Stress-intensity factors at the interface edge of a partially detached fibre

• Fibre debonding phenomenon is considered.
• Fibre–matrix relative sliding is quantified through a simple scalar function.
• Fibre–matrix detachment is modelled by fracture mechanics and shear lag approach.
• A simple mechanical model for the fibre–matrix interface is developed.
• Effects of fibre–matrix interface fracture energy on debonding is studied.

Fibre-reinforced composites (FRCs) are multiphase materials characterised by high engineering performances. However, some degrading effects in such materials (the loss of their bearing capacity, related to the matrix–fibre detaching phenomenon also known as debonding, fibre breaking, matrix cracking) must be carefully taken into account in the assessment of the FRC safety and durability. In the present paper, the fibre–matrix detaching phenomenon is examined from the fracture mechanics point of view. The stress singularity arising at the extremities of a perfectly bonded fibre is studied, and the related Stress-Intensity Factors (SIFs) are used to assess the detachment initiation up to the appearance of a debonded region at the two ends of the fibre. The circular shape boundary line representing the edge of the debonded region is analysed as a 3D crack front located between two different materials, and the Stress-Intensity Factors are determined for different remote loadings and composite characteristics.