Crack path tracking from full field measurements: A novel empirical methodology

Abstract

The identification of crack growth models requires the knowledge of the crack path geometry and, in particular, of the crack tip position. The objective of the present paper is to provide a criterion for the detection of the crack tip position regardless of the loading conditions or the material behavior. The novelty of the proposed approach is its ability to provide a good estimation of the crack tip even when large plastic deformations occur. The proposed empirical criterion uses the evolution of the displacement gradient standard deviation along a potential crack path to locate the crack tip. It thus relies on full field measures that are relatively smooth while providing accurate displacement vectors even close to the lips. We successfully apply the proposed criterion in two cases of fatigue crack growth: A straight crack at high temperature and a curved crack at room temperature involving large plastic deformations.

Fatigue crack growth in bearing steel under cyclic mode II + static biaxial compression

“…The crack indeed corresponds to a high and localized displacement gradient (figure 3(a)). A crack path tracking algorithm [39] is used, inspired by ridge tracking algorithms, to obtain the crack path by approximating the ridge line of a scalar field that presents a local extremum at the crack lips. To detect the crack tip location, the criterion proposed by The results from this approach were compared with those from the direct optical observations and a good agreement on crack tip location was observed (error of about 2% on the measured crack length).…”

“…-Test #4 was performed on 58NCD13 steel at 5 Hz, with loading conditions also summarized in Table 2, to grow a crack in pure II mode at relatively high propagation rate. Since the contacts on the crack lips make an identification based on Williams series solution inaccurate, the crack tip position was deduced from the measured displacement field, an approach based on the evolution of the displacement gradient standard deviation along a potential crack path was used [39,40]. The map of the maximum gradient of the displacement norm, gm, is chosen as an accuracy indicator of the estimated crack path:…”

“…The crack indeed corresponds to a high and localized displacement gradient (figure 3(a)). A crack path tracking algorithm [39] is used, inspired by ridge tracking algorithms, to obtain the crack path by approximating the ridge line of a scalar field that presents a local extremum at the crack lips. To detect the crack tip location, the criterion proposed by .…”

Full-field analysis of damage under complex thermomechanical loading

“…Pattern speckle processing has been the object of intensive work these last years [15], and a recently developed LASER-engraved speckling is found to be a robust candidate to enable a full-field acquisition at high temperature [16,17]. Although DIC aims to assess strain fields, measured displacements fields may be used to detect crack initiation or crack path through the detection of DIC residues and/or discontinuous displacements [18,19,20,14]. Adding machine learning (ML) to these techniques, offers new possibilities in terms of both spatial resolution and nature of the objects to be detected such as micro-cracks.…”

Application of high‐performance DIC for a comprehensive evaluation of biaxial fatigue crack growth experiments

“…However, there is only a little literature on the automatic evaluation of crack tip position on curved paths under biaxial conditions. [9][10][11] Real-time DIC data processing is challenging due to the enormous computational load of the related algorithms. Therefore, graphics processing unit (GPU)-based 2D and 3D implementations have become increasingly popular in recent years, [12] with almost all of them concentrating on full-field evaluations.…”