On the Development of Viable Cruciform-Shaped Specimens: Towards Accurate Elevated Temperature Biaxial Testing of Lightweight Materials

2010 ◽  
Vol 433 ◽  
pp. 93-101 ◽  
Author(s):  
Fadi K. Abu-Farha ◽  
Louis G. Hector ◽  
Mohammed A. Nazzal
Keyword(s):  
Plastic Deformation ◽  
Elevated Temperature ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Digital Camera ◽  
Image Correlation ◽  
Geometrical Parameters ◽  
Biaxial Testing ◽  
Strain Fields ◽  
Lightweight Materials

This paper is focused on the development of viable cruciform-shaped specimen geometries where large biaxial plastic deformation can be achieved within their gauge areas. A custom-built balanced biaxial testing fixture is used to plastically deform a variety of carefully-designed AZ31B-H24 magnesium specimens until failure. Images recorded from a digital camera positioned to monitor deformation in the gauge area of each specimen are used to compute the strain fields with a digital image correlation (DIC) algorithm. The viability of each design is validated based on the extent of biaxiality of measured strains and its ability to promote plastic deformation within its gauge area up until failure. The study provides key insights into the influences of certain geometrical parameters on deformation-biaxiality in cruciform specimens.

scholarly journals Mechanical Behavior of Differently Oriented Electron Beam Melting Ti–6Al–4V Components Using Digital Image Correlation

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Edel Arrieta ◽  
Mohammad Haque ◽  
Jorge Mireles ◽  
Calvin Stewart ◽  
Cesar Carrasco ◽  
...  
Keyword(s):  
Electron Beam ◽  
Digital Image Correlation ◽  
Failure Analysis ◽  
Digital Image ◽  
Electron Beam Melting ◽  
Measuring Method ◽  
Image Correlation ◽  
Layer By Layer ◽  
Strain Fields ◽  
Shear Effects

Mechanical properties of additive manufactured metal components can be affected by the orientation of the layer deposition. In this investigation, Ti–6Al–4V cylindrical specimens were fabricated by electron beam melting (EBM) at four different build angles (0 deg, 30 deg, 60 deg, and 90 deg) and tested as per ASTM E8 Standard Test Methods for Tension Testing of Metallic Materials. With the layer-by-layer fabrication suggesting granting anisotropic properties to the builds, strain fields were recorded by digital image correlation (DIC) in the search for shear effects under uniaxial loads. For the validation of this measuring method, axial strains were measured with a clip extensometer and a virtual extensometer, simultaneously. Failure analysis of the specimens at different orientations was conducted to evidence the recording of shear strain fields. The failure analysis included fractography, optical micrographs of the microstructure distribution, and failure profiles displaying different failure features associated with the layering orientation. Additionally, an experimental study case of how the failure mode of components can potentially be designed from the fabrication process is presented. At the end, remarks about the shear effects found, and an insight of the possibility of designing components by failure for safer structures are discussed.

scholarly journals Robust Filtering Options for Higher-Order Strain Fields Generated by Digital Image Correlation

2020 ◽  
Vol 1 (4) ◽  
pp. 174-192
Author(s):  
Nedaa Amraish ◽  
Andreas Reisinger ◽  
Dieter H. Pahr
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Tensile Tests ◽  
Image Correlation ◽  
Field Strain ◽  
Strain Fields ◽  
Full Field ◽  
Low Pass ◽  
Discrete Measurement ◽  
Mean Filtering

Digital image correlation (DIC) systems have been used in many engineering fields to obtain surface full-field strain distribution. However, noise affects the accuracy and precision of the measurements due to many factors. The aim of this study was to find out how different filtering options; namely, simple mean filtering, Gaussian mean filtering and Gaussian low-pass filtering (LPF), reduce noise while maintaining the full-field information based on constant, linear and quadratic strain fields. Investigations are done in two steps. First, linear and quadratic strain fields with and without noise are simulated and projected to discrete measurement points which build up strain window sizes consisting of 6×5, 12×11, and 26×17 points. Optimal filter sizes are computed for each filter strategy, strain field type, and strain windows size, with minimal impairment of the signal information. Second, these filter sizes are used to filter full-field strain distributions of steel samples under tensile tests by using an ARAMIS DIC system to show their practical applicability. Results for the first part show that for a typical 12×11 strain window, simple mean filtering achieves an error reduction of 66–69%, Gaussian mean filtering of 72–75%, and Gaussian LPF of 66–69%. If optimized filters are used for DIC measurements on steel samples, the total strain error can be reduced from initial 240−300 μstrain to 100–150 μstrain. In conclusion, the noise-floor of DIC signals is considerable and the preferable filters were a simple mean with s*¯ = 2, a Gaussian mean with σ*¯ = 1.7, and a Gaussian LPF with D0*¯ = 2.5 in the examined cases.

Digital Image Correlation as a Tool for Monitoring Crack Networks on the Surface of MgO-Based Refractory Castables

2014 ◽  
Vol 92 ◽  
pp. 242-247
Author(s):  
Rafael G.M. Saracura ◽  
Rodrigo B. Canto ◽  
Victor Carlos Pandolfelli ◽  
Nicolas Schmitt ◽  
François Hild
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Displacement Field ◽  
Digital Camera ◽  
Experimental Results ◽  
Image Correlation ◽  
Post Processing ◽  
Climatic Chamber ◽  
Refractory Castables

This paper deals with the characterization of crack networks on the surface of refractory castable slabs, which are induced by stresses arising during the curing and drying (CD) stages. Images of the surface of castable samples placed in a house-made climatic chamber were recorded during the CD stages with a digital camera and processed by Digital Image Correlation (DIC) tomeasure the displacement field. Post-processing of DIC results were performed to estimate the length, orientation and opening of cracks in networks. The methodology is detailed and first analyses of experimental results are shown.

The Wavelike Plastic Deformation of Single Crystal Copper

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Russell J. McDonald ◽  
Christos Efstathiou ◽  
Peter Kurath
Keyword(s):  
Plastic Deformation ◽  
Digital Image Correlation ◽  
Strain Rate ◽  
Single Crystal ◽  
Digital Image ◽  
Surface Deformation ◽  
Image Correlation ◽  
Nominal Strain Rate ◽  
Single Crystal Copper ◽  
Nominal Strain

The purpose of this work is to explore nonuniform plastic flow at small length- and time-scales. Pure single crystal copper tensile specimens were pulled along the [6¯ 5 6] crystal axis at three nominal strain-rates: 0.01%/s, 0.04%/s, and 0.10%/s. Simultaneously, the surface deformation was monitored with in situ digital image correlation over a length-scale of ∼100 μm and a time-scale of 0.07–0.2 s. Sequential digital image correlation strain-rate fields show compelling evidence of a wavelike plastic deformation that is proportional to the nominal strain-rate and decelerates with increasing strain hardening. While a mechanism responsible for the waves is not identified, a methodology correlating observations of multiple researchers is forwarded.

scholarly journals The Application of Digital Image Correlation for Measuring Residual Stress by Incremental Hole Drilling

2008 ◽  
Vol 13-14 ◽  
pp. 65-73 ◽  
Author(s):  
Jerry D. Lord ◽  
David Penn ◽  
P. Whitehead
Keyword(s):  
Residual Stress ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Strain Gauge ◽  
Biaxial Stress ◽  
Image Correlation ◽  
Hole Drilling ◽  
Validation Data ◽  
Strain Fields ◽  
Incremental Hole Drilling

The measurement of residual stress using the incremental hole drilling is well established, but the main limitations with the conventional strain gauge approach are the requirements for surface preparation, the need for accurate alignment and drilling, the restricted range of hole geometries commensurate with the specific gauge designs, and the limited range of strain data averaged over the footprint of the strain gauge grid. Recent attempts to extend the method have seen the application of full field optical techniques such as electronic speckle pattern interferometry and holographic interferometry for measuring the strain fields around the hole, but these methods are sensitive to vibration and this limits their practical use to controlled laboratory environments. There are significant potential benefits therefore of using a more robust technique based on Digital Image Correlation (DIC), and work is presented in this study on the development of the method for measuring surface displacements and strain fields generated during incremental hole drilling. Some of the practical issues associated with the technique development, including the optimization of applied patterns, the development of the optical system and integration with current hole drilling equipment are discussed, and although measurements are only presented for a single load case - the equi-biaxial stress state introduced during shot peening - the novel aspect of this work is the integration of DIC measurements with incremental drilling and an application of the Integral Method analysis to measure the variation of residual stress with depth. Validation data comparing results from conventional strain gauge data and FE models is also presented.

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