Masters Theses
Effect of fiber fabric orientation on the mechanical behavior of continuous fiber ceramic composites
Date of Award
12-1994
Degree Type
Thesis
Degree Name
Master of Science
Major
Metallurgical Engineering
Major Professor
Peter K. Liaw
Committee Members
T.T. Meel, N. Yu
Abstract
Continuous fiber ceramic composites (CFCCs) are candidate materials for high temperature and structural applications. CFCCs are quite advantageous because they are lightweight structural materials that exhibit a much higher resistance to high temperatures and aggressive environments than metals and other conventional engineering materials. Cyclic fatigue is always an important issue in the mechanical behavior of structural materials. It is important to note that the damage mechanisms of CFCCs in fatigue are quite different from those experienced under monotonic mechanical loading.
The objective of this work was to provide some understanding into the monotonic and fatigue behavior of Nextel 312 and Nicalon plain-weave fiber fabric reinforced SiC matrix composites. Specifically, this was accomplished by examining the effect of fabric orientation with respect to the loading axis on the monotonic and fatigue behavior of the composite. Two geometries were investigated: transverse, where the fiber fabric was perpendicular to the loading direction; and edge-on where the fabric was parallel to the loading axis.
The edge-on geometry showed higher monotonic strengths than the transverse orientation. The different failure mechanisms in edge-on and transverse were due to, strong in-plane shearing of the fiber fabric and weak interlaminar shear of the plies, respectively. In cyclic fatigue, stress versus cycles (S-N) curves showed high fatigue endurance limits in both orientations, with the edge-on orientation having higher fatigue resistance.
In-plane shear strengths were higher than interlaminar shear strengths in both composite systems, which also explains the behavior of the two orientations in bending. Finite element analysis was successfully used in modeling stress distributions in the two orientations. In the transverse orientation a compliant layer between two composite layers was used to simulate porosity and gap elements were used to simulate the extent of friction during bending. Friction and sliding effects were not present in the edge-on orientation.
Finite element results served to show that sliding and enhanced stresses caused premature failure in the transverse orientation, and the absence of friction effects accounted for higher strengths in the edge-on orientation.
Recommended Citation
Chawla, Nikhilesh, "Effect of fiber fabric orientation on the mechanical behavior of continuous fiber ceramic composites. " Master's Thesis, University of Tennessee, 1994.
https://trace.tennessee.edu/utk_gradthes/11485