Effect of Surface Roughness and Fiber-Volume Fraction Variation on Strain Measurements

Leonhardt, David
Variability in material properties is a well-known difficulty encountered when dealing with carbon fiber reinforced polymer (CFRP) composites and is of interest to the Fertig Research Group. Digital image correlation (DIC) is used by the group in order to measure 2-D strain fields on the surface of CFRP specimens. In the course of testing, strain bands, areas with higher or lower strain than expected, were observed. This project focused on possible explanations for this observation. Two possible causes were analyzed using finite element analysis (FEA) techniques. The effect of both thickness variation and variations in fiber-volume fraction (FVF) in the specimen were examined. Data on the degree of variation of both thickness and FVF in various specimens were obtained by use of a ROMER measurement device and computer analysis of images obtained through digital microscopy, respectively. Analyzing FEA models built using the gathered data yielded similar results in both cases. Both models exhibited strain bands very similar to those obtained using DIC. These results represent a step toward understanding the effects of minor variation in both thickness and FVF on strain, and therefore stress, in CFRPs.
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