Dynamic Compressive Response of Polymeric Foams Subjected to Direct Impact Loading

摘要

Dynamic compressive response of rigid closed-cell polymeric foams underrnhigh strain rate direct impact loading conditions is investigated. The foam specimensrnare subjected to direct impact loading, while their deformation response is observedrnand quantified using high speed photography in conjunction with 3D digital imagerncorrelation. A modified single stage shock tube apparatus with an aluminum projectilernare used to generate the direct impact loading. The load applied on the specimen isrnmeasured using the load-cells at the other end of the specimen. The major challenge inrnhigh strain experiments, i.e. achieving equilibrium at the early stages of therndeformation, has been compensated by performing an inverse analysis and accountingrnfor the effect of inertia stresses into the analysis. The full-field accelerationrndistribution has first been calculated over the entire regions of interest. Then the inertiarnstresses are determined considering a one-dimensional equation of motion, andrnsuperimposed to the stress magnitude measured from the load-cells. The effects ofrnmaterial compressibility and the local change of density have also been included in thernanalysis. For this purpose, a mathematical model based on the principle ofrnconservation of mass is proposed which enables the calculation of the local materialrndensity as a function of initial density, local plastic strain and local plastic Poisson’srnratio. Finally, the dynamic stress-strain responses of the foam specimens are presentedrnas a function of foam density. The failure mechanisms as a function of foam densityrnand loading rate are discussed.