Multiaxial experiments with radial loading paths on a polymeric foam

Abstract

Cellular materials such as polymeric foams in particular have been widely studied under uniaxial loading conditions. Many experimental studies have been focusing recently, however, on the responses of these foams to multiaxial loads. In the present study, a novel experimental hexapod device was used to perform combined uniaxial compression and simple shear tests. Using a post-processing method of analysis which can be used to study elementary mechanical behavior, the authors show the occurrence of non-proportional stress paths in the material under investigation although proportional kinematic paths were imposed. A failure limit criterion is presented for use with the foam of interest. The results of the present analysis yield useful information for meeting our future objective, namely to develop a numerical model for simulating multiaxial loading conditions.

On the determination of viscoelastic properties of EPP foam in dependence on pre-strain and loading direction

“…Inserting the above acquired values for E* and G*, equation ( 1) yields a plausible value for ν* of approximately 0.35, which is slightly higher than the values published by Morton et al and Donnard et al 7,11 In these works, it is further highlighted that the Poisson's ratio of EPP gradually increases under tension, while it decreases and approaches zero under compression. The relative change of the measured moduli in this work supports this assumption as the decrease of the compressive modulus in the nonlinear regime is more pronounced compared to the tensile modulus.…”

“…Cell wall bending and collapsing are considered to be the main drivers for the onset of nonlinear behavior. As these appear much earlier under compression than under tension and shear [8][9][10][11] different LVR limts are observed.…”

“…10 Under tension and shear loading, completely different microscopic deformation mechanisms are activated. 8,10,11 While collapsing and bending are less important in these directions, intra-or inter-bead fracture may occur in dependence on the degree of fusion. 12 Due to frequent use of bead foams in crash structures and the relevance of their energy absorption behavior, [1][2][3] experimental analyses often focus on the stress-strain behavior at large compressive deformations.…”

“…Under tension and shear loading, completely different microscopic deformation mechanisms are activated. 8,10,11 While collapsing and bending are less important in these directions, intra- or inter-bead fracture may occur in dependence on the degree of fusion. 12…”

A new method for the study of parabolic impact of foam-core sandwich panels

“…A comparison of the shear response of EPP foam showed that the shear stiffness in the LS-Dyna model using MAT83 was lower than the experimental curves and that shear rupture was not captured in the model. Other material models such as the constitutive law proposed by Deshpande and Fleck which models the foam core as an isotropic porous solid with a principal stress-yield surface under compression and a quadratic-yield surface elsewhere in the stress space [33] may produce better comparison with experiments [34]. A physically based, multi-scale modelling approach incorporating stochastic aspects of the foam microstructure can also provide detailed predictions of all aspects of the mechanical response of foams but such a model doesn't exist presently [35] and the implementation of a comprehensive material law for the simulation of foams is left as a topic for a future study.…”