Foam modeling including pore gas interaction for crashworthiness analysis
Abstract: 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 interiorpanels, and structural stiffening, e.g. as filling material for thin sheet metal beams.This thesis focuses on constitutive modeling of such foams for computationalcrash simulation.The modeling approach is phenomenological and the foam is regarded as atwo-phase material, a mixture of solid phase and pore gas, within the Theory ofPorous Media (TPM). The solid skeleton is described by an elasto-viscoplasticmodel, including material hardening during compaction and loading-rate dependentresponse. Regarding the contribution to the response from the gas phase,the ideal gas law is adopted and the interaction between the phases is modeledin 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 coupledfinite element problem and a staggered solution technique is suggested forresolving this. Both a single-phase model, and the coupled two-phase model areimplemented 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 testdata. For the coupled model, we have utilized the thermal solver in LS-DYNA tomodel the gas flow, and a study of the influence of the permeability is included.
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