Comparative Study on the Determination of Creep Properties by Using Different Types of Small Specimens

Abstract

The application of small specimen creep test techniques in determination of creep properties of materials in-service has been increasing. There exists a number of small specimen creep testing techniques, such as sub-size uniaxial specimen, small punch specimen, shear punch specimen, impression specimen, three-point bending specimen, cantilever beam specimen, beam specimen with fixed constraint, circular ring specimen and tow-bar specimen. The diversity in specimen types and dimensions will affect the evaluation of creep properties. It is hence necessary to make a comparison among different small specimen creep tests. A comprehensive review has been made on the effect of the specimen dimension, stress state, conversion equation, creep properties, strain sensitivity and other influence factors. The results show that different small specimens result in different creep curves. Influenced by many factors, the small punch specimen has a very complicated data interpretation. With a large equivalent gauge length, the cantilever beam and circular ring specimens can obtain rather accurate creep data. Large deformation effect exists for the three-point bending, cantilever beam and circular ring specimens, which can be controlled by the critical load approach. Because of the low frictional sensitivity, the beam specimen with fixed constraint can obtain creep rupture data of high accuracy. A code of practice is then recommended for selecting a proper small specimen to evaluate the creep properties for in-service components.