Mechanical properties, hysteretic behavior, and healing efficiency of a bio-based thermoplastic composite leaf spring

The growing demand for automotive lightweighting and eco-efficient manufacturing calls for high-performance structural composites that also offer reparability. This study introduces a repairable composite leaf spring made from a bio-based thermoplastic polyamide (PA56), leveraging its intrinsic thermal repair capability to enable damage recovery through hot-pressing. A rapid hot-press forming process was developed by integrating Classical Lamination Theory (CLT) with Finite Element Analysis (FEA) for stiffness prediction, supported by experimental validation. This approach reduced processing time by 90% compared to conventional thermosets, implying a significant potential for reducing manufacturing energy consumption. The resulting leaf springs retained 93.3% of the quasi-static stiffness and 83.5% of the strength of epoxy-based counterparts. Regarding rate-dependent response, they exhibited a 58% higher strain rate sensitivity and reduced hysteretic energy dissipation to just one-sixth of that observed in epoxy springs at high rates. Following hot-press repair, the springs recovered 94.3% of stiffness, 88% of strength, 80% of strain rate sensitivity, and nearly identical hysteretic behavior. This work demonstrates the potential of bio-thermoplastics in creating a repairable and more sustainable pathway for next-generation automotive composite structures.