Experimental Characterization of Bearing/Bypass Interaction and Bolted Joint Fatigue in a Three-Dimensional Woven Carbon Composite

Carbon fiber reinforced composite materials have become very attractive for structural components in aerospace applications due to high strength-to-weight and stiffness-to-weight ratios when compared to traditionally used materials such as aluminum, steel, and titanium. In particular, the use of composite materials with three-dimensional woven fiber reinforcement have become materials of interest over traditional laminates with two-dimensional reinforcement due to increased damage tolerance and through-thickness properties such as strength and stiffness. These advantages can be leveraged in aircraft component design to achieve potential cost savings over the life of an aircraft. The research presented in this thesis serves to expand the scope of knowledge regarding the mechanical behavior of a three-dimensional woven carbon/epoxy composite material through comparison to a two-dimensional woven quasi-isotropic laminate. Quasi-static in-plane evaluation was conducted to determine the mechanical properties of each material. In addition, the open-hole tensile and compressive properties were evaluated for the three-dimensional woven composite. Single-bolt bearing was investigated for both composites in double-lap and single-lap joints. The bearing/bypass interaction was investigated for the three-dimensional woven composite, and an interaction diagram was constructed to aid in design of bolted joints using this material. This investigation consisted of filled-hole tensile and compressive evaluation, as well as single-bolt and double-bolt bearing in single-lap joints under tensile and compressive loading. Un-notched specimens oriented to the warp direction, as well as notched specimens oriented to the warp and bias directions, were evaluated under tension-tension fatigue loading. Finally, single-bolt joints were evaluated under fatigue loading in two orientations in the three-dimensional woven composite, and one orientation for the two-dimensional woven laminate. A novel method was developed to measure fastener rotation within the bolted joints in both composites in an effort to better understand the contribution of fastener rotation to fatigue failure in mechanically fastened joints. A micro-computed tomography analysis was conducted on a warp-oriented joint in the three-dimensional woven composite to investigate damage onset and progression during fatigue loading