An element test specimen with ply drops to study fatigue crack growth rates at geometry transitions

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Many advanced lightweight composite structures, such as wind turbine blades, have often a complicated shape, including variable thickness, to optimise aerodynamic efficiency and reduce weight. In composite structures, the varying thickness is achieved by terminating or dropping off plies (ply drops) [1,2]. Ply drops, however, result in material and geometrical discontinuities along composite structures, which induce stress concentrations. Cracks can be potentially initiated at these ply drop sites and evolve to delaminations which can propagate under service loading [3,4] severely reducing the load carrying capability of composite structures.

Tapering of laminates can be realised in many different ways [5] and several studies have been carried out to find the optimal ply drop design. Efficient ply drop designs, e.g. using chamfered plies [6], can significantly delay the occurrence of the delamination initiation. However, once a delamination initiates, then its growth rate under cyclic loading is critical for the integrity of the composite structure.

An element test specimen with several ply drops is used (see Fig. 1) in the present study to investigate damage initiation from a ply drop and its propagation under cyclic loading. The use of an element test specimen, which includes design features (ply drops), can replicate the damages modes of a real composite structure but at the same time more insight to the damage mechanisms can be gained.
Original languageEnglish
Publication date2019
Publication statusPublished - 2019
Event9th International Conference on Composites Testing and Model Identification - Luleå, Sweden
Duration: 27 May 201929 May 2019


Conference9th International Conference on Composites Testing and Model Identification
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ID: 181972220