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This paper investigates the application of the theta projection method for the analysis and extrapolation of uniaxial constant stress data to both constant load tension and constant internal pressure conditions, as part of an evaluation of its potential as a design tool for high temperature components. Two heat exchanger materials, Alloy 800H at 850 C, and the ferritic steel 2 1/4 Cr 1Mo at 550 C were selected for the study. A series of high accuracy constant stress tests was carried out for both alloys, and the creep curves fitted using the theta projection method. The extrapolation potential of the theta parameters was evaluated by comparing the predictions with data for constant load uniaxial tension and internal pressure (multiaxial) tests, also performed as part of the work, and for longer term stress rupture data from the literature. For both alloys, deviations from the standard theta procedure were required to obtain reasonable predictions. In the case of 2 1/4 Cr 1Mo, truncation of the baseline constant stress creep curves was necessary to arrive at sufficiently consistent theta stress dependence functions. For Alloy 800H, an apparent change of primary creep mechanism at lower stress levels and under multiaxial loading required use of a modified 5-theta parameter model.

Additional information

Authors: TAYLOR N G, MAN Technologie AG, Munich (DE);TWADDLE B R, Babcock Technology Centre, Renfrew (GB);HURST R C, JRC Petten (NL)
Bibliographic Reference: Paper presented: Fourth International Conference on Creep and Fracture of Engineering Materials and Structures, Swansea (GB), April 1-6, 1990
Availability: Available from (1) as Paper EN 35265 ORA
Record Number: 199010875 / Last updated on: 1994-12-01
Original language: en
Available languages: en
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