Novel numerical approach for predicting the cyclic mechanical behaviour of stretchable resistive sensors based on PDMS/MWCNT micro-composites

In conventional mechanical characterisation of stretchable sensors including elastomers, changes in structural behaviour under cyclic loading have not been considered due to their viscoelastic behaviour. However, in practical wearable sensors, aimed at measuring repetitive motions within a short period of time, it is challenging to expect complete recovery of the sensor structure. Hence, it is required evaluating the mechanical behaviours of wearable sensors, taking into account cyclic loading conditions. To address this issue, this research presents a novel simulation method that accurately and simply predicts the cyclic tensile behaviour of stretchable sensors by considering both residual strain and stress softening induced by cyclic tension. This approach is useful as it can comprehensively accommodate changes in parameters such as materials and loading conditions (maximum tensile range, strain rate). A customised UMAT subroutine is developed to mimic cyclic behaviours of the sensors, and its reliability was validated by comparing with actual test data. Finite element simulations are conducted and predicted the actual cyclic tensile behaviour of PDMS/MWCNT micro-composite sensors with a high accuracy. Our findings provide valuable insights into the mechanical characteristic of stretchable sensors under cyclic tension and the reliable and practical simulation methods that can mimic the cyclic tensile behaviours.