Novel methods of assessing inter-ply properties of toughened prepregs in application to the analysis of fibre path defects

The inter-ply properties of prepregs, broadly described by the notions of adhesion, friction sliding, and tack, are critical for the formation of fibre path defects (FPD). Conventional methods of interface testing, such as tack tests, friction pull-out and pull-through tests, can successfully characterize the conditions of stationary ply motion when the scale of relative ply displacement is of an order of 10's of mm. However in reality FPD often occur at much smaller movements of ply (sub-mm scale). This paper discusses a simple experimental technique which can offer the required resolution and, in contrast to the other methods, allows assessing the mode of a defect formation as a function of processing conditions. It was found that a large variety of FPD modes may be observed. The paper also shows that characteristic adhesion values can be derived from optical examination of the defects generated in a controlled fashion.