Predicting Damage and Failure under Low Cycle Fatigue in a 9Cr Steel

AUTHOR/S: Biglari, Farid; Imperial College London, Mechanical Engineerin Lombardi, Paolo; Centro Sviluppo Materiali Budano, Sergio; Centro Sviluppo Materiali Davies, Catrin; Imperial College London, Mechanical Engineering Nikbin, Kamran; Imperial College London, Mechanical Engineering PAPER PRESENTED TO: Fatigue and Fracture of Engineering Materials and Structures

ABSTRACT

Numerical and experimental investigations of low-cycle fatigue life of a 9Cr steel have been presented in this paper with the view of predicting damage under low cycle fatigue conditions. A set of experimental uniaxial tensile and cyclic tests on the material have been conducted over a range of temperatures.

 

The 9Cr steel exhibited both cyclic softening and nonlinear kinematic hardening behaviours. The finite element analysis of cyclic loading of the material was based on a nonlinear kinematic hardening criterion using the Chaboche constitutive equations and the hysteresis strain energy concept for damage derivation.

 

Therefore the cyclic softening is combined with damage initiation and evolution models to predict the remaining life of the specimen. As a result, a novel approach employing a local ductile damage initiation and failure model using the hysteresis total stress-strain energy concept combined with element removal has been employed to predict failure in laboratory tests. The cyclic softening model in conjunction with the progressive damage evolution model successfully predicted the failure times of the experimental tests for 9Cr steels performed.

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