High Tensile Strain Research Articles

Influence of high temperatures on the residual mechanical properties of a hybrid fiber-reinforced strain-hardening cementitious composite

Abstract Recent studies have shown improved mechanical performance of Fiber-Reinforced Concretes (FRC) compared to conventional concrete at high temperatures. While polymer fibers in FRC improve the compressive behavior by providing pathways for moisture to escape through melting of fibers at high temperatures, steel fibers in FRC improve the tensile behavior through crack-bridging at high temperatures. The goal of this research is to investigate the influence of utilizing both polymer and steel fibers in a single FRC for improving compressive and tensile properties at high temperatures, simultaneously. For this purpose, a Polyvinyl Alcohol (PVA)-steel Hybrid Fiber-Reinforced Strain Hardening Cementitious Composite (HFR-SHCC) was developed. SHCC is a special class of FRC with strain-hardening behavior under direct uniaxial tension. The residual compressive and tensile properties of HFR-SHCC after being subjected to temperatures of up to 800 °C were experimentally determined. Additional FRCs, including a conventional SHCC with only PVA fibers and a fiber-reinforced concrete with only steel fibers (steel FRC), as well as conventional concretes of two different compressive strengths were tested with the same protocol for a comprehensive comparison. The HFR-SHCC shows clear improvement over conventional SHCC, steel FRC and conventional concretes in terms of residual tensile strength after exposure to high temperatures, while simultaneously retaining the benefits of conventional SHCC, which include high tensile strain capacity and microscopic crack widths at normal temperatures and improved retention of compressive strength after exposure to high temperature.

High-Performance Flexible ZnO Thin-Film Transistors by Atomic Layer Deposition

Flexible zinc oxide thin film transistors (ZnO TFTs) with a mobility of $ {13}~\text {cm}^{2}/\text {V}\cdot \text {s}$ and an I $_{\text {on}}/\text{I}_{\text {off}}$ ratio of $ {1.5}\times {10}^{8}$ have been fabricated on polyimide substrate, where the ZnO channel is deposited by atomic layer deposition (ALD) at 140 °C. High bending stability has been achieved due to excellent interface quality between alumina (Al2O3) dielectric and ZnO channel with a sharp interface topography. The flexible ZnO device exhibits excellent electrical characteristics even after being bent for 200 000 cycles with a tensile strain of 0.63%. Electrical measurement under a high tensile strain of 2.08% has also been carried out. Moreover, the electrical performance dependence of flexible ZnO TFTs with a tensile strain of 0.78% on temperature from 20 °C to 140 °C has been investigated for the first time.

Effects of Phosphorus Doping and Postgrowth Laser Annealing on the Structural, Electrical, and Chemical Properties of Phosphorus-Doped Silicon Films

Phosphorus has low solubility in silicon, but nonequilibrium incorporation of phosphorus exhibits unusual high strain and low contact resistance for advanced Si-based metal-oxide-semiconductor field-effect transistors. Despite recent technological breakthroughs, the origin of tensile strain and electrical deactivation in P-doped Si films is not yet fully understood. Here, by using a combination of experiments and first-principles calculations, we investigate the effect of nonequilibrium phosphorus incorporation into Si lattices and subsequent annealing on structural, electrical, and bonding properties of P-doped Si films. Quantitative structural analyses reveal that the high tensile strain is generated by the incorporation of P into Si substitutional sites irrespective of the distribution of P atoms. More importantly, we found that advanced postgrowth annealing lead to significantly enhanced electrical properties while keeping the same physical states without loss of induced strain. To explore the reason ...

Highly stretchable patternable conductive circuits and wearable strain sensors based on polydimethylsiloxane and silver nanoparticles

Patterned circuits on highly stretchable conductive films are critical in the practical application of next-generation flexible and wearable devices. Currently, most patterned circuits do not exhibit highly stretchable properties, and a lithography process in vacuum is required. In this study, silver nanoparticles (AgNPs) and liquid polydimethylsiloxane (PDMS) are mixed together to form liquid conductive adhesives (CAs). Various stretchable patterned circuits are prepared using this CA to achieve all required functions. Six basic patterns, including rhombus, straight lines, serpentine, triangle, ellipses, and fold line, are studied for their stretchable and electrical properties. The film is found to maintain excellent conductivity after withstanding tensile strain of up to 320% and more than 10 000 stretching-releasing cycles of 0%–150%. More than 86% of visible lights can be penetrated through the film due to the transparent substrates. Functional and wearable devices are manufactured, and devices fabricated from rhombus-pattern circuits are found to exhibit stable electrical conductivity when subjected to very high tensile strains. According to the sensitivity of the straight-line patterned circuit to strain, a repeatable use sensitive strain sensor is studied. Also, two types of artificial electrical skin are demonstrated.

Structural stability and electronic properties of different cross-sectional unstrained and rectangular cross-sectional strained GaP nanowires

The stability and electronic properties of the hexagonal, trigonal and rectangular cross-sectional GaP nanowires in wurtzite (WZ) phase are investigated using full potential linear augmented plane waves method. The rectangular cross-sectional nanowires are found more stable than the hexagonal and trigonal ones. The indirect bandgap structure of the nanowires is transformed into the direct bandgap one at a critical size connected to the geometry of the cross-section. The energy bandgap of the nanowires in the same cross-sectional group is enlarged by the quantum size effect. The effective carrier masses in the nanowires, calculated to be larger than those in bulk GaP, are found to slightly increase with the decrease in the size of the nanowires in the same cross-sectional groups. The mechanical strain effect on the electronic band structure is investigated for the rectangular GaP nanowires under the uniaxial and lateral strains. It is found that the indirect bandgap structures of the rectangular nanowires are transformed into the direct bandgap ones by the uniaxial high compression strains. It is also found that this transformation can be triggered by small uniaxial tensile and high lateral tensile strains in addition to the effect of size increase. The energy bandgap of the rectangular nanowires is determined to be narrowed by the uniaxial/lateral strains. It is obtained that the small rectangular nanowire is in the indirect bandgap structure for all the lateral strains and the larger one can be transformed into the direct bandgap structure more easily by the [Formula: see text]-directional lateral tensile strains compared to the [Formula: see text]-directional ones. The effective electron and hole masses are found to be reduced by the uniaxial highest tensile and compression strains of this work. It is determined that the lateral strains are not effective in making the electrons of the nanowires more mobile, but the [Formula: see text]-directional lateral high tensile strains make the holes more mobile by reducing the effective hole mass in the small rectangular nanowire.

Development of a Galfenol actuator for operation under tension

A Galfenol-based actuator has been designed to generate output forces while operating under tensile strains, demonstrating successful long term operation with no appreciable change in performance. Two prototype actuators were manufactured and tested under quasi-static and dynamic conditions. Dynamic power requirements included a 15–16 amp DC bias and up to 25–26 amp AC (pk-pk). Two cooling fans were used to provide convection cooling of the drive coils during dynamic operation, allowing for 100% duty cycle at 300 Hz; without the use of cooling fans, 100% duty cycle operation would be limited to frequencies below 150 Hz. In quasi-static displacement mode (0.5 Hz, no applied force), the actuators were capable of outputting between 5.78 and 7.12 kN (1300–1600 lbf). While the output force decreased with applied tensile stress and operational frequency, significant forces were measured up to 0.14% (0.0014 mm mm−1) applied tensile strain using 300 Hz tones. The magnitude of the measured dynamic force output was limited by the matched stiffness between the MTS 810 load frame (140 kN mm−1 or 0.8 × 106 lbf in−1) and the prototype actuators (122.6 kN mm−1 or 0.7 × 106 lbf in−1). By connecting to stiffer loads, larger force outputs and higher tensile strains could be applied. Long term testing of the actuator at 63 Hz and alternating tensile loads of 4.45 and 22.24 kN (1000 and 5000 lbs) has continued to over one billion cycles, with no change in actuator performance. Demonstration of the Galfenol technology in this unique tensile application provides a capability that does not exist with current off-the-shelf transducer technologies.

Negative effects of high mechanical tensile strain stimulation on chondrocyte injury in vitro

The mechanism underlying the development of osteoarthritis induced by high tensile strain is unclear. In this study, the effects of different degrees of mechanical tensile strain stimulation on Sprague–Dawley rat chondrocytes were explored. Rat chondrocytes were subjected to mechanical tensile strain at different intensities and frequencies (control group, low tensile strain group, intermediate tensile strain group, and high tensile strain group) using a self-made in vitro tensile strain device. After applying mechanical tensile strain, chondrocytes were collected to detect the expression of collagen II, Aggrecan, matrix metalloproteinase 13 (MMP13), ADAMTS5, and uncoupling protein 2 (UCP2) by real-time quantitative PCR and western blotting as well as reactive oxygen species (ROS) by fluorescence probes. Mechanical tensile strain at different frequencies and intensities had different effects on the biological functions of chondrocytes. Compared with the control group, the expression levels of Col II and Aggrecan in the low and intermediate tensile strain groups increased significantly, while the expression of MMP13 and ADAMTS5 decreased. There were no significant differences between the low and intermediate tensile strain groups. Col II and Aggrecan levels were significantly lower in the high tensile strain group than in the control group, while MMP13 and ADAMTS5 levels were higher. There were no significant differences in ROS production between the low and intermediate tensile strain groups and the control group, but the high tensile strain group exhibited significantly increased ROS production. The expression of UCP2 was significantly lower in the high tensile strain group than in all other groups. These results showed that stimulation with different levels of mechanical tensile strain has different effects on chondrocytes. Repeated high tensile strain promoted the anabolic function of chondrocytes, increased ROS production, and decreased UCP2. These results provide a potential mechanism by which osteoarthritis is induced by high mechanical tensile strain.

SiGe films and graded buffers grown by liquid phase epitaxy from different growth solution compositions

SiGe films were grown on Si (0 0 1) by liquid phase epitaxy from short growths (950–940 °C) with different solution compositions (2% Ge, 4% Ge, 5% Ge). The initial growth transitions from the characteristic crosshatch morphology into a more three-dimensional morphology with increasing Ge content in the solution. We found that the highest Ge film that maintains two-dimensional film growth is 3.1% Ge. The initial film changes from fully strained to 30% partially relaxed and back to fully strained as the composition increases from 1.4% Ge to 3.1% Ge. In addition, SiGe graded buffers were grown with different solution compositions (2% Ge, 4% Ge, 5% Ge) from 950 to 750 °C. The initial film of each graded buffer (the first film to form on the substrate) is fully relaxed at high temperature but experiences tensile strain after cooling to room temperature while the part of the graded buffer further from the substrate experiences increasing compressive strain as the film thickness increases and becomes richer in Ge. The threading dislocation density of graded buffers (i.e. thicker films) grown with the 4% Ge- and 5% Ge-content-solutions is ∼106 cm−2, one order of magnitude lower than their own initial films (the film grown in the first ∼10 °C growth interval) while the threading dislocation density of the graded buffers grown with 2% Ge-content-solution is similar to its initial film’s threading dislocation density, ∼106 cm−2.

Shock induced damage and fracture in SiC at elevated temperature and high strain rate

Large-scale molecular dynamics simulations are used to investigate shock-induced damage and fracture in 3CSiC single crystals at an elevated initial temperature of 2000 K and a high tensile strain rate of ∼1010 s−1. Three crystal orientations have been evaluated: [001], [110] and [111]. A comprehensive comparison has been made between cases at 2000 K and at 300 K to address the effects of high temperature on the mechanical performance of SiC under shock loading. Results show that for shock compression, the high temperature decreases the longitude elastic wave speeds as well as the shock stresses. The shock-induced plasticity is mainly in the form of deformation twinning at 300 K, but twinning is absent at 2000 K. The high temperature decreases the structural phase transition threshold pressure in SiC from ∼90 GPa at 300 K (for all three orientations) to ∼75 GPa in [001], ∼57 GPa in [110] and ∼64 GPa in [111] at 2000 K, with corresponding particle velocities of 2.75 km/s, 2.0 km/s, and 2.25 km/s, respectively, in agreement with trends observed in recent experiments. The spall fracture behavior reveals that high temperature reduces the spall strength with an average spall strength of ∼20.7 GPa in [001], ∼21.4 GPa in [110] and ∼22.5 GPa in [111] at 2000 K in the classical spall regime, which are about 33% lower than strengths measured at 300 K. However, in the micro-spall regime the spall strengths are very similar at both temperatures. The corresponding thresholds of particle velocity to trigger spall decrease at elevated temperature except for [001] loading, as well as the thresholds for generating overdriven phase transition waves.

Exciton transport in strained monolayer WSe2

We experimentally demonstrate the visualization of exciton energy transport in a non-uniformly strained WSe2 monolayer by monitoring the propagation of exciton densities via spectrally, temporally, and spatially resolved photoluminescence measurements at room temperature. Our measurements indicate that excitons in the WSe2 monolayer exhibit anomalous diffusion due to disorder in the system, which leads to a time-varying diffusion coefficient. In addition, we show that the sensitivity of monolayer WSe2's bandgap to strain gives rise to a built-in excitonic potential that results in the funneling of excitons towards high tensile strain points. The observed drift and diffusion agree reasonably with our proposed model that takes into account the strain field on the monolayer to describe the exciton dynamics.

Tensilely Strained Ge Films on Si Substrates Created by Physical Vapor Deposition of Solid Sources

The development of Si-compatible active photonic devices is a high priority in computer and modern electronics industry. Ge is compatible with Si and is a promising light emission material. Nearly all Ge-on-Si materials reported so far were grown using toxic precursor gases. Here we demonstrate the creation of Ge films on Si substrates through physical vapor deposition of toxin-free solid Ge sources. Structural characterization indicates that a high tensile strain is introduced in the Ge film during the deposition process. We attribute the presence of such a tensile strain to the difference in thermal expansion coefficient between Si and Ge. A Ge peak, centered at ~2100 nm, is evident in the photoluminescence spectra of these materials, which might result from direct band gap photoluminescence alone, or from superposition of direct band gap and indirect band gap photoluminescence. These Ge-on-Si materials are therefore promising in light emission applications.

Towards a Supertough Thermoplastic Polyisoprene Elastomer Based on a Biomimic Strategy.

Natural rubber is one of most famous self-reinforced rubbers thanks to the phenomenon of strain-induced crystallization. It is usually used in a vulcanized form to enhance the mechanical strength but this results in recycling issues. Herein a thermoplastic analogue of vulcanized natural rubber is obtained as a structural mimic. Terminally functionalized polyisoprene rubber B-4A-PIP was prepared by using tetra-analine as physical crosslinking units. The strong binding of tetra-analine groups gave B-4A-PIP a high tensile strength (15 MPa) and breaking strain of 890 %, which is much higher than those of undecorated copolymer B-OH-PIP. B-4A-PIP has a similar onset strain of crystallization and crystallization index to vulcanized natural rubber. Randomly functionalized polyisoprene R-4A-PIP showed a much lower mechanical strength and SIC properties although R-4A-PIP and B-4A-PIP possessed similar molecular weights and amounts of tetra-analine groups.

Towards a Supertough Thermoplastic Polyisoprene Elastomer Based on a Biomimic Strategy

AbstractNatural rubber is one of most famous self‐reinforced rubbers thanks to the phenomenon of strain‐induced crystallization. It is usually used in a vulcanized form to enhance the mechanical strength but this results in recycling issues. Herein a thermoplastic analogue of vulcanized natural rubber is obtained as a structural mimic. Terminally functionalized polyisoprene rubber B‐4A‐PIP was prepared by using tetra‐analine as physical crosslinking units. The strong binding of tetra‐analine groups gave B‐4A‐PIP a high tensile strength (15 MPa) and breaking strain of 890 %, which is much higher than those of undecorated copolymer B‐OH‐PIP. B‐4A‐PIP has a similar onset strain of crystallization and crystallization index to vulcanized natural rubber. Randomly functionalized polyisoprene R‐4A‐PIP showed a much lower mechanical strength and SIC properties although R‐4A‐PIP and B‐4A‐PIP possessed similar molecular weights and amounts of tetra‐analine groups.

Localized thinning for strain concentration in suspended germanium membranes and optical method for precise thickness measurement

We deposited Ge layers on (001) Si substrates by molecular beam epitaxy and used them to fabricate suspended membranes with high uniaxial tensile strain. We demonstrate a CMOS-compatible fabrication strategy to increase strain concentration and to eliminate the Ge buffer layer near the Ge/Si hetero-interface deposited at low temperature. This is achieved by a two-steps patterning and selective etching process. First, a bridge and neck shape is patterned in the Ge membrane, then the neck is thinned from both top and bottom sides. Uniaxial tensile strain values higher than 3% were measured by Raman scattering in a Ge membrane of 76 nm thickness. For the challenging thickness measurement on micrometer-size membranes suspended far away from the substrate a characterization method based on pump-and-probe reflectivity measurements was applied, using an asynchronous optical sampling technique.

Experimental Analysis on Tensile Behavior of Engineered Cementitious Composite (ECC) using Polypropylene Fiber

The high demand of tensile strength in concrete is always a critical issue for engineers, as 10% of the compressive strength is not sufficient to withstand higher loadings. Lesser ductility and strain capacity is another major issue of normal concrete. In the queue of modern researches, this paper is an attempt to study Engineered Cementitious Composite (ECC) from research of Professor Victor Li, the University of Michigan. ECC is an ultra-ductile cementitious composite which is highly crack resistant, with a high tensile strain capacity over that of normal concrete. The composite replaces coarse aggregates and fine aggregates by sand and fly ash respectively. ECC is made up of OPC, sand (passing from 250 µm and retained on 150µm), Fly Ash (Class F) with addition of Polypropylene fiber on different percentages i.e. 0%, 0.25%, 0.5%, 0.75%, 1.0% were studied. Tensile Strength of ECC was measured by casting & testing cylinders of 4”x 8” in Universal Testing Machine (UTM). The experimental results revealed that 111.40% increment in tensile strength was found at 0.5% PP fiber at ECC 1:1:1 and an increment of 74.74% was observed at ECC 1:0.8:1.2 at 1% PP fiber. The study concludes that this composite could substitute the normal concrete where high tension is the ultimate requirement with higher strain capacity.

Thermal vibration contribution to continuum stress in the elastic regime

Homogeneous deformation of an ordered crystalline solid at finite temperature can cause non-affine transformation of atomic trajectories. In such a case, continuum measures based on affine transformation of trajectories are insufficient to ensure energetic equivalence between the atomic and continuum scales. We use molecular dynamics simulation of fcc aluminum in NVT ensembles to demonstrate that the second moments of atomic positions about equilibrium show increasing deviation from affine behavior with strain and temperature. While the Cauchy-Born rule enforces affine deformation of the crystal in the static sense, second moments have been used to quantify non-affinity in thermal vibrations due to atomic trajectory transformation under macroscopic deformation. The evolution of second moments with applied strain becomes highly non-linear at high temperatures in the tensile regime as a result of the anharmonic potential energy surface of the material. The vibrational entropy is computed using the time-averaged second moments of position from the molecular dynamics simulation. Stress computed using the resulting free energy is significantly lower than the virial stress in the high tensile strain – high temperature regimes.

Triple-crosslinkedβ-cyclodextrin oligomer self-healing hydrogel showing high mechanical strength, enhanced stability and pH responsiveness

A novel self-healing hydrogel was prepared from a cationic β-cyclodextrin oligomer allyl ether [C(βCD−OM)AE] using a triple cross-linking strategy combining electrostatic interaction, host–guest complexation, and CC bonds as the macrocrosslinker. Here, the C(βCD−OM)AE@Ad gel was successfully prepared by polymerization of synthesized C(βCD−OM)AE, 1-adamantyl acrylate, and acrylic acid. The triple cross-linked hydrogel shows multi-functionality of high mechanical strength, enhanced stability, cytocompatibility, pH responsiveness as well as self-healing ability. Based on the cooperative and synergetic forces of non-covalent and covalent bonds, the C(βCD−OM)AE@Ad gel shows a high tensile strain up to 1,590%, and the self-healed gel could restore up to 84% of its initial length within 24 h. Furthermore, drug release in the hydrogel was controlled by the surrounding pH and slowly released. The present work reveals the cooperativity of multiple cross-links for a 3D structured polymeric material, and the developed self-healable hydrogel can possibly be applied in various biomedical applications.

Finite-temperature stress calculations in atomic models using moments of position

Continuum modeling of finite temperature mechanical behavior of atomic systems requires refined description of atomic motions. In this paper, we identify additional kinematical quantities that are relevant for a more accurate continuum description as the system is subjected to step-wise loading. The presented formalism avoids the necessity for atomic trajectory mapping with deformation, provides the definitions of the kinematic variables and their conjugates in real space, and simplifies local work conjugacy. The total work done on an atom under deformation is decomposed into the work corresponding to changing its equilibrium position and work corresponding to changing its second moment about equilibrium position. Correspondingly, we define two kinematic variables: a deformation gradient tensor and a vibration tensor, and derive their stress conjugates, termed here as static and vibration stresses, respectively. The proposed approach is validated using MD simulation in NVT ensembles for fcc aluminum subjected to uniaxial extension. The observed evolution of second moments in the MD simulation with macroscopic deformation is not directly related to the transformation of atomic trajectories through the deformation gradient using generator functions. However, it is noteworthy that deformation leads to a change in the second moment of the trajectories. Correspondingly, the vibration part of the Piola stress becomes particularly significant at high temperature and high tensile strain as the crystal approaches the softening limit. In contrast to the eigenvectors of the deformation gradient, the eigenvectors of the vibration tensor show strong spatial heterogeneity in the vicinity of softening. More importantly, the elliptic distribution of local atomic density transitions to a dumbbell shape, before significant non-affinity in equilibrium positions has occurred.

Mechanoporation is a potential indicator of tissue strain and subsequent degeneration following experimental traumatic brain injury

BackgroundAn increases in plasma membrane permeability is part of the acute pathology of traumatic brain injury and may be a function of excessive membrane force. This membrane damage, or mechanoporation, allows non-specific flux of ions and other molecules across the plasma membrane, and may ultimately lead to cell death. The relationships among tissue stress and strain, membrane permeability, and subsequent cell degeneration, however, are not fully understood. MethodsFluorescent molecules of different sizes were introduced to the cerebrospinal fluid space prior to injury and animals were sacrificed at either 10 min or 24 h after injury. We compared the spatial distribution of plasma membrane damage following controlled cortical impact in the rat to the stress and strain tissue patterns in a 3-D finite element simulation of the injury parameters. FindingsPermeable cells were located primarily in the ipsilateral cortex and hippocampus of injured rats at 10 min post-injury; however by 24 h there was also a significant increase in the number of permeable cells. Analysis of colocalization of permeability marker uptake and Fluorojade staining revealed a subset of permeable cells with signs of degeneration at 24 h, but plasma membrane damage was evident in the vast majority of degenerating cells. The regional and subregional distribution patterns of the maximum principal strain and shear stress estimated by the finite element model were comparable to the cell membrane damage profiles following a compressive impact. InterpretationThese results indicate that acute membrane permeability is prominent following traumatic brain injury in areas that experience high shear or tensile stress and strain due to differential mechanical properties of the cell and tissue organization, and that this mechanoporation may play a role in the initiation of secondary injury, contributing to cell death.

Fabrication of Zinc–Tungsten Carbide Nanocomposite Using Cold Compaction Followed by Melting

Zinc (Zn) is an important material for numerous applications since it has pre-eminent ductility and high ultimate tensile strain, as well high corrosion resistivity and good biocompatibility. However, since Zn suffers from low mechanical strengths, most of the applications would use Zn as a coating or alloying element. In this study, a new class of Zn-based material with a significantly enhanced mechanical property is developed. The zinc-10 vol % tungsten carbide (Zn-10WC) nanocomposite was fabricated by cold compaction followed by a melting process. The Zn-10WC nanocomposites offer a uniform nanoparticle dispersion with little agglomeration, exhibiting significantly enhanced mechanical properties by micropillar compression tests and microwire tensile testing. The nanocomposites offer an over 200% and 180% increase in yield strength and ultimate tensile strength (UTS), respectively. The strengthening effect could be attributed to Orowan strengthening and grain refinement induced by nanoparticles.