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 ...

Polyvinylidene fluoride (PVDF) is a polymer prized for its unique material properties, including a high resistance to corrosive acids such as HCL and HF and its piezoelectric potential based on the proper microstructure arrangement. In this work, the effects of fused filament fabrication (FFF) routine parameters on printed PVDF film properties were investigated using a variety of experimental methods. The influence of in-fill angle (0°, 45°, and 90°) on the effective Young"s Modulus, Poisson"s ratio, and yield strength were evaluated using tensile testing and a digital image correlation (DIC) analysis. The phase content, in particular the β-phase amount, within the semi-crystalline PVDF films was determined as a function of processing parameters using the FTIR method. Considered parameters included the extrusion temperature, horizontal speed, in-situ applied hot end voltage, and bed material. Results showed that higher β-phase content was associated with lower extrusion temperatures, faster extrusion rates, and higher hot end voltages. While all "as printed" films demonstrated little to no measurable piezoelectricity, PVDF films printed with a high β-phase content and subjected to a post-printing corona poling procedure showed a small, but consistent piezoelectric response. Based on a static deflection cantilever beam experiment, the d 31 coefficient of the poled specimens was estimated at 1.19 pm/V.

Piezoelectric properties of three sol-gel derived Pb͑Zr 0.53 Ti 0.47 ͒O 3 thin film specimens of different thicknesses integrated onto Pt/ Ti/ SiO 2 ʈ Si substrates are investigated to delineate the influence of residual stress on the strain-field response characteristics from other thickness related effects. Residual tensile stresses are determined from wafer curvature measurements for films ranging in thickness from 190 to 500 nm. Field-induced strains are measured interferometrically for each film under either a large ac driving voltage or a small ac ripple applied over a range of dc biases. Higher residual stresses decrease measured piezoelectric response, while thickness variations with no accompanying change in residual stress state produce little change in strain-field behavior. The diminished performance associated with high residual stresses is attributed to reductions in both linear and nonlinear contributions, including decreased polarization switching and domain motion.

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