Finite element study for determination of material’s creep parameters from small punch test

Abstract

Compared with the conventional tensile creep test, it is much more difficult to obtain the creep properties of a material by the small punch creep test due to the complex deformation response and stress distribution in the miniature specimen of the material. Although creep behavior has been investigated by the small punch test, most studies have been limited to a specimen geometry and therefore, cannot be extended to other conditions conveniently. In this study, a new developed analysis routine is presented to derive the creep parameters of a material using data obtained from the small punch creep test. With the aid of the finite element method, the displacement and the displacement rate of the small punch are obtained for different load levels. The relationship between the stress and creep strain of the specimen and the applied load and the punch displacement is obtained by a dimensional analysis and the membrane stretching model. The creep properties obtained from small punch tests and the conventional creep tests are also compared. The values of the creep properties between the two types of tests agree well with each other within an acceptable accuracy range. This indicates that it is possible to obtain the creep parameters of a material from the small punch creep test instead of the conventional creep test by the analysis routines proposed in this study. Some suggestions for data reduction of the small punch creep tests are also presented to obtain more accurate material creep parameters.

A Renaissance in the Use of the Small Punch Testing Technique

“…The final fractures in such cases have little to do with membrane stretching and it is possible that the applied loads can be resisted even though the disc appears to be severely cracked because there is no thinning around the circumference where stretching would have been predicted for a ductile material. A similar situation is revealed during the testing of Even for ductile materials alternatives to the CoP equation 1have been proposed by Chen et al (2013), Chen et al (2010) and Ma et al (2009) along with the 'General' strain approach by Hyde et al (2014). A new evaluation scheme based on the deflection curves from individual tests by Gulcimen and Haehner (2013) was expected to give a better explanation for the evolution of effective stresses both in the early stages of the test where bending and pronounced initial yielding occurred but also during pronounced thinning, however, according to the authors, the small difference between the results derived from this method for the zones of a P91 weldment compared to the CoP results are indicative of other factors such as possibly strain hardening which should be introduced into their effective stress based methodology.…”

On the effects of friction modelling on small punch creep test responses: A numerical investigation

“…In view of these advantages, many researchers have investigated the methods used for the interpretation of SPCT data, in order to improve the understanding of the mechanisms governing the response of the specimen and to establish a reliable procedure to correlate the results of the small punch creep test with those of the conventional uniaxial creep test. 1,5,[7][8][9][10][11][12][13][14][15][16] No universally accepted data conversion method is yet available, due to the very complex mechanical response of the specimen, characterised by various interacting non-linear features, such as large deformations, large strains, non-linear material behaviour and non-linear contact (and contact friction) between the specimen and the punch.…”

“…In view of these advantages, many researchers have investigated the methods used for the interpretation of SPCT data, in order to improve the understanding of the mechanisms governing the response of the specimen and to establish a reliable procedure to correlate the results of the small punch creep test with those of the conventional uniaxial creep test. 1,5,7–16…”

Small punch creep test in a 316 austenitic stainless steel

“…Evans and Wang (2008) used numerical methods for analyzing the small punch creep test. Chen et al (2010) employed the finite element method for the analysis of this text to obtain creep parameters. Komazaki et al (2009) analyzed the influence of different testing factors on this test.…”