Automatic glass fiber length measurement for discontinuous fiber-reinforced composites

Severe fiber breakage occurs in injection molding, affecting the mechanical performance of discontinuous fiber-reinforced composites. Accurate measurement of the residual fiber length distribution is crucial to experimentally investigate the physics of fiber breakage. This work proposes an automatic glass fiber length measurement method, based on the algorithm CT-FIRE for individual fiber detection. The main parameters of the algorithm were optimized to minimize the average systematic error between measurements performed with CT-FIRE and with a high-accuracy CMM. An approach to the evaluation of the measurement uncertainty based on substitution measurements was proposed and verified for a large size sample. For the scanner used in this study the uncertainty was 0.651 mm. Eventually, the developed automatic measurement method was used to investigate fiber breakage during plastication of long glass fiber-reinforced PP. The results obtained using the optimized algorithm parameters showed that significant breakage is due to the presence of the dynamic mixer.