Characterization of the torsional behavior of photosensitive polymer obtained by stereolithography

An experimental and numerical mixed method based on the torsion test with and without warping of cross sections has been developed in order to characterize the shear behavior of a polymer material obtained layer by layer from a photosensitive resin (CiBA SL5170) polymerized by laser beam by the stereolithography technique. In this article, first the stereolithography technique is briefly presented, as well as the torsion device with and without warping of cross sections. Experimental and numerical results in static torsion of the polymer SL5170 are presented: shear modulus and strength of the material. From test results, a modeling of the superposition ratio of tensile and torsion stresses is proposed. It shows that the torsion of beams is complex. Torsion stresses and the tensile stress owed to the warping of section are superposed. In small-deformations state, material behavior behaves in a linear elastic way; experimental and numerical results are quantitatively and qualitatively coherent and conform to predictions of the elastic torsion theory. From experimental analysis of fatigue and elastoplastic damage behavior of the polymer, a phenomenological approach of the isotropic damage model is proposed. Based on the thermodynamics of irreversible processes, this local approach starts from a variant of the Chaboche-Lemaître model coupling plasticity and damage. This formulation is justified by the necessity to take into account the real stress state produced in the polymer during the torsion test.