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Date of Award

12-2002

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Yi Zhao

Committee Member

Dr. Eric v. K. Hill

Committee Member

Dr. Frank J. Radosta

Abstract

Presently there is a lack of confidence amongst engineers when specifying the preload of a mechanical fastener in a composite joint due to a lack of a fundamental knowledge base regarding the behavior of composites under fastener compressive load. As such, a novel experimental procedure was developed herein to determine the through-the-thickness compressive (TTTC) material properties. A total of 206 property tests were performed on four different graphite/epoxy material systems. The results confirmed that TTTC material properties vary with fiber orientation, laminate thickness, fiber volume fraction, and even laminate surface finish. Hence, the 'rule of mixtures' provides a poor estimate of the TTTC modulus in that it fails to account for any of these variables.

Finally, acoustic emission nondestructive testing, along with a modified approach to MSFC-STD-486B, Torque Limits for Standard Threaded Fastener, were used to determine the torque limit of a fastener in a single lap joint. The laminate configuration examined in these tests was manufactured in accordance with the MIL-HDBK-17 design code. The results demonstrated the inability of the fasteners employed to damage the one composite system investigated: fastener thread failure occurred first. Further study is necessary to confirm or refute these results for other composite systems and joint configurations.

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