As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.

https://iopscience.iop.org/article/10.1088/0957-0233/20/6/062001/pdf

Two-dimensional digital image correlation for in-plane displacement and strain measurement: a review

A deformation measurement system based on particle image velocimetry (PIV) and close-range photogrammetry has been developed for use in geotechnical testing. In this paper, the theory underlying this system is described, and the performance is validated. Digital photography is used to capture images of planar soil deformation. Using PIV, the movement of a fine mesh of soil patches is measured to a high precision. Since PIV operates on the image texture, intrusive target markers need not be installed in the observed soil. The resulting displacement vectors are converted from image space to object space using a photogrammetric transformation. A series of validation experiments are reported. These demonstrate that the precision, accuracy and resolution of the system are an order of magnitude higher than previous image-based deformation methods, and are comparable to local instrumentation used in element testing. This performance is achieved concurrent with an order of magnitude increase in the number of meas...

Soil deformation measurement using particle image velocimetry (PIV) and photogrammetry

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

American Society of Civil Engineers

Root elongation in drying soil is generally limited by a combination of mechanical impedance and water stress. Relationships between root elongation rate, water stress (matric potential), and mechanical impedance (penetration resistance) are reviewed, detailing the interactions between these closely related stresses. Root elongation is typically halved in repacked soils with penetrometer resistances >0.8‐2 MPa, in the absence of water stress. Root elongation is halved by matric potentials drier than about ‐0.5 MPa in the absence of mechanical impedance. The likelihood of each stress limiting root elongation is discussed in relation to the soil strength characteristics of arable soils. A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that ;10% of penetration resistances were >2 MPa at a matric potential of ‐10 kPa, rising to nearly 50% >2 MPa at ‐ 200 kPa. This suggests that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops. Root tip traits that may improve root penetration are considered with respect to overcoming the external (soil) and internal (cell wall) pressures resisting elongation. The potential role of root hairs in mechanically anchoring root tips is considered theoretically, and is judged particularly relevant to roots growing in biopores or from a loose seed bed into a compacted layer of soil.

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Root elongation, water stress, and mechanical impedance: a review of limiting stresses and beneficial root tip traits

The comparison between model and experimental outcomes was made possible by the laboratory data set generated by Gemma Bullard during her PhD research (Bullard, Mulligan, Carreira, & Take, 2019; Bullard, Mulligan, & Take, 2019). A. Franci acknowledges support from an AXA Research Fund (AXA) post‐doctoral grant (Grant Number 2017‐AXAPDOC1‐ 099) and the Spanish Ministry of Economy and Competitiveness (Ministerio de Economia y Competitividad [MINECO]) through the project PRECISE (BIA2017‐83805‐ R). Funding for the design and construction of the large‐scale landslide flume from the Canada Foundation for Innovation is gratefully acknowledged. This research was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants to R. P. Mulligan (RGPIN/04043‐2018) and W. A. Take (RGPIN/04245‐2015).

/pdf/simulations-of-landslide-wave-generation-and-propagation-52im9bjm17.pdf

Simulations of Landslide Wave Generation and Propagation Using the Particle Finite Element Method

Identification of seasonal slope behaviour mechanisms from centrifuge case studies

In this paper, quantitative observations of dry granular flows subject to varying magnitude and direction of Coriolis acceleration are presented in order to assess the robustness of the Savage–Hutt...

Physical and numerical modelling of dry granular flows under Coriolis conditions

Numerical simulation of impulse wave generation by idealized landslides with OpenFOAM

Rayleigh backscatter fiber optic sensing permits dynamic strains to be measured along an optical fiber with a gauge spacing and temporal resolution sufficient for rail applications. However, this s...

https://tspace.library.utoronto.ca/bitstream/1807/92212/1/cgj-2017-0163.pdf

W.A. Take

Papers

Simulations of Landslide Wave Generation and Propagation Using the Particle Finite Element Method

Identification of seasonal slope behaviour mechanisms from centrifuge case studies

Physical and numerical modelling of dry granular flows under Coriolis conditions

Numerical simulation of impulse wave generation by idealized landslides with OpenFOAM

Use of fiber optic sensing to measure distributed rail strains and determine rail seat forces under a moving train