Crashworthiness performances of an innovative cylindrical carbon fiber composite employing advanced fiber textile architectures

The following Master Thesis presents an experimental investigation into the crashworthiness performance of an innovative tri-axial braided Carbon Fiber Reinforced Composite (CFRC) cylinder under dynamic crushing loading. Two different test methods were employed, a drop tower test rig and a Very High-Speed (VHS) machine test, using both flat and conical impactors. The specimens were manufactured via a novel resin infusion process directly onto the mandrel utilized for the braided process, avoiding any dry fiber damage. The Specific Energy Absorption (SEA), peak load, steady-state crushing load, and Crushing Efficiency (CE) were evaluated and compared against literature data for each test configuration. The tri-axial braided architecture and the unidirectional stacked ply architecture have been compared to understand the possible differences under crashworthy performance and the different fracture mechanisms that characterize the phenomenon. It has been proven that braided shows a fracture mechanic where biaxial fiber breaking, and 0 degrees fiber kinking are highly emphasized. In contrast, in the unidirectional, the inter-ply delamination and 0 degrees fiber kinking is predominantly. Thus, the mechanical interlocking, characteristics of the woven textile such as braided, is an important feature that allows for high energy absorption. The flat impactor resulted in higher energy absorption due to fiber fragmentation but lower CE from a high initial peak load. Conversely, the conical impactor exhibited higher CE from smoother load initiation, but lower energy absorption dominated by friction and delamination mechanisms. Braided architecture has demonstrated SEA values consistent with the literature while providing higher CE than comparable unidirectional laminates, suggesting the suitability of this architecture for crashworthy applications. However, the contrasting impactors' results highlight the need to carefully consider prioritizing either high energy absorption or low peak acceleration for the specific design scenario.