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The discipline of time-dependent fracture mechanics has traditionally focused on the creep crack growth behavior of high-temperature materials that display creep-ductile behavior, such as stainless steels and chromium-molybdenum steels. Elevated temperature aluminum alloys, however, have been developed that exhibit creep-brittle behavior; in this case, the creep crack growth rate correlates with the stress intensity factor, K. The fracture characteristics of aluminum alloy 2519-T87 were studied at 135°C, and the creep and creep crack growth behavior were characterized utilizing experimental and numerical methods.
The strain to failure for creep deformation specimens was limited to only 1.2 to 2.0%. Creep crack growth tests revealed a unique correlation between the creep crack growth rate and K, a result consistent with creep-brittle behavior. No experimental correlation was found between the creep crack growth rate and the Ct, parameter. Microscopy of fracture surfaces revealed distinct regions of intergranular and transgranular fracture, and the transition between the fracture regions was found to occur at a critical K-level. Experimental results also appeared to show that initiation of crack growth (incubation) is controlled by the accumulation of a critical amount of damage ahead of the crack tip and that a correlation exists between the incubation time and K. Total time to failure is viewed as a summation of the incubation period and the crack growth period, and the design importance of incubation time is discussed.
creep, creep crack growth, creep-brittle, aluminum alloys, crack initiation, incubation
Graduate research assistant, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
Assistant professor, Louisiana Tech University, Ruston, LA
Professor and chair, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA
Regent's professor, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA