Composite Materials

· The broken fibers carry some load because they are still bonded to the matrix and are loaded by the interfacial matrix-fiber shear stress.
· Pulling the de-bonded sections of the broken fibers out of the matrix contributes to the effective matrix flow stress and increases the material toughness.

· The photomicrograph shown uses polarized light to reveal the matrix stress concentration at the location of fiber breaks. Load previously carried by the fiber is transferred locally to the matrix.
· This local matrix stress may initiate fracture in other fibers in the composite.

From: van Vlack, "Elements of Materials Science & Engineering," Addison Wesley (1989)