High-resolution Strain Mapping Research Articles

Anomalous two-step repair mechanism of Al–Cu alloy regulated by the surroundings during E-beam irradiation

Understanding the repair mechanisms of defects is essential for gaining insight into improving the quality and enhancing the performance of materials. While new structures and elemental segregation always exist around defects, the influence of the surroundings on the repair mechanism has rarely been investigated on the atomic scale. Here, by tracking the morphological and microstructural evolution of Al2Cu nanopores with and without Cu-rich phases in the vicinity under electron beam irradiation, our in-situ transmission electron microscopy (TEM) study revealed a surrounding-dependent repair behavior. In contrast to the Al2Cu nanopores without Cu-rich neighborhoods, which display an isotropically shrinking from all directions, the Al2Cu nanopores with Al4Cu9 nearby exhibit an anomalous two-step repair mechanism. First, new Al4Cu9 structures nucleated from the Cu-rich region and evolved to fill the nanopores. Second, Al4Cu9 reacted with Al atoms and gradually transformed into Al2Cu. High-resolution TEM (HRTEM) images and strain maps demonstrate that the repair is imperfect as the eventual repaired region contains both Al4Cu9 and Al2Cu. This is caused by the simultaneous sputtering and depositing effects of electron beams (E-Beam). Our findings provide critical insights into the modulatory function of surroundings on the nanopore repair mechanism.

High-resolution local trabecular strain within trabecular structure under cyclic loading

Trabecular bone structure is a complex microstructure consisting of rods and plates, which poses challenges for its mechanical characterization. Digital image correlation (DIC) offers the possibility to characterize the strain response on the surface of trabecular bone. This study employed DIC equipped with a telecentric lens to investigate the strain state of individual trabeculae within their trabecular structure by assessing the longitudinal strain of the trabeculae at both the middle and near the edges of the trabeculae. Due to the high-resolution of the used DIC system, local surface strain of trabeculae was analyzed too. Lastly, the correlation between longitudinal trabecular strain and the orientation and slenderness of the trabeculae was investigated. The results showed that the strain magnification close to the edge of the trabeculae was higher and reached up to 8-folds the strain along the middle of the trabeculae. On the contrary, no strain magnification was found for most of the trabeculae between the longitudinal trabecular strain along the middle of the trabeculae and the globally applied strain. High-resolution full-field strain maps were obtained on the surface of trabeculae showing heterogeneous strain distribution with increasing load. No significant correlation was found between longitudinal trabecular strain and its orientation or slenderness. These findings and the applied methodology can be used to broaden our understanding of the deformation mechanisms of trabeculae within the trabecular network.

High-resolution 3D strain and orientation mapping within a grain of a directed energy deposition laser additively manufactured superalloy

The industrialization of Laser Additive Manufacturing (LAM) is challenged by the undesirable microstructures and high residual stresses originating from the fast and complex solidification process. Non-destructive assessment of the mechanical performance controlling deformation patterning is therefore critical. Here, we use Dark Field X-ray Microscopy (DFXM) to map the 3D subsurface intragranular orientation and strain variations throughout a surface-breaking grain within a directed energy deposition nickel superalloy. DFXM results reveal a highly heterogenous 3D microstructure in terms of the local orientation and lattice strain. The grain comprises ≈ 5 μm-sized cells with alternating strain states, as high as 5 ×10−3, and orientation differences <0.5°. The DFXM results are compared to Electron Backscatter Diffraction measurements of the same grain from its cut-off surface. We discuss the microstructure developments during LAM, rationalising the development of the deformation patterning from the extreme thermal gradients during processing and the susceptibility for solute segregation.

Microstructural effects on fatigue crack initiation mechanisms in a near-alpha titanium alloy

The role of different microstructural constituents on crack initiation in two-phase titanium alloys is still an area of great controversy. The present study investigates the effects of primary α volume fraction and concomitant macrozones on two different fatigue crack initiation modes concurrently observed in a near-α titanium alloy. Statistically representative regions were monitored in quasi-in-situ studies by interrupting fatigue testing to detect slip trace formation leading to crack initiation. In addition, high-resolution 2D strain maps were generated to quantify in-plane shear strains of slip traces related to microstructural features. The detailed analysis demonstrates that at 90% of the proof stress basal 〈a〉 slip plays a crucial role in crack initiation, regardless of whether cracking is transgranular or intergranular. In addition, a distinct shift from transgranular to intergranular crack initiation was observed with increasing αp fraction driven by the increased number of αp/αp grain boundaries. The high-resolution 2D strain mapping suggest that these intergranular cracks initiated from a burst of basal 〈a〉 slip starting from (0001) twist grain boundaries but penetrating one side of the grain pair in case of a partial (0001) twist grain boundary. From these observations, a new criterion for intergranular cracking is proposed based on a geometrical grain boundary parameter and the preference of neighbouring αp grain pair well aligned for basal 〈a〉 slip. It was found that while (0001) twist grain boundaries increase with increasing αp fraction, macrozones do not further enhance their frequency. However, macrozones of hard orientated grains did enhance transgranular crack formation by potentially higher local stress and increasing slip length over clustered αp grains with low misorientation reducing the requirement for out-of-plane shear.

Data for "High-resolution Interseismic Strain Mapping from InSAR Phase-Gradient Stacking: Application to the North Anatolian Fault with Implications for the Non-uniform Strain Distribution Related to Historical Earthquakes" manuscript

Data for "High-resolution Interseismic Strain Mapping from InSAR Phase-Gradient Stacking: Application to the North Anatolian Fault with Implications for the Non-uniform Strain Distribution Related to Historical Earthquakes" manuscript

Detecting irradiation-induced strain localisation on the microstructural level by means of high-resolution digital image correlation

Materials subjected to irradiation damage often undergo local microstructural changes that can affect their expected performance. To investigate such changes, this work proposes a novel approach to detect strain localisation caused by irradiation-induced damage in nuclear materials on the microstructural level, considering a statistically relevant number of grains. This approach determines local strains using high-resolution digital image correlation (HRDIC) and compares them with the underlying material microstructure. Sets of images captured before and after irradiation are compared to generate full-field displacement maps that can then be differentiated to yield high-resolution strain maps. These strain maps can subsequently be used to understand the effects of irradiation-induced dimensional change and cracking on the microscale. Here, the methodology and challenges involved in combining scanning electron microscopy (SEM) with HRDIC to generate strain maps associated with radiation-induced damage are presented. Furthermore, this work demonstrates the capabilities of this methodology by analysing three different materials subjected to proton irradiation: a zircaloy-4 (Zry-4) metal irradiated to 1 & 2 dpa, and two ceramics based on MAX phase compounds, i.e., the Nb4AlC3 ternary compound and a novel (Ta,Ti)3AlC2 solid solution, both irradiated to -0.1 dpa. These results demonstrated that all materials show measurable expansion, and the very high strains seen in the MAX phase ceramics can be easily attributed to their microstructure. Grain-to-grain variability was observed in Zry-4 with a macroscopic expansion along the rolling direction that increased with irradiation damage dose, the Nb4AlC3 ceramic showed significant expansion within individual grains, leading to intergranular cracking, while the less phase-pure (Ta,Ti)3AlC2 ceramic exhibited very high strains at phase boundaries, with limited expansion in the binary carbide phases. This ability to measure irradiation-induced dimensional changes at the microstructural scale is important for designing microstructures that are structurally resilient during irradiation.

Mapping the Evolution of Surface Strain in PtCo Core-Shell Catalysts By 4D-STEM

With the recent shift in attention from light-duty to heavy-duty vehicles for fuel cell research, the efficiency and durability requirements for catalyst materials have significantly increased [1]. As a result, it is more important than ever to understand the effects of degradation on catalyst nanoparticle surface structure and properties. Surface strain, for example, plays an important role in dictating the activity of catalyst nanoparticles [2], and understanding its evolution over the lifetime of a cell is therefore important. State-of-the-art PtCo core-shell catalyst nanoparticles contain complex strain gradients since, in addition to the surface strain that can occur for even single-metal nanoparticles [3], the lattice constant of the ordered PtCo core is smaller than that of the Pt shell [4]. These strain gradients may evolve over the lifetime of the cell due to cycling-induced metal dissolution, leading to compositional and shell thickness changes. Since these particles are generally <10 nm in diameter and have Pt shells only a few monolayers thick, a technique that can directly reveal their surface strain with high spatial resolution is needed to enable a better understanding of the relationship between surface strain and the performance and durability of heavy-duty fuel cells.High-resolution strain mapping can be performed by conventional high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) techniques, for example through geometric phase analysis [5] or direct tracking of atomic column positions [6,7]. These methods require the material to be tilted to a low-order zone axis for data acquisition, a very time-consuming process for randomly oriented nanoparticles that significantly limits the number of particles, and hence the statistically relevant information, that can be included in a given study [6-8]. Four-dimensional (4D)-STEM provides an alternative approach for mapping strain at high resolution by tracking diffraction disk shifts in patterns recorded in a two-dimensional STEM scan [9]. Recently, 4D-STEM was shown to offer advantages over more conventional methods for nanoparticle strain mapping, such as reduced noise and/or artifacts [10]. While initial demonstrations of off-axis 4D-STEM strain measurements have been shown [11], strain analysis based on 4D-STEM typically still requires particles to be oriented on a zone axis, which again limits the number of particles measurable for a given study. A strain mapping technique that incorporates the strengths of 4D-STEM while allowing off-axis measurements to be made would therefore significantly increase the throughput of the technique, enabling statistically relevant information about particle surface strain as a function of size, composition, or cycling history to be obtained.In this talk, we will demonstrate advancements in 4D-STEM strain mapping that allow strain to be mapped in off-axis particles, therefore enabling hundreds of catalyst nanoparticles to be measured with unit-cell spatial resolution in a single instrument session. This allows mean strain profiles to be generated for the particles as a function of distance from the surface and correlate this with particle size, composition, and cycling history. By significantly increasing the throughput of high-resolution strain mapping, this technique paves the way to a better understanding of the role strain plays in catalyst performance and degradation, accelerating development of advanced heavy-duty fuel cell catalyst materials [12].

A machine learning approach for magnetic resonance image-based mouse brain modeling and fast computation in controlled cortical impact.

Computational modeling of the brain is crucial for the study of traumatic brain injury. An anatomically accurate model with refined details could provide the most accurate computational results. However, computational models with fine mesh details could take prolonged computation time that impedes the clinical translation of the models. Therefore, a way to construct a model with low computational cost while maintaining a computational accuracy comparable with that of the high-fidelity model is desired. In this study, we constructed magnetic resonance (MR) image-based finite element (FE) models of a mouse brain for simulations of controlled cortical impact. The anatomical details were kept by mapping each image voxel to a corresponding FE mesh element. We constructed a super-resolution neural network that could produce computational results of a refined FE model with a mesh size of 70μm from a coarse FE model with a mesh size of 280μm. The peak signal-to-noise ratio of the reconstructed results was 33.26dB, while the computational speed was increased by 50-fold. This proof-of-concept study showed that using machine learning techniques, MR image-based computational modeling could be applied and evaluated in a timely fashion. This paved ways for fast FE modeling and computation based on MR images. Results also support the potential clinical applications of MR image-based computational modeling of the human brain in a variety of scenarios such as brain impact and intervention.Graphical abstract MR image-based FE models with different mesh sizes were generated for CCI. The training and testing data sets were computed with 5 different impact locations and 3 different impact velocities. High-resolution strain maps were estimated using a SR neural network with greatly reduced computational cost.

Frame overlap Bragg edge imaging

Neutron Bragg edge imaging enables spatially resolved studies of crystalline features through the exploitation and analysis of Bragg edges in the transmission spectra recorded in each pixel of an imaging detector. Studies with high spectral resolutions, as is required e.g. for high-resolution strain mapping, and with large wavelength ranges have been largely reserved to pulsed neutron sources. This is due to the fact, that the efficiency for high wavelength resolution measurements is significantly higher at short pulse sources. At continuous sources a large fraction of the available neutrons must be sacrificed in order to achieve high wavelength resolution for a relevant bandwidth e.g. through a chopper system. Here we introduce a pulse overlap transmission imaging technique, which is suited to increase the available flux of high wavelength resolution time-of-flight neutron Bragg edge imaging at continuous neutron sources about an order of magnitude. Proof-of-principle measurements utilizing a chopper with a fourfold repeated random slit distribution of eight slits were performed at a thermal neutron beamline. It is demonstrated, that disentanglement of the overlapping pulses is achieved with the correlation theorem for signal processing. Thus, the Bragg edge pattern can be reconstructed from the strongly overlapping Bragg edge spectra recorded and the results demonstrate the feasibility of the technique.

High resolution strain mapping of a single axially heterostructured nanowire using scanning X-ray diffraction

Axially heterostructured nanowires are a promising platform for next generation electronic and optoelectronic devices. Reports based on theoretical modeling have predicted more complex strain distributions and increased critical layer thicknesses than in thin films, due to lateral strain relaxation at the surface, but the understanding of the growth and strain distributions in these complex structures is hampered by the lack of high-resolution characterization techniques. Here, we demonstrate strain mapping of an axially segmented GaInP-InP 190 nm diameter nanowire heterostructure using scanning X-ray diffraction. We systematically investigate the strain distribution and lattice tilt in three different segment lengths from 45 to 170 nm, obtaining strain maps with about 10−4 relative strain sensitivity. The experiments were performed using the 90 nm diameter nanofocus at the NanoMAX beamline, taking advantage of the high coherent flux from the first diffraction limited storage ring MAX IV. The experimental results are in good agreement with a full simulation of the experiment based on a three-dimensional (3D) finite element model. The largest segments show a complex profile, where the lateral strain relaxation at the surface leads to a dome-shaped strain distribution from the mismatched interfaces, and a change from tensile to compressive strain within a single segment. The lattice tilt maps show a cross-shaped profile with excellent qualitative and quantitative agreement with the simulations. In contrast, the shortest measured InP segment is almost fully adapted to the surrounding GaInP segments.

Comparison of sub-grain scale digital image correlation calculated using commercial and open-source software packages

High-resolution strain mapping is an increasingly prominent technique for characterising the deformation behaviour of metals. In this study, HRDIC analysis was performed on materials exhibiting either more or less intense planar slip, using different software packages to highlight any issues that might arise depending on the algorithm that is used to calculate the displacements. The differences between the algorithms were investigated using frequency distributions, strain profiling and Burgers vector direction analysis to determine their significance in terms of any subsequent interpretation of the data. A dilute zirconium alloy showed maximum strain concentrations of <4.5 and similar to previous comparison studies of different software packages on optical images, little difference was observed in the resulting strain maps. However, in a more highly alloyed two-phase titanium alloy with significant planar slip and strain values of up to 20 times the applied strain, one of the algorithms had difficulty tracking the features particularly at low strains when the difference between the strain in a slip trace is markedly higher than that in the neighbouring region. The consequences of inaccurate displacement data around a slip trace region were highlighted by an incorrect prediction of the Burgers vector when using the relative displacement ratio for slip system identification.

Optical coherence elastography by ambient pressure modulation for high-resolution strain mapping applied to patterned cross-linking.

The purpose of this study was to develop a novel non-contact optical coherence elastography (OCE) approach to measure laterally and axially highly resolved corneal strain distribution at different stages of patterned corneal cross-linking (CXL). Freshly enucleated rat eyes were obtained and prepared for accelerated patterned CXL treatment with distinct ultraviolet (UV) patterns (central, peripheral, bow-tie irradiation). Each cornea was measured repeatedly, in three different conditions: (i) virgin, (ii) after epithelial debridement and 0.5% hypo-osmolar riboflavin instillation for 30 min, and (iii) after patterned CXL at 9 mW cm-2 for 10 min. For biomechanical assessment, the corneal deformation response to an ambient pressure variation of -2 mmHg was recorded by OCE. Strain maps were obtained from phase and magnitude changes in the complex optical coherence tomography signal. Virgin corneas presented negative strain (-2.7 ± 1.1‰) in the anterior cornea and positive strain (1.9 ± 1.3‰) in the posterior cornea. A pronounced shift towards positive strains in the anterior cornea (particularly in UV-irradiated regions) was observed after CXL. Patterned UV irradiation induced localized strain alterations closely matching the geometry of the irradiation pattern. This study demonstrates the possibility of non-contact OCE by ambient pressure modulation, which could substantially improve the early diagnosis of corneal degeneration, advance research in small-animal eyes and refine in vitro mechanical investigation.

Identification of active slip mode in a hexagonal material by correlative scanning electron microscopy

Metals with a hexagonal close packed structure can deform by several different slip modes with different Critical Resolved Shear Stresses, which provides a great deal of complexity when considering mechanical performance of Mg, Ti and Zr alloys. Hence, an accurate but also statistically meaningful analysis of active slip systems and their contribution to plasticity is of great importance for the understanding of deformation mechanism. In the present study, a correlative scanning electron microscopy-based method of slip trace analysis has been utilised to provide statistical, accurate information of slip behaviour in a weakly textured Ti–6Al–4V alloy with a plastic strain of ∼2%. This is achieved through grain orientation mapping by Electron Backscatter Diffraction and strain mapping by High Resolution Digital Image Correlation. The initial identification of slip mode was performed by comparing the slip trace captured in the high-resolution effective shear strain map with all theoretical slip planes with an angle acceptance criterion of ±5°. Ambiguity in slip mode identification was further resolved using the Relative Displacement Ratio method, which enables the determination of the Burgers vector directly from the displacement data. The correctness of the identified slip modes has been confirmed by detailed dislocation analysis using Bright Field Scanning Transmission Electron Microscopy on thin foils extracted from specific grains employing Focused Ion Beam. This detailed investigation demonstrates the robustness of the slip trace analysis based on grain orientation and high-resolution strain mapping.

Microscopic strain partitioning in Lüders band of an ultrafine-grained medium Mn steel

This paper is focused on the determination and understanding of the microscopic strain partitioning in the Lüders band of an ultrafine-grained medium Mn transformation-induced plasticity (TRIP) steel with austenite-ferrite dual phase microstructures. First, a microscopic digital image correlation (μ-DIC) method is developed that enables high-resolution strain mapping at the subgrain scale. Thanks to the local Lüders strain assessment, the strain partitioning between ferrite and retained austenite is quantified. It reveals that the average Lüders strain in ferrite is about 10.1% and that in austenite about 9.1% at a macroscopic Lüders strain 9.5%, thus it indicates that both phases are important to the plastic deformation in the Lüders band. Besides the strain partitioning between the two phases, a more striking finding is the significant heterogeneity of Lüders strain within the same phase. The microstructural origins for the strain partitioning are investigated using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) in combination with the strain field analysis. The results show that the main cause for strain heterogeneity formation in Lüders band can be attributed to the heterogenous distribution of mobile dislocations in the initial microstructure before tensile deformation. And the effects of grain size and crystallographic texture are proofed to be the secondary factors that may only have minor influence on Lüders strain distribution.

Developing High Resolution and High Precision Strain Mapping Methodologies for Materials Research and Semiconductor Technology

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Interface affected zone for optimal strength and ductility in heterogeneous laminate

Interfaces have been reported to significantly strengthen and toughen metallic materials. However, there has been a long-standing question on whether interface-affected-zone (IAZ) exists, and how it might behave. Here we report in situ high-resolution strain mapping near interfaces in a copper–bronze heterogeneous laminate, which revealed the existence of IAZs. Defined as the zone with strain gradient, the IAZ was found to form by the dislocations emitted from the interface. The IAZ width remained largely constant with a magnitude of a few micrometers with increasing applied strain. Interfaces produced both back stress strengthening and work hardening, which led to both higher strength and higher ductility with decreasing interface spacing until adjacent IAZs started to overlap, after which a tradeoff between strength and ductility occurred, indicating the existence of an optimum interface spacing for the best mechanical properties. These findings are expected to help with designing laminates and other heterogeneous metals and alloys for superior mechanical properties.

Verification of Strain-Induced Fast Ionic Conduction in Thin-Film Electrolyte Via Experimental and Computational Study

Epitaxial strain engineering in nanostructured oxides has attracted great attention to various energy storage and conversion devices requiring fast ionic conduction, such as solid-oxide fuel cells (SOFCs), catalytic membranes, and electrochemical sensors. Recently, remarkable enhancement of ionic conductivity has been achieved by the epitaxial strain in ultra-thin epitaxial and multi-layered films.1-3 However, the strain engineering still has some lack of understanding of how much enhancement can be achieved by strain, and how to maximize the strain in nanostructured oxides. Herein, for the reliable and effective strain engineering for fast ionic conduction, strain effect on oxygen ion conductivity of thin films (Gd0.2Ce0.8O1.9-δ (100) : GDC) was investigated through both experimental study and density functional theory (DFT) calculations. We measured the oxygen ion conductivity of GDC films grown in island growth mode on Nb-doped SrTiO3 (STO) substrate. According to the conductivity measurement via electrochemical impedance spectroscopy (EIS), the activation energy for oxygen ion migration in out-of-plane direction was reduced with increase of film thickness. Furthermore, through careful strain analysis using high-resolution X-ray diffraction (HR-XRD) and strain mapping in transmission electron microscopy (TEM), the intrinsic tensile strain along column boundaries (CB) was found to be more predominant than the epitaxial strain formed at the film-substrate interface, thereby more strong tensile strain was observed in a thicker film having higher CB density. This general tendency of the activation energy change with respect to tensile strain was also verified by atomic-scale simulation in a highly doped CeO2 structure. To the best of our knowledge, this is the first experimental and theoretical verification to show the critical role of intrinsic strain on fast ion conduction in thin film electrolyte. From this presentation, you will get a great inspiration to the strain-induced fast ionic conduction in oxide thin films to improve the availability of various energy devices. References S. Schweiger, M. Kubicek, F. Messerschmitt, C. Murer, and J. L. M. Rupp, ACS Nano 8, 5032 (2014).S. Sanna, V. Esposito, J. W. Andreasen, J. Hjelm, W. Zhang, T. Kasama, S. B. Simonsen, M. Christensen, S. Linderoth, and N. Pryds, Nat. Mater. 14, 500 (2015)A. Fluri, D. Pergolesi, V. Roddatis, A. Wokaun, and T. Lippert, Nat. Commun. 7, 10692 (2016)

The Effect of Strain Localization on Galvanic Corrosion Pitting in AA7050

Corrosion is the primary failure mechanism for sea-based structures, as it plays an important role in material degradation and structural integrity. The localized corrosion behavior is affected by the micromechanics and the electrochemistry of the material; however, there are very limited studies where both mechanisms are studied jointly, let alone relative to microstructural attributes, i.e., at the mesoscale. High-resolution strain maps are created on pre-loaded AA7050 in the transverse-short orientation via digital image correlation to identify strain accumulation with respect to the microstructure. Afterward, this material is subjected to a galvanic corrosion environment. In order to investigate the driving force for localized corrosion, the microstructure, the cathodic particles, the localized strain, and the evolution of surface topology caused by corrosion pitting are spatially characterized in the region of interest. The evolution of the corroded surface is tracked every 24 h throughout the 20 d of corrosion that the material was immersed in 0.6 M NaCl solution. Specifically, three representative sized cathodic particles are monitored throughout the corrosion study, to identify their evolution of pitting before and after the particles fallout from contact with the matrix. Finally, the relationship between strain and localized galvanic corrosion is quantitatively investigated using Gaussian process modeling to identify the underlying correlations. The results show that localized strains within ±3σ of the macroscopic residual strain do not affect the corrosion rate of the material; however, extreme values beyond that threshold associated with the cracking of the particle itself seem to heavily promote the growth of localized galvanic corrosion.

Enabling high resolution strain mapping in zirconium alloys

High Resolution Digital Image Correlation (HRDIC) has been established recently as a novel displacement mapping technique during mechanical loading experiments to quantify strain localisation down to the level of individual slip traces. This is achieved by the creation of a nano-scale gold pattern naturally formed during remodelling of a thin gold layer that was sputtered onto the region of interest. To date, the gold remodelling is carried out in a water vapourisation environment, which excludes the technique to be applied to materials that readily form noticeable oxide layers in such environments. The current paper describes a recently developed gold remodelling technique using a styrene-argon environment at substantially lower temperatures than the water-vapour based technique. The material used in the present work is a zirconium alloy where we first demonstrate the problem of oxide formation during remodelling in water vapour and the benefit of the modified remodelling procedure. The error associated with the spatial drift was assessed for different interrogation window sizes followed by detailed analysis of the subsequent strain maps produced using the styrene remodelled patterns after tensile deformation to nominal applied strains of ~3.5% and ~7.0%. The level of detail captured demonstrate the suitability of styrene-argon-based remodelling for materials like Zr alloys with the strain maps showing clear strain patterning on both a transgranular and single grain scale with the possibility of quantifying strain across a single slip trace.

Controllable assembly of silver nanoparticles based on the coffee-ring effect for high-sensitivity flexible strain gauges

An effective and facile strategy was developed to assemble silver nanoparticle (AgNPs) into a series of close-packed silver nanoparticles wires (AgNWs), and successfully construct a high-sensitivity strain gauge on the flexible PET substrate. In this work, AgNPs were directly ink-jet printed onto the flexible PET substrate and assembled into paralleled twin lines induced by the coffee-ring effect. By regulating the coffee-ring effect, a series of well-organized AgNWs were controllably fabricated with a line width of 5–6μm. Due to the exponential dependence of relative resistance variation to the applied mechanical strains, the assembled AgNWs-based strain gauge could achieve highly sensitive strain detection, exhibiting a high gauge factor approximately G=50–60 and a lowest strain level of 0.061% detection limit. Moreover, the AgNWs-based strain gauge demonstrated a reversible and reliable electrical response as a mechanical strain was periodically supplied at various frequencies. This simple, efficient and nonlithographic approach would be considered as an universal method to construct highly sensitive and reliable strain gauges for high resolution strain mapping fields.