Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : October 07, 2017 - October 09, 2017
Evaluation of creep rupture lifetime of high temperature components which undergo multiaxial loading is important. This paper investigates biaxial creep properties, especially creep deformation, from comparison of biaxial tensile creep tests with principal stress ratios (λ) of 0.0 and 1.0 at 923 K using a cruciform specimen and an originally designed biaxial creep machine. Here, λ is the principal stress ratio defined as λ=σy/σx. σx and σy are the principal stresses in x- and y-directions, respectively. The λ=0.0 test corresponds to a uniaxial tensile creep test, while the λ=1.0 test corresponds to an equi-biaxial tensile creep test. The creep rupture lifetime in the λ=1.0 test was comparable to that in the λ=0.0 test at same Mises equivalent stress of σeq=100 MPa. In contrast, creep curve in the λ=1.0 test was different from that in the λ=0.0 test. Creep deformation in the λ=0.0 test proceeded at late stage. On the other hand, creep deformation in the λ=1.0 test proceeded from early stage. In order to clarify the creep deformation mechanism, observation of fractured surface was performed using a scanning electron microscope (SEM). Although many dimples were observed in both tests, the number of dimples in the λ=1.0 test is twice than that in the λ=0.0 test. In the λ=1.0 test, all directions on the xy plane are principal stress directions, which leads to promotion of the dimple generations. It was confirmed that accelerated creep deformation was caused by the dimples generated from early stage.
