Measurement of elastic and rotation fields during irreversible deformation using Heaviside-digital image correlation

Abstract

The recent development of the high resolution and discontinuity-tolerant digital image correlation technique enables the extraction of discontinuities within a displacement field. The technique provides quantitative analysis of discontinuities arising from slip, shear bands, cracks, and grain boundary sliding in a variety of material systems, including polycrystalline metallic materials. The discontinuity-tolerant digital image correlation method can be implemented to retrieve not only quantitative discontinuity analysis but also the local strain and rotation fields that operate near these discontinuities. The present implementation includes high-resolution digital image correlation (HR-DIC) measurements collected in a scanning electron microscope for analysis of both the plastic and elastic fields that develop during deformation of polycrystalline metallic materials. The combination of the discontinuity-tolerant DIC technique with the computation of internal gradients enables extraction of non-localized strain and rotation fields during plastic deformation of a nickel-based superalloy. Therefore the lattice rotation/expansion and plastic localization that occur during deformation can be determined in a single experiment. This method is validated using synthetic images with preset deformation, and experimental measurements using the electron back scatter diffraction (EBSD) technique.

Bringing to Life a Newly Discovered Signature of Fatigue Crack Initiation via Multimodal Characterizations

“…First, the crack initiation theory of Villechaise et al and Larrouy et al connected crack initiationb in nickel-based superalloys to the impingement of slip localization on a grain boundary where slip transmission is not facilitated [6,7]. Second, Stinville et al used the microscopic strain and orientation fields provided by H-DIC and 2D-EBSD surface measurements to directly connect the impingement of slip localization physically shearing a neighboring grain boundary to microvolumes [8]. With this information at hand, we conducted a multimodal approach that combined the microscopic strain fields of surface H-DIC measurements and orientation fields of surface and volumetric EBSD measurements with the time-resolved orientation and grain-scale mechanical information of ff-HEDM measurements to investigate the effectiveness of using the statistics of DSGODs as a signature of grains with with high CIP.…”

“…Specifically in nickel-based superalloys, prior studies by Villechaise et al and Larrouy et al theorize that areas where localized slip impinges on a neighboring grain boundary, but the slip cannot transmit into the neighboring grain, are favorable crack initiation sites due to the slip shearing the physical grain boundary [6,7]. A recent high-resolution deformation study by Stinville el al on the Inconel-718 nickel-based superalloy furthered these findings by coupling two-dimensional electron backscatter diffraction (2D-EBSD), an microscopic orientation field measurement, and heaviside digital image correlation (H-DIC), a microscopic strain field measurement, to spatially correlate the same slip impingement behavior with plumes of intense intragrain lattice rotation (up to 10 • ), termed microvolumes, as shown in Figure 1 [6][7][8][9][10][11]. These observations, when combined with the crack initiation theory above, provide microvolumes as measurable features that may indirectly identify grains with the most potential for initiating a fatigue crack.…”

“…ff-HEDM cannot provide spatial information to the DSGODs, but a CIP signature, once validated through the electron characterization methods listed above, can be tracked in-situ for large collections of both surface and subsurface grains as they evolve under cyclic loading. The data in [8], along with these additional characterizations, provide a one-of-a-kind opportunity to explore our hypothesis.…”

Multi-modal Dataset of a Polycrystalline Metallic Material: 3D Microstructure and Deformation Fields

“…The in-plane slip displacements represent the physical displacement in the plane of the surface produced by a slip event. More details on the Heaviside-DIC method can be found elsewhere 12 . The amplitude (norm) of slip is measured in nanometers for each measured point and is given in Fig.…”

“…The values at each pixel in the images are the quantitative physical value of the displayed full fields given in unit length for the strain field ε xx , in pixels for the in-plane slip amplitude, and in radians for the in-plane slip direction. We refer the reader to 10 , 12 for more information about the physical meaning of these quantities. The data can be downloaded from the DRYAD repository 29 .…”