The digital image correlation (DIC) technique is successfully applied across multiple length scales through the generation of a suitable speckle pattern at each size scale. For microscale measurements, a random speckle pattern of paint is created with a fine point airbrush. Nanoscale displacement resolution is achieved with a speckle pattern formed by solution deposition of fluorescent silica nanoparticles. When excited, the particles fluoresce and form a speckle pattern that can be imaged with an optical microscope. Displacements are measured on the surface and on an interior plane of transparent polymer samples with the different speckle patterns. Rigid body translation calibrations and uniaxial tension experiments establish a surface displacement resolution of 1 mm over a 5Â6 mm scale field of view for the airbrushed samples and 17 nm over a 100Â100 mm scale field of view for samples with the fluorescent nanoparticle speckle. To demonstrate the capabilities of the method, we characterize the internal deformation fields generated around silica microspheres embedded in an elastomer under tensile loading. The DIC technique enables measurement of complex deformation fields with nanoscale precision over relatively large areas, making it of particular relevance to materials that possess multiple length scales.

Recent advances in nanotechnology have enabled the fabrication of a new generation of materials with highly complex structures. The characteristic length scale of these materials has now outpaced the ability of current techniques to make full-field, nanoscale mechanical property measurements in real time. In addition, biological materials also possess complex structures at the nanoscale, which can affect their resulting larger-scale response. Measurements of bulk properties, while important, offer little information about how the nanostructure influences performance. Localized measurements, such as nanoindentation, provide data that are often difficult to extend to larger length scales. High-resolution imaging techniques such as atomic force or scanning tunneling microscopy (AFM/STM) [1] and near-field scanning optical microscopy (NFSOM), [2] despite being full-field techniques, involve bringing a tip on or very near the surface and thus are not entirely suitable for use with soft (e.g., biological) materials. In addition, these methods require rastering, which limits real-time visualization capability (e.g., of fracture, of the motion and growth of cells, and so on). Fluorescent dyes and particles have enabled a different set of experimental tools for imaging displacements. Fluorescent particles have been widely used in flow visualization and measurement techniques. [3,4] In biological studies, fluorescent dyes indicate the presence of particular microorganisms or track the growth and development of cellular structures. [5][6][7][8] Recent advances in optical techniques have improved discrete fluorescent particle imaging, [9][10][11][12] making laboratory nanoscale measurements feasible. Single-particle tracking (SPT) via confocal laser scanning microscopy is a tool used in biophysical research to observe trajectories of small fluorescent particles with nanometer-scale precision. [13,14] Here, we present a powerful full-field technique, fluorescencebased digital image correlation (FDIC), to measure nanoscale deformation in materials using fluorescent nanoparticles. To demonstrate the capabilities of the method, we characterize the complex deformation fields generated around silica microspheres embedded in an elastomer under tensile loading. Displacement resolutions of 20 nm are obtained over a 100 100 mm field of view.Digital image correlation (DIC) is a data analysis method, which applies a mathematical correlation algorithm to obtain kinematic information from digital images acquired during deformation. [15,16] For conventional two-dimensional (2D) DIC, samples are prepared for testing by the application of a random speckle pattern to their surface. Comparison of successive images reveals a deformed speckle pattern relative to the initial, nondeformed one. The correlation works by matching small square subsets of the nondeformed image (Figure 1 a) to locations in the deformed image (Figure 1 b). The core of the DIC method lies in the optimization of a correlation coefficient between the two subsets over six ...

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Polymer matrix composites (PMCs) are attractive structural materials due to their high stiffness to low weight ratio. However, unidirectional PMCs have low shear strength and failure can occur along kink bands that develop on compression due to plastic microbuckling that carry strains large enough to induce nonlinear matrix deformation.Reviewing the literature, a large fraction of the existing work is for uniaxial compression, and the effects of stress gradients, such as those present during bending, have not been as well explored, and these effects are bound to make difference in terms of kink band nucleation and growth. Furthermore, reports on experimental measurements of strain fields leading to and developing inside these bands in the presence of stress gradients are also scarce and need to be addressed to gain a full understanding of their behavior when UDCs are used under bending and other spatially complex stress states.In a light to bridge the aforementioned gaps, the primary focus of this work is to understand mechanisms for kink band evolution under an influence of stress-gradients

Corrugations can dramatically change the effective mechanical properties of a thin sheet. Such alternating ridges and grooves are typically fabricated by mechanical processing. Herein, the ability to trigger and tune corrugations within thin (≈300 µm thick) thermoplastic sheets rapidly (≈seconds) using only light is reported. Patterns of black ink on the otherwise transparent, flimsy sheet preferentially adsorb external IR light, inducing localized heating of the underlying polymer. This heating causes localized shrinkage of the polymer, producing folds in the sheets; collectively, these folds result in corrugations of controlled geometry. Depending on orientation, these corrugations dramatically increase stiffness or extensibility, similar to corrugated roofs (stiff) or accordions (extensible). In the direction parallel to the folds, the maximum load‐carrying capacity increases by two orders of magnitude relative to the non‐corrugated sheet; perpendicular to the folds, the effective modulus decreases by four orders of magnitude. In addition to tuning effective mechanical properties, the ability to corrugate flat surfaces using light has implications for assembling 3D objects from substrates printed in 2D (such as lithographically patterned electronics) or 3D structures shipped in a flat state. Herein, the process of forming such structures is discussed and their properties are characterized.

Background Nitric oxide synthase (iNOS) is induced in hepatocytes by shock and inflammatory stimuli. Excessive NO from iNOS mediates shock-induced hepatic injury and death so understanding the regulation of iNOS will help elucidate the pathophysiology of septic shock. In vitro, cytokines induce iNOS expression through activation of signaling pathways including mitogen-activated protein kinases and Nuclear Factor κB. Cytokines also induce calcium (Ca2+) mobilization and activate calcium-mediated intracellular signaling pathways, typically through activation of calmodulin-dependent kinases (CaMK). Calcium regulates NO production in macrophages but the role of calcium and calcium-mediated signaling in hepatocyte iNOS expression has not been defined. Materials and Methods Primary rat hepatocytes were isolated, cultured, and induced to produce NO with proinflammatory cytokines. Calcium mobilization and Ca2+-mediated signaling were altered with ionophore, Ca2+ channel blockers, and inhibitors of CaMK. Results The Ca2+ ionophore A23187 suppressed cytokine-stimulated NO production while EGTA and nifedipine increased NO production, iNOS mRNA, and iNOS protein expression. Inhibition of CaMK with KN93 and CBD increased NO production but the calcineurin inhibitor FK 506 decreased iNOS expression. Conclusions These data demonstrate that calcium-mediated signaling regulates hepatocyte iNOS expression and does so through a mechanism independent of calcineurin. Changes in intracellular calcium levels may regulate iNOS expression during hepatic inflammation induced by pro-inflammatory cytokines.

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-i - AbstractIn this thesis, the influence of various dilute Nb additions (0.005-0.02 wt%) on austenite microstructure evolution along thermomechanical processing, in terms of austenite recrystallisation and grain growth, were investigated using steels with three carbon content levels.At the homogenisation temperature of 1250°C, all dilute Nb additions were dissolved in low carbon steels whereas the Nb dissolution limits for 0.4 wt% and 0.6 wt% C steels were 0.012 wt% and 0.08 wt%, respectively. Dilute Nb additions did not show significant influence on homogenised austenite grain size. The dramatic increase in C contents was more influential, which decreased the homogenised austenite grain size.The influence of dilute Nb additions and C contents on dynamic recrystallisation behaviour was studied by rough rolling at high deformation temperature with low strain rate. The dilute Nb additions were found to increase the critical strain of dynamic recrystallisation whereas C contents showed no influence on the dynamic recrystallisation behaviour.The austenite recrystallisation behaviour after finish rolling and after the holding period between finishing passes were studied by means of interrupted plane strain compression (PSC) tests and double hit PSC tests. It was found that with low Nb supersaturation, recrystallisation happened prior to Nb precipitation. Solute Nb in austenite delayed the onset of austenite recrystallisation through solute drag effect.With high Nb supersaturation, Nb precipitation occurred before the onset of recrystallisation which completely retarded austenite recrystallisation.The austenite grain growth during the holding period between finish rolling passes was studied by the evolution of prior-austenite grain size before and after the 20s holding period at the highest finish rolling temperature (1050°C). There was no Nb precipitation found and the difference in austenite grain growth behaviour was Abstract -iiattributed to the solute drag effect from both Nb and C in solution. It was found that Nb in solution suppressed austenite grain growth. However, the effectiveness of solute Nb in suppressing austenite grain growth was affected by the C content. Acknowledgement