Determining a Length Scale of FRP Composite Microstructures

Abstract

Carbon fiber reinforced plastics (CFRPs) have become the material of choice for many low weight, high strength applications. One problem associated with these materials is a scatter of mechanical properties. Efforts have been made to correlate these results with random fiber packing using 2-D representative volume elements (RVEs). While these efforts have shown that fiber distribution is important, scans have shown fiber position is a function of 3-D morphology. For example, fiber meandering and entanglement can only be seen when variation along the fiber direction is studied. While the optimal scale for 2-D RVEs is well researched, little has been done to find the effective length in which the 3-D behavior of real samples can be observed. As such, the construction and analysis of 3-D RVEs with a requisite length in the fiber direction is necessary. The scope of this work is to study the fibers within a CFRP sample in order to recreate the microstructure. In this work, long micro-CT scans from an aerospace-grade are used to obtain the fiber positions. In addition, scans from an automotive grade specimen with a high fiber count manufactured using VARTM were analyzed due to the high potential for entanglement. Descriptive metrics were then generated to fiber behavior within both samples. The variance of these metrics was captured using the change in Pearson’s Correlation Coefficient (R) with respect to position along the fiber length. One