DIRECT CREEP CURVE ASSESSMENT AND OPTIMIZATION OF CREEP EQUATIONS FORHIGH-TEMPERATURE ALLOYS

The conventional use of a time temperature parameter method for the ba sic assessment of a multi-heat creep data set facilitates the establis hment of a creep equation for a material type. However, the parameter can introduce some distortion to the creep data and hence the creep eq uation. To avoid this disadvantage, a new method for the direct creep curve assessment of multi-heat data was developed. Systematic deviatio ns in creep behaviour of individual test materials in respect to the m ean behaviour of the multi-heat data set are reduced and the creep cur ves for individual stresses are transformed to mid creep curves of a l imited number of stress classes. With this method large multi-heat cre ep data sets of Alloy 100 and Alloy 738 LC could be reduced to mean cr eep curves. On this basis, existing parameter based creep equations we re examined and optimized, if necessary. Further, the confidence limit s of these equations were determined. With a stress modification the c reep behaviour of a material similar in structure can be described. In finite element analyses some verification experiments which simulate typical loading conditions of components could be successfully recalcu lated with the optimized creep equations.