The microstructure of glass fibre reinforced polyester resin composites

SUMMARY The microstructure of a composite material is commonly defined by the volume fraction occupied by the fibres. An attempt is made to gain a more quantitative definition of the microstructure of unidirectional glass fibre reinforced polyester resin using data derived from a Quantimet 720 Image Analysing Computer. Sections to be examined under the Quantimet were cut perpendicular to the fibre direction and polished and etched such that the fibres appeared black. Values of the area covered by the fibres inside a small test cell, moved around the cross‐section in a contiguous grid, were determined; values for larger cells, made up of several adjacent test cells, were calculated from these. Two methods of analysis are presented. The first method involves the determination of the variance of the values of fractional area covered for different cell sizes. Information regarding the nature of the fibre distribution is sought both from comparing the variance values with those predicted for the null hypothesis, a random distribution, and from examining the shape of a surface defined by a variance matrix. The second method of analysis is based on the concept that a structure may be defined by its relationship to a structuring element. In the present case, structuring elements are squares and rectangles of empty space; the probability of finding such empty space is estimated. Information regarding the nature of the fibre distribution is sought from the probability matrices.