Failure mechanisms and energy dissipation in composite off-axis tension specimens with open holes
Predicting failure of fabric composite laminates in the presence of flaws such as cracks and stress raisers has been an important research problem for the last two decades. Most of the existing models for predicating notched strength are of a ‘cure fit’ nature, wherein the model parameters e.g. characteristic distance or damage zone sizes are chosen so as to fit the experimental data. Such parameters have been shown to depend on notch size and laminate orientation, and as such, cannot be considered material constants for the composite system. The energy dissipation is a physical phenomenon that captures the collective behavior of the failure mechanisms without requiring an explicit knowledge of the mechanisms, and it can also be related to local stiffness changes, leading to a form of nonlinear structural behavior. An approach to characterize failure behavior and degree of load induced internal damage in single lamina of satin weave fabric with off-axis loading and having a central notch is proposed. From the experimental results it was found that energy absorption for notched and un notched woven fabric composite is a function of fiber orientation and notch size. Energy absorption increases as the fiber orientation increases but decreases with increase in the notch size. The failure loads for hysteresis loading were about the same as that of one time loading, indicating that no damage growth occurred due to unloading and subsequent reloading. The energy density is directly proportional to fiber orientation indicating that higher energy densities for higher off-axis angles. The failure modes and the fracture propagating direction for the off-axis notched specimen were very much dependent on the fiber orientation. Recommendations were made for future work for the determination energy absorption characteristics, from lamina level to laminate level and for different weave types.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering