A novel, high-sensitivity, small specimen creep test

Abstract

This paper describes a novel, high-sensitivity, ring-type of small specimen creep test method, which can be used to obtain accurate creep strain data. A full theoretical description of the test technique is given; this is based on the complementary strain energy approach, which leads to an analytical solution for the load line deformation of an elliptical ring. Using the analytical solution, a reference stress approach is used to establish the conversion relationships between the applied load and the equivalent uniaxial stress and between the experimentally measured creep deformations and the equivalent uniaxial creep strains. The main features of the test method are: (a) the ring specimen has a significantly larger equivalent gauge length (EGL), when compared with that of other small specimen types; (b) the method is suitable for testing at lower stresses compared with commonly used current small-specimen test methods (this is because relatively low strains can be obtained from relatively large deformations); (c) specimens have simple geometries and the tests are easy to perform, and (d) the conversion relationships are material independent and practically insensitive to geometry change due to deformation. Experimental validation of the test method is made using the results obtained from creep tests for a P91 steel at 650 °C. Practical applications and future exploitation of the technique are addressed.