Characteristics of Uniform Deformation in Uniaxial Creep Specimen with Slits Introduced in the Extensometer Limbs

Abstract

Constant stress creep test instead of conventional constant load one should be performed to create an accurate constitutive equation of creep at designing modern high temperature machines and structures. However constant stress creep testing machines have not been widely employed yet because of their complex structures. Furthermore even if the constant stress creep machine were employed, constraint of limbs attached on a gauge part of the creep specimen for measuring creep strain would be another inevitable issue. These extensometer limbs on the uniaxial creep specimen usually prevent uniform deformation along the gauge part. In order to release the deformation of circumferential constraint by extensometer limbs, 24 slits were introduced in each limb. After these slits were machined in the limb of the uniaxial creep specimen, uniaxial tensile tests were firstly carried out to measure the strain distribution along the gauge part employing low alloy and austenitic stainless steels. Subsequently Finite Element Analyses were performed to examine the validity of introducing these slits into the extensometer limb. The analytic results showed that the uniaxial specimen with slits could release the circumferential constraint and raise the uniform deformation along the gauge part. It was also found that there was an optimum depth of the slit to deform uniformly for each material and that its depth depended on the work hardening property of the material.