Arresting unstable compressive crack growth in fibre reinforced polymer laminates – going beyond the ‘no-growth’ design dogma

• Crack-arrest feature for unstable compressive failure of fibre-reinforced composite. • Feature validation via mechanical testing and comparison to a suitable baseline. • Fractographic exploration of failure initiation and arrest mechanisms. • Successful, significant, and reproducible crack arrest. • Over one-third enhancement in ultimate failure strain. The design of fibre-reinforced composites is currently constrained by their poor performance under compression, compared to their tensile behaviour, especially when in-service damage is present. Accentuating this disparity is the absence of effective methods to safely control fracture propagation once unstable compressive failure initiates in a component. Consequently, composites are perceived as brittle and unsafe, restricting industry to a ‘no-damage growth’ design philosophy. Developing methods to tolerate compression crack growth, particularly in larger structures, would represent a significant advance towards fully realising the structural potential of composites. Thus, this study aims to enhance compressive response of fibre-reinforced structures by developing a concept for failure-tolerant components. This concept seeks to arrest unstable failures, compartmentalizing the loss of mechanical properties and extending structural performance following an initial failure. A ply-discontinuity feature is proposed, locally replacing 0° oriented plies with carefully selected off-axis ones. This feature effectively reflects and diverts the energy associated with compressive kink-band propagation while also modifying the laminate’s failure modes. As a result, the laminate successfully arrests rapidly growing cracks (propagating at ∼ 1 km/s) and increases the strain upon final element failure. To validate the proposed concept, test elements were designed and manufactured using IM7/8552 carbon-fibre-reinforced epoxy. Mechanical tests demonstrated the effectiveness of the feature, remarkably enhancing the strain tolerance upon final failure by over a third, compared to a suitable baseline. Fractography was employed to characterise the failure mechanisms, such as microbuckling and in-plane shear, and to deepen the understanding of the morphological aspects of the arrest feature.