scholarly journals A novel specimen shape for measurement of linear strain fields by means of digital image correlation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nedaa Amraish ◽  
Andreas Reisinger ◽  
Dieter Pahr
Keyword(s):  
Digital Image Correlation ◽  
Image Correlation ◽  
Strain Gauges ◽  
Linear Strain ◽  
Strain Fields ◽  
Strain Gradients ◽  
Full Field ◽  
Strain Measurements ◽  
Deformation Stages ◽  
Specimen Shape

AbstractStrains on the surface of engineering structures or biological tissues are non-homogeneous. These strain fields can be captured by means of Digital Image Correlation (DIC). However, DIC strain field measurements are prone to noise and filtering of these fields influences measured strain gradients. This study aims to design a novel tensile test specimen showing two linear gradients, to measure full-field linear strain measurements on the surface of test specimens, and to investigate the accuracy of DIC strain measurements globally (full-field) and locally (strain gauges’ positions), with and without filtering of the DIC strain fields. Three materials were employed for this study: aluminium, polymer, and bovine bone. Normalized strain gradients were introduced that are load independent and evaluated at two local positions showing 3.6 and 6.9% strain change per mm. Such levels are typically found in human bones. At these two positions, two strain gauges were applied to check the experimental strain magnitudes. A third strain gauge was applied to measure the strain in a neutral position showing no gradient. The accuracy of the DIC field measurement was evaluated at two deformation stages (at $$\approx $$ ≈ 500 and 1750 μstrain) using the root mean square error (RMSE). The RMSE over the two linear strain fields was less than 500 μstrain for both deformation stages and all materials. Gaussian low-pass filter (LPF) reduced the DIC noise between 25% and 64% on average. As well, filtering improved the accuracy of the local normalized strain gradients measurements with relative difference less than 20% and 12% for the high- and low-gradient, respectively. In summary, a novel specimen shape and methodological approach are presented which are useful for evaluating and improving the accuracy of the DIC measurement where non-homogeneous strain fields are expected such as on bone tissue due to their hierarchical structure.

Full-field strain measurements at the micro-scale in fiber-reinforced composites using digital image correlation

2016 ◽  
Vol 140 ◽  
pp. 192-201 ◽  
Author(s):  
Mahoor Mehdikhani ◽  
Mohammadali Aravand ◽  
Baris Sabuncuoglu ◽  
Michaël G. Callens ◽  
Stepan V. Lomov ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Image Correlation ◽  
Fiber Reinforced Composites ◽  
Field Strain ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
Full Field ◽  
Strain Measurements ◽  
Micro Scale

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.

scholarly journals Evaluation of a low-cost approach to 2-D digital image correlation vs. a commercial stereo-DIC system in Brazilian testing of soil specimens

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
M. Arza-García ◽  
C. Núñez-Temes ◽  
J. A. Lorenzana ◽  
J. Ortiz-Sanz ◽  
A. Castro ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Accuracy Assessment ◽  
Low Cost ◽  
Field Measurements ◽  
Image Correlation ◽  
Strain Gauges ◽  
Source Image ◽  
Full Field ◽  
Cost Approach

AbstractDue to their cost, high-end commercial 3D-DIC (digital image correlation) systems are still inaccessible for many laboratories or small factories interested in lab testing materials. These professional systems can provide reliable and rapid full-field measurements that are essential in some laboratory tests with high-strain rate events or high dynamic loading. However, in many stress-controlled experiments, such as the Brazilian tensile strength (BTS) test of compacted soils, samples are usually large and fail within a timeframe of several minutes. In those cases, alternative low-cost methods could be successfully used instead of commercial systems. This paper proposes a methodology to apply 2D-DIC techniques using consumer-grade cameras and the open-source image processing software DICe (Sandia National Lab) for monitoring the standardized BTS test. Unlike most previous studies that theoretically estimate systematic errors or use local measures from strain gauges for accuracy assessment, we propose a contrast methodology with independent full-field measures. The displacement fields obtained with the low-cost system are benchmarked with the professional stereo-DIC system Aramis-3D (GOM GmbH) in four BTS experiments using compacted soil specimens. Both approaches proved to be valid tools for obtaining full-field measurements and showing the sequence of crack initiation, propagation and termination in the BTS, constituting reliable alternatives to traditional strain gauges. Mean deviations obtained between the low-cost 2D-DIC approach and Aramis-3D in measuring in-plane components were 0.08 mm in the perpendicular direction of loading (ΔX) and 0.06 mm in the loading direction (ΔY). The proposed low-cost approach implies considerable savings compared to commercial systems.

Validation of Digital Image Correlation Techniques for Strain Measurement in Biomechanical Test Models

2013 ◽  
Author(s):  
Renee D. Rogge ◽  
Scott R. Small ◽  
Derek B. Archer ◽  
Michael E. Berend ◽  
Merrill A. Ritter
Keyword(s):  
Aluminum Alloy ◽  
Digital Image Correlation ◽  
Polyurethane Foam ◽  
Digital Image ◽  
Measurement Techniques ◽  
Image Correlation ◽  
Principal Strain ◽  
Strain Gages ◽  
Full Field ◽  
Strain Measurements

Many previous biomechanical studies of bone and bone substitutes have estimated strains in these materials using strain gages. The purpose of this study was to compare digital image correlation (DIC) strain measurements to those obtained from strain gages in order to assess the applicability of DIC technology to common biomechanical testing scenarios. Compression and bending tests were conducted on aluminum alloy, polyurethane foam, and laminated polyurethane foam specimens. Results showed no significant differences in the principal strain values (or the variances) between strain gage and DIC measurements on the aluminum alloy and laminated polyurethane foam specimens. There were significance differences between the principal strain measurements of the non-laminated polyurethane foam specimens, but the deviation from the theoretical results was similar for both measurement techniques. In summary, DIC techniques provide similar results to those obtained from strain gages and also provide full field strain results.

scholarly journals Full-field microscale strain measurements of a nitinol medical device using digital image correlation

2020 ◽  
pp. 104221
Author(s):  
Kenneth I. Aycock ◽  
Jason D. Weaver ◽  
Harshad M. Paranjape ◽  
Karthikeyan Senthilnathan ◽  
Craig Bonsignore ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Medical Device ◽  
Digital Image ◽  
Image Correlation ◽  
Full Field ◽  
Strain Measurements

scholarly journals ASSESSMENT OF 2D-DIC STOCHASTIC PATTERNS

2017 ◽  
Vol 13 ◽  
pp. 1 ◽  
Author(s):  
Jakub Antoš ◽  
Václav Nežerka ◽  
Michael Somr
Keyword(s):  
Digital Image Correlation ◽  
Open Source ◽  
Mechanical Loading ◽  
Digital Image ◽  
Experimental Testing ◽  
Image Correlation ◽  
Specimen Surface ◽  
Strain Gauges ◽  
Full Field ◽  
Field Information

Cost of experimental testing of materials and structures subjected to mechanical loading often constitutes a significant portion of a project budget. Therefore a collection of data in a maximum possible amount is desirable. Extensometers and strain-gauges attached to the specimen surface often fail and cannot provide full-field information about the development of displacements and strains. Digital Image Correlation (DIC) is capable of providing such information. Unsuitable texture or artificially applied pattern, essential for DIC analysis, can spoil the DIC outcomes completely. An additional investment into preparation of new experimental testing can be avoided with the use of tools employing algorithms for stochastic pattern assessment. The development of such algorithms and their implementation into an open-source DIC software is the goal of the presented research.

scholarly journals Accurate Strain Field Measurement During Strip Rolling by Exploiting Recurring Material Motion with Time-Integrated Digital Image Correlation

2021 ◽  
Author(s):  
J. P. M. Hoefnagels ◽  
K. van Dam ◽  
N. Vonk ◽  
L. Jacobs
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Deformation Zone ◽  
Rolling Force ◽  
Image Correlation ◽  
Strip Rolling ◽  
Strain Fields ◽  
Full Field ◽  
Integrated Digital Image Correlation ◽  
Image Pairs

Abstract Background 95% Of all metals and alloys are processed using strip rolling, explaining the great number of existing strip rolling optimization models. Yet, an accurate in-situ full-field experimental measurement method of the deformation, velocity and strain fields of the strip in the deformation zone is lacking. Objective Here, a novel time-Integrated Digital Image Correlation (t-IDIC) framework is proposed and validated that fully exploits the notion of continuous, recurring material motion during strip rolling. Methods High strain accuracy and robustness against unavoidable light reflections and missing speckles is achieved by simultaneously correlating many (e.g. 200) image pairs in a single optimization step, i.e. each image pair is correlated with the same average global displacement field but is multiplied by a unique velocity corrector to account for differences in material velocity between image pairs. Results Demonstration on two different strip rolling experiments revealed previously inaccessible subtle changes in the deformation and strain fields due to minor variations in pre-deformation, elastic recovery, and geometrical irregularities. The influence of the work roll force and entry/exit strip tension has been investigated for strip rolling with an industrial pilot mill, which revealed unexpected non-horizontal material feed. This asymmetry was reduced by increasing the entry strip tension and rolling force, resulting in a more symmetric strain distribution, while increased distance between the neutral and entry point was found for a larger rolling force. Conclusions The proposed t-IDIC method allows for robust and accurate characterization of the strip’s full-field behavior of the deformation zone during rolling, revealing novel insights in the material behavior.

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