Impact properties of an end of life tires’ rubber. Numerical validation considering large strain and strain rate conditions

The objective of the authors is to demonstrate that the inclusion of renewed rubber from recycled end of life tires (ELT) can improve the performance of any structural system designed to dissipate impact energy. An interesting application would be its use in road safety barriers. This research starts with the rigorous characterization of the recycled material in order to include it in a viable numerical model. The authors presented, in a previous work (*), the experimental viscoelastic properties of recycled rubber, obtained under impact conditions. Bergström–Boyce (BB) nonlinear viscoelastic model was selected as the most suitable to fit the material behavior. This model is defined by nine material constants that are impossible to obtain, uniquely and directly, considering that only compression test results are available as input data. To overcome this challenge, optimization methods were applied resulting in as many sets of parameters as used optimization methods were considered and, moreover, remarkable differences between constants were observed. Solving this problem is the motivation of the present research: the validation of the optimization method by mean of the numerical evaluation of the obtained sets. The software considered for the numerical evaluation of impact tests (LS-DYNA®) had two slightly different implementations for the BB model: the original, based on the work published in 2009 by Dal & Kaliske and a more recent one implemented by Bergström, based on his works published in 1998 and 2000. This leads to a new question: which is the most appropriate implementation-optimization method for calibrating this material? This paper provides the answer to this question carrying out a complete comparative numerical analysis of all sets by means of explicit dynamics simulations. All calibrations, using the original LS-DYNA® implementation, were in perfect agreement with the experimental results. However, only one optimization method produced acceptable results for the most recent approach. A robust method to characterize recycled rubber from recycled tires using the Bergström–Boyce nonlinear viscoelastic model is presented, despite the experimental limitations (González-Vega et al. 2022).