Uprating and life assessment under fatigue-creep conditions

Abstract Uprating and life assessment exercises require an understanding of the likely failure mechanisms and confidence that appropriate life predictive expressions are being employed. Principal trends in fatigue-creep response of a wide range of engineering alloys have been identified, although it is emphasised that a single alloy may exhibit all types of response if the appropriate conditions prevail. The quality of the available data has been assessed in terms of its variability, arising from material and testing factors, and its representation of service conditions that allow greater scope for material ageing and deterioration. Similarly, the assumptions of popular life prediction methods based upon linear cumulative damage have been examined. Where possible, experimental evidence is cited to estimate the significance of such effects. The general case of uprating, as achieved by an increase in temperature, strain range and dwell duration, is explored in terms of the fatigue and creep damage fractions.

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