AIMETA 2017 - Proceedings of the XXIII Conference of the Italian Association of Theoretical and Applied Mechanics

Mechanical characterization and modeling of elastomers under different load conditions have attracted the interest of the scientific community in the last 50 years; despite the wide literature and the related scientific and industrial activity in this field, many different phenomena are to date not yet well understood. In order to fill in some of these gaps, a hybrid approach has been here used by integrating the use of forefront techniques like the Digital Image Correlation with mechanical testing machines able to perform non-standard biaxial tests in static and dynamic loading conditions. In a first part of the work, some components of a planar biaxial testing device (BiaxTester, developed by Coesfeld GmbH.) able to perform mechanical testing on elastomeric materials have been partially redesigned, in order to optimize reliability of the results obtained in terms of stress-strain curves. As shown, control of the boundary conditions through adequate optimization of the clamping system and of the specimen shape may lead in fact to more homogeneous strain fields, thus excluding, or at least reducing, edge effects such as shear strains or compressive phenomena around the clamps. Successively, the aforementioned system optimization led to investigate the arise of different phenomena connected to the Mullins effect in filled elastomers, which emerge as a consequence of the complex network interactions among the elastomeric matrix and the rigid reinforcement particles, finally resulting in a combination of stress softening, permanent set, hysteresis and induced anisotropy. The BiaxTester, together with the instruments of Digital Image Correlation and proper mechanical modeling strategies, have all shown to be invaluable instruments to control the actual stress and strain fields in complex loading conditions, so allowing to gain crucial information and new insights for predicting with high accuracy static and dynamic mechanical behaviors of elastomers.