Numerical investigation of frictional effect on measuring accuracy of different small specimen creep tests

Small specimen test methods have distinct advantages in life prediction of components operating at high temperatures. Yet some factors which can be ignored in traditional bulk material creep tests should be considered in the small specimens. In the present paper four different miniature specimens used to evaluate high-temperature creep properties of materials, such as small punch, impression, three-point bending and cantilever beam specimens, are discussed. Combined with Kachanov–Rabotnov creep damage constitutive equations, finite element models are established and applied to analyze the creep properties of small specimens. The effect of friction on the steady and tertiary creep properties is further investigated for four different small specimen tests. The results show that the friction existing between the specimen and clamp has a significant influence on the evaluation of creep properties and is more pronounced than that between the specimen and punch. In comparison with the small punch, impression, and three-point bending specimens with friction constraints the three-point bending specimens with fixed ends and the cantilever beam specimens give better results. Smaller ratio of characteristic punch size to gauge length, fixed constraint and smaller or no sliding between the punch and specimen are accordingly recommended.