Slant strained band development during flat to slant crack transition in AA 2198 T8 sheet: in situ 3D measurements

Abstract

International audienceIn this work 3D strain and damage analyses are performed in the immediate vicinity of the notch root of a at CT-like specimen made of aluminum alloy. Experimental data, partially exploited by Morgeneyer et al (2014b), were obtained by using synchrotron laminography and the 3D reconstructed volumes are subsequently analyzed via Digital Volume Correlation. These data enable for in situ assessments of strain elds and ductile damage in the zone where the stress triaxiality evolves from elevated to lower levels, which is accompanied by at-to-slant crack transition. The measured strain eld patterns in this area are analyzed herein in a systematic manner by studying the incremental strain activity during several loading steps. It is shown that from the very beginning of the loading history multiple slant strained bands appear in front of the notch root while the corresponding damage growth sets in at later loading stages and higher strains. The activity of the dierent strained bands at the notch root is alternating between dierent locations over the loading history. However, the band leading to nal rupture is always active. The region where slant fracture occurs is identied to be in plane strain condition with respect to the crack propagation direction

Digital Volume Correlation: Review of Progress and Challenges

“…If one element lacks contrast but its surrounding ones are contrasted then global DVC may still converge and succeed in determining the displacement field [156,30,157,28]. Most applications of global DVC were based upon finite element discretizations of the ROI.…”

“…In the case of large deformations, there is always the possibility of updating the reference configuration, which becomes the deformed configuration of the previous calculation. So-called incremental DVC procedures have been implemented [103,30,157]. It is worth remembering that displacement fields have then to be interpolated in order to have access to cumulative displacement fields.…”

“…When compared to µCT [131], it leads to higher levels of measurement uncertainties [156], which are partly due to the missing spatial frequencies and reduced resolution of laminographic scans along the rotation axis [238]. However, it could still be used to analyze the flat-to-slant transition of ductile tearing of aluminum alloys for low stress triaxialities with global DVC [156,158,30] and regularized DVC [214,157]. failure mechanisms.…”

Numerical modeling of ductile fracture at the microscale combined with X-ray laminography and digital volume correlation

“…• X-ray laminography to get 3D pictures of an in situ test in a synchrotron facility [2,3]. The ability to use flat specimens is of particular interest in the field of mechanics of materials since sheet-like samples allow for a wide range of engineering relevant boundary conditions.…”

“…To achieve this goal, three modern techniques are seamlessly coupled, namely, laminography to image in situ tested large flat samples made of ductile materials [2], digital volume correlation (DVC) to measure 3D displacement (and strain) fields in the bulk [3], and 2D/3D finite element simulations using the experimental information on multiple length-scales [4]. In this paper, the overall methodology will be presented first to show how these three techniques can be combined.…”