On the Limitation and Modification of Cocks-Ashby Model Based Multiaxial Creep Design Criteria

doi:10.3901/JME.2017.16.141

Abstract

Abstract: Structure analysis of creep deformation under multiaxial stress state is the theoretical basis of high temperature equipment design. The classic cavity growth theory(CGT) Cocks-Ashby multiaxial power-law creep model and its simplification have the limitation and strict applicable condition that is only suitable for modeling the creep behavior whose main damage mechanism is the grain boundary voids growth. The multiaxial creep factor, which serves as the conversion between uniaxial and multiaxial creep ductility, in the simplified model has the problem that the values in low triaxiality are lower than the experimental data. Based on WITCHTMANN's work that gives a simple modification of this problem, a new multiaxial creep factor is proposed to give a better modification. A blade model has been built in a simplified static stress field to calculate the equivalent multiaxial creep strain distribution. Results show that the mid zone of the blade root has a relatively large equivalent multiaxial creep deformation because of the relatively large triaxiality and relatively small multiaxial creep factor, leading to significant increase of the total potential failure area after correction by multiaxial creep factor.

Key words: Cocks-Ashby model, multiaxial creep, simplified model modification, viscoplasticity

CLC Number:

O345

HU Jingdong, LIU Changjun, XUAN Fuzhen. On the Limitation and Modification of Cocks-Ashby Model Based Multiaxial Creep Design Criteria[J]. Journal of Mechanical Engineering, 2017, 53(16): 141-147.

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