Investigation of the grid method for accurate in-plane strain measurement

Bădulescu, Claudiu; Grédiac, Michel; Mathias, Jean‐Denis

doi:10.1088/0957-0233/20/9/095102

Cited by 84 publications

(120 citation statements)

References 18 publications

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“…Two pieces of thin copper film were bonded onto the foam support right at the edge of the specimen so that when the projectile reaches, it contacts both pieces of film which closes an electrical circuit, providing the triggering signal. The specimen was cut to the dimensions of that in figure 2 from a carbon/epoxy 49], also more recently referred to as sampling moiré [50]. A grid was transferred onto the specimens using the procedure described in [51].…”

Section: First Experimental Validation (A) Experimental Set-upmentioning

confidence: 99%

Beyond Hopkinson's bar

Pierron

Zhu

Siviour

2014

Phil. Trans. R. Soc. A.

122

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In order to perform experimental identification of high strain rate material models, engineers have only a very limited toolbox based on test procedures developed decades ago. The best example is the so-called split Hopkinson pressure bar based on the bar concept introduced 100 years ago by Bertram Hopkinson to measure blast pulses. The recent advent of full-field deformation measurements using imaging techniques has allowed novel approaches to be developed and exciting new testing procedures to be imagined for the first time. One can use this full-field information in conjunction with efficient numerical inverse identification tools such as the virtual fields method (VFM) to identify material parameters at high rates. The underpinning novelty is to exploit the inertial effects developed in high strain rate loading. This paper presents results from a new inertial impact test to obtain stress–strain curves at high strain rates (here, up to 3000 s −1 ). A quasi-isotropic composite specimen is equipped with a grid and images are recorded with the new HPV-X camera from Shimadzu at 5 Mfps and the SIMX16 camera from Specialised Imaging at 1 Mfps. Deformation, strain and acceleration fields are then input into the VFM to identify the stiffness parameters with unprecedented quality.

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Section: First Experimental Validation (A) Experimental Set-upmentioning

confidence: 99%

Beyond Hopkinson's bar

Pierron

Zhu

Siviour

2014

Phil. Trans. R. Soc. A.

122

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“…A main advantage of the grid method is that it offers a good compromise between strain resolution and spatial resolution [36]. However, this full-field measurement technique have not yet been employed to investigate phase-change intermittency in memory materials.…”

Section: Introductionmentioning

confidence: 99%

Strain intermittency in shape-memory alloys

et al. 2015

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We study experimentally the intermittent progress of the mechanically-induced martensitic transformation in a Cu-Al-Be single crystal through a full-field measurement technique: the grid method. We utilize an in-house especially designed gravity-based device, wherein a system controlled by water pumps applies a perfectly monotonic uniaxial load through very small force increments. The sample exhibits hysteretic superelastic behavior during the forward and reverse cubic-monoclinic transformation, produced by the evolution of the strain field of the phase microstructures. The in-plane linear strain components are measured on the sample surface during the loading cycle, and we characterize for the first time the strain intermittency in a number of ways, showing the emergence of power-law behavior for the strain avalanching over almost six decades of magnitude. We also describe the non-stationarity and the asymmetry observed in the forward vs. the reverse transformation. The present experimental approach, which allows for the monitoring of the reversible martensitic transformation both locally and globally in the crystal, proves useful and enhances our capabilities in the analysis and possible control of transition-related phenomena in shape-memory alloys.

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“…The grid method [11] is one of the full-field techniques for measuring in-plane displacement and strain of a specimen subjected to a load, and consequently lightly deformed. It consists in first depositing a regular grid on the surface of a material and then taking high-resolution pictures of the grid before and after deformation.…”

Section: The Grid Methods In Experimental Mechanicsmentioning

confidence: 99%

Sensor Noise Modeling by Stacking Pseudo-Periodic Grid Images Affected by Vibrations

Sur

Grédiac²

2014

IEEE Signal Process. Lett.

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This letter addresses the problem of noise estimation in raw images from digital sensors. Assuming that a series of images of a static scene are available, a possibility is to characterize the noise at a given pixel by considering the random fluctuations of the gray level across the images. However, mechanical vibrations, even tiny ones, affect the experimental setup, making this approach ineffective. The contribution of this letter is twofold. It is shown that noise estimation in the presence of vibrations is actually biased. Focusing on images of a pseudo-periodic grid, an algorithm to discard their effect is also given. An application to the generalized Anscombe transform is discussed.

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Investigation of the grid method for accurate in-plane strain measurement

Cited by 84 publications

References 18 publications

Beyond Hopkinson's bar

Beyond Hopkinson's bar

Strain intermittency in shape-memory alloys

Sensor Noise Modeling by Stacking Pseudo-Periodic Grid Images Affected by Vibrations

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