Structural characterisation and failure mechanisms of high-performance marine stringers in out-of-plane bending loads

Hat stringers are structural components that stiffen and strengthen composite hull panels of high-performance racing yachts. The failure mechanisms of stringer structures are complex, and the relationships between geometric parameters and failure modes are not well understood. This is due to a lack of experimental validation resulting from the cost and complexity in experimentally testing as-designed and in-service load cases. This leads to the reliance on experiential knowledge and coupon data. Experiments based on a 3-point bend provide an alternate method to the testing of full panels to determine structural behaviour and failure mechanisms This can be used to validate designs and better inform design choices. In this work, the structural performance of shear- and bending-dominated marine omega stringer structures are characterised experimentally and numerically under 3-point bending to understand strain states under load, failure mechanisms, and the validity of coupon data when designing complex composite structures. Strain state predictions from the numerical model are well-validated at proof loads, while comparisons at failure are complicated by stochastic laminate defects, geometric features, and discrepancies in predicting based on coupon data. The results of this study highlight the differences between as-designed and actual strengths in marine stringer structures.