Experimental investigation and modelling of strain- induced crystallisation in natural rubber in different ageing conditions

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Strain-induced crystallisation (SIC) in natural rubber (NR) is considered to be the main source of its outstanding properties such as self-reinforcement and high tear resistance, especially when NR is further stiffened by nanoparticle fillers. For this reason, NR is often used in vehicle tires, vibration isolators, pipes and engine mounts. This fundamental project is not about examining, modeling and simulation of parts or structures, but of material properties. As SIC reduces the speed of crack propagation, the applications mentioned above serve only as a motivator for the project. The interdisciplinary SICX project has the following targets: (1) further investigations of the kinetics of SIC on different scales; (2) development of a physically based three-dimensional model, for the material behaviour of NR under SIC, which would be robust at large strain for various thermomechanical paths; (3) understanding and modelling the impact of environmental conditions on issues (1) and (2). The ultimate purpose of advanced materials science is the modelling of technical materials under real operating conditions, based on correctly identified physical mechanisms. This project is the first step on the way to an application in a three-dimensional finite element software. Hence, real parts and systems can then be modelled in future in order to predict their response under realistic loading conditions. Environmental conditions commonly lead to a degradation of elastomers. Besides thermal and thermo- oxidative ageing, there is fatigue caused by cyclic deformations or ageing due to the exposure to solvents and ultraviolet irradiation. All aspects are of enormous importance for practical applications but not all can be explored in this project. Therefore, the SICX project is focussed only on a limited number of environmental conditions and their interactions with SIC of NR; with the following three objectives: 1) Identification of the physical mechanisms associated with SIC, which have not been fully examined yet or remain partly controversial in the scientific community. 2) Quantification of the impact of the most important environmental conditions on SIC. 3) Collection of physically-based micro- and macroscopic experimental data suitable for continuum mechanical modelling of the behaviour of elastomers exhibiting SIC in real operating conditions.