Reinforcing Bus Living Space with Recycled Carbon Fibers from Expired Prepreg in the Aircraft Industry

Due to increasing mobility and energy conservation needs, improving bus and coach safety without adding weight is essential. Many crashes with fatal outcomes for vehicle occupants are associated with the rollover of the vehicle, revealing the structural weakness of the steel pillars between windows, which must resist high levels of bending during rollovers. This study aims to reinforce these pillars with expired carbon fiber prepreg from the aircraft industry, improving safety and reducing environmental waste. To manufacture the pillars, shot-blasted hollow S275 steel tubes with a side length of 25 mm and a thickness of 1.5 mm were used. Bidirectional GG600T woven carbon fiber, CF, and aircraft-grade recycled carbon fiber-reinforced plastic, rCFRP, prepreg M21EV/IMA/3 were used as composite reinforcements. The first composite was made from a CF weave using the rigid epoxy resin Sicomin^® 8500/Sicomin^® SD8601. The rCFRP composite was frayed, and a new composite was made with the same rigid epoxy resin. Both composites were joined to the steel tube using a tough structural adhesive (SikaPower^® 1277). A third composite was obtained using the frayed rCFRP and the structural adhesive as a polymer matrix. All composites were treated with an APPT (atmospheric-pressure plasma torch) before being joined to the steel pillar with the structural adhesive. The comparison of the three reinforcements showed that the steel reinforced with the recycled prepreg composite manufactured with the rigid adhesive performed best, with a 50% increase in specific bending strength and only a 32% increase in weight. It also absorbed 71% more energy, which shows that this novel option for upcycling can noticeably increase the crashworthiness of structures.