Plasticity models for materials and structures LCF simulation

Mathematical simulation of processes prior to low-cycle fatigue (LCF) crack initiation and describing its propagation is actual for many high-loaded structures in conditions of nonstationary cyclic loading. Success of LCF lifetime prediction depends on solution results of a number of related problems: creation of plasticity models, adequately describing processes taking place during alternating elasto-plastic deformation; formulating criterions of low-cycle fatigue damage; development of effective numerical methods of simulation. Phenomenon of LCF is directly coupled with the process of plastic deformation of structure, because development of failure has two stages. The first stage of hidden damage accumulation in the construction material is prior to the second – crack nucleation and propagation. During cycle loading in process of crack nucleation, propagation and growth alternating nontationary plastic deformation occurs near crack end, leading to damage accumulation with following material fracture and crack propagation. In this paper current state of the problem is examined considering modern conception of methods and models of non-isothermal deformation during cyclic loading [1,2]. Low-cycle fatigue phenomenon formulates tight requirements to models accuracy and numerical methods efficiency. LCF criterions could be formu- lated being dependent only on cycle plastic deformations (high level of stress or strain), or both on plastic strains and alternating elastic strains of the cycle (transition region between LCF and classical fatigue). Process of alternating or complex loading in plastic zone leads, depending on "deformation history", to changing of original elastic and plastic material parameters: modulus of elasticity, Bauschinger's effect parameters, nonlinear parameters of hard- ening. According to parameters taken into account, scalar or vector models of damage is considered.