A Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys – Intra‐Granular Heterogeneity

Abstract

For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state‐of‐the‐art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra‐granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [εmax = f(εpcum), where εmax is the maximum plastic strain and εpcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni‐axial and multi‐axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long‐range internal stresses in order to formalize, in a simple composite scheme, the intra‐granular stress–strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated.

Microplasticity in Polycrystals: A Thermomechanical Experimental Perspective

“…The estimation of the Critical Resolved Shear Stress within the considered grain gives a value close to 32 MPa, for the material point where the first thermal deviation from linearity appears. This value is of the same order of magnitude as the one observed for a AISI 316L stainless steel single crystal [31] during a tensile test. This shows the consistency and accuracy of the proposed method.…”

Material characterisation and finite element modelling of cyclic plasticity behaviour for 304 stainless steel using a crystal plasticity model

“…The stabilised region is proposed to be resulted from the development of the unique dislocation structure corresponding to a unique applied loading [40]. The relationship between the dislocation structure and the applied loading can be referred to the work by Mughrabi [41] and the review by Feaugas and Pilvin [19]. For example, fatigue test at strain range of ±0.6% stopped at cycle number 1790, and a dominant crack of length 5mm was observed.…”

“…In addition, a variety of damage initiation criteria were applied to aggregates of different surface roughness to investigate the sensitivity of these criteria to the roughness profile and pre-hardening. Feaugas and Pilvin [19] reviewed the dislocation pattern related to the hardening stages, and introduced the dislocation structure into the constitutive equations of a single crystal, including walls and channels. Li et al [20,21] considered the softening effect in the stainless steel and studied the overload effect and the influence of the loading path.…”

Latent hardening effects in low cycle fatigue of copper single crystals

“…This is observed in single and multi-slip samples with the same crystallographic orientation of the tensile axis, which may exhibit different hardening kinetics before saturation, but they show a similar level of saturation stress. Thus, the results indicate that the fatigue conditions during early cycles, which have been known to influence the fatigue process of polycrystals [33][34][35][36][37] or wavy-slip material fatigue under stress-controlled mode [61], affect the hardening rate of single crystals in total-strain-controlled fatigue cycling in the pre-saturation region, but they do not determine the stress level at the saturation.…”

“…The fatigue properties of polycrystalline materials are often history dependent and the cyclic stress-strain behavior is influenced by factors such as the mean stress, the peak stress, fatigue creep, the materials' texture and the preexisting substructure [33][34][35][36][37]. It is believed that the type and the behavior of the dislocation structure [33,34,37] and/or the distribution of the internal stresses and their evolution during cycling in polycrystalline aggregate [35,36] are responsible for this effect.…”