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Session: Session 10: Structural integrity of composite laminates
Session starts: Wednesday 28 June, 09:00
Presentation starts: 09:20
Room: Theatre room: plenary

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Wenjie Tu (Department of Aerospace Structures & Materials, Faculty of Aerospace Engineering, Delft University of Technology)
John-Alan Pascoe (Department of Aerospace Structures & Materials, Faculty of Aerospace Engineering, Delft University of Technology)
René Alderliesten (Department of Aerospace Structures & Materials, Faculty of Aerospace Engineering, Delft University of Technology)

Abstract:
Delamination growth is a key damage mode threatening the structural integrity of fibre reinforced polymer composite structures. To guide design and damage management of composite structures, research efforts have been made to understand delamination behaviours and establish standardized evaluation methods based on mainly one-dimensional delamination tests. However, as most delamination growth in real structures will be planar, the question arises whether these approaches are adequate enough to evaluate planar delamination behaviour. Thus, the objective of this study was to better comprehend the physical mechanisms underlying the planar delamination behaviour and to inspire the development of a more reliable damage evaluation method for composite structures. A novel experimental method was developed to investigate the planar delamination behaviour under quasi-static out-of-plane loading. The planar central loaded split (PCLS) specimen was designed to investigate the planar delamination behaviour under mode II loading condition. By analysing digital image correlation (DIC) and C-scan data, the delamination progress was monitored. Acoustic emission (AE) system was used to capture the initiation of damage and to identify different damage types. In the oral presentation, planar delamination patterns of carbon fibre reinforced polymer (CFRP) composite panels and the underlying mechanisms will be illustrated. The planar delamination growth was found to be dependent on the stacking sequence and interface properties. Additionally, it was found that positioning a rubber mat between the indenter and the specimen prevented the occurrence of delaminations at undesired interfaces. The artificially embedded delamination propagated in the direction to which the fibre orientation of the layer above the crack interface was parallel, but migrated initially to an upper interface at the place where the fibre was perpendicular. Although the delamination propagated as the loading increased, a constant stiffening process due to in-plane stretching was discovered. Only when there were substantial matrix and surface cracks did significant stiffness degradation occur. The research results provide a clearer understanding of the mechanisms of planar delamination under out-of-plane loading. Now that a reliable test method has been established, qualitative and quantitative analysis based on fracture mechanics will be employed to establish a prediction model for planar delamination growth.