Stress–strain behavior in uniaxial compression of polymer gel beads

Abstract A method for carrying out mechanical testing on spherical microparticles (Versabeads™) has been evaluated using an incompressible viscoelastic finite element model. The mechanical test is based on the compression of a single bead from which stress–strain data are obtained. Simulations based on the finite element model are used to investigate whether or not an apparent elastic modulus found as the slope of the initial close to linear stress–strain curve can be related to the real elastic modulus. The numerical results indicate that the apparent modulus is in fact related to the elastic shear modulus and that the relation E app ≈ 4 G can be used to obtain the shear modulus from the mechanical test. These results, however, only apply for purely elastic beads. The finite element solution has also been compared to the Hertz's expression relating axial displacement and compression force. Good agreement with the Hertz's expression is obtained at axial displacements below 10% and fit of the Hertz's expression to simulated force–displacement curves leads to a Hertz's modulus that is equal to 4 G. This is expected for incompressible materials. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3037–3047, 2006