Micromechanical Analysis Of Local Micro-deformation Behaviour And Exploration Of Finite Element Characterization Of Duplex Stainless Steel

Duplex stainless steel components are often subjected to cyclic loads in its application,but due to the discontinuous mechanical properties of duplex stainless steel,the stress concentration when it is under load is relatively serious.It may have produced a large local cyclic plastic deformation under a small macroscopic load.In order to meet the structural design requirements of components,the main contents and conclusions of this article are as follows:(1)For the austenite and ferrite phases of duplex stainless steel,unidirectional and cyclic nanoindentation experiments under different loading modes(contact load and indentation displacement)and different loading waveforms are performed.At the same time,combined with digital image correlation technology(DIC)to observ e the local microscopic deformation behaviour and evolutionary characteristics of duplex stainless steel under uniaxial tensile load.(2)Finite element inversion of the unidirectional and cyclic nanoindentation experiments of the austenite and ferrite phases in duplex stainless steel is designed to describe the plasticity and cycle deformation of the austenite and ferrite phases in duplex stainless steel,and the modified Abdel-Karim-ohno constitutive model parameters are determined.The finite element analysis results are compared with macro and micro experiments to confirm that the constitutive model and parameters are reasonable and available.(3)Based on the representative element of duplex stainless steel microstructure,the finite element analysis of uniaxial tensile and cyclic deformation behaviour was conducted to verify and discuss the distribution and evolutionary characteristics of local deformation.The analysis shows that the strength and hardness of the ferrite phase in the duplex stainless steel compare with those of the austenite phase,and there is a definite interaction between the two phases through the grain boundaries.The material at the grain boundary of each phase will affect the mechanical properties of the adjacent phase.Under cyclic loading conditions,both the austenite phase and the ferrite phase will produce a significant indentation ratchet phenomenon and the austenite phase will produce larger indentation ratchet deformation than the ferrite phase,and the higher the load level,the higher the pressure ratchet deformation is.In addition,the method for describing the cyclic plastic behaviour of duplex stainless steel developed in this paper is reasonable and available after comparison with experiments.And the local microscopic deformation behaviour and evolutionary characteristics of duplex stainless steel under uniaxial tensile load observed by digital image correlation technology(DIC)are consistent with the results of finite element analysis.The characterization method for the cyclic plastic behaviour of duplex stainless steel developed in this paper is compared with experiments and confirmed to be reasonably available.The distribution of local stress and strain is related to the grain distribution,shape,the size,grain interaction and load.The strain of duplex stainless steel under tensile and cyclic load is concentrated in austenite,and the stress is concentrated in ferrite.The maximum strain is mainly concentrated in the narrow and sharp regions of austenite grains,while the maximum stress mainly occurs in the narrow and sharp regions of ferrite grains.