The Influence Of Stress Level On The Measurement Of Creep Strain Rate Based On Small Specimen Techniques

Using traditional uniaxial creep test to measure the creep properties of the material in service was restricted because standard specimen requires bulk materials which are not available in some components. Small specimen creep test technology has thus become a hot topic of research in recent decades. The small specimens such as small punch, three-point bending, impression and others may involve different stress levels resulting in different deformation mechanisms. Previous researches, however, did not consider the influence of stress level on the determination of the material parameters based on small specimen. In this paper, a two-bar structure is used to demonstrate the possible errors, which has a material following different Norton's laws at high and low stress levels. On this basis, beam specimens with fixed constraint of a material which has a single Norton's relation and dual Norton relations are studied, in order to find the errors of measurement. Beam specimen creep testing is carried out to further understand the errors introduced due to the change of creep deformation mechanisms. It has been proved that deviation can be significant when the stress is near the turning point stress of different creep deformation mechanisms. It is therefore suggested that attention should be paid to the selection of stress levels when using small specimen to get material creep parameters in order to avoid large measurement errors.