Direction Of Applied Strain Research Articles

Flexible multicolor biaxial sensor for strain direction identification based on sandwich-structured mechanoluminescent materials.

Strain sensors capable of recognizing the direction of strain are crucial in applications such as robot attitude adjustment and detection of strain states in complex structures. In this study, a sandwich-structured flexible biaxial strain sensor was developed using polydimethylsiloxane as the substrate, mechanoluminescent materials as the luminescent elements, and rubber-ink as the light-blocking layer. By correlating the emitted light color with the stretching state, precise identification of the applied strain direction is achieved. Additionally, the mechanoluminescence of the sensor is collected by a photodiode, generating photocurrent that can be analyzed. This provides a solution for practical applications of sensor.

Tuning the electronic properties of Stone-Wales defected graphene using uniaxial longitudinal and horizontal strain: A first-principles study

We investigated the influence of horizontal and longitudinal strain on the electronic proprieties of Stone-Wales defected honeycomb graphene structure using the density functional theory. Tensile and compressive uniaxial strains were independently applied on the armchair (horizontal) and the zigzag (longitudinal) directions of a defected honeycomb graphene monolayer. We found the responses of the band gap are dependent on the applied strain direction. Likewise, the induced band gap openings show evident correlations between Stone-Wales defect orientations and the applied strain directions. Our results show that by choosing the strain values and directions the band gap values can be precisely achieved. Additionally, the effects of the applied strain were calculated and analyzed for the Fermi level, work function and the charge distributions. For both the defect-free and the defected samples, Fermi level shifts up in response to the compressive strain while it shifts down in response to the tensile strain. Our study shows the electronic properties are significantly affected by the alignment between the Stone-Wales C-C middle bond orientation and the applied stain direction. Finally, we hope providing a precise tuning for the electronic properties of defected graphene will allow for future nanodevice applications.

Electrical Percolation in Metal Wire Network-Based Strain Sensors

Metal wire networks rely on percolation paths for electrical conduction, and by suitably introducing break-make junctions on a flexible platform, a network can be made to serve as a resistive strain sensor. Several experimental designs have been proposed using networks made of silver nanowires, carbon nanotubes and metal meshes with high sensitivities. However, there is limited theoretical understanding; the reported studies have taken the numerical approach and only consider rearrangement of nanowires with strain, while the critical break-make property of the sensor observed experimentally has largely been ignored. Herein, we propose a generic geometrical based model and study distortion, including the break-make aspect, and change in electrical percolation of the network on applying strain. The result shows that when a given strain is applied, wire segments below a critical angle with respect to the applied strain direction end up breaking, leading to increased resistance of the network. The percolation shows interesting attributes; the calculated resistance increases linearly in the beginning and at a higher rate for higher strains, consistent with the experimental findings. In a real scenario, the strain direction need not necessarily be in the direction of measurement, and therefore, strain value and its direction both are incorporated into the treatment. The study reveals interesting anisotropic conduction features; strain sensitivity is higher parallel to the strain, while strain range is wider for perpendicular measurement. The percolation is also investigated on direct microscopic images of metal networks to obtain resistance-strain characteristics and identification of current percolation pathways. The findings will be important for electrical percolation in general, particularly in predicting characteristics and improvising metal network-based strain sensors.

The Biaxial Strain Dependence of <italic>J</italic>C of a (RE)BCO Coated Conductor at 77 K in Low Fields

Recently, we designed and commissioned a “crossboard” sample holder that can apply biaxial strains in the plane of a (RE)BCO coated conductor. It allows us to measure the critical current density ${\boldsymbol{J}_C}$ for arbitrary combinations of x - and y -strain. Understanding the in-field, in-plane, biaxial strain dependence of a tape's ${\boldsymbol{J}_{\bf{C}}}({\boldsymbol{B},{\boldsymbol{\varepsilon }_{\boldsymbol{xx}}},{\boldsymbol{\varepsilon }_{\boldsymbol{yy}}}})$ is crucial for applications such as CORC or Roebel cables, as the cables are subjected to multiaxial strains during manufacturing and operation. Here, we present experimental data for ${\boldsymbol{J}_{\bf{C}}}({\boldsymbol{B},{\boldsymbol{\varepsilon }_{\boldsymbol{xx}}},{\boldsymbol{\varepsilon }_{\boldsymbol{yy}}}})$ on a SuperPower SCS4050 APC tape in magnetic fields up to 0.7 T, at 77 K. We also outline a theoretical model for the biaxial strain dependence of ${\boldsymbol{J}_{\bf{C}}}$ and use it to parameterize our data and show that the fraction of A-domains and B-domains are roughly equal $({\boldsymbol{f} = 0.49 \pm 0.03})$ and that the strain sensitivity of the critical temperature is 1.8 ± 0.1 K%−1 and −1.3 ± 0.1 K%−1 along their a - and b- axes, respectively, for all the domains in this (RE)BCO tape. For the first time, we show both parabolic and linear strain dependencies of ${\boldsymbol{J}_{\bf{C}}}$ in a single tape by changing the angle between the applied strain direction and the twin boundaries in the (RE)BCO layer.

Stretchable, Bifacial Si-Organic Hybrid Solar Cells by Vertical Array of Si Micropillars Embedded into Elastomeric Substrates.

Stretchable electronics has enabled many unforeseen applications in a variety of fields. Mechanical design concepts to achieve the stretchability without affecting the device functionality, however, are limited to few known practices, such as mechanical buckling, serpentine shape, or simple elastomeric composites. In this paper, we propose another mechanics design principle for high stretchability (>100%) based on the composite of vertical array of Si micropillars embedded into elastomer poly(dimethylsiloxane). The orthogonalization of active functional elements to applied strain direction enables highly stretchable electronic devices, where the applied strain is mostly absorbed into elastomer on interpillar space. On the other hand, the vertical pillars do not experience any noticeable strain at all. As a proof-of-concept demonstration, we fabricate stretchable Si-organic hybrid solar cells using such a design and the cell shows reasonable level of cell efficiency compared with planar counterparts. The cell can be stretched reversibly without any noticeable performance degradation. Furthermore, the cell can be operated in a bifacial mode by employing stretchable, transparent Ag nanowire-based electrodes. The mechanical design for stretchability demonstrated here would provide new opportunities for stretchable electronics.

Mesoscopic friction and network morphology control the mechanics and processing of carbon nanotube yarns

Carbon nanotube (CNT) yarns are synthetic nanomaterials of interest for diverse applications. To bring fundamental understanding into the yarn formation process, we perform mesoscopic scale distinct element method (mDEM) simulations for the stretching of CNT networks. The parameters used by mDEM, including the mesoscale friction, are based on full atomistic results. By bridging across the atomistic and mesoscopic length scales, our model predicts accurately the mechanical response of the network over a large deformation range. At small and moderate deformations, the microstructural evolution is dominated by zipping relaxations directed along the applied strain direction. At larger deformations, the occurrence of energetic elasticity promotes yarn densification, by lowering CNT waviness and eliminating squashed pores. Next, by varying the mesoscopic dissipation as well as the network structure, we reveal that the mesoscale friction and film morphology are key factors for the yarn formation: While lack of friction compromises the strain-induced alignment process, phononic and polymeric friction promote CNT alignment by enabling load transfer and directed zipping relaxations, especially in networks containing long and entangled CNTs. Yarns drawn from cellular networks are shown instead to maintain high porosity, even with enhanced polymeric friction.

Strain-induced changes of the electronic properties of B -site ordered double-perovskite Sr2CoIrO6 thin films

B-site ordered thin films of double perovskite Sr$_2$CoIrO$_6$ were epitaxially grown by a metal-organic aerosol deposition technique on various substrates, actuating different strain states. X-ray diffraction, transmission electron microscopy and polarized far-field Raman spectroscopy confirm the strained epitaxial growth on all used substrates. Polarization dependent Co $L_{2,3}$ X-ray absorption spectroscopy reveals a change of the magnetic easy axis of the antiferromagnetically ordered (high-spin) Co$^{3+}$ sublattice within the strain series. By reversing the applied strain direction from tensile to compressive, the easy axis changes abruptly from in-plane to out-of-plane orientation. The low-temperature magnetoresistance changes its sign respectively and is described by a combination of weak anti-localization and anisotropic magnetoresistance effects.

Core structure of a screw dislocation in Ti from density functional theory and classical potentials

Previous density functional theory (DFT) studies of the 1/3 〈12¯10〉 screw dislocation in titanium have shown metastable core structures depending on the initial position of the dislocation line. We investigate this problem by modeling a screw dislocation with two initial positions using both DFT and a modified embedded atom (MEAM) potential for Ti with flexible boundary conditions. Both DFT and MEAM produce initial-position-dependent core structures. The MEAM potential stacking fault energies and core structures are in good agreement with DFT. MEAM potential computes the core energies and shows the behavior of both cores under applied strain. We found that the higher-energy core always reconstructs into the lower-energy one independent of the applied strain direction. Transformation from low- to high-energy core was not observed. Therefore, at T=0K, only the low-energy core is stable under applied strain.

Anisotropic Structure and Charge Transport in Highly Strain‐Aligned Regioregular Poly(3‐hexylthiophene)

AbstractA novel method of strain‐aligning polymer films is introduced and applied to regioregular poly(3‐hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge‐mobility anisotropy, where the in‐plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two‐dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane‐on and edge‐on packing configurations, as the strain alignment is found to induce a significant face‐on orientation of the originally highly edge‐on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge‐mobility anisotropy of 9, providing a simple and effective method to investigate charge‐transport mechanisms in polymer semiconductors.

Strain-induced orientation response of endothelial cells: effect of substratum adhesiveness and actin-myosin contractile level.

Endothelial cells subjected to cyclic stretching change orientation so as to be aligned perpendicular to the direction of applied strain in a magnitude and time-dependent manner. Although this type of response is not the same as motility, it could be governed by motility-related factors such as substratum adhesiveness and actin-myosin contractile level. To examine this possibility, human aortic endothelial cells (HAEC) were uniaxially, cyclically stretched on silicone rubber membranes coated with various concentrations of fibronectin, collagen type IV and laminin to produce differing amounts of adhesiveness (measured using a radial flow detachment assay). Cells were subjected to 10% pure cyclic uniaxial stretching for three hours at a rate of 10%/sec. Time-lapse images revealed that cells underwent large morphological changes without moving. For each type of protein there was a parabolic dependence on initial adhesiveness with optimal cell orientation occurring at very similar adhesive strengths. The effect of actin-myosin contractile level was examined by stretching cells treated with different doses of 2,3-butanedione monoxime (BDM) and Blebbistatin. Each drug induced a dose-dependent decrease in orientation angles after three hours of cyclic stretching. Furthermore, cell and stress fiber orientations were tightly coupled for untreated and Blebbistatin-treated cells but were uncoupled for BDM-treated cells. Even though orientation response to cyclic stretching is not a spontaneous motile response, it is determined, in large part, by the same factors that affect spontaneous motility--the cell-substratum adhesiveness and actin-myosin contractile level.

Strain-impedance properties of a CoSiB/Cu/CoSiB layered film

A type of strain sensor element utilizing the magnetostrictive effect and the magneto-impedance effect was presented and the strain-impedance properties of the element were evaluated. The strain-impedance (SI) element constructed from a CoSiB/Cu/CoSiB layered film was prepared on a Corning No. 0313 glass substrate by magnetron sputtering under a magnetic field. The element was composed of an inner copper conductive layer and outer magnetostrictive layers which covered the conductive layer. The Co73Si12B15 negative magnetostriction films (λ=−6×10−6) were adopted as magnetostrictive layers and magnetic anisotropy was induced perpendicular to the applied strain direction. Impedance Z drastically changed with applied compressive strain ε up to −2×10−3 and exhibited a good reversibility and reproducibility. The impedance change ratios ΔZ/Z0=(Zmax−Z[ε=0])/Z[ε=0] of the element were 40% at 15 MHz and 24% at 1 MHz. The maximum gauge factor Gmax defined as the maximum fractional change in impedance to strain (ΔZ/Z)/ε was 960–1910 in low frequency ranges from 1 to 15 MHz. These values were much larger than those of the single layer SI element constructed from only a CoSiB film and ten times larger than those of conventional semiconductor strain gauges. Therefore, the layered SI element will be very useful for the application of sensing small amounts of strain.

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A strain sensor element utilizing inverse magnetostrictive effect and magnetoimpedance effect was developed, and the strain-impedance properties of the element were investigated. The Strain-Impedance (SI) element constructed from a CoSiB/Cu/CoSiB layered film was prepared on a Corning No. 0313 glass substrate by magnetron sputtering under a magnetic field. Co73Si12B15 negative magnetostriction films (λ= -6 × 10-6) were selected as magnetostrictive layers, and magnetic anisotropy was induced parallel or perpendicular to the applied strain direction. In the SI element, applied strain e was detected as a change in impedance Z, inductance L or resistance R in the range from 1 MHz to 15 MHz. By applying strain (e =±2 × 10-3), we dramatically changed the impedance through the change in permeability of the magnetostrictive layers. The maximum gauge factor, Gmax, which was defined as the maximum fractional change in impedance to strain, (ΔZ/Z)/e, was 1500 - 2000 at 1 - 15 MHz. These values were much larger than those of the single-layer CoSiB element. This layered SI element will be very useful for sensing small amounts of strain.

ANISOTROPIC STRAIN EFFECT ON MORPHOLOGY AND ATOMIC STRUCTURE OF VICINAL Si(001) SURFACE

On vicinal Si(001) surfaces, dependence of growth morphology on the applied strain direction and formation of vacancy lines from Ag-induced missing dimer vacancies are studied. Both phenomena are intimately related to the anisotropic nature of the strain field which originates from the surface dimerization. Strain relief mechanism, reflecting on the surface morphology, is shown to be different in two orthogonal directions. Normal to the steps, step-pair bunching and waving lead to formation of hillocks and pits. Along the step direction, bending of step pairs forms a cusp which later develops into a deep groove. Toward the atomic scale, the formation of the vacancy lines is driven by the short-range attractive interaction between the vacancies in adjacent dimer rows and the long-range repulsive interaction between them in the same dimer row. A full form and magnitudes of the interactions are derived from the thermally-excited wandering of the vacancy lines formed by a nominal amount of Ag depositing onto the surface.