On the Determination of Material Creep Constants Using Miniature Creep Test Specimens

Full size creep test specimens, i.e., conventional uniaxial creep test specimen and Bridgman notch specimens are usually used to determine the full set of material constants for any creep model. However, in many situations, sufficient material is not available for theses specimens to be manufactured from it. Therefore, small creep test specimens have been introduced and used to determine (i) creep constants and (ii) the remaining life time for engineering components. Two commonly used small creep specimen types, i.e., the impression and the small ring creep tests, are used in this paper to determine the steady state creep constants. However, these specimen types are limited for use in determining the secondary creep properties, i.e., they are unable to determine the full set of material creep constants for creep damage models. In this paper the recently developed small two-bar creep test specimen and the newly developed small notched specimen test are described and used to determine a full set of material constants for Kachanov and Liu-Murakami creep damage models. The small notched specimen manufacturing, loading and testing procedures are described in this paper. P91 steel at 600 °C and (Bar-257) P91 steel at 650 °C have been used to compare the material constants obtained from the small two-bar and the small notched creep test specimens with those obtained from the conventional uniaxial creep test specimens and Bridgman notch specimens. The results show remarkably good agreement between the two sets of results.