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TITLE AND SUBTITLE:
Verification of Experimental Techniques for Flow Surface Determination
AUTHOR(S):
Lissenden, Cliff, J.; Lerch, Bradley, A.; Ellis, John, R.; Robinson, David, N.
REPORT DATE:
1996-02-01
FUNDING NUMBERS:
WU-505-63-12
PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135-3191
PERFORMING ORGANIZATION REPORT NUMBER:
E-9900
SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration Washington, D.C. 20546-0001
REPORT TYPE AND DATES COVERED:
Technical Memorandum
SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA/TM-107053
SUPPLEMENTARY NOTES:
Cliff J. Lissenden, Pennsylvania State University, University Park, Pennsylvania 16802, and Summer Faculty Fellow at Lewis Research Center; Bradley A. Lerch and John R. Ellis, NASA Lewis Research Center; David N. Robinson, University of Akron, Akron, Ohio 44325-3905. Responsible person, Bradley A. Lerch, organization code 5220, (216) 433-5522.
ABSTRACT:
The concept of a yield surface is central to the mathematical formulation of a classical plasticity theory. However, at elevated temperatures, material response can be highly time-dependent, which is beyond the realm of classical plasticity. Viscoplastic theories have been developed for just such conditions. In viscoplastic theories, the flow law is given in terms of inelastic strain rate rather than the inelastic strain increment used in time-independent plasticity. Thus, surfaces of constant inelastic strain rate or flow surfaces are to viscoplastic theories what yield surfaces are to classical plasticity. The purpose of the work reported herein was to validate experimental procedures for determining flow surfaces at elevated temperature. Since experimental procedures for determining yield surfaces in axial/torsional stress space are well established, they were employed-except inelastic strain rates were used rather than total inelastic strains. In yield-surface determinations, the use of small-offset definitions of yield minimizes the change of material state and allows multiple loadings to be applied to a single specimen. The key to the experiments reported here was precise, decoupled measurement of axial and torsional strain. With this requirement in mind, the performance of a high-temperature multiaxial extensometer was evaluated by comparing its results with strain gauge results at room temperature. Both the extensometer and strain gauges gave nearly identical yield surfaces (both initial and subsequent) for type 316 stainless steel (316 SS). The extensometer also successfully determined flow surfaces for 316 SS at 650 ºC. Furthermore, to judge the applicability of the technique for composite materials, yield surfaces were determined for unidirectional tungsten/Kanthal (Fe-Cr-Al).
SUBJECT TERMS:
Flow surface; Yielding; Composite; Stainless steel; Axial-torsional testing
NUMBER OF PAGES:
23
PDF AVAILABLE FROM URL:
1996/TM-107053.pdf ( 629 KB )
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