Adaptation of Open Source 2D DIC Software Ncorr for Solid Mechanics Applications

This study focuses on establishing the utility of open source, MATLAB based 2D Digital Image Correlation (DIC) software Ncorr for solid mechanics applications. Various experiments like ring under diametral compression and beam under four point loading are conducted and corresponding displacement and strain fields are estimated using Ncorr. These results are compared with commercially available 2D DIC software Vic 2D from correlated solutions. The results generated from Ncorr are found to be in good agreement with its commercial counterpart Vic 2D

Effect of interpolation on noise propagation from images to DIC displacement maps

International audienceThis paper introduces and validates a new prediction of sensor noise propagation from images of randomly marked surfaces to displacement maps obtained by Digital Image Correlation (DIC). Images are indeed often affected by sensor noise, which propagates to DIC output. We consider here the 2D global DIC (G-DIC), for which this output is the in-plane displacement calculated at a set of nodes. Predictive formula for the resolution of the displacement at these nodes is already available in the literature. The contribution of the present paper is to revisit this formula to take into account the interpolation required by sub-pixel displacement. A generalization is also proposed to predict the displacement resolution throughout the field of view. It is then extended to several kinds of DIC. The correlation procedure is thoroughly described in order to emphasize the role of the interpolation. A numerical assessment on synthetic data validates the new prediction and shows the improvement brought about by the proposed formula

High-Speed 2D-Digital Image Correlation to Quantify Energy Mitigation Behaviors of Engineered Elastomeric Materials Subjected to Shock

Engineered, elastomeric material damping systems have revealed striking ability to attenuate shock loads at the macroscopic level. Reports suggest that this capability is associated with the reversible elastic buckling of internal beam constituents observed in quasistatic characterizations. Yet, the presence of buckling members induces non-affine response at the microscale, so that clear understanding of the exact energy dissipation mechanisms remains clouded. In this report, we examine a mechanical metamaterial that exhibits both microand macroscopic responses under impact loads and devise an experimental method to visualize the resulting energy dissipation mechanisms using 2D Digital Image Correlation (DIC). Without existing standards for applying 2D-DIC for studying high strain rates of absorbent, viscoelastic material structures, a novel approach for executing 2D-DIC visualization was implemented using charcoal powder. Simultaneously collected force transmission data and DIC analysis associated with the deformation of test specimens under impact loading reveal a bridge for studying the microscale interactions that culminate in macroscale deformation. To illustrate the potential of this application, this experiment was carried out on specimens with varying, but known, quasistatic loading behaviors to verify and validate discrepancies between quasi-static and dynamic loading. This process illuminates the influence of dynamic strain distribution throughout the material’s in-plane cross-section on its overall tendency to buckle uni- or bimodally, thus dissipating injected force with varying degrees of force transmission and pulse duration. With this understanding, we uncover a strategy for geometrically programming the macroscopic deformation to enhance impact mitigation properties.Haythornthwaite FoundationOwens Corning Science and TechnologyNo embargoAcademic Major: Mechanical Engineerin

Real-time quantitative Schlieren imaging by fast Fourier demodulation of a checkered backdrop

A quantitative synthetic Schlieren imaging (SSI) method based on fast Fourier demodulation is presented. Instead of a random dot pattern (as usually employed in SSI), a 2D periodic pattern (such as a checkerboard) is used as a backdrop to the refractive object of interest. The range of validity and accuracy of this "Fast Checkerboard Demodulation" (FCD) method are assessed using both synthetic data and experimental recordings of patterns optically distorted by small waves on a water surface. It is found that the FCD method is at least as accurate as sophisticated, multi-stage, digital image correlation (DIC) or optical flow (OF) techniques used with random dot patterns, and it is significantly faster. Efficient, fully vectorized, implementations of both the FCD and DIC/OF schemes developed for this study are made available as Matlab scripts.Comment: 21 pages, 7 figures, 1 appendi

A new digital image correlation software for displacements field measurement in structural applications

Recently, there has been a growing interest in studying non-contact techniques for strain and displacement measurement. Within photogrammetry, Digital Image Correlation (DIC) has received particular attention thanks to the recent advances in the field of low-cost, high resolution digital cameras, computer power and memory storage. DIC is indeed an optical technique able to measure full field displacements and strain by comparing digital images of the surface of a material sample at different stages of deformation and thus can play a major role in structural monitoring applications. For all these reasons, a free and open source 2D DIC software, named py2DIC, was developed at the Geodesy and Geomatics Division of DICEA, University of Rome "La Sapienza". Completely written in python, the software is based on the template matching method and computes the displacement and strain fields. The potentialities of Py2DIC were evaluated by processing the images captured during a tensile test performed in the Lab of Structural Engineering, where three different Glass Fiber Reinforced Polymer samples were subjected to a controlled tension by means of a universal testing machine. The results, compared with the values independently measured by several strain gauges fixed on the samples, demonstrate the possibility to successfully characterize the deformation mechanism of the investigated material. Py2DIC is indeed able to highlight displacements at few microns level, in reasonable agreement with the reference, both in terms of displacements (again, at few microns in the average) and Poisson's module

Short-term fate of phytodetritus in sediments across the arabian sea oxygen minimum zone

The short-term fate of phytodetritus was investigated across the Pakistan margin of the Arabian Sea at water depths ranging from 140 to 1850 m, encompassing the oxygen minimum zone (~100–1100 m). Phytodetritus sedimentation events were simulated by adding ~44 mmol 13C-labelled algal material per m2 to surface sediments in retrieved cores. Cores were incubated in the dark, at in situ temperature and oxygen concentrations. Overlying waters were sampled periodically, and cores were recovered and sampled (for organisms and sediments) after durations of two and five days. The labelled carbon was subsequently traced into bacterial lipids, foraminiferan and macrofaunal biomass, and dissolved organic and inorganic pools. The majority of the label (20 to 100%) was in most cases left unprocessed in the sediment at the surface. The largest pool of processed carbon was found to be respiration (0 to 25% of added carbon), recovered as dissolved inorganic carbon. Both temperature and oxygen were found to influence the rate of respiration. Macrofaunal influence was most pronounced at the lower part of the oxygen minimum zone where it contributed 11% to the processing of phytodetritus

Molecular engineering of chiral colloidal liquid crystals using DNA origami

Establishing precise control over the shape and the interactions of the microscopic building blocks is essential for design of macroscopic soft materials with novel structural, optical and mechanical properties. Here, we demonstrate robust assembly of DNA origami filaments into cholesteric liquid crystals, 1D supramolecular twisted ribbons and 2D colloidal membranes. The exquisite control afforded by the DNA origami technology establishes a quantitative relationship between the microscopic filament structure and the macroscopic cholesteric pitch. Furthermore, it also enables robust assembly of 1D twisted ribbons, which behave as effective supramolecular polymers whose structure and elastic properties can be precisely tuned by controlling the geometry of the elemental building blocks. Our results demonstrate the potential synergy between DNA origami technology and colloidal science, in which the former allows for rapid and robust synthesis of complex particles, and the latter can be used to assemble such particles into bulk materials