Damage deflection and subsequent damage diffusion in carbon–boron fibre hybrid composites under longitudinal compression

Carbon–boron fibre hybrid composites are claimed to possess outstanding properties under longitudinal compression, and are therefore extremely attractive for lightweight structures. However, no study exists on these materials yet; consequently, the reasons behind their performance and the mechanisms involved in their failure process remain unknown. In this work, we investigated the longitudinal compressive failure of carbon–boron fibre hybrid composites for the first time. To do so, we manufactured a tailored hybrid cross-ply plate and produced several small-scale single edge notched specimens. We tested the specimens using a micromechanical testing device. Our experiments reveal that boron fibres strongly interact with damage, favouring a hugely effective deflection mechanism, typically observed in biological materials like human cortical bone; to the best of our knowledge, such mechanism has never been observed in continuous fibre reinforced composites under longitudinal compression. Interestingly, such deflection mechanism promoted the appearance of diffused longitudinal compressive damage, another phenomenon that, to the best of our knowledge, has never been observed in any continuous fibre reinforced composite under longitudinal compression. Despite the presence of such diffused damage, the specimens were still able to carry further load, revealing a remarkable tolerance to compressive damage. This study provides a novel understanding of the failure behaviour under longitudinal compression of carbon–boron fibre hybrid composites, highlighting fundamental aspects that may explain the exceptional properties reported for these materials. Furthermore, the insight obtained from this work may prove fundamental in inspiring the design and development of novel bio-inspired materials and structures with outstanding mechanical properties. • Carbon–boron fibre-hybrid longitudinal compression failure mechanisms revealed. • Boron fibres promotes hugely effective damage deflection mechanisms seen in bone. • In turn, deflection promotes a never seen before damage diffusion phenomenon. • These mechanisms could inspire design of novel materials and structures.