A computational lifetime prediction of a thermal shock experiment. Part II: discussion on difference fatigue criteria

Abstract

A B S T R A C TThe SPLASH experiment has been designed in 1985 by the CEA to simulate thermal fatigue due to cooling shocks on steel specimens and is similar to the device reported by Marsh in Ref.[1]. The purpose of this paper is to discuss the application of different fatigue criteria in this case. The fatigue criteria: dissipated energy, Manson Coffin, Park and Nelson, dissipated energy with a pressure term, are determined for the experiment using results from FEM computations presented in the first part of the paper (Part I) 2 and compared with results from uniaxial and multiaxial experiments from literature. The work emphasizes the evolution of the triaxiality ratio during the loading cycle.A = elastic 4th order tensor c, k = thermal capacity and conductivity E, ν = young's modulus and Poisson's coefficient J 2 = second invariant of the deviatoric stress tensor P = hydrostatic pressure p = cumulated plastic strain q = thermal flux r = heat source T = temperature field TF = triaxiality factor u = displacement field W p = dissipated energy density per cycle σ , = equivalent stress and strain ranges , e = strain tensor and its deviatoric part e , p = elastic and plastic strain tensors ρ = volumic mass σ Y = elastic limit σ, s = stress tensor and its deviatoric part I N T R O D U C T I O NIn Part I of this paper, we discussed the complete mechanical analysis of the SPLASH experiment and presented a first lifetime estimation with a modified dissipated energy with a pressure term fatigue criterion.We recall that the experiment is a thermal shock fatigue test. The sample is heated during the complete thermal cycle (7.75 s) by Joule effect and is cyclically cooled down during a very short period (0.25 s) by a water spray on a small area on two opposite faces. This leads to high gradients in the specimen and as a consequence a complete structural analysis is needed in order to estimate the values of the thermomechanical fields. The test is characterized by the temperature difference T between the

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