M.S. Thesis Presentation by Rodney D. Averett
Friday, March 26, 2004
( Dr. Mary Lynn Realff, Co-Chair and Dr. Richard W. Neu, Co-Chair)
A fracture mechanics protocol appropriate for small fibers (35?m dia.) is presented, which allows for the determination of the strength limitations of high performance nylon 6,6 fibers. Specifically, linear elastic fracture mechanics (LEFM) techniques are employed in addition to elastic-plastic fracture mechanics (EPFM) theories to achieve this.
We assume that a minute semi-elliptical flaw of an unknown size exists in the specimen, as a result of the detrimental effects of the manufacturing process (melt spinning). Next, we seek to propagate this flaw in a stable manner through an ancillary process such as high cycle or low cycle fatigue (load-unload). After propagation, uniaxial tensile experiments are performed on the fatigued samples, by which the crack growth eventually becomes catastrophic during the process. After performing scanning electron microscopy (SEM) techniques and reviewing fractography, we are able to determine the critical flaw size and ligament length that leads to unstable crack propagation. These results are substituted into the appropriate LEFM equations and are in close agreement with published values for nylon 6,6.