matrix and gas,thereby dispersing shock waves.(4)Core arrangement also have a significant effect on stress attenuation within aluminum foam core.When the total thickness was identical,multi-layered aluminum foam outperformed that of a single layer in terms of the peak stress attenuation ratio.Compared to foam core with a single layer,deformation/failure modes became more complex,the introduced friction between the foam layers was useful for extending the damage area of foams.