Foam modeling including pore gas interaction for crashworthiness analysis

Licentiate thesis, 2006

Foams are used in vehicles for three main functions: enhancing comfort, e.g. soft foams used in seats cushions, energy absorbtion, e.g. in bumpers and interior panels, and structural stiffening, e.g. as filling material for thin sheet metal beams. This thesis focuses on constitutive modeling of such foams for computational crash simulation. The modeling approach is phenomenological and the foam is regarded as a two-phase material, a mixture of solid phase and pore gas, within the Theory of Porous Media (TPM). The solid skeleton is described by an elasto-viscoplastic model, including material hardening during compaction and loading-rate dependent response. Regarding the contribution to the response from the gas phase, the ideal gas law is adopted and the interaction between the phases is modeled in terms of a non-linear Darcy law, where the permeability is deformation dependent. In modeling the response of the two-phase material, we end up with a coupled finite element problem and a staggered solution technique is suggested for resolving this. Both a single-phase model, and the coupled two-phase model are implemented in the finite element code LS-DYNA. For the single-phase model, the material parameters are calibrated to fit experimental data found in the literature, and the response in a dynamic impact simulation is compared to test data. For the coupled model, we have utilized the thermal solver in LS-DYNA to model the gas flow, and a study of the influence of the permeability is included.