Multiaxial creep of transversely isotropic foams

Based on the method of the geometric stretch, the elongated tetrakaidecahedron and Voronoi models in the rise direction have been established to investigate the multiaxial creep behavior of approximately transversely isotropic open-cell foams. A stretch factor R (the ratio of the cell length in the rise direction to that in the transverse direction) is introduced to quantificationally characterize the degree of transverse isotropy. Uniaxial simulation results indicate that, for the open-cell foams, the relative density has significant influence on the secondary creep rate and the effects of the microstructure cannot be ignored. Additionally, a modified phenomenological model is proposed to predict the multiaxial secondary creep rate of transversely isotropic foams, and the corresponding material constants are determined as a function of the stretch factor R by modifying the theoretical equations or fitting the FEA results. Then, the capability of the modified model is examined by simulating the creep behavior under axisymmetric loading. The simulation results indicate that the modified phenomenological model can give a good description of the uniaxial/multiaxial creep response of the transversely isotropic foams.