Determination of Short Glass-Fiber Volume Fractions in Compression Molded Thermoset Composites—Experimental

Prediction of volume fraction of short glass-fibers in compression molded thermoset composites parts such as sheet molding compounds (SMC) is of importance since their distribution affects the mechanical property and surface quality. In the present study, a simple approach based on digital image processing technique was applied in determining the fiber volume fraction distribution in the compression molded flat plate of SMC. Although the present digital image processing approach does not have the resolution to distinguish individual fiber diameters, it is capable of determining fiber concentrated regions, and thus an effective means of determining the global distribution of fibers in a single process is provided. As molding conditions, two different molding temperatures and velocities as well as two different compression ratios were investigated to determine the influence of molding parameters on the glass-fiber volume fraction distributions. It was found that a rather uniform distribution of glass-fibers was obtained under the condition with smaller compression ratios and faster mold closing speeds, whilst the effect of mold temperature on volume fraction distribution being negligible. The validity of the proposed scheme was estimated by comparing the predicted volume fraction distribution with the experimental result obtained from the conventional burning-test measurement. The comparison clearly demonstrates the simplicity and capability of the digital image processing technique applied under the present condition.