Fatigue crack closure: A myth or a misconception?

Abstract

In this paper, we have extended our previous study on fatigue crack closure to examine the phenomenon of crack opening displacement (COD) and its impact on the crack tip fields in both 2D and 3D specimen geometries using full‐field experimental measurements and integrated finite element modelling. Digital image correlation (DIC) and digital volume correlation (DVC) were used to measure the near‐tip material responses on the surfaces (DIC) and the interior (DVC) of the specimens. Materials with elastic‐plastic and large plastic characteristics were chosen for the study, where plasticity‐induced premature contact between the crack flanks is known to occur. Displacement maps around the cracks were obtained using DIC and DVC at selected load increments and were introduced as boundary conditions into the finite element (FE) models to obtain the “effective” crack driving force in terms of J‐integral, and the results were compared with those “nominal” from the standard FE analysis. Both visual observation and compliance curves were used to determine the “crack opening” levels; whilst the impacts of the crack opening on the crack driving force J and the normal strains ahead of the crack tip were evaluated in 2D and 3D. The results from the study indicate that, crack closure, although clearly identifiable in the compliance curves, does not appear to impact on global crack driving force, such as J‐integral, or strains ahead of the crack tip; hence, it may well be a misconception.

The application of digital image correlation (DIC) in fatigue experimentation: A review

“…In an extension of their previous study, 135 Tong et al 137 used surface DIC and volumetric DVC displacement map outputs concurrently with FE modeling to provide more evidence that crack closure, although clearly identifiable in compliance curves in the presence of significant plasticity, does not appear to have an impact on global crack driving force, such as the J‐integral, or strains ahead of the crack tip and, hence, may be a misconception. Analysis with 2D‐DIC was performed on 316L SS CT fatigue specimens, and DVC analysis was performed on SGI corner notched tension fatigue specimens with a resolution of 3.2 μm/voxel.…”

Effects of surface roughness on fatigue behavior of additively manufactured stainless steel 316L

“…The elastic and plastic parameters determined by Tong et al [6] and enters ABAQUS[7],which are listed in Table 1.…”

Fatigue crack growth modeling considering a hybrid propagation strategy

“…The growth and nucleation of micro-voids was shown to influence da/dN and crack closure itself, exposing an interdependency of mechanisms at the crack tip. Despite the controversy in this matter, 33 crack closure has been observed experimentally [34][35][36][37] and shown to be dominant over residual stresses in the Paris Regime, whereas, in the threshold region, the opposite is expected to occur. 38 The crack closure level was increased by considering growth and nucleation of micro-voids because the porous damage accumulation rises both the size of the plastic zone ahead of the crack tip and the intensity of plastic deformation.…”