On the Identification of Power-Law Creep Parameters from Conical Indentation

Load and hold conical indentation responses calculated for materials having creep stress exponents of 1.15, 3.59 and 6.60 are regarded as input “experimental” responses. The creep parameters are identified using the Bayesian-type statistical approach of Zhang et al. [1] for noise-free and noise-contaminated data. A database for the Bayesian-type analysis is created using finite element calculations for a relatively coarse set of parameter values with interpolation used to create the refined database used for parameter identification. The uniaxial creep and stress relaxation responses using the identified creep parameters provide a very good approximation to those of the “experimental” materials with stress exponents of 1.15 and 3.59. The sensitivity to noise increases with increasing stress exponent. The uniaxial creep response is more sensitive to the accuracy of the predictions than is the uniaxial stress relaxation response. Good agreement with the indentation response does not guarantee good agreement with the uniaxial response. If the noise level is sufficiently small, the model of Bower et al. [2] provides a good fit to the “experimental” data for the three values of creep stress exponent considered, while the model of Ginder et al. [3] provides a good fit for a creep stress exponent of 1.15.