The effects of geometrical inaccuracies of the experimental set-up on small punch creep test results

The small punch creep testing technique is able to provide creep properties from a very small amount of material. However, a universal and robust technique, to convert small punch creep testing results to corresponding uniaxial creep test data, has still not been established. In addition, the experimental output can be affected by several sources of uncertainty, such as friction between the components of the test rig and the specimen, and inaccuracies in the geometry of the experimental set-up and the testing procedures. This article reports the results of three-dimensional elastic/creep finite element analyses of small punch creep testing, taking into account geometrical inaccuracies in the initial punch position and the loading direction. The results of the calculations show that the initial position of the punch and the loading direction can considerably affect the variation in the specimen’s central deflection with time and the final time to failure. The minimum displacement rate was found to decrease when the punch moves away from the centre of the specimen and when the angle between the loading direction and the axis of the test rig increases. The time to failure increases when the punch deviates from the perfect axi-symmetric configuration. The effects of the direction of the load increase as the initial distance of the punch from the centre of the specimen increases. Analytical correlations, corresponding to the inaccuracies investigated, are also proposed.