Experimental study of long T300 carbon fibre undulations during the curing of LY556 epoxy resin

An experimental device is presented for real time video recordings of long fibre undulations which occur during the curing of thermo-setting systems. Very few data exist in the literature about observation of the fibre undulation phenomenon and its mechanism. The video recordings presented in this paper allowed the detection of fibre instability during the curing of a T300 carbon fibre impregnated with LY556 epoxy resin. The recordings show that the fibre undulations are generated after approximately 10 s during the hot stage of the cure cycle. Some relaxation effects were observed which produced the viscous behaviour of the matrix during formation and a glass transition phenomenon. The exothermal behaviour of the cure, the fibre undulation sensibility of the heating rate and the mass effect are established. The aim of the study is to obtain a better understanding of the appearance of undulations using real-time waviness monitoring and a quantitative data set-up for the description of fibre undulation versus the cure cycle.