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