1 Fracture of 2D Triaxially Braided Carbon Fiber Composites and Resin Effects on the Energy Absorption

Results from an experimental program to investigate the propagation of damage in 2D triaxially braided carbon fiber textile composites (2DTBC) under static conditions are reported. A methodology is presented in which classical concepts from fracture mechanics are generalized to address damage growth in an orthotropic and heterogeneous structural material. Along with results from the experimental program, a novel numerical technique that employs ideas from cohesive zone modeling and implemented through the use of finite element analysis is also presented. The inputs that are required to implement such a discrete cohesive zone model (DCZM) are identified. Compact tension specimen (CTS) fracture tests were carried out by loading 2DTBC coupons cyclically and monotonically. Load and load point displacement were measured. The crack initiation, propagation and crack path history was recorded using high resolution digital photography. The measurements were used to extract the fracture energy (GIC) as a function of crack tip position. Notched Tension tests were carried out to measure the maximum stress in the composites, which provides the cohesive strength (σ c) of these composites. The material constants so obtained and the DCZM modeling strategy were independently verified by conducting single edge notched bend (SENB) fracture tests using a modified three-point bend test fixture. The experimental and numerical analyses were carried out for two different types of 2DTBC made from two different resin systems to confirm the usefulness of the proposed methodology