Nuclear fusion High Heat Flux Components (HHFCs) experience large thermal gradients and high heat flux variations which induce severe thermal cyclic loadings. The most critical design issue for these components is the endurance strength under the required number of thermal cycles. The aim of this work is to provide procedures to perform the multiaxial creep-fatigue life assessment of HHFCs. Since the existing Design Codes do not propose procedures for the multiaxial fatigue verification considering interactive effects of creep-fatigue and local stress and temperature conditions, verification methods and rules are developed starting from the available scientific literature. The new verification methods identify the shape of the most damaging hysteresis loop considering plasticity and creep strains both in tensile and compressive conditions. The developed procedures are used to post-process the thermo-mechanical results of finite element (FE) analyses. They foresee the calculation of the creep-fatigue damage in each node and for each cyclic loading of the analyzed FE model by using the fatigue curve correspondent to the shape of the local hysteresis loop. Furthermore, the most fatigued areas are bounded and the causes of damage are identified allowing the improvement of the local design. The fatigue damage is evaluated considering the effects of local conditions: temperature, multiaxial stress-strain state, strain intensity range, effect of local mean stresses, material shakedown, accumulated damage for multiple cyclic loads, combined effect of creep-fatigue, hold periods, neutron flux. The developed procedures are successfully verified as they reproduce the creep damage effects that result by examining available experimental data. This paper presents a description of the procedures and design rules focusing in particular the innovative aspects in comparison to existing Standards. The new procedures have been developed in the framework of the activities for the design, manufacturing and procurement of the ITER Neutral Beam Injector and they are applied for creep-fatigue verifications of the in-vessel HHFCs.
Procedures for Multiaxial Creep-Fatigue Verification of Nuclear Components
Dalla Palma M;Zaccaria P
2011
Abstract
Nuclear fusion High Heat Flux Components (HHFCs) experience large thermal gradients and high heat flux variations which induce severe thermal cyclic loadings. The most critical design issue for these components is the endurance strength under the required number of thermal cycles. The aim of this work is to provide procedures to perform the multiaxial creep-fatigue life assessment of HHFCs. Since the existing Design Codes do not propose procedures for the multiaxial fatigue verification considering interactive effects of creep-fatigue and local stress and temperature conditions, verification methods and rules are developed starting from the available scientific literature. The new verification methods identify the shape of the most damaging hysteresis loop considering plasticity and creep strains both in tensile and compressive conditions. The developed procedures are used to post-process the thermo-mechanical results of finite element (FE) analyses. They foresee the calculation of the creep-fatigue damage in each node and for each cyclic loading of the analyzed FE model by using the fatigue curve correspondent to the shape of the local hysteresis loop. Furthermore, the most fatigued areas are bounded and the causes of damage are identified allowing the improvement of the local design. The fatigue damage is evaluated considering the effects of local conditions: temperature, multiaxial stress-strain state, strain intensity range, effect of local mean stresses, material shakedown, accumulated damage for multiple cyclic loads, combined effect of creep-fatigue, hold periods, neutron flux. The developed procedures are successfully verified as they reproduce the creep damage effects that result by examining available experimental data. This paper presents a description of the procedures and design rules focusing in particular the innovative aspects in comparison to existing Standards. The new procedures have been developed in the framework of the activities for the design, manufacturing and procurement of the ITER Neutral Beam Injector and they are applied for creep-fatigue verifications of the in-vessel HHFCs.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
