Tailored Fiber Alignment and its Effect on Strength of Notched Carbon Fiber Composites

Event Date/Time: 
December 1, 2017 - 10:45am
Event Location: 
1538 Engineering
Speaker: 
Emma Floyd
MS Thesis Defense

Abstract

Drilling holes in continuous fiber composite laminates causes fiber breakage, introduces delamination and can cause reduction in strengths by up to 60%. Tailored fiber alignment (TFA) involves placing fiber tows/bundles around the holes to deliver net-shapes that do not require cutting/drilling thereby eliminating fiber-discontinuity/breakage.

In this work, the effect of notch/holes of varying diameters, namely ¼" (6.25 mm.), ½" (12.50 mm.) and ¾" (18.75 mm.) on the strength of drilled and TFA produced carbon fiber composites was experimentally studied. Finite Element Analyses (FEA) were performed to obtain the load path (S11 contours) and the fibers were stitched/laid on the load path including around the holes. The resulting layup/fabric was infused with SC15 epoxy using vacuum assisted resin transfer molding (VARTM) process. The strengths of drilled and TFA-stitched holes were compared with pristine (no-hole) composites.

Results show that TFA based 'composites with holes' behave statistically equivalent to 'pristine composites without holes' at smaller diameters. Also, TFA based samples on an average had ~40% higher tensile strengths relative to similar diameter drilled samples. While the results are promising, further statistically significant experimental testing needs to be done to fully understand the behavior of fiber alignment around holes. Nevertheless, the results show great potential of TFA on maximizing the load carrying capacity of fiber, eliminating cutting/drilling and associated stress concentrations, thereby allowing creation of lightweight structural components.