Characterization of free edge effects: influence of mechanical properties,microstructure and structure effects

Abstract

The elastic property mismatch between plies with different orientations induces stress concentrations near free edges. This free edge effect can cause early delamination of composite structures. Laminates with 15° and –15° plies are studied experimentally to highlight the free-edge effect and the induced micromechanism damage. Full field measurements under tensile loading are performed at macroscopic and mesoscopic scales on edges of the sample. Results show displacement gradients and strain concentrations near interlaminar interfaces. Residual displacement gradients are measured after unloading, which highlights local damage at interlaminar interfaces. Observations at the microscopic scale show that cracks appear at fibre/matrix interfaces and propagate between adjacent fibres along interlaminar interfaces. A comparison of the results obtained on different composites highlights the influence of mechanical properties and material microstructure on edge effects. The study of samples with dropped plies highlights the influence of the combination of both geometric and material singularities on edge effects.

Keywords

Laminated structure polymer matrix composite free-edge effect

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