Towards understanding residual strength and damage evolution in damaged composite laminates

Fibre reinforced polymer composites have found increasing use in aircraft structures. This means that fleet managers need damage assessment tools for such materials, in order to decide on appropriate sustainment strategies. Developing such tools is hindered by the difficulty of generalising from lab tests to predict the behaviour of full-scale structures. A more focussed research effort is needed to address the knowledge gaps that prevent such generalisations. This paper highlights the limitations of current non-destructive inspection techniques, and how this can lead to misinterpretation of experimental results. Furthermore, it discusses differences between coupons and full-scale structures caused by 1D vs 2D delamination growth and the effects of lay-up. New test methods to deal with these issues are discussed and some preliminary results are presented. Finally, the paper discusses the prediction of residual strength and the difficulties of determining a suitable end-point for damage propagation analyses. While the residual strength in the presence of a given damage can be accurately modelled for small components, if sufficiently computational resources are available, further development is needed to develop tools that can be implemented for sustainment of operational aircraft.