Long-term life prediction of wearable CFRP lower limb exoskeleton suit by applying a multi-scale FEA and time-temperature superposition

Abstract

This study explores the application of Carbon Fiber Reinforced Plastics (CFRP) in lightweight design for wearable exoskeleton suits, crucial for success in industrial settings. We aimed to predict the lifespan of the exoskeleton in terms of temperature and time rather than merely confirming its ability to withstand loads. The material's viscoelastic behavior, establishing a master curve for long-term creep compliance, was characterized using Dynamic Mechanical Analysis (DMA). We also performed mechanical tests under various temperature conditions to measure strength in the load and fiber directions and carried out statistical analysis. From the test results, we constructed the master curves considering the probability of predicting the long-term strength variations. Subsequently, A multi-scale model assessed the exoskeleton frame's failure, revealing no failures in the current model under given load conditions, with the highest failure index of 0.7 for matrix tensile failure. Combining the predicted long-term strength results, the lifespan prediction for matrix tensile failure under a reference temperature of 50 degrees C was approximately five years. The findings and methodology of this study can serve as a guide for predicting long-term performance and lifespan when applying CFRP to exoskeletons.