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Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field. [ABSTRACT FROM AUTHOR]

Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field.

Achieving nanoscale strain fields mapping in intricate van der Waals (vdW) nanostructures, like twisted flakes and nanorods, presents several challenges due to their complex geometry, small size, and sensitivity limitations. Understanding these strain fields is pivotal as they significantly influence the optoelectronic properties of vdW materials, playing a crucial role in a plethora of applications ranging from nanoelectronics to nanophotonics. Here, a novel approach for achieving a nanoscale‐resolved mapping of strain fields across entire micron‐sized vdW nanostructures using four‐dimensional (4D) scanning transmission electron microscopy (STEM) imaging equipped with an electron microscope pixel array detector (EMPAD) is presented. This technique extends the capabilities of STEM‐based strain mapping by means of the exit‐wave power cepstrum method incorporating automated peak tracking and K‐means clustering algorithms. This approach is validated on two representative vdW nanostructures: a two‐dimensional (2D) MoS2 thin twisted flakes and a one‐dimensional (1D) MoO3/MoS2 nanorod heterostructure. Beyond just vdW materials, the versatile methodology offers broader applicability for strain‐field analysis in various low‐dimensional nanostructured materials. This advances the understanding of the intricate relationship between nanoscale strain patterns and their consequent optoelectronic properties.

Fluorescent reporters of cardiac electrophysiology provide valuable information on heart cell and tissue function. However, motion artifacts caused by cardiac muscle contraction interfere with accurate measurement of fluorescence signals. Although drugs such as blebbistatin can be applied to stop cardiac tissue from contracting by uncoupling calcium-contraction, their usage prevents the study of excitation-contraction coupling and, as we show, impacts cellular structure. We therefore developed a robust method to remove motion computationally from images of contracting cardiac muscle and to map fluorescent reporters of cardiac electrophysiological activity onto images of undeformed tissue. When validated on cardiomyocytes derived from human induced pluripotent stem cells (iPSCs), in both monolayers and engineered tissues, the method enabled efficient and robust reduction of motion artifact. As with pharmacologic approaches using blebbistatin for motion removal, our algorithm improved the accuracy of optical mapping, as demonstrated by spatial maps of calcium transient decay. However, unlike pharmacologic motion removal, our computational approach allowed direct analysis of calcium-contraction coupling. Results revealed calcium-contraction coupling to be more uniform across cells within engineered tissues than across cells in monolayer culture. The algorithm shows promise as a robust and accurate tool for optical mapping studies of excitation-contraction coupling in heart tissue. [ABSTRACT FROM AUTHOR]

The comprehensive characterization of cardiac structure and function is critical to better understanding various murine models of cardiac disease. We demonstrate here a multimodal analysis approach using high-frequency four-dimensional ultrasound (4DUS) imaging and proteomics to explore the relationship between regional function and tissue composition in a murine model of metabolic cardiomyopathy (Nkx2-5183P/+). The presented 4DUS analysis outlines a novel approach to mapping both circumferential and longitudinal strain profiles through a standardized framework. We then demonstrate how this approach allows for spatiotemporal comparisons of cardiac function and improved localization of regional left ventricular dysfunction. Guided by observed trends in regional dysfunction, our targeted Ingenuity Pathway Analysis (IPA) results highlight metabolic dysregulation in the Nkx2-5183P/+ model, including altered mitochondrial function and energy metabolism (i.e., oxidative phosphorylation and fatty acid/lipid handling). Finally, we present a combined 4DUS-proteomics z-score-based analysis that highlights IPA canonical pathways showing strong linear relationships with 4DUS biomarkers of regional cardiac dysfunction. The presented multimodal analysis methods aim to help future studies more comprehensively assess regional structure-function relationships in other preclinical models of cardiomyopathy. NEW & NOTEWORTHY A multimodal approach using both four-dimensional ultrasound (4DUS) and regional proteomics can help enhance our investigations of murine cardiomyopathy models. We present unique 4DUS-derived strain maps that provide a framework for both cross-sectional and longitudinal analysis of spatiotemporal cardiac function. We further detail and demonstrate an innovative 4DUS-proteomics z-score-based linear regression method, aimed at characterizing relationships between regional cardiac dysfunction and underlying mechanisms of disease. [ABSTRACT FROM AUTHOR]

Nanoscale strain mapping by four-dimensional scanning transmission electron microscopy (4D-STEM) relies on determining the precise locations of Bragg-scattered electrons in a sequence of diffraction patterns, a task which is complicated by dynamical scattering, inelastic scattering, and shot noise. These features hinder accurate automated computational detection and position measurement of the diffracted disks, limiting the precision of measurements of local deformation. Here, we investigate the use of patterned probes to improve the precision of strain mapping. We imprint a "bullseye" pattern onto the probe, by using a binary mask in the probe-forming aperture, to improve the robustness of the peak finding algorithm to intensity modulations inside the diffracted disks. We show that this imprinting leads to substantially improved strain-mapping precision at the expense of a slight decrease in spatial resolution. In experiments on an unstrained silicon reference sample, we observe an improvement in strain measurement precision from 2.7% of the reciprocal lattice vectors with standard probes to 0.3% using bullseye probes for a thin sample, and an improvement from 4.7% to 0.8% for a thick sample. We also use multislice simulations to explore how sample thickness and electron dose limit the attainable accuracy and precision for 4D-STEM strain measurements.

Spatially resolved studies of crystalline structures, e.g. lattice spacings, are enabled by recording the transmitted spectra in neutron Bragg edge imaging. The recorded signals are, however, a result of through-thickness averaging of the probed specimen in the beam direction. Therefore, it is challenging to extract the strain distribution when the strain varies across the thickness, which applies for studies on different materials or material states along the beam. Here we introduce the approach to disentangle contributions to the recorded signals, i.e. separating the transmission spectra of two different material states. This is particularly applicable to powder bed additive manufacturing environments where operando strain characterization of the printed specimen using neutrons is intended. In this work, Laser Powder Bed Fusion (PBF-LB/M)-built 316L and IN718 samples embedded in their corresponding powders are used, extracting the desired spectra of the printed specimen. The disentanglement is proven to be satisfactory by obtaining coinciding strain maps of identical specimens embedded in powder layers of different thicknesses. Furthermore, the obtained residual strain distributions of 316L samples were verified by conventional neutron diffraction with lower spatial resolution due to the gauge volume averaging.

Using ex-situ transmission electron microscopy and the recently developed nanoprobe diffraction (NPD) technique, we characterize a nanoindented solution treated gum metal. Lattice rotations are resolved at a 1.2 nm length-scale and shown to be continuous within the nanoindentation pit; further, it is shown that these can be accommodated by a reasonable number of geometrically necessary dislocations at a density of ∼1015/m2. We additionally provide direct evidence that dislocations within the nanoindent, rather than secondary phase nanoparticles, can serve as potent barriers to dislocation motion. We also demonstrate that plasticity in these alloys under nanoindentation can be accommodated solely by dislocation nucleation and propagation, with no competing deformation mechanisms present. Conventional transmission electron microscopy and “g•b” analysis reveal the presence of dislocations on 〈1¯11〉{110} slip systems and highly localized plastic deformation in the form of shear bands on {1¯1¯2} slip systems, similar to previously observed “giant faults”.

As rubber materials are used for damping, clarifying the relationship between the loss factor and microstructure would help develop high-performance damping materials. Although nondestructive observations using X-ray computed tomography (CT) under repetitive deformation have been reported, no observations have been reported at the submicron order that capture low-strain deformation, such as vibration exposure. The internal deformation behavior of materials with different loss factors has not yet been evaluated. This study proposes a dynamic X-ray CT method for specimens under tensile amplitudes, directly evaluating the internal deformation behavior of materials under dynamic conditions. The proposed 4D-CT has an excitation of 1 Hz and a spatial resolution of 0.5 μm. The local strain was obtained from X-ray CT at each phase, and the deformation behavior was evaluated. The results revealed that the peak of the local strain amplitude distribution curve decreased and the distribution widened as fine particles were mixed.

In this paper, we present a new approach to contrast-agent-free angiographic visualization in optical coherence tomography (OCT). The proposed approach has much in common with imaging of local interframe strains in OCT-based elastography and utilizes the fact that the interframe motion of blood particles leads to discontinuity of strains within the vessel cross section. By this reasoning, we call this approach "elastography-inspired". Here, we first elucidate the essence and main features of the elastography-inspired approach using numerical simulation of OCT data. The simulations allow one to introduce both moving scatterers imitating blood flow in vessels as well as various masking motions imitating natural motions of living "solid" tissue surrounding the vessels. Second, using real OCT signals, we present comparative results of angiographic processing using the proposed elastography-inspired approach and a realization of OCA based on high-pass filtering of temporal variability of a series of OCT B-scans. The two methods can use the same initial dataset and the high-pass filtering OCA has already been routinely applied in both animal experiments and on patients. The new elastography-inspired method has a similar computational efficiency, and it is intrinsically able to compensate spatially-inhomogeneous masking tissue motions and demonstrates high robustness with respect to motion artefacts. Thus, the new approach looks very promising for enabling wider application of OCA in both laboratory studies on animals and, most importantly, for wider clinical applications on patients. [ABSTRACT FROM AUTHOR]

Neutron diffraction is a useful technique for mapping residual strains in dense metal objects. The technique works by placing an object in the path of a neutron beam, measuring the diffracted signals and inferring the local lattice strain values from the measurement. In order to map the strains across the entire object, the object is stepped one position at a time in the path of the neutron beam, typically in raster order, and at each position a strain value is estimated. Typical dwell times at neutron diffraction instruments result in an overall measurement that can take several hours to map an object that is several tens of centimeters in each dimension at a resolution of a few millimeters, during which the end users do not have an estimate of the global strain features and are at risk of incomplete information in case of instruments outages. In this paper, we propose an object adaptive sampling strategy to measure the significant points first. We start with a small initial uniform set of measurement points across the object to be mapped, compute the strain in those positions and use a machine learning technique to predict the next position to measure in the object. Specifically, we use a Bayesian optimization based on a Gaussian process regression method to infer the underlying strain field from a sparse set of measurements and predict the next most informative positions to measure based on estimates of the mean and variance in the strain fields estimated from the previously measured points. We demonstrate our real-time measure-infer-predict workflow on additively manufactured steel parts—demonstrating that we can get an accurate strain estimate even with 30%–40% of the typical number of measurements—leading the path to faster strain mapping with useful real-time feedback. We emphasize that the proposed method is general and can be used for fast mapping of other material properties such as phase fractions from time-consuming point-wise neutron measurements.

Mouse models of cardiac disease have become essential tools in the study of pathological mechanisms, but the small size of rodents makes it challenging to quantify heart function with noninvasive imaging. Building off recent developments in high-frequency four-dimensional ultrasound (4DUS) imaging, we have applied this technology to study cardiac dysfunction progression in a murine model of metabolic cardiomyopathy. Cardiac knockout of carnitine palmitoyltransferase 2 (Cpt2M-/-) in mice hinders cardiomyocyte bioenergetic metabolism of long-chain fatty acids, and leads to progressive cardiac hypertrophy and heart failure. The proposed analysis provides a standardized approach to measure localized wall kinematics and simultaneously extracts metrics of global cardiac function, LV morphometry, regional circumferential strain, and regional longitudinal strain from an interpolated 4-D mesh of the endo- and epicardial boundaries. Comparison of metric changes due to aging suggests that circumferential strain at the base and longitudinal strain along the posterior wall are most sensitive to disease progression. We further introduce a novel hybrid strain index (HSI) that incorporates information from these two regions and may have greater utility to characterize disease progression relative to other extracted metrics. Potential applications to additional disease models are discussed that could further demonstrate the utility of metrics derived from 4DUS imaging and strain mapping. [ABSTRACT FROM AUTHOR]

In this paper, we present a new approach to contrast-agent-free angiographic visualization in optical coherence tomography (OCT). The proposed approach has much in common with imaging of local interframe strains in OCT-based elastography and utilizes the fact that the interframe motion of blood particles leads to discontinuity of strains within the vessel cross section. By this reasoning, we call this approach “elastography-inspired”. Here, we first elucidate the essence and main features of the elastography-inspired approach using numerical simulation of OCT data. The simulations allow one to introduce both moving scatterers imitating blood flow in vessels as well as various masking motions imitating natural motions of living “solid” tissue surrounding the vessels. Second, using real OCT signals, we present comparative results of angiographic processing using the proposed elastography-inspired approach and a realization of OCA based on high-pass filtering of temporal variability of a series of OCT B-scans. The two methods can use the same initial dataset and the high-pass filtering OCA has already been routinely applied in both animal experiments and on patients. The new elastography-inspired method has a similar computational efficiency, and it is intrinsically able to compensate spatially-inhomogeneous masking tissue motions and demonstrates high robustness with respect to motion artefacts. Thus, the new approach looks very promising for enabling wider application of OCA in both laboratory studies on animals and, most importantly, for wider clinical applications on patients.

Focused ion beam (FIB) techniques are commonly used to machine, analyse and image materials at the micro‐ and nanoscale. However, FIB modifies the integrity of the sample by creating defects that cause lattice distortions. Methods have been developed to reduce FIB‐induced strain; however, these protocols need to be evaluated for their effectiveness. Here, non‐destructive Bragg coherent X‐ray diffraction imaging is used to study the in situ annealing of FIB‐milled gold microcrystals. Two non‐collinear reflections are simultaneously measured for two different crystals during a single annealing cycle, demonstrating the ability to reliably track the location of multiple Bragg peaks during thermal annealing. The thermal lattice expansion of each crystal is used to calculate the local temperature. This is compared with thermocouple readings, which are shown to be substantially affected by thermal resistance. To evaluate the annealing process, each reflection is analysed by considering facet area evolution, cross‐correlation maps of the displacement field and binarized morphology, and average strain plots. The crystal's strain and morphology evolve with increasing temperature, which is likely to be caused by the diffusion of gallium in gold below ∼280°C and the self‐diffusion of gold above ∼280°C. The majority of FIB‐induced strains are removed by 380–410°C, depending on which reflection is being considered. These observations highlight the importance of measuring multiple reflections to unambiguously interpret material behaviour. [ABSTRACT FROM AUTHOR]

Recently, the reinvigoration of research interest in in strain-mediated composite multiferroic structures resulted in translational magnetoelectric devices with superior performance than their traditional counterparts. Full-filed measurements and visualization of mechanical strain, with a focus at the interface, offer new possibilities for the advancement of magnetoelectric devices regardless of the material system. Here, we report spatiotemporal strain maps of composite magnetoelectric cylinders using a novel approach combining stable laser ultrasonic vibrometer and 2D motion system measurement technique. The physical measurement technique is augmented with a robust analysis algorithm that capable of effectively and consistently detect the interface. With the spatiotemporal maps, we forecast additional utility through the concurrent extraction of polarization and magnetization maps; hence highlighting the complex interactions between the involved order parameters. Understanding the converse magnetoelectric response in strain-mediated composite multiferroics is essential for the development of devices such and motors, antennas, and wireless power transferors. Given the dependence of the converse magnetoelectric response on the strain generation and transduction, mapping the mechanical response is essential for advancement of efficient devices. This mapping approach is challenging due to the dynamic nature of the response as well as the magneto-electro-mechanical coupling. Spatiotemporal maps of in-plane and out-of plane displacement and strain components were measured concurrently off the surface of a composite structure. To generate spatiotemporal strain maps, a laser-ultrasonic vibrometer mounted on a 2D gantry system was employed to map the in-plane and out-of-plane displacement components of a strain-mediated, concentric multiferroic composite cylinder. The strain maps provided insights on the behavior of the strain mediation mechanisms within the investigated composite structure including amplification of the strain due to the disparity in the mechanical properties of the constituents, which will result in a non-uniform distribution of magnetization and polarization responses. Additionally, the method to calculate the strain maps was shown to be robust for different spatial measurement resolutions. [ABSTRACT FROM AUTHOR]

Using ex-situ transmission electron microscopy and the recently developed nanoprobe diffraction (NPD) technique, we characterize a nanoindented solution treated gum metal. Lattice rotations are resolved at a 1.2 nm length-scale and shown to be continuous within the nanoindentation pit; further, it is shown that these can be accommodated by a reasonable number of geometrically necessary dislocations at a density of ∼10 15 /m 2 . We additionally provide direct evidence that dislocations within the nanoindent, rather than secondary phase nanoparticles, can serve as potent barriers to dislocation motion. We also demonstrate that plasticity in these alloys under nanoindentation can be accommodated solely by dislocation nucleation and propagation, with no competing deformation mechanisms present. Conventional transmission electron microscopy and “ g•b ” analysis reveal the presence of dislocations on 〈 1 ¯ 11 〉 {110} slip systems and highly localized plastic deformation in the form of shear bands on <111> { 1 ¯ 1 ¯ 2 } slip systems, similar to previously observed “giant faults”. [ABSTRACT FROM AUTHOR]

In this paper, we point out some practical obstacles arising in realization of compressional optical coherence elastography (OCE) that have not attracted sufficient attention previously. Specifically, we discuss (i) complications in quantification of the Young modulus of tissues related to partial adhesion between the OCE probe and soft intervening reference layer sensor, (ii) distorting influence of tissue surface curvature/corrugation on the subsurface strain distribution mapping, (iii) ways of signal-to-noise ratio (SNR) enhancement in OCE strain mapping when periodic averaging is not realized, and (iv) potentially significant influence of tissue elastic nonlinearity on quantification of its stiffness. Potential practical approaches to mitigate the effects of these complications are also described.

Aluminium based composite with dispersed graphite particles was processed by means of mechanical alloying, cold compression, sintering and hot extrusion. Samples for High Resolution Electron Microscopy (HRTEM) were obtained from extruded bars and were prepared using ultrasonic cutting, mechanical grinding, jet electropolishing and ion milling. Significant strain gradients are created in the metal matrix composites because of thermal mismatch between matrix and reinforcement particles. The main objective of this work was to determine by HRTEM in a quantitative way, the strain gradients in the matrix, in order to be able to predict the increments in the flow stress and the modification in the precipitation kinetics in future works. The geometric phase analysis (GPA) technique was employed to measure strain in the vicinity of the graphite particles. In order to avoid commonly observed errors in strain maps generated from HRTEM images we applied the GPA technique to the exit face wave function reconstructed from a focal series of HRTEM micrographs. It was possible to establish that the matrix is subjected to tension strain gradients that extend out to about 5 nm around the graphite particles. It was observed that the strain in transverse direction (εxx) was higher than the longitudinal (εyy). According to the results obtained the strain was heterogeneous and had a maximum value of 2.2 % in areas close to the particles. [ABSTRACT FROM AUTHOR]

In this paper, we point out some practical obstacles arising in realization of compressional optical coherence elastography (OCE) that have not attracted sufficient attention previously. Specifically, we discuss (i) complications in quantification of the Young modulus of tissues related to partial adhesion between the OCE probe and soft intervening reference layer sensor, (ii) distorting influence of tissue surface curvature/corrugation on the subsurface strain distribution mapping, (iii) ways of signal-to-noise ratio (SNR) enhancement in OCE strain mapping when periodic averaging is not realized, and (iv) potentially significant influence of tissue elastic nonlinearity on quantification of its stiffness. Potential practical approaches to mitigate the effects of these complications are also described. [ABSTRACT FROM AUTHOR]

Strain analysis from high-resolution transmission electron microscopy (HRTEM) images offers a convenient tool for measuring strain in materials at the atomic scale. In this paper we present a theoretical study of the precision and accuracy of surface strain measurements directly from aberration-corrected HRTEM images. We examine the influence of defocus, crystal tilt and noise, and find that absolute errors of at least 1-2% strain should be expected. The model structures include surface relaxations determined using molecular dynamics, and we show that this is important for correctly evaluating the errors introduced by image aberrations. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscopy (STEM) data with atomic resolution can contain a large amount of information about the structure of a crystalline material. Often, this information is hard to extract, due to the large number of atomic columns and large differences in intensity from sublattices consisting of different elements. In this work, we present a free and open source software tool for analysing both the position and shapes of atomic columns in STEM-images, using 2-D elliptical Gaussian distributions. The software is tested on variants of the perovskite oxide structure. By first fitting the most intense atomic columns and then subtracting them, information on all the projected sublattices can be obtained. From this, we can extract changes in the lattice parameters and shape of A-cation columns from annular dark field images of perovskite oxide heterostructures. Using annular bright field images, shifts in oxygen column positions are also quantified in the same heterostructure. The precision of determining the position of atomic columns is compared between STEM data acquired using standard acquisition, and STEM-images obtained as an image stack averaged after using non-rigid registration. [ABSTRACT FROM AUTHOR]

The role of boron in promoting ductility at high temperature in a prototype nickel-based superalloy designed for industrial gas turbines is studied. Both a boron-containing and boron-free variant are tested in tension at 750 °C, with further in-situ tests carried out using scanning electron microscopy (SEM), to clarify the mechanism of ductility improvement. The improvement in ductility is observed to be greater at the lowest investigated strain rate, where the grain boundary character plays a significant role on the mechanical properties; no ductility improvement was observed at the highest investigated strain rate. The in-situ tests were also performed at 750 °C and revealed directly the greater susceptibility of the grain boundary morphology in the boron-free case to fracture and – in the boron-containing case – the mechanism of ductility enhancement. The findings are supported further by high-resolution electron backscattered diffraction (HR-EBSD) strain mapping which confirms that the distribution of elastic strain and geometrically necessary dislocation (GND) content are influenced markedly by boron addition. The mechanism through which boron indirectly enhances the mechanical properties at elevated temperatures is discussed. [ABSTRACT FROM AUTHOR]

Additive manufacturing via selective laser melting of gas-atomized equiatomic powder was used to fabricate a CoCrFeMnNi high-entropy alloy. Analytical transmission electron microscopy, nanobeam diffraction, atom probe tomography and nanoindentation were employed to provide a comprehensive overview on the evolution of microstructure and nano-hardness upon annealing at a moderate temperature of 550∘C motivated by a maximum heat release at that temperature. A complex mechano-chemical coupling was observed, which leads to segregation and phase separation at grain boundaries. The as-manufactured material contained alternating regions of equiaxed and columnar grains. The corresponding microstructure is composed of high-angle grain boundaries and intrinsic dislocation networks, which displayed heterogeneous segregation of Mn and to some extent Ni. Longer annealing led to Cr enrichment at high-angle grain boundaries, and later to a phase separation with neighboring Cr-rich and MnNi-rich regions. Synergetic effects of segregation, nano-precipitation and dislocation accumulation at high-angle grain boundaries give rise to built up stresses which increase and homogenize hardness in the 3D-printed CoCrFeMnNi alloy. • Laser evaporates Mn during synthesis and leads to Mn enrichment at different boundaries as it diffuses back in the matrix. • Different solidification conditions dictate the shape of Mn-rich dislocation networks in columnar and equiaxed grains. • The GBs are curved in equiaxed grains and segmented in columnar grains with heterogeneous Ni enrichment in certain segments. • The fusion of Ni and Mn is the driving force to the enrichment of Ni at certain segments of HAGBs and dislocation networks. • The Cr-rich sigma phase nucleates and grows along the same direction as the grain after heat treatment at 550°C for 10 h. [ABSTRACT FROM AUTHOR]

AbstractWe present a study by transmission electron microscopy (TEM) of the strain state of individual InN quantum dots (QDs) grown on GaN substrates. Moiré fringe and high resolution TEM analyses showed that the QDs are almost fully relaxed due to the generation of a 60° misfit dislocation network at the InN/GaN interface. By applying the Geometric Phase Algorithm to plan-view high-resolution micrographs, we show that this network consists of three essentially non-interacting sets of misfit dislocations lying along the directions. Close to the edge of the QD, the dislocations curve to meet the surface and form a network of threading dislocations surrounding the system.

The multi-scale complexity of lath martensitic microstructures requires scale-bridging analyses to better understand the deformation mechanisms activated therein. In this study, plasticity in lath martensite is investigated by multi-field mapping of deformation-induced microstructure, topography, and strain evolution at different spatial resolution vs. field-of-view combinations. These investigations reveal site-specific initiation of dislocation activity within laths, as well as significant plastic accommodation in the vicinity of high angle block and packet boundaries. The observation of interface plasticity raises several questions regarding the role of thin inter-lath austenite films. Thus, accompanying transmission electron microscopy and synchrotron x-ray diffraction experiments are carried out to investigate the stability of these films to mechanical loading, and to discuss alternative boundary sliding mechanisms to explain the observed interface strain localization. [ABSTRACT FROM AUTHOR]

In compressional optical coherence elastography, phase-variation gradients are used for estimating quasistatic strains created in tissue. Using reference and deformed optical coherence tomography (OCT) scans, one typically compares phases from pixels with the same coordinates in both scans. Usually, this limits the allowable strains to fairly small values <10-4 to 10-3, with the caveat that such weak phase gradients may become corrupted by stronger measurement noises. Here, we extend the OCT phase-resolved elastographic methodology by (1) showing that an order of magnitude greater strains can significantly increase the accuracy of derived phase-gradient differences, while also avoiding error-phone phase-unwrapping procedures and minimizing the influence of decorrelation noise caused by suprapixel displacements, (2) discussing the appearance of artifactual stiff inclusions in resultant OCT elastograms in the vicinity of bright scatterers due to the amplitudephase interplay in phase-variation measurements, and (3) deriving/evaluating methods of phase-gradient estimation that can outperform conventionally used least-square gradient fitting. We present analytical arguments, numerical simulations, and experimental examples to demonstrate the advantages of the proposed optimized phase-variation methodology. [ABSTRACT FROM AUTHOR]

As rubber materials are used for damping, clarifying the relationship between the loss factor and microstructure would help develop high-performance damping materials. Although nondestructive observations using X-ray computed tomography (CT) under repetitive deformation have been reported, no observations have been reported at the submicron order that capture low-strain deformation, such as vibration exposure. The internal deformation behavior of materials with different loss factors has not yet been evaluated. This study proposes a dynamic X-ray CT method for specimens under tensile amplitudes, directly evaluating the internal deformation behavior of materials under dynamic conditions. The proposed 4D-CT has an excitation of 1 Hz and a spatial resolution of 0.5 μm. The local strain was obtained from X-ray CT at each phase, and the deformation behavior was evaluated. The results revealed that the peak of the local strain amplitude distribution curve decreased and the distribution widened as fine particles were mixed. • The phase-locked loop imaging allows using a micro X-ray CT under repetitive deformation have been reported. • 4D-CT with an excitation of 1 Hz and spatial resolution of 0.5 μm for measurements of internal deformation in polymer specimens was realized. • As the loss factor increased with the particulate composites, the peak height of local strain amplitude distribution decreased. [ABSTRACT FROM AUTHOR]

We determined inhomogeneity of strains around discontinuities as well as changes in orientation of collagen fibrils under applied load in skin. Second Harmonic Generation (SHG) images of collagen fibrils were obtained at different strain magnitudes. Changes in collagen orientation were analyzed using Fast Fourier Transforms (FFT) while strain inhomogeneity was determined at different distances from hair follicles using Digital Image Correlation (DIC). A parameter, defined as the Collagen Orientation Index (COI), is introduced that accounts for the increasingly ellipsoidal nature of the FFT amplitude images upon loading. We show that the COI demonstrates two distinct mechanical regimes, one at low strains (0%, 2.5%, 5% strain) in which randomly oriented collagen fibrils align in the direction of applied deformation. In the second regime, beginning at 5% strain, collagen fibrils elongate in response to applied deformation. Furthermore, the COI is also found to be linearly correlated with the applied stress indicating that collagen fibrils orient to take the applied load. DIC results indicated that major principal strains were found to increase with increased load at all locations. In contrast, minimum principal strain was dependent on distance from hair follicles. These findings are significant because global and local changes in collagen deformations are expected to be changed by disease, and could affect stem cell populations surrounding hair follicles, including mesenchymal stem cells within the outer root sheath. [ABSTRACT FROM AUTHOR]