Effects of constrained foam deformation in aluminum tubes under quasi-static and dynamic axial compression loading.

摘要

The primary objective of this research is to investigate the effects of constrained foam deformation in aluminum tubes under quasi-static and dynamic axial compression loading. Computational models will be developed to correctly predict quasi-static and dynamic experimental results (the instantaneous crushing force, mean crushing force, fold formation).;In this research, we have observed that specific energy absorption (SEA) for foam-filled circular aluminum tube can be increased significantly by utilizing initiators to deform the foam inside aluminum tube under the effect of constraint of the tube wall.;The experimental aspects include rigid polyurethane (PU) foam material manufacturing, foam selection for energy absorption applications and mass management, specimens preparation, and quasi-static and dynamic experimental setup, have been presented.;Experimental results from quasi-static and dynamic tests for empty cylindrical shells, foam-filled without initiators, and foam-filled with initiators have been presented. The SEA from the experimental results will be analyzed, and a comparison between the results has been discussed.;The constitutive model for elastoplastic porous materials has been developed. Using the geometric interpolation of the yield surface, the hydrostatic stresses have been related to the uniaxial stresses. The closed form of elastic-plastic stiffness matrix for general elastoplastic porous material has been derived. Assuming no change in the shape of the yield surface during the hardening (or softening), general hardening law for the model has been developed, and special cases related to metallic foams, soils, and crushable (rigid) polyurethane (PU) foam material have been discussed.;Since the closed-form solution would be represented by complicated formulae that do not increase insight into the problem. The constitutive model has been evaluated incrementally using numerical solutions. Incrementally, numerical solution by the radial return mapping using the implicit backward Euler scheme method has been described. The model has been implemented into the finite element (FE) ABAQUS code as a user material.;A simple theoretical approach for foam-filled thin-walled with initiators, subjected to axial loading conditions has been derived. The theoretical approach is able to predict the initial linear-elastic behavior, the average stress of the constrained foam, the pre-elastic deformation of the cylindrical shell, the peak forces, and the average load for the foam and the tube.;Finally, a numerical solution using the finite element analysis (FEA) approach has been used to predict the experimental results made for empty tube, foam-filled without initiators, and foam-filled with initiators, subjected to quasi-static and dynamic axial compression loading conditions. The explicit dynamic procedure will be used to solve two transient dynamic response calculations and quasi-static simulation, which involving complex nonlinear effects (most commonly problems involving complex contact conditions like 3-D self-contact).