Thin ply carbon/glass hybrid laminates to activate new damage mechanisms under indentation

Fotouhi, M. and Jalalvand, M. and Prato, A. and Wisnom, M. R.; (2020) Thin ply carbon/glass hybrid laminates to activate new damage mechanisms under indentation. In: 18 European Conference on Composite Materials (ECCM 18). European Conference on Composite Materials, ECCM, GRC.

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Low velocity impacts on composite laminates can cause a significant amount of delamination that is often referred to as barely visible impact damage (BVID). This damage can cause significant degradation of structural properties, especially the compressive strength after impact. The aim of this work was to utilise thin ply carbon/glass hybrid laminates to activate new types of damage mechanisms under indentation (quasi-static impact) that are more gradual and easier to detect. Therefore, 3 different types of hybrid composite plates fabricated from novel hybrid architectures of thin ply high modulus carbon (HS40) and standard thickness S-glass laminates were investigated. For comparison, a laminate containing only S-glass plies was investigated as well. The investigated specimens were interrupted at different load-levels and a detailed assessment of the damage evolution was carried out using X-ray Computed Tomography (CT). For all the hybrid configurations, a larger damage area was observed mostly under the indenter and the delaminations were smaller in the middle plies compared to the upper plies. In contrast, for the Glass laminates the delaminations were larger in the middle plies compared to the upper plies. For the hybrid laminates, the percentage of the first load drop in the global load-displacement curves was lower whereas the percentage of the stiffness reduction after the first load drop was higher, compared to the Glass laminate. Overall the hybrid results showed some different damage mechanisms, i.e. carbon ply fibre fracture and delamination under the indenter, with a gradual failure behaviour and less damage to the inner layers. The degradation mechanisms were visually detectable from the indented face from the early stage of the loading for some of the hybrid configurations, which can act as impact damage indicator.