Plastic zone evolution during fatigue crack growth: Digital image correlation coupled with finite elements method

Abstract

et al.. Plastic zone evolution during fatigue crack growth: Digital image correlation coupled with finite elements method. International Journal of Solids and Structures, Elsevier, 2019, 171, pp.Abstract Nonlinearities effects at the crack tip, due to the elastic-plastic material behavior, impact the crack growth rate and path. This paper is devoted to the study of the plastic zone evolution in the crack tip region. The methodology relies on coupling an elastic-plastic Finite Elements Method (FEM) model and experimental displacements measured by Digital Image Correlation (DIC). These latter are introduced as Dirichlet boundary conditions in the finite elements analysis. The considered FEM domain is constant, i.e. the same mesh with a centered crack is moved to each new crack tip position deduced from DIC. The new boundary conditions are updated and the residual stresses and plastic strains of the former computation are interpolated and actualized on the mesh shifted to the new crack tip position in order to incorporate them in the numerical model. The coupling method allowed applying experimental boundary conditions in order to be as close as possible to real experimental conditions and to observe the plasticity evolution from small to large scale yielding conditions. A fatigue test was conducted to validate the proposed approach. The identification residues are proved to be lower than those obtained with an experimental displacements projection onto Williams' series basis, which is a method commonly used with DIC. The coupling results present an attractive similarity with Irwin's model regardless of the crack length. Thus, the definition of the mask needed for the displacements fields projection on Williams' model can be deduced with a reliable estimate of Irwin's plastic radius.

Review on Strain Localization Phenomena Studied by High‐Resolution Digital Image Correlation

“…Finally, DIC serves for modeling and parameter identification (e.g., ref. [33]). The chronological overview starts in 2000 and includes scientific publications until 2020.…”

“…Hosdez et al [33] studied the evolution of a plastic zone in front of a crack tip using coupled elastic-plastic FEM simulations and experimental DIC measurements. The model approach was validated by a fatigue crack growth experiment on silicon and molybdenum-alloyed cast iron with spheroidal graphite.…”

“…Another example was presented by Song et al [32] for the formation of bainite in the steel 100Cr6 using ab initio calculations and PF modeling in combination with advanced characterization techniques such as atom probe tomography (APT) and TEM. As a third example, the recently published approach of Hosdez et al [33] demonstrates the coupling of an elastic-plastic FEM model and experimental measurements of displacements using DIC for the investigation of the evolution of the plastic zone during fatigue crack growth in a cast iron with spheroidal graphite. The coupling of FEM and DIC combines the accuracy and the large amount of information provided by DIC with the wide possibility range of FEM.…”

“…As a possible way out of this restriction, the coupling of CT and 3D FEM was postulated, which seems to be promising for cast iron due to the excellent contrast between graphite and iron. [33] The aim of the Review is twofold. On one hand, the Review highlights the richness, versatility, and usefulness of full-field measurements using DIC for investigations of strain localization phenomena in the field of materials science and engineering (MSE).…”

Fatigue crack growth in compacted and spheroidal graphite cast irons

“…The retained DIC methodology is based on a local approach with a non-continuous description. The projection is carried out on the Williams' model which expresses displacements in a cracked medium in the small scale yielding conditions [35,36,33] under the form of expansion series [37]. More details about the projection method can be found in [33].…”