Slow-growth damage tolerance for fatigue after impact in FRP composites: Why current research won’t get us there

Impact damage in CFRP structures is currently managed using the ‘no-growth’ concept, meaning that damage is not allowed to grow under fatigue loading. This requires that stresses in the material are kept below the fatigue limit, imposing a significant weight penalty. A ‘slow-growth’ concept would allow more efficient structural designs, but several knowledge gaps need to be addressed before this is possible. These gaps exist in three main areas: (1) damage characterisation, (2) fatigue driven delamination growth after impact, and (3) final failure of impacted laminates. The paper highlights open questions and the shortcomings of current research in addressing them, and suggests avenues for future research.