Sustained load crack growth in zircaloy-4 at elevated temperatures
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Sustained Load Crack Growth in Zircaloy-4 at Elevated Temperatures U R B A N M. CORSO A N D R I C H A R D A. Q U E E N E Y The application of Zircaloy-4 in nuclear reactor component design demands a knowledge of elevated temperature response of the alloy in order to predict structural member lifetime. Accordingly, extensive studies have been conducted and reported to characterize creep strain and creep rupture behavior of the alloy. TM These studies seek to evaluate the parametric response constants encountered in conventional creep testing, such as stress exponents, activation energies, and so forth. An alternative approach to creep rupture lifetimes has been developed recently, wherein a knowledge of the growth rates of creep cracks may be used to conservatively predict total creep lifetimes. The cracks in question may be generated by fatigue load history, by aggressive environments, or the usual void coalescence at grain boundaries. Primary interest to date has centered on alloy steels, 5-8 including stainless varieties, that are commonly encountered in high temperature energy conversion systems. The present communication reports the results of studies initiated in a Zircaloy-4 alloy. The alloy sample contained (by weight) 1.53 pct Sn, 0.21 pct Fe, 0.10 pct Cr, 0.14 pct O, and remainder Zr. The alloy was beta-quenched from 1050 ~ hot-rolled at 950 ~ to a final thickness of 0.4 cm, and annealed at 950 ~ for one hour. Room temperature mechanical response, for loading in the rolling direction, indicated a yield strength of 138 MPa, tensile strength of 221 MPa, and 48 pct elongation at fracture. Compact tension specimens were prepared according to Fig. 1, with a total initial crack length "a" consisting of a machined slot 1.10 cm deep and a fatigued crack, driven at room temperature, measuring an additional 0.30 cm. These samples were loaded, with constant tensile force, in air at temperatures of 315, 370, and 430 ~ The crack length was determined, as a function of elapsed time at load/temperature, with an optical comparator through a viewing port in the thermal jacketing. The results of the crack growth rate tests are shown in Fig. 2, where the logarithm of growth rate, da/dt, is correlated with the stress intensity factor Kt, calculated from: 9 a
K I = 0.66P V/~ 29.6 - 185.5~
1 R. G. Davies: Met. Trans. A, 1978, vol. 9A, pp. 41-52. R. G. Davies: Met. Trans. A, 1978, vol. 9A, pp. 451-455. R. G. Davies: Met. Trans. A, 1978, vol. 9A, pp. 671-679. Formable HSLA and Dual Phase Steels, A. T. Davenport, ed., p. 25, The Metallurgical Society of A I M E , New York, 1979. 5. S. T. Mileiko: J. Mat. Sc., 1969, vol. 4, pp. 974-977. 6. H. Fischmeister and B. Karlsson: Z. Metallkunde, 1977, vol. 68, pp. 311-327.
1. 2. 3. 4.
METALLURGICAL TRANSACTIONS A
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URBAN CORSO, Research Assistant in EngineeringMechanics, and RICHARD A. QUEENEY, Associate Professorof Engineering Mechanics, are at the PennyslvaniaState University,University Park, PA 16802. Manuscript submitted April 14, 1980.
ISSN 0360-2133/81/0211-0357500.75/0 9 19
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