Materials and Structure

Three modes of crack formation due to transverse loading are illustrated.
In (a) the bonding between the fiber and the matrix fails and the crack results from the stress induced delamination.

If the matrix is weaker in tension than the matrix-fiber bond, the stress concentration near the fiber may initiate a matrix crack (b).

The fiber may also fail under transverse loading, and (c) shows such a crack propagating into the matrix from the fiber.

From: Hull, "Introduction to Composite Materials," Cambridge (1992)