Experimental Characterization of Crack Tip Deformation Fields in Alloy 718 at High Temperatures

[+] Author and Article Information
Jin Liu, Jed Lyons, Michael Sutton, Anthony Reynolds

Center for Mechanics of Materials and NDE, Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208

J. Eng. Mater. Technol 120(1), 71-78 (Jan 01, 1998) (8 pages) doi:10.1115/1.2806840 History: Received February 04, 1996; Revised June 02, 1997; Online November 27, 2007


A series of fracture mechanics tests were conducted at temperatures of 650°C and 704°C in air, using Inconel® 718. A noncontacting measurement technique, based on computer vision and digital image correlation, was applied to directly measure surface displacements and strains prior to and during creep crack growth. For the first time, quantitative comparisons at elevated temperatures are presented between experimentally measured near-crack-tip deformation fields and theoretical linear elastic and viscoelastic fracture mechanics solutions. The results establish that linear elastic conditions dominate the near-crack-tip displacements and strains at 650°C during crack growth, and confirm that KI is a viable continuum-based fracture parameter for creep growth characterization. Postmortem fractographic analyses indicate that grain boundary embrittlement leads to crack extension before a significant amount of creep occurs at this temperature. At higher temperatures, however, no crack growth was observed due to crack tip blunting and concurrent stress reduction after load application.

Copyright © 1998 by The American Society of Mechanical Engineers
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