Surface Decoration for Improving the Accuracy of Displacement Measurements by Digital Image Correlation in SEM

Winiarski, B.; Schajer, G. S.; Withers, Philip J.

doi:10.1007/s11340-011-9568-y

Cited by 60 publications

(30 citation statements)

References 32 publications

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“…Yttria-stabilized Zirconia (YSZ) nano-particles were used for surface decoration to obtain optimum image contrast for high accuracy DIC analysis. It must be noted that though the YSZ nano-particles are able to provide asharply defined surface decoration over reasonably large surface areas, the particle size distribution may be locally inhomogeneous[16]. Unsolved facets due to such local heterogeneity in the particle sizes, were omitted from the calculations.Stress distribution at sub-microscopic length scales need not always be homogeneous i.e.…”

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confidence: 99%

Measurement of spatial stress gradients near grain boundaries

2017

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A correlative method based on Electron Back Scattered Diffraction and Focused ion-beam-Digital image correlation slit milling technique was used to quantitatively determine spatially resolved stress profiles in the vicinity of grain boundaries in pure titanium. Measured local stress gradients were in good agreement with local average misorientation and experimentally calculated geometrically necessary dislocation densities. Stress profiles within few hundred to thousand nanometers near the grain boundary display a local minimum, followed by a typical Hall-Petch type variation of "one over square root of distance". The observed trends allude to local stress relaxation mechanisms active near grain boundaries. The term "residual stress" prescribes to locked in stresses, which remain after materials processing. These stresses span across different length scales. The influence of microstructure i.e. spatial distribution of grains and phases, is significant on local residual stress distribution. In particular, grain boundaries contribute significantly to build up of such internal stresses, owing to varied mechanical response of different grain orientations during plastic deformation. In metals, the motion and interaction of dislocations within the material microstructure and their resultant impact on micro scale plasticity is crucial for understanding the macroscopic mechanical performance and failure resistance of a component. Dislocations can not only interact among themselves but also with other crystal defects such as grain boundaries, often giving rise to complex geometrical configurations of stored dislocations that are associated with long-range elastic stress fields. Superposition of such stress fields invariably results in a strong spatial heterogeneity in local stress states, which directly determines preferential zones for damage nucleation and thereby fracture characteristics in materials. Stored dislocations are generally classified into two types viz. geometrically necessary dislocations (GNDs) that accommodate a lattice curvature from a deformation gradient; and Marked_manuscript_revised Click here to view linked References

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confidence: 99%

Measurement of spatial stress gradients near grain boundaries

2017

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“…(a) Overview of the instrumentation, (b) detail of the laser video sample alignment system and coordinate system used methods are presented below). These measurements were performed using a FEI Nova NanoLab 600i Dualbeam FIB-SEM microscope 1 with digital image correlation of surface features [53]. Since the RS profile changes with the depth from the surface (as discussed in the next section), the Set II measurements are designed to sample at the same depth as that probed by μXRD.…”

Section: Methodsmentioning

confidence: 99%

“…In order to reduce the rate of re-deposition of the excavated material, to improve the topographic contrast and prevent overexposure to Ga + [42,43,53] when FIB milling we used a Gatan PECS 682 etching-coating system equipped with a Gatan 681.20000 thickness metre to sputter a~10 nm-thick carbon film on the specimen surface prior to FEGSEM imaging and FIB milling. The carbon target was exposed to a broad argon-ion beam of the current of 550 μA accelerated with the electric potential of 10 kV in a vacuum environment of~2 × 10 −5 Torr.…”

Section: Methodsmentioning

confidence: 99%

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High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

et al. 2016

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The moderately high lateral RS gradients (on the order of tens of MPa/μm) near shot peened notches in conjunction with the shallow treatment depth (some hundreds of microns) limit the application of far-field and/or high resolution synchrotron diffraction residual stress measurement techniques. Recently proposed Focused Ion Beam -Scanning Elecron Microscope -Digital Image Correlation (FIB-SEM-DIC) based micro mechanical stress relaxation methods for the measurement of residual stress at the micron scale became suitable techniques for local evaluation of residual stresses and stress gradients in shot peened specimens. In this paper ultra-high resolution (~0.5-0.8 μm depth and 5-10 μm lateral resolution) mechanical relaxation stress measurements were used to evaluate the stress variation local to individual peening dimples in ceramic (60-120 μm diameter beads) shot peened Al-7075-T651 double notched samples having 0.15, 0.5 and 2.0 mm radii using Micro-Hole Drilling (μHD), Micro-Slot Cutting (μSC) and micro X-ray Diffraction (μXRD) methods. The micron-sized sampling volumes enabled the stress to be evaluated in individual impact craters (dimples) showing significant point-to-point variation (~+/−150 MPa) (with certain dimples even recording tensile stresses). After around 30 μm of layer removal the heavily deformed region had largely been removed and the stress profile became much more homogeneous. At this depth the μHD and μSC results were in good accord with those from μXRD measurements which sample over a much larger volume (~40 μm depth × 50 μm laterally) showing an in-plane compressive stress of around 150 MPa far from the notches with the residual stress rising to about 200 MPa at a blunt (2 mm) notch and 500 MPa for a sharp (0.15 mm) one. Further, these recorded variations of residual stresses were correlated with microstructural features, e.g. grains, networks of sub-surface cracks, intermetallics and highly deformed sub-surface regions, revealed by large volume Serial Sectioning Tomography using Plasma Xe + Focus Ion Beam -Scanning Electron Microscope (PFIB-SEM), EDS and EBSD maps. This allowed for the first time characterize large volume (100 × 66 × 30 μm 3 ) of shot peened regions with resolution of dozens of nanometers and correlate residual stress depth profiles with 3D microstructural features. Finally, in (Benedetti et al. 2016, Int. J. Fatigue) these RS measurements are used to reconstruct the RS field through finite element (FE) analyses.

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“…8(b). Fine-scale Pt patterns have been used extensively in the literature for DIC on SEM images [39,40]. Here, however, the Pt pattern has been optimized (in terms of speckle size and contrast) to yield the maximum displacement resolution for DIC applied to optical profilometry images, which explains the choice for a much coarser pattern with smooth edges of the speckles.…”

Section: Force and Displacement Measurement And Stress-strain Curvementioning

confidence: 99%

A Uni-Axial Nano-Displacement Micro-Tensile Test of Individual Constituents from Bulk Material

Hoefnagels

Bergers

et al. 2017

Exp Mech

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For both single-phase and multiphase metallic materials, it is necessary to understand the mechanical behavior on the grain-size scale in detail to get information that is not obtainable from macro-scale mechanical characterizations. This paper presents a methodology for uniaxial tensile testing of micro-specimens isolated from a bulk material. The proposed concept of multiple parallel micro-tensile specimens at the tip of a macro-sized wedge reduces the alignment work and offers an easy way for specimen handling. The selection of site-specific specimens is based on detailed microstructural and crystallographic characterization. Three kinds of representative specimens are presented to illustrate the wide range of application of the methodology for a variety of materials. Accurate, reproducible measurement of force (2.5 μN resolution) and displacement (~10 nm resolution) is demonstrated, while accurate alignment (in-plane rotational and out-of-plane tilt misalignment of <0.2°) limits the stress due to bending to <0.2% of the imposed uni-axial stress. Combined with detailed material characterization on both sides of the microspecimens, this method yields detailed insights into the micro-mechanics of bulk materials which is hard to obtain from traditional macro-mechanical tests.

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Surface Decoration for Improving the Accuracy of Displacement Measurements by Digital Image Correlation in SEM

Cited by 60 publications

References 32 publications

Measurement of spatial stress gradients near grain boundaries

Measurement of spatial stress gradients near grain boundaries

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

A Uni-Axial Nano-Displacement Micro-Tensile Test of Individual Constituents from Bulk Material

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