Published: Jan 1982
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Materials data are essential to the proper formulation of fatigue-design guidelines for pressure-vessel systems. These data are needed for two main reasons: (1) to develop and evaluate prediction methods used in fatigue-damage analysis and (2) to quantify the fatigue behavior of various alloys from which pressure vessels are fabricated. The former reason involves verification of models of the fatigue-damage process and must include both deformation and life prediction as well as demonstrating that the reference damage basis and damage rules are relevant to actual hardware. The latter reason relates to the establishment of an adequate data base and must incorporate material variability, environmental effects, and temperature effects.
In the above context, this paper addresses the data needs within the framework of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Low-temperature (negligible creep) and high-temperature (significant creep) regimes and crack-initiation and crack-propagation damage criteria are addressed. The background for existing fatigue-design guidelines of the ASME Code is briefly reviewed. Areas where fatigue-damage criteria need to be improved are creep/fatigue/environmental interaction at low strain ranges and long times, thermal-mechanical fatigue, multiaxial fatigue, and long-life fatigue. Existing guidelines for crack initiation are based mainly on strain cycling of uniaxially loaded specimens. There are some crack-initiation data on notch effects at low temperature, but more information is needed for high temperatures and welded components. Additionally, crack-initiation data are needed for multiaxial conditions, especially nonproportional loading, for thermal-mechanical cycling, and for high-cycle fatigue. To apply fatigue crack growth methodology, data on the size, shape, and distribution of initial flaws, methods of dealing with small cracks, and techniques for treating cracks in inelastic strain fields are required. With these requirements in mind, guidelines for the development of fatigue data are discussed, and recommended guidelines for data development are outlined.
materials, fatigue data, fatigue design, tests, pressure vessels, piping
Research Scientist, Physical Metallurgy Section, Materials Department, Battelle Columbus Laboratories, Columbus, Ohio