Development of Multiaxial Creep Testing Machine Using Cruciform Specimen

Abstract

This paper describes the development of multiaxial creep testing machine using cruciform specimens in a wide range of biaxial stress conditions of 0≤λ≤1 and the multiaxial creep rupture tests at 923K, where λ denotes the ratio of the minimum principal stress to the maximum principal stress. The developed test machine has a loading capacity of 98KN and the maximum temperature is 923K. Three dimensional finite element (FE) creep analyses were made to determine the shape and dimensions of the cruciform specimen having uniform stress distribution along the gage length. The specimen shape determined by the FE analyses has a 32mm×32mm parallel part with 5mm thickness. In the biaxial Mises' stress constant creep tests using type 304 stainless steel cruciform specimens, creep rupture time increased with increasing λ, so that the biaxial stress has an effect on rupture time. The rupture data did not depend on λ when correlated with the equivalent stress based on crack opening displacement, but they depended on λ with Huddleston's stress. Huddleston's stress gave more conservative equi-biaxial tension creep rupture time than the Mises' stress. The Mises' equivalent strain rate decreased with increasing λ in multiaxial creep tests.