Case study of the applicability of cyclic hardening material descriptions in finite element simulation of cyclic thermal shocks

Abstract

A B S T R A C T Finite element simulation of cyclic thermal loading induced fatigue can be used to predict the service time of components in industrial environments. Various damage criteria for low cycle fatigue have been developed, which require a temperature-dependent description of the cyclic plastic hardening of the material. In these descriptions the shape of the stress-strain loop is coupled to its cyclic evolution, which leads to problems under specific loading conditions and/or for materials not exhibiting a quick cyclic stabilization. The applicability of a basic, nonlinear kinetic-isotropic cyclic hardening description combined with an approach in which its parameters depend on the accumulated plastic strain and temperature is evaluated in a case study mimicking boundary conditions that occur in the primary cooling circuit of nuclear power plants. The model is calibrated with experimental data for a material that exhibits cyclic softening, requiring a modification of the hardening description.C = kinematic hardening parameter F = yield surface H r = ratchet hardening parameter N = cycle number p = accumulated plastic strain T = temperature x a = subscript 'a' refers to the amplitude in a cyclic condition x = underlined symbol means it is a tensoṙ x = dotted symbol refers to the time derivative α = back stress ε = strain ε p = plastic strain γ = kinematic hardening parameter σ = stress σ 0 = yield stress I N T R O D U C T I O NCyclic thermal shock occurring in different components in the primary cooling circuit of a nuclear plant can induce fatigue damage, in some cases leading to unexpected component failure. 1 A detailed analysis of such loading conditions has been determined as one of the applied research goals in nuclear power industry. 2 The problem at hand is multidisciplinary, and requires knowledge about the fluid dynamics of the cooling medium, the heat transfer between the coolant and the structure, the stress-strain response of the material and, finally, the damage introduced in the material. Substantial research programs have been mounted to address this complexity, which include both experimental and computational analyses. The work presented in this article must be seen within such a context and concerns a finite element analysis of the local 562

Experimental characterisation of a CuAg alloy for thermo‐mechanical applications. Part 1: Identifying parameters of non‐linear plasticity models

“…Although this work focuses on the material characterization of a copper alloy for a mould, the proposed procedure can be also extended to other applications and materials: for example, a similar copper alloy is adopted in the water‐cooled part of anodes for electric arc furnaces, where the scrap steel is melted . Cyclic hardening material models are also of interest for the simulation of cyclic thermal shocks in steel parts and can be used, for instance, to develop numerical analyses for life prediction in tool steel . Automotive component design can also benefit from accurate simulations with thermo‐mechanical loads, as suggested in Thomas et al…”