This paper describes a method for predicting key structural properties of carbon fiber reinforced composite materials containing ply waviness several times the nominal ply thickness. These socalled marcelled regions have been observed in a number of highly loaded thick structural components. The origins of these defects are not fully understood, although several contributing factors have been identified. The goal of this work is to develop an analysis based disposition criterion for components where fabrication process changes cannot be readily implemented to eliminate marcel defects. Work to date has focused on developing a micro-mechanics-based procedure for modeling the strength and stiffness properties of a marcelled region given basic properties of the material and simple geometric parameters of the marcel that can be measured nondestructively. The result is a general constitutive model that can be used in global structural analysis packages to assess the effects marcel defects have on component performance. Analyses of test coupons containing marcelled regions have been carried out to illustrate the method and establish the validity of the modeling approach. Results indicate that the degree to which marcel defects affect structural properties depends not only on the maximum fiber misalignment angle, but also on the location and size of the marcelled region and nominal applied strain field.

Fatigue of fiber-reinforced polymer matrix composites has been studied exhaustedly over the years. However, most fully reversed fatigue testing has concentrated on flexural fatigue. The resulting stress state through the laminate thickness is non-uniform and as such may give rise to unconservative life estimates. Fully reversed (R=−1) axial testing has not been heavily reported due to the difficulties associated with precluding local or global buckling of the axial specimen. The few reported fully reversed axial tests utilize either cylindrical specimens or fixturing that is very large, expensive to fabricate, and difficult to handle. Herein we report on a simple side support fixture that allows the use of standard ASTM tensile test specimens (D3039 or D638, depending on test material), which are readily prepared. The fixture allows fully reversed axial fatigue testing as well as static baseline compression and residual compression strength characterization. Also presented herein are tension-tension (R=0.1) and fully reversed tension-compression (R=−1) S-N diagrams for an E-glass/epoxy composite.