Available at: http://digitalcommons.calpoly.edu/theses/425
Date of Award
MS in Aerospace Engineering
Faysal Kolkailah, Ph.D. P.E.
Carbon fiber composites are continually seeing increased use in aerospace applications. It is necessary to understand their failure modes in order to properly design and perform analysis on structures constructed primarily from them. This thesis studies woven carbon fiber composites with and without double-edge notches in a series of static and fatigue tests performed on an Instron 8801 servo-hydraulic testing system.
Specimens were constructed of Advanced Composites Group product # LTM45EL woven carbon fiber pre-preg/epoxy and were cut to approximately 9-inch in length and 1-inch in width. Notches were cut into some of the specimens using a slitting saw blade of 0.006-in. thickness.
Ultimate strength, Young’s modulus and Poisson’s ratio for specimens were determined to be 119,418 psi, 7,149,000 psi and 0.05, respeictively. Fracture stress for specimens with notch depths of 0.10, 0.15, 0.20, 0.25, 0.30 and 0.35 was determined to be 93,481 psi, 88,193 psi, 86,968 psi, 81,112 psi, 84,197 psi and 81,955 psi, respectively. The results from these tests showed that the specimens followed Griffith’s model for brittle failure.
Average number of cycles to failure was determined to be 6,600, 37,200, 94,300 and 293,400 for fatigue tests with maximum stresses of 72.5%, 75%, 77.5% and 80% of the ultimate strength. Fatigue tests performed on notched specimens produced data that was too scattered from which to draw a statistically significant result. Numerical modeling in Abacus showed comparable results to experimental tests for stress and strain.