Unstrained Conditions Research Articles

Simulation experiment for tellurium-induced intergranular cracking in oxidizing molten salt environment

One user-friendly laboratory investigation method for tellurium-induced intergranular cracking has been preliminarily developed in this study. The Te exposure experiments were carried out using FLiNaK salts with NiF2 and Cr3Te4 at 700 °C in GH3535 alloy tubes. Te exists in the form of intergranular segregation without the formation of surface tellurides, and Te-induced intergranular cracking can occur under unstrained conditions, which agrees with the observations in molten salt reactors. The acceleration effect of NiF2 can be ascribed to its reaction with Cr3Te4 to form Te metal.

A Numerical Investigation on Effects of Hydrogen Enrichment and Turbulence on NO Formation Pathways in Premixed Ammonia/Air Flames

ABSTRACT NO x emission reduction is one of the major challenges when using ammonia/hydrogen blends as an alternative fuel for carbon-free combustion. In this study, chemical reaction pathways of NO formation in planar premixed flames of stoichiometric ammonia/hydrogen/air at atmospheric pressure and reactants temperature of 298 K are investigated under laminar and decaying turbulent conditions using quasi-DNS with detailed chemistry and the mixture-averaged transport model. The sweep parameter, , is the volumetric ratio of hydrogen to the ammonia/hydrogen mixture. Here, for unstrained laminar conditions, = 0, 0.4, and 0.6 and for turbulent condition, = 0.4 within the thin reaction zones region ( 34.2) are studied. Under 1D laminar conditions, increasing enhances NO formation drastically, around 3 times when comparing = 0 and 0.6. At different , despite the high activity of the reactions which belong to the Zeldovich pathway, the contribution of this pathway is insignificant in NO formation. However, HNO and N2O pathways have the most significant roles. For instance, at = 0.4, R85 (NH+NO N2O+H) in the N2O pathway and R144 (HNO+H NO+H2) in the HNO pathway have major roles in NO formation. Higher NO formation at larger is found to be due to the increased H and O radicals within the reaction zone as well as the increased reaction rates because of the higher flame temperature. Under the 3D turbulent condition ( = 0.4), it is observed that turbulence does not switch the pathways trends across the flame brush compared to the laminar condition. In the reaction zone, however, it is observed that NO formation is lower (higher) in the regions convex (concave) toward the reactants. The underlying reason for this effect is the preferential diffusion of H2 to the regions of the flame front convex toward the reactants, which consumes NO and also depletes O and OH radicals, which are necessary for NO formation.

Electrochemical characterization of a Fe-based shape memory alloy in an alkaline medium and the behaviour in aggressive conditions

A Fe-17Mn-6Si-19Cr-4Ni-1(V,C) shape memory steel (SMS) was characterised electrochemically in its unstrained and pre-strained conditions. The work focused on analysing the passive films generated in alkaline conditions, and on the behaviour of those passive samples in various Cl−/OH− ratios. The passive films were developed by cyclic voltammetry and their characterisation was performed by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS); these tests were also carried out in 304 L stainless steel specimens for comparison purposes. The results indicated that the film characteristics (thickness and composition) were similar in all the samples, although higher corrosion resistance was observed in the 304 L due to the higher Cr content. In addition, the behaviour of the passive samples in aggressive conditions was assessed by potentiodynamic measurements. The results stated that the shape memory steels were more sensitive than the stainless steel to the aggressive conditions, especially when the alloy was pre-strained. It was also observed that the SMS exhibited a characteristic corrosion morphology localized at the grain boundaries.

Low Cycle Fatigue Behavior of Plastically Pre-Strained HSLA S355MC and S460MC Steels.

Cold roll forming used in the manufacturing of lightweight steel profiles for racking storage systems is associated with localized, non-uniform plastic deformations in the corner sections of the profiles, which act as fatigue damage initiation sites. In order to obtain a clearer insight on the role of existing plastic deformation on material fatigue performance, the effect of plastic pre-straining on the low cycle fatigue behavior of S355MC and S460MC steels was investigated. The steels were plastically deformed at different pre-strain levels under tension, and subsequently subjected to cyclic strain-controlled testing. Plastic pre-straining was found to increase cyclic yield strength, decrease ductility, and induce cyclic softening, which, in S460MC, degrades fatigue resistance compared to the unstrained material. In unstrained conditions, the materials present a cyclic softening to hardening transition with increasing plastic strain amplitude, which in S355MC occurs at lower strain amplitudes and degrades its fatigue resistance with regard to the pre-strained material. Pre-straining also leads to a reduction in transition life from low to high cycle fatigue. SEM fractography, performed following the onset of crack initiation, revealed that plastic pre-straining reduces the fatigue fracture section as well as striation spacing, predominantly in the S355MC steel.

Stress corrosion cracking of AISI 304 under chromium variation within the standard limits: Failure analysis implementing microcapillary method

This study focuses on the failure analysis of an industrial part made of AISI 304 that severely ruptured, while another identical part operated under identical service conditions has no sign of fracture. Various electrochemical polarization responses and stress corrosion cracking (SCC) susceptibility were compared by employing the microcapillary method on representative samples. The dominant factor was identified to be the chromium (Cr) content variation within the range of standard designations. Various concentration levels of sodium chloride aqueous solution were studied for both strained and unstrained conditions. Results highlighted higher susceptibility to pitting and SCC for the specimens with lower Cr content, indicating a more severe condition at higher chloride concentrations.

Effects of p-type conductive properties of triaxial strain-regulated ZnO (S, Se, Te) system

P-type ZnO materials are a difficult problem worldwide. The strain caused by doping, substrate and sample lattice constant mismatch, and thermal expansion coefficient mismatch is often ignored. First principle calculation is used to select the appropriate strain range and solve this problem. The effect equivalent to the actual strain is simulated to study the conductive properties and the mechanism of a doping system. Studies have shown that under unstrained conditions, the binding energies of undoped ZnO and all doped systems are negative, and the stability is relatively high. The formation energy of all doped systems increases, and their stability decreases with the increase in tensile strain or compressive strain. This study shows for the first time that when the compressive strain is −5%, the hole mobility of the same doping systems of Zn36SO35, Zn36SeO35, and Zn36TeO35 is relatively maximum. The difference between the hole concentration of the Zn36MO35 (M = S, Se, Te) systems is extremely small regardless of tensile strain or compressive strain. When the compressive strain is −5%, the hole conductivity of the Zn36SO35 system is the best. These findings can serve as guide in the experimental design and preparation of new p-type ZnO conductive functional materials.

First-principle study of the effects of biaxial strain on the photocatalytic and magnetic mechanisms of ZnO with Sm doping and point defects (VZn, Hi)

The influence of Sm doping on the physical properties of ZnO has been widely investigated. However, the potential point defects and interstitial H in the Sm-doped ZnO system and the influence of strain on the physical properties of ZnO remain poorly understood. First-principle studies on the effects of biaxial strain on the photocatalysis and magnetic mechanisms of ZnO with Sm doping and point defects (VZn, Hi) are rarely reported. In this work, a method based on first-principle plane wave super soft pseudopotential + U under the framework of density functional theory was adopted. A ZnO system with Sm doping and point defects (VZn, Hi) was constructed, and its formation energy, photocatalysis, and magnetic mechanism were studied within the strain range from −6% to 6%. Results showed that regardless of tensile/compressive strain, the formation energy increased in the doped system compared with that in the unstrained doped system. By contrast, stability was relatively decreased. Under the same strain conditions, the Zn34SmHiO36 system had relatively low formation energy and relatively good stability. In addition, interstitial H can effectively increase the separation speed of electron–hole pairs, thereby prolonging the carrier life. Redshift effect, electric dipole moment, oxidation/reduction reactions, and decisive carrier lifetime are affected by the photocatalytic performance of the actual doping system. Under −4% compressive strain, the Zn34SmHiO36 system acts as an excellent catalyst of light. Regardless of tensile/compressive strain, the Zn34SmO36 and Zn34SmHiO36 systems exhibit magnetic properties, and the interstitial H improves the magnetic properties of the doped system. This finding is consistent with the Ruderman–Kittel–Kasuya–Yosida (RKKY) magnetic theory. Under unstrained conditions, the Zn34SmHiO36 system exhibits a semi-metallic characteristic with 100% hole spin polarization. This research has application value for the design and preparation of novel dilute magnetic semiconductors with spin-hole injection source.

Synergistic vacancy defects and mechanical strain for the modulation of the mechanical, electronic and optical properties of monolayer tungsten disulfide.

Monolayer transition metal dichalcogenides (TMDs) are the potential candidate materials in nanoelectronic and optoelectronic applications due to their unique physical and chemical properties. Although both defect and strain greatly alter the structural, physical and chemical properties of monolayer TMDs, the defective monolayer TMDs under applied strain have not been adequately studied. In this paper, the synergistic effects of sulfur vacancy defects and mechanical strain on the mechanical, electronic and optical properties of monolayer tungsten disulfide (WS2) have been systematically studied using first principles density functional theory. The results indicate that the sulfur vacancy formation energy increases linearly with increasing sulfur vacancy concentration under different strains. The strain energy and stress of monolayer WS2 with different sulfur vacancy concentrations increase with increasing applied strain in the strain range of -10% to 10%. The band gap of monolayer WS2 decreases with increasing sulfur vacancy concentration under different strains. Moreover, compared with unstrained conditions, 5% compressive strain increases the band gap at a larger vacancy concentration and the case is just opposite at a smaller vacancy concentration, while 5% tensile strain decreases the band gap. The band gap of monolayer WS2 with different sulfur vacancy concentrations firstly increases and then shrinks with increasing applied strain under compressive strain, whereas it decreases monotonically under tensile strain in the strain range of -10% to 10%. In the visible-light wavelength region, the out-of-plane absorption coefficient under different strains increases with increasing sulfur vacancy concentration. Furthermore, 5% compressive strain enhances the absorption coefficient and 5% tensile strain decreases the absorption coefficient. Hence, the synergistic effects of sulfur vacancy defects and mechanical strain in monolayer TMDs can open new avenues for their applications in nanoelectronic and optoelectronic devices.

Application of unrestrained conscious rats with acute inflammatory ankle pain to study of acupuncture analgesia

To compare the analgesic effect of manual acupuncture(MA) stimulation of "Zusanli" (ST36) in rats with inflammatory pain under unrestrained conscious, restrained and general anesthesia conditions, so as to explore the applicability of unrestrained conscious model in the evaluation of acupuncture analgesia effect. Male SD rats were divided into 5 groups: blank control (n=9), pain model (n=7), unrestrained conscious conditions+MA (n=6), restrained conditions+MA (n=6), and general anesthesia (GA)+MA(n=6). The acute pain model was established by injection of complete Freund's adjuvant (CFA) into the left ankle joint 48 h ahead of acupuncture. Subsequently, a single 20 min session of MA was applied to the left ST36. The mechanical and thermal pain thresholds (MPT and TPT) were determined before and after injection of CFA, and after MA stimulation. In order to evaluate the autonomic behavior activities, rats were randomly divided into blank control (n=11), pain model (n=11) and conscious-unrestrained conditions +MA (n=12) groups. The rats' exploratory movements were assessed by open field tests. Both MPT and TPT were significantly decreased after injection of CFA in the model group relevant to the blank control group (P<0.001), and significantly higher in the three MA groups than in the model group (P<0.001). Comparison among the three MA groups showed that both MPT and TPT were significantly higher in the conscious unrestrained conditions+MA group than in the restrained conditions+MA and GA+MA groups (P<0.05, P<0.01). Open filed tests showed that the total moving distance in the open field and wall climbing times were significantly lower in the model group than in the blank control group (P<0.01), and the wall climbing times were obviously more in the unstrained conditions+MA group than in the model group (P<0.05). The central area resistance time was significantly shorter in the model group than in the control group (P<0.05), and was moderately increased after MA despite no evident significance (P>0.05). No significant changes were found in the total moving distance after MA and in the central area moving distance after modeling and MA (P>0.05). MA has a better therapeutic effect in relieving pain and pain-induced depression-like behavior in conscious unrestrained rats than in restrained and GA rats, implying a higher applicability of unrestrained conscious pain model to the assessment of acupuncture analgesia.

Effects of triaxial strain on carrier activity, carrier lifetime, and absorption spectrum of (S, Se, Te) and 2 N Co-doped ZnO

The acceptor (N)-isovalent (S, Se, Te) elements that separately co-dope ZnO is a novel doping technology. However, the effects of triaxial strain on the photocatalytic performance and mechanism of doped systems are often neglected in experimental studies. Moreover, the influence of interstitial H on the doped ZnO system is not considered. This paper adopted first-principles and selected the appropriate strain range and step length. Assuming the equivalent effect of several strain points of tensile strain or compressive strain, we used simulation calculation to fit the complex strain problem in the actual process (such as doping, the strain problem caused by the difference of the lattice constant and thermal expansion coefficient of the substrate and the doping system), and then studied physical properties of the doped system. The planar wave ultrasoft pseudopotential + U method based on the first-principles generalized gradient approximation under the framework of density functional theory was used to calculate (S, Se, Te) and 2 N co-doped ZnO. The interstitial H-doped Zn36SO33N2 was studied as a representative ZnO system. Results showed that the binding energy of all doping systems under unstrained conditions was negative with a relatively high stability. The strain increased under tensile strain and compressive strain. As the formation energy of the doping systems increased, system stability decreased. Although the band gap of all compressive strain systems widened, impurities formed in the band gap, and valence band electrons absorbed photons of low energy to transition to the energy level of the impurities and then to the energy level of conduction band. The photoexcited electron-graded transitions induced the absorption spectrum to red-shift. The band gap of the system widened, whereas the band gaps of other tensile strain systems narrowed, except for when the tensile strain was 1%. However, regardless of whether the band gap of the tensile strain system became narrow or wide, the photoexcited electrons were still able to transition in stages. Hence, the absorption spectrum of the tensile strain system still red-shifted. The stability, activity, carrier separation, and lifetime of Zn36SHiO33N2 were relatively better than those of Zn36SO33N2 at 5% tensile strain. These properties make Zn36SHiO33N2 an ideal photocatalyst. This study provides a theoretical reference for the experimental design and preparation of novel ZnO photocatalysts.

Strain Rate Effects on Head-on Quenching of Laminar Premixed Methane-air flames

Head-on quenching is a canonical configuration for flame-wall interaction. In the present study, the transient process of a laminar premixed flame impinging on a wall is investigated for different strain rates, while previous studies with detailed chemistry and transport focused only on unstrained conditions. Increasing strain rate leads to a reduction in the normalized quenching distance, and an increase in the normalized wall heat flux, both are considered as global flame quantities. Looking more into the local microstructure of the quenching process, CO formation and oxidation near the wall are shifted to higher temperatures under higher strain rates. Further, the local flame structure and the thermochemical state are affected by differential diffusion driven by differences in species’ gradients and diffusivities. Quenching leads to increased species’ gradients and consequently differential diffusion is amplified near the wall compared to propagating flames. However, this effect is suppressed for increasing strain rates, which is explained in more detail by a source term analysis of the transport equation for the differential diffusion parameter ZHC. Results for the global quantities and the local flame structure show that the impact of the strain rate weakens for higher wall temperatures. Finally, the analyses of the thermo-chemical quantities in the composition space shows that H2 can be a good parameter to characterize the strain rate both for propagating and quenching flamelet.

The Limits of Electromechanical Coupling in Highly-Tensile Strained Germanium.

Speculations regarding electronic and photonic properties of strained germanium (Ge) have perpetually put it into contention for next-generation devices since the start of the information age. Here, the electromechanical coupling of <111> Ge nanowires (NWs) is reported from unstrained conditions to the ultimate tensile strength. Under tensile strain, the conductivity of the NW is enhanced exponentially, reaching an enhancement factor of ∼130 at ∼3.5% of strain. Under strains larger than ∼2.5%, the electrical properties of Ge also exhibit a dependence on the electric field. The conductivity can be further enhanced by ∼2.2× with a high bias condition at ∼3.5% of strain. Cyclic loading tests confirm that the observed electromechanical responses are repeatable, reversible, and related to the changing electronic band structure. These tests reveal the excellent prospects for utilizing strained Ge NWs in photodetector or piezoelectronic transistor applications, but significant challenges remain to realize strict direct band gap devices.

Effect of biaxial strain on the p-type of conductive properties of (S, Se, Te) and 2 N co-doped ZnO

Although the physical properties of ZnMxO1-x-yNy (M = S, Se, Te) p-type doping have been reported, the effects of biaxial strain on (S, Se, Te) and 2 N co-doped ZnO are rarely investigated by first-principles studies. Therefore, this study employs the first-principle plane wave ultra-soft pseudopotential method based on density functional theory to explore the formation energy and conductive properties of the doping system with a co-doping ratio of M and N in ZnO of M:N = 1:2 under the strain range of ‒5 % to 5 %. Under unstrained conditions, the M-N doping position is fixed and the other N is closer to M. The closer the N-N distance, the smaller the formation energy of the same doping system, and the higher the stability of the doping system. Regardless of the tensile or compressive strain, the formation energy of the doping system is higher than that of the unstrained doping system. The stability decreases relatively, but the formation energy is negative and the stability is still high. When the compressive strain is ‒5 %, the hole conductivity of the ZnSe0.0278O0.9166N0.0556 doping system is greater than that of the unstrained ZnSe0.0278O0.9166N0.0556. The vertical and horizontal comparisons show that the p-type effect and hole conductivity of ZnSe0.0278O0.9166N0.0556 are optimal when the compressive strain is ‒5 %. This study can be used as a guide for the design and preparation of new p-type ZnO conductive functional materials.

Direct Observation via In Situ Heated Stage EBSD Analysis of Recrystallization of Phosphorous Deoxidised Copper in Unstrained and Strained Conditions

Recrystallization of phosphorous deoxidised copper used for strength critical applications at elevated temperatures was investigated by means of in situ heated stage EBSD analysis using a Gatan Murano heated stage mounted within a Carl Zeiss Sigma FEGSEM electron microscope. The influence of applied strain as the result of deformation within a Nakajima test as an analogue for industrial forming on the recrystallization temperature was investigated, the impact of increased heating rates on microstructural evolution was also investigated. Inverse pole figure plots combined with regions of reduction in local misorientations and variations in geometrically necessary dislocations were used to establish the point of recrystallization and the recrystallized fraction of the material. Recrystallization was observed to occur at temperatures as low as 130 °C in highly strained samples compared to around 300 °C within the annealed samples dependent upon heating rate. Increased heating rates were observed to produce a finer final grain structure but had little effect on presence of <111> 60° grain twins, which was influenced more by initial material condition.Graphic

Effects of strain on the optical and magnetic properties of Ce-doped ZnO

The magnetic and optical properties of Ce-doped ZnO systems have been widely demonstrated, but the effects of different strains of Ce-doped ZnO systems remain unclear. To solve these problems, this study identified the effects of biaxial strain on the electronic structure, absorption spectrum, and magnetic properties of Ce-doped ZnO systems by using a generalized gradient approximation + U (GGA + U) method with plane wave pseudopotential. Under unstrained conditions, the formation energy decreased, the system became stable, and the doping process became easy with the increase in the distances between two Ce atoms. The band gap of the systems with different strains became narrower than that of undoped ZnO without strain, and the absorption spectra showed a red shift. The band gap narrowed, and the red shift became weak with the increase of compressive strain. By contrast, the band gap widened, and the red shift became significant with the increase of tensile strain. The red shift was significant when the tensile strain was 3%. The systems with −1%, 0%, and 1% strains were ferromagnetic. For the first time, the magnetic moment of the system with −1% strain was found to be the largest, and the system showed the greatest beneficial value for diluted magnetic semiconductors. The systems with −3%, −2%, 2%, and 3% strains were non-magnetic, and they had no value for diluted magnetic semiconductors. The ferromagnetism of the system with −1% strain was mainly caused by the hybrid coupling of Ce-4f, Ce-5d, and O-2p orbits. This finding was consistent with Zener's Ruderman–Kittel–Kasuya–Yosida theory. The results can serve as a reference for the design and preparation of new diluted magnetic semiconductors and optical functional materials.

Fully Soft 3D-Printed Electroactive Fluidic Valve for Soft Hydraulic Robots.

Soft robots are designed to utilize their compliance and contortionistic abilities to both interact safely with their environment and move through it in ways a rigid robot cannot. To more completely achieve this, the robot should be made of as many soft components as possible. Here we present a completely soft hydraulic control valve consisting of a 3D-printed photopolymer body with electrorheological (ER) fluid as a working fluid and gallium-indium-tin liquid metal alloy as electrodes. This soft 3D-printed ER valve weighs less than 10 g and allows for onboard actuation control, furthering the goal of an entirely soft controllable robot. The soft ER valve pressure-holding capabilities were tested under unstrained conditions, cyclic valve activation, and the strained conditions of bending, twisting, stretching, and indentation. It was found that the max holding pressure of the valve when 5 kV was applied across the electrodes was 264 kPa, and that the holding pressure deviated less than 15% from the unstrained max holding pressure under all strain conditions except for indentation, which had a 60% max pressure increase. In addition, a soft octopus-like robot was designed, 3D printed, and assembled, and a soft ER valve was used to stop the fluid flow, build pressure in the robot, and actuate six tentacle-like soft bending actuators.

Analysis of Stress Effect on (110)-Oriented Single-Gate SOI nMOSFETs Using a Silicon-Thickness-Dependent Deformation Potential.

The stress effect in uniaxially strained (100)- and (110)-oriented single-gate (SG) silicon-on-insulator (SOI) n-type metal-oxide-semiconductor field-effect transistors (MOSFETs) was analyzed. A model of a silicon-thickness-dependent deformation potential (D(as_T(si))) was used for accurate calculation of mobility using a Schrödinger-Poisson solver. The simulation results obtained using the D(ac_T(si)) model exhibited excellent agreement with the measured mobility for both strained and unstrained conditions. The enhancements in electron mobility under conditions of longitudinal tensile strain were analyzed as a function of the silicon thickness and strain. As the silicon thickness decreased, the mobility enhancement in (100) SG MOSFETs reached a peak, whereas it diminished in (110) SG MOSFETs. As the strain increased, mobility enhancement increased in the (110) case, whereas it saturated in the (100) case. Therefore, larger mobility enhancement in the (110) orientation is expected. These differences in enhancement between the (100) and (110) cases resulted from differences in the quantization mass, which affect the energy difference between the 1st subbands of two-fold and four-fold degenerate valleys, as well as occupancy change.

Paper No P24: Effect of Mechanical Strain on Charge‐Transfer VT‐Shift Compensation Circuits for Flexible AMOLED Displays

AbstractA 4‐thin‐film transistor (TFT) voltage‐programmed pixel circuit is fabricated using low‐temperature (170°C) hydrogenated amorphous silicon (a‐Si:H) TFTs process on flexible polyethylene naphthalate substrate. The electrical stability of the 4‐TFT circuit was characterized under mechanical strain and flat (unstrained) conditions. The compensated drive current degraded approximately 5% under electrical bias and tensile strain. This result was similar to pixel circuits fabricated at high temperature (300°C) on rigid glass substrates.

Precipitation response of the magnesium alloy WE43 in strained and unstrained conditions

The precipitation behavior of the magnesium alloy WE43 (Mg–4%Y–2.3%Nd–0.5%Zr) has been studied in strained and unstrained conditions using Transmission Electron Microscopy (TEM). Ageing treatments were carried out at three temperatures, namely 210°C, 230°C and 260°C. The precipitation sequence during static aging of solution treated (ST) samples has been identified as ST→β″→β′ followed by the formation of β1 and equilibrium β precipitates form after very long ageing periods. Dynamic precipitation was observed during high temperature deformation, leading to the formation of β′ and intermediate β1 precipitates. The strained samples, when further heat treated, resulted in the transformation of β1 into β equilibrium precipitates. The sequence of dynamic precipitation is ST→β1→β and ST→β′.

Strain-induced energy gap variation in ZnTe/ZnMgTe core/shell nanowires

Strain-induced changes of ZnTe energy gap in ZnTe/ZnMgTe core/shell nanowires arising from lattice mismatch between the core and the shell semiconductor are studied by means of optical methods. It is shown that the increase of the Mg content in the shell, as well as the increase of the shell thickness result in an effective redshift of the near band edge photoluminescence from ZnTe nanowire cores, which reflects directly the decrease of energy gap under tensile strain conditions. The conclusions are supported by theoretical calculations in terms of the valence force field model. The observed change of ZnTe energy gap can be as large as 120 meV with respect to the unstrained conditions and can be tuned in a continuous manner by adjusting shell parameters, which open a path towards an effective band gap engineering in these structures.