Drives to develop more efficient pressure vessel and piping systems has led to complex geometry containing discontinuities such as holes, grooves, gaskets, crevices, notches etc. A multiaxial state of stress often develops in complex engineering components subject to creep conditions. Under multiaxial creep, the rupture life and creep ductility are not consistent with uniaxial creep experiments. A common practice to account for multiaxial creep is to introduce a scalar representative stress or strain that describes the multiaxial state within the materials enabling accurate predictions of rupture and creep ductility. Many functions have been proposed in literature and international pressure vessel and piping codes and standards. The ASME B&PV III, French RCC-MR, and British R5 recommends different phenomenological approaches to multiaxial creep. In this study, seven representative stress and eight representative strain functions are evaluated. The skeletal point approach to calibrating these functions is discussed. The incompressibility of the representative stress functions is analyzed. Rupture surfaces of the representative stress functions under biaxial stress conditions are generated to compare the advantages and limitations of the functions. Several functions are found to exhibit divide by zero errors and/or imaginary number errors leading to unstable and discontinuous rupture surfaces. It is observed that the selection of an appropriate representative function is dependent on loading condition, geometry, and material properties. The Hayhurst and Huddleston representative stress functions are found as the most suitable functions to predict multiaxial rupture for a general multiaxial stress states. Finally, a guideline to the selection of the appropriate representative stress function and the associated incompressibility condition is presented.

This content is only available via PDF.
You do not currently have access to this content.