Deformation And Damage Of Porous Aluminum Under High Stain-rate Loading

Plate impact experiments are conducted to study the compaction and spall properties of 5%-porosity aluminum.Velocity histories of the rear free surface of samples are measured with Doppler pin system(DPS),and the Hugoniot elastic lifit(HEL)and spall strengths are derived.The scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),and x-ray computed tomography(XCT)are used to characterize 2-dimensional and 3-dimensional microstructures.Based on the experimental data,we obtained the follow conclusion:Results show that the HEL depends on both the sample thickness and impact velocity,but it eventually approaches a constant when the thickness of sample and impact velocity goes to a limit value.The spall strength increases with the increase of peak stress due to compaction-induced densification.The initial voids in the material are collapsed by the shock wave when the peak stress increases to some value,which leads to the change of damage and fracture mechanism from brittle fracture to ductile damage.With the lower speed impact,the microvoids,as the nucleation points in the material,will grow along the boundary between particles,which is the reason why the fracture is brittle.With the increasing of impact speed,the void on the boundary will nucleates and grows at random,which leads to ductile damage.This is also responsible for a distinct decrease in the reacceleration and damage extent at the highest impact velocities.In spallation zones,the bigger voids formed due to tensile stress lead to obvious shear and tension localizations,and consequently a wavy fracture surface.It is the first time to preform 3-dimensional pore-topology analyses on porous aluminum.A lot of information about damage mechanisms,such as size distribution,orientation,shape and connectivity of pores,are obtained.