Length-scale dependence of variability in epoxy modulus extracted from composite prepreg

Property variability in conjunction with morphological variability are important sources of uncertainty in composite modeling. While image processing of experimental microstructures has enabled accurate quantification of morphological variability, the characterization of material variability is not as well established. In this study, the local material properties of epoxy extracted from a prepreg sheet was determined using nanoindentation with a spherical indenter tip with a radius of 50 μm. Indentations were carried out at four different indentation depths to evaluate the change in the variability of epoxy modulus with the sampling volume. For each length scale studied, 40 indentations were carried out to determine the variability in epoxy modulus. A significant decrease was observed in the coefficient of variation as the indentation depth increased. The corresponding modulus distributions were quantified. The results suggest that, similar to morphological variability, material variability is length-scale dependent and the appropriate variability associated with the selected length scale must be considered for stochastic modeling of composite structures.