Transverse crack patterns in cross-ply laminates from micromechanical analysis using Phase-Field fracture.

  • Macias, Juan (Universidade do Porto)
  • Arteiro, Albertino (Universidade do Porto)
  • Otero, Fermín (Universitat Politècnica de Catalunya)
  • Camanho, Pedro (Universidade do Porto)
  • García, Israel (Universidad de Sevilla)
  • Reinoso, Jose (Universidad de Sevilla)

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Transverse fracture patterns in cross-ply laminates have been extensively studied, initially from a purely experimental point of view, but later on using analytical approaches and numerical tools. The main focus of these studies is to understand the relation between the critical deformation for crack initiation, the formation of different crack patterns and crack densities with respect to certain layup parameters such as the layup configuration, ply thickness and material properties. The majority of the work done so far to understand phenomena such as the formation of oblique cracks and evolution of crack densities has been performed almost exclusively from a meso-scale perspective, where individual plies are considered anisotropic and homogeneous, and the interaction between them is defined either as a perfect bond or as a cohesive region. The current work provides additional insight into the formation and evolution of transverse crack patterns from a micro-mechanical perspective using the Phase-Field method to capture matrix fracture and cohesive interfaces to model fibre-matrix decohesion. It was found that phenomena such as the in-situ effect and its relation with higher crack densities, as well as the formation of oblique crack patterns are deeply related with the thickness of the inner transverse ply as it is commonly known, but also with the difference in stiffness with respect to the outer supporting layers and specially with the size of the resin rich region where the homogeneous assumption breaks down. It is shown that the homogeneous assumption when there are artificial sharp crack surfaces leads to singularities in the stress analysis that may end up hiding the true zones of fracture propagation and potential areas prone to fracture initiation. This is particularly important for the study of oblique cracks, which unlike what is commonly believed, do not originate from the ply interface but from the interface decohesion on the fibres in the highly stressed regions surrounding the transverse crack.