Correlation Factor Study of Small Punch Creep Test and Its Life Prediction

A small punch test is one of the innovative methods that can be used to evaluate the properties of a material without destructive harm to the in-service component. Conventionally identifying material properties by a uniaxial test is widely applied to engineering. How the properties obtained from a small punch test can be applied with the same utility has been a goal. In 2006, European Code of Practice (CoP) of small punch tests was first released, in which the correlation factor, ksp, was introduced to bridge the gap between the above methods. The author investigates the relationship between a uniaxial creep text and a small punch creep test by exploring the correlation factor k(sp). Various sets of experiments and a comparative study of the conventional uniaxial creep test and small punch creep test were carried out. Methods including Norton, Larson-Miller and Time versus Stress relation were employed to identify the value of k(sp). Different k(sp) values were found in different materials, which indicate that k(sp) values of materials need to be identified separately. In addition, the life prediction of a small punch creep test was carried out and the results of the life prediction predict a reasonable accuracy, which indicates that the small punch creep test is a reliable method for life prediction.