LFT-D Composite Spare Wheel Well for Automotive Body-in-White: Achieving 35% Mass Reduction

Thermoplastic composites offer substantial lightweighting potential for body-in-white (BIW). However, the application of long-fibre-reinforced thermoplastic direct processing (LFT-D) to deep-drawn rear-body parts remains largely unexplored. This work presents the first documented LFT-D glass-fibre/polypropylene spare wheel well for a production electric vehicle, validated under a full vehicle-level durability programme. Fibre orientation was characterised by X-ray computed tomography, and both isotropic and orthotropic finite element models were built. Prototypes passed six component-level validation tests: stiffness, constrained modal, thermal cycling, low-temperature impact, stone impact, and a 7000 km road simulation; the orthotropic model, validated against these tests, reduced the first natural frequency prediction error to 3.9%. No structural damage occurred in any test. The composite part achieved 35% mass saving at component level and 54% at system level versus the steel assembly. Adding up to 20 wt% regrind retained >89% of virgin tensile strength (95% confidence interval [CI] lower bound: 89.2%) and >92% of impact strength, and cradle-to-gate CO2 emissions dropped by 42%. These results show that LFT-D can be applied to large, structurally critical BIW components, delivering both lightweighting and closed-loop recyclability for electric vehicles.