Morphology analysis of microvoids in SMC: Ageing effects

A quantitative morphological analysis of the porosity in sheet moulding compound (SMC) has been made by using image processing, especially for the microvoids resulting from shrinkage compensation. The first result is that, for the virgin SMC, the microporosity is 5-8% in the external skin of the part and ∼24% in its core. After hydrothermal ageing the microvoids in the core are partially closed again, the total microporosity being reduced to ∼5%. In the skin, the microporosity remains unaffected. Moreover, the size distribution is modified, as the largest microvoids are subdivided into smaller ones. In addition, the morphology of the microvoids has been studied through their fractal behaviour. The characteristic fractal dimension of their complex shape for the virgin material (D = 1.35) becomes Euclidean (D = 1) after ageing. Ageing for 6 and 2570 h and drying indicate the morphology changes to be only partly reversible. In summary, swelling due to water occurs internally, and the irregular shape of the microvoids is smoothed.