Date of Award

1-1-2010

Document Type

Campus Access Thesis

Department

Mechanical Engineering

First Advisor

Michael A Sutton

Second Advisor

David S. Dawicke

Abstract

Ductile structural elements are often times subjected to complex loading conditions during normal operational conditions due to a combination of tension and torsion, resulting in mixed mode loading of flaws. When subjected to such conditions, the flaw is likely to undergo stable crack growth (SCG) in ductile materials. Understanding such fracture events in ductile materials is an important component of structural integrity analysis for ductile structures, especially since there are no general fracture criterion available to predict the direction and onset of mixed mode fracture in such materials.

The first objective of this research was to understand SCG under mixed mode loading conditions in three thicknesses of flat plates, with the long-term goal of developing a comprehensive data base for characterization and evaluation of various crack growth criteria. Results from a series of torsion-tension experiments for single edge cracked 2024-T3 aluminum specimens with thicknesses of 0.09in, 0.25in and 0.5in and torsion tension ratios of 0, 0.25, 0.5, 0.75, 1.00 and 3.00 are reported. The second objective was to gain a basic understanding of the influence of thickness on integral structures. Results from torsion-tension experiments on integral stiffened structures are also reported for varying cross sectional geometries. Experimental measurements obtained during these experiments include (a) axial load-axial displacement, (b) three- dimensional crack surface shape, (c) three-dimensional crack front shape for several values of surface crack extension, and (d) axial load-surface crack extension.

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