Observation of edge effect in flexural fatigue test of composites using large field of view microscopy

Free-edge effects in fibre reinforced composites can produce premature damage at the composite edges due to mechanical, geometrical and hygro–thermal effects. Observation of damage on the free-edge of a composite plate is therefore different than what can be observed inside the material. The amount of individually broken fibres in a composite is counted by observing a test specimen with a polished edge and by cutting test specimens to observe damage inside the material. The amount of damage observed on a polished edge is found to greatly exceed that which is observed inside test specimens subjected to the same testing conditions. It is shown that the progression of important damage mechanisms can be observed on polished edges, but also that invalid damage mechanism may be observed using free-edge microscopy.