Percentage Of Strains Research Articles

Electrical properties of AlGaN/GaN HEMTs in stretchable geometries

Many biological materials are naturally soft and stretchable, far more so than crystalline semiconductors. Creating systems that can be placed directly on a surface such as human skin has required new approaches in electronic device design and materials, a field known as stretchable electronics. One common method for fabricating a highly brittle semiconductor device able to survive tens of percent strain is to incorporate stress relief structures (‘waves’). Although the mechanical advantages of this approach are well known, the effects on the electrical behavior of a device such as a transistor compared to a more traditional geometry have not been studied. Here, AlGaN/GaN high electron mobility transistors (HEMTs) grown on rigid sapphire substrates were fabricated in a common wavy geometry, a sinusoid, with dimensions similar to those used in stretchable electronics. The study analyzes control parameters available to the designer including gate location along the sinusoid, angle the source-drain contacts make with the gate, as well as variation of the gate length at the peak of the sinusoid. Common electrical parameters such as saturation current density, threshold voltage, and transconductance were compared between the sinusoidal and conventional straight geometries and results found to fall to within experimental uncertainty, suggesting shifting to a stretchable geometry is possible without appreciably degrading semiconductor device performance.

Multilayer Mg–Stainless Steel Sheets, Twinning and Texture Evolution

In the present study, different combinations of multilayer sheets were prepared from 1 and 2 mm Mg AZ31 along with 0.25, 0.5, and 1 mm 304 L stainless steel. The texture and microstructure of the elongated samples (20 and 30 pct strain) were studied. It was found that the transversal stress plays an important role in both texture evolution and twinning in these composites. The obtained pole figures revealed an axial texture tilt with increasing steel layer volume fraction (Vf). It was found that this is a direct effect of transverse stress, which becomes more significant upon reducing Mg Vf. This extra stress component tilts the basal planes away from the original normal direction in monolithic samples. Moreover, our results indicate that with decreasing Mg Vf, twinning activity was increased in the 20 pct deformed samples but reduced in the samples with 30 pct elongation. It is known that at high strains where sufficient transverse stress is generated, the activity of prismatic slip is significantly enhanced, which promotes the motion of dislocations and reduces the necessity of twinning. With decreasing Mg Vf, stronger transversal stress is generated and Mg reaches the critical threshold of prismatic activity at lower strains.

High Elastic Strain Directly Tunes the Hydrogen Evolution Reaction on Tungsten Carbide

Elastic strain provides a direct means to tune a material’s electronic structure from both computational and experimental vantage points and can thus provide insights into surface reactivity via changes induced by electronic structure shifts. Here we investigate the role of elastic strain on the catalytic activity of tungsten carbide (WC) in the hydrogen evolution reaction. WC makes an interesting material for such investigations as it is an inherently promising catalyst that can sustain larger elastic strains (e.g., −1.4 to 1.4%) than common transition-metal catalysts, such as Pt or Ni (e.g., −0.4 to 0.4%). On the basis of density functional theory calculations, a compressive uniaxial strain is expected to cause weakening of the surface–hydrogen interaction of 10–15 meV per percent strain, while a tensile strain is calculated to strengthen the surface–hydrogen interaction by a similar magnitude. Sabatier analysis suggests that weakening of the surface-hydrogen interaction would enhance catalysis. We prep...

Modelling and simulation of cyclic thermomechanical behaviour of NiTi wires using a weak discontinuity approach

In this contribution, a thermodynamically consistent and mathematically canonical modelling framework for the investigation of the cyclic thermomechanical behaviour of Nickel-Titanium shape memory alloy wires is developed. Particular focus is placed on the self-heating of the material subjected to multiple load cycles. The relatively high load rates necessitates the consideration of inertia terms, the applied load amplitudes of six percent strain motivates the use of a non-linear, Hencky-type strain measure. Comparisons of the results with experimental data on the one hand reveal reasonable results and on the other hand underline the necessity of further model enhancements.

On drying shrinkage in alkali-activated concrete: Improving dimensional stability by aging or heat-curing

The problem of excessive drying shrinkage in alkali-activated concrete (AAC) is well-documented in the literature. The magnitude of drying shrinkage is often three or more times that in portland cement concrete. This study investigates the effects of binder type, activator concentration, strength, age, and curing method on the manifestation of drying shrinkage in alkali-activated fly ash and slag cement concrete. Early-age shrinkage strains in excess of 1200με (0.12 percent strain) are observed in AAC. This is attributed to delayed hydration, microstructure refinement, and strength development. The resulting damage is far more significant than in portland cement concrete. Shrinkage and resulting damage are greatly reduced when specimens are dried at later age and after heat-curing. Alkali-activated slag cement concrete is more sensitive to water loss than portland cement or alkali-activated fly ash concrete. This results from a finer pore structure in alkali-activated slag binders.

Experimental and numerical study on vibrations and static deflection of a thin hyperelastic plate

The hyperelastic behavior of a thin square silicone rubber plate has been investigated analytically, numerically and experimentally; the case of small-amplitude vibrations has been considered, as well as the case of large static deflection under aerostatic pressure. The Mooney-Rivlin hyperelastic model has been chosen to describe the material nonlinear elasticity. The material parameters have been identified by a fitting procedure on the results of a uniaxial traction test. For the analytical model, the equations of motion have been obtained by a unified energy approach, and geometrical nonlinearities are modeled according to the Novozhilov nonlinear shell theory. A numerical model has also been developed by using a commercial Finite-Element code. In the experiments, the silicone rubber plate has been fixed to a heavy metal frame; a certain in-plane pre-load, applied by stretching the plate, has been given in order to ensure a flatness of the surface. An experimental modal analysis has been conducted; results have been used to identify the applied in-plane loads by optimization procedure with two different models: a numerical and an analytical one. The first four experimental and numerical natural modes and frequencies are in good agreement with the experiments after the pre-load identification. The static deflection has been measured experimentally for different pressures. Results have been compared to those obtained by analytical and numerical models. The static deflections are also satisfactorily compared, up to a deflection 50 times larger than the plate thickness, corresponding to a 30 percent strain.

Application of strain and calibration of Förster Resonance Energy Transfer (FRET) emission for in vitro live cell response to cytoskeletal deformation

Cellular mechanotransduction is an integral part of many crucial physiological processes, but non-invasive tools for quantifying intracellular strain in vivo are not available for complex tissues such as bone. As a first step to address this gap, we have utilized a novel, non-invasive approach to quantify cellular strain in vitro by employing a transfected alpha-actinin Förster Resonance Energy Transfer (FRET) sensor. Following validation experiments, mouse fibroblasts transfected to express FRET sensors were seeded to a silicone membrane and subjected to up to 10% tensile strain mounted on a multi-photon microscope. During tensile strain, fluorescent emission of acceptor (YFP) and donor (CFP) proteins was quantified. YFP/CFP ratio was normalized to the initial baseline (unstretched) ratio for each cell which demonstrates a negative linear correlation between the relative proximity ratio of emission spectra and cell strain, with a mean decrease of 1.017% normalized ratio for every percent strain experienced by the cell. The exciting implications of our findings are that the discovery of the stable correlation between loss of FRET and experimentally applied strain opens intriguing possibilities for future use of this technology with in vivo research, leading to discoveries improving disease treatments in mechanically sensitive tissues such as bone.

(Invited) Ab Initio Studies of Strain Effects on Perovskite Oxygen Vacancy Formation and Migration Energetics

Oxygen active materials are capable of rapidly transporting oxygen and exchanging it with the environment and have a wide range of applications, including solid oxide fuel cells, gas separation membranes, oxygen sensors, chemical looping devices, and memristors. Recent work has shown that epitaxial strain can play a significant role in altering the transport of oxygen through oxygen active materials, particularly in fluorite structured compounds. However, transition metal perovskites are an important class of oxygen active materials that have received only limited attention. In this work we use ab initio methods to model the coupling of biaxial epitaxial strain with oxygen vacancy formation and migration energetics in a range of transition metal perovskites. We focus on materials of the form LaBO3, where B = [Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga]. We predict the formation volume and strain response of oxygen vacancy formation energy, demonstrating that non-linear coupling of strain and vacancy formation can yield responses qualitatively different than those expected from simple elasticity arguments. In particular, as first observed in Ref. [1], we show that in some cases the vacancy can weaken the bonding and lower the elastic constants, which allows the formation of a vacancy to reduce the strain energy. This effect leads to stabilization of the vacancy under both compressive and tensile strain, even though the vacancy has positive formation volume. We also predict the migration volume and the strain response of oxygen migration energetics, here finding that values are quite consistent with a simple elastic strain model.[2] We find that tensile (compressive) biaxial strain reduces (enhances) the oxygen vacancy migration barrier approximately linearly across the systems studied (Figure 1). The average decrease in migration energy is 66 meV per percent strain for a single selected hop, with a low of 36 and a high of 89 meV decrease in migration barrier per percent strain across all the systems studied. In general we find that the oxygen transport kinetics can be altered by orders of magnitude in perovskites through strain effects on both vacancy content and migration energetics. These effects could play a significant role on materials performance at interfaces and in thin-film devices. [1] W. Donner, C. L. Chen, M. Liu, A. J. Jacobson, Y. L. Lee, M. Gadre, and D. Morgan, Epitaxial Strain-Induced Chemical Ordering in La0.5Sr0.5CoO3-delta Films on SrTiO3, Chemistry of Materials 23, p. 984-988 (2011). [2] T. Mayeshiba and D. Morgan, Strain Effects on Oxygen Migration in Perovskites, Phys. Chem. Chem. Phys. 17, p. 2715-2721 (2015 ). Figure 1

Mechanical and Functional Behavior of High-Temperature Ni-Ti-Pt Shape Memory Alloys

A series of Ti-rich Ni-Ti-Pt ternary alloys with 13 to 18 at. pct Pt were processed by vacuum arc melting and characterized for their transformation behavior to identify shape memory alloys (SMA) that undergo transformation between 448 K and 498 K (175 °C and 225 °C) and achieve recoverable strain exceeding 2 pct. From this broader set of compositions, three alloys containing 15.5 to 16.5 at. pct Pt exhibited transformation temperatures in the vicinity of 473 K (200 °C), thus were targeted for more detailed characterization. Preliminary microstructural evaluation of these three compositions revealed a martensitic microstructure with small amounts of Ti2(Ni,Pt) particles. Room temperature mechanical testing gave a response characteristic of martensitic de-twinning followed by a typical work-hardening behavior to failure. Elevated mechanical testing, performed while the materials were in the austenitic state, revealed yield stresses of approximately 500 MPa and 3.5 pct elongation to failure. Thermal strain recovery characteristics were more carefully investigated with unbiased incremental strain-temperature tests across the 1 to 5 pct strain range, as well as cyclic strain-temperature tests at 3 pct strain. The unbiased shape recovery results indicated a complicated strain recovery path, dependent on prestrain level, but overall acceptable SMA behavior within the targeted temperature and recoverable strain range.

Recrystallization and the Development of Abnormally Large Grains After Small Strain Deformation in a Polycrystalline Nickel-Based Superalloy

The formation of abnormally large grains has been investigated in the polycrystalline nickel-based superalloy Rene 88DT. Cylindrical specimens with a 15 μm grain size were compressed to plastic strains up to 11.0 pct and subsequently rapidly heated to above the γ′ solvus at 1423 K (1150 \(^\circ \)C) and held for 60 seconds. All deformed samples partially recrystallized during the heat treatment, with the recrystallized grain size varying with the degree of deformation. The largest final grain size occurred in samples deformed to approximately 2 pct strain, with isolated grains as large as 700 μm in diameter observed. It is proposed that abnormally large grains appear due to nucleation-limited recrystallization, not abnormal grain growth, based on the high boundary velocities measured and the observed reduction in grain orientation spread.

A new model for the cracking process and tensile ductility of Strain Hardening Cementitious Composites (SHCC)

Strain Hardening Cementitious Composites (SHCC) are materials exhibiting tensile hardening behavior up to several percent strain accompanied by the formation of fine multiple cracks. Their tensile ductility is governed by the spacing and opening of cracks, which depend on the stress transfer between the fibers and the matrix. In this article, a new analytic model which takes into consideration the effects of non-uniform matrix strength, post-cracking increase in fiber bridging stress and fiber rupture on stress transfer and multiple cracking behavior of SHCC is developed. Using material parameters within the range reported in the literature, simulation results can reach reasonable agreement with test data on SHCC for two different fiber contents. The effect of fiber length on tensile behavior of SHCC is then simulated to illustrate the applicability of the model to material design. The new model should be helpful to the micromechanics-based design of SHCC for various ductility requirements.

Effects of Curing Time, Temperature, and Vacuum Pressure on Asphalt Emulsion Residue Recovered by Vacuum Drying Method

Abstract This study included five different recovery methods for six emulsions (CRS-2, CRS-2P, CRS-2L, SS-1, SS-1L, and SS-1H) and their corresponding unaged base binders. These five recovery methods consisted of different curing times, temperatures, and vacuum pressures. The goal of this study was to understand the effect of these variables on the rheological properties of the recovered asphalt emulsion residue during the recovery process. Rheological properties such as G*/sin δ, phase angle, and average percent strain recovery were determined to quantify stiffness, oxidative aging, and change in creep recovery due to polymer modification. One new recovery method using a vacuum drying oven was explored in this study. This method reduced the effects of oxidative aging and reduced the recovery time to 6 h. The results show that this newly proposed vacuum drying method ensured better drying of the sample and produced residue that was not unnecessarily aged and was similar to unaged base binder in stiffness, whereas with ASTM D7497 oxidative aging plays a significant role in residue stiffness by almost doubling the stiffness relative to unaged base binder. Also, this 6-h vacuum drying method allowed us to clearly identify the presence of polymer. Overall, this report explains the reasons for the differences between the stiffnesses of unaged base binder and emulsion residue, considering oxidative aging, remaining moisture, emulsifier, and polymer modification.

Morphology and Mechanical Properties of Polyoxymethylene and Acrylonitrile-Butadiene-Styrene Blends with Compatibilizer

The effects of polypropylene-graft-maleic anhydride (PP-g-MA) compatibilizers on the morphology and mechanical properties of polyoxymethylene (POM)/acrylonitrile-butadiene-styrene (ABS) blends were investigated. Two types of compatibilizers, PP-g-MA with maleic anhydride 0.50 wt% (PP-g-MA1) and PP-g-MA with maleic anhydride 1.31 wt% (PP-g-MA2) were used to study the interfacial adhesion of POM and ABS. POM/ABS blends with and without PP-g-MA compatibilizer were prepared by an internal mixer and molded by compression molding. Scanning electron microscope (SEM) was used to investigate the morphology of ABS phase in POM matrix. The results found that POM/ABS blends clearly demonstrated a two phase separation of dispersed ABS phase and the POM matrix phase, and ABS phase dispersed as spherical domains in POM matrix in a range of ABS 10-30 wt% and the blends containing ABS more than 30 wt% showed the elongated structure of ABS phase. The addition of PP-g-MA could improve the interfacial adhesion of POM/ABS blends due to the domain size of ABS phase decreased after adding PP-g-MA. The mechanical properties showed that the impact strength of POM/ABS blends decreased in a range of 10-20 wt% and did not change after 20 wt%. The addition of PP-g-MA did not change the impact strength of POM/ABS blends. The Young’s modulus of POM/ABS blends increased up to 30 wt% of ABS and then decreased. While the blends showed the decrease of tensile strength and percent strain at break with increasing ABS content. The addition of PP-g-MA increased the tensile strength of POM/ABS blends in a range of 30-40 wt% of ABS. The above results indicated that the morphology had an effect on the mechanical properties of polymer blends.

Transverse Creep of Nickel-Base Superalloy Bicrystals

A liquid metal cooled (LMC) solidification technique was used to produce nickel-base GTD 444 and Rene N4 superalloy bicrystals with varying degrees of misorientation. Creep experiments with loading normal to the bicrystal boundaries were conducted at 1255 K (982 °C). Despite the similar overall compositions of these two alloys, the GTD 444 alloy with higher levels of carbon and boron displayed significantly higher tolerance to high-angle boundaries. Creep ductilities at rupture of greater than 5 pct were observed in GTD444 for boundaries misoriented by greater than 20 deg. Electron backscatter diffraction analysis showed significant lattice rotation adjacent to the bicrystal boundary in GTD444. In contrast, the Rene N4 bicrystal accumulated damage along the grain boundary early in creep, failing at less than 2 pct strain.

Mechanical and Morphological Properties of Poly(Methyl Methacrylate)/Ethylene-Octene Copolymer/Clay Composites

The effects of the montmorillonite clay surface modified with 25-30 wt% octadecylamine (clay) on mechanical and morphological properties of poly (methyl methacrylate) (PMMA)/ ethylene-octene copolymer (EOC)/clay composites were investigated. The composites of blends of PMMA/EOC with clay were prepared by melt mixing in an internal mixer. The results showed that the Young’s modulus of the composites increased with increasing clay content. The ratio of PMMA and EOC was 80/20 by weight and the clay content was 3 and 5 phr. The results showed Young’s modulus of the composites increased with increasing clay content. While the impact strength, tensile strength and percent strain at break of the composites decreased with increasing clay content. Scanning electron microscopy analysis showed that the droplet of dispersed EOC phase in PMMA matrix was changed to the elongated structure after adding clay.

Regression models for estimating ultimate and serviceability limit states of underground rock caverns

Performances of underground rock caverns can be unsatisfactory as a result of either instability (collapse) or excessive movements. Collapse refers to ultimate limit state failure, in which the stresses exceed the strength of the rock masses. Failure of the serviceability limit state refers to excessive deformations resulting in difficulties during excavation such as lining placement and reinforcement installation. Both distinct limit states may need to be considered in design. This study used numerical modeling to assess both the ultimate and the serviceability limit states of underground single and twin rock caverns. The global factor of safety is used as the criterion for the ultimate limit state and the calculated percent strain around the cavern opening is adopted as the serviceability limit state criterion. Based on the numerical results, simple regression models were developed for estimating the global factor of safety and the induced percent strain of the single and twin caverns, respectively. Charts for assessing cavern stability for preliminary design use were developed. In addition, the use of the critical strain concept and the elastic and design line methodology to limit the induced strains was discussed.

Shape Actuation via Internal Stress-Induced Crystallization of Dual-Cure Networks.

We demonstrate a single-phase, two-way shape actuator that, in the absence of an external load, elongates upon cooling and reversibly contracts upon heating. In a simple and straightforward process, a partially cross-linked, semicrystalline poly(ε-caprolactone) (PCL) network is melted, stretched to several hundred percent strain, and further cross-linked. Upon removal of the applied load, the elastic double network adopts a "state-of-ease" that retains part of its former strain. When cooled, internal stress-induced crystallization causes further elongation of configurationally biased chains. When heated, crystallites melt, and the sample returns to its equilibrium state-of-ease. Under optimized conditions, reversible actuation >15% strain can be reproducibly achieved, and samples can be cycled multiple times with highly uniform actuation with no observable creep. The mechanism behind such actuation was further confirmed via calorimetry and X-ray scattering.

Multivariate adaptive regression splines model for reliability assessment of serviceability limit state of twin caverns

Construction of a new cavern close to an existing cavern will result in a modification of the state of stresses in a zone around the existing cavern as interaction between the twin caverns takes place. Extensive plane strain finite difference analyses were carried out to examine the deformations induced by excavation of underground twin caverns. From the numerical results, a fairly simple nonparametric regression algorithm known as multivariate adaptive regression splines (MARS) has been used to relate the maximum key point displacement and the percent strain to various parameters including the rock quality, the cavern geometry and the in situ stress. Probabilistic assessments on the serviceability limit state of twin caverns can be performed using the First-order reliability spreadsheet method (FORM) based on the built MARS model. Parametric studies indicate that the probability of failure Pf increases as the coefficient of variation of Q increases, and Pf decreases with the widening of the pillar.

Effects of Compatibilizer on the Properties of Polyoxymethylene/Acrylonitrile-Butadiene-Styrene Blends

The effects of styrene-co-maleic anhydride (SMA) compatibilizer on the mechanical thermal and morphological properties of polyoxymethylene (POM)/acrylonitrile-butadiene-styrene (ABS) blends were inverstigated. POM/ABS blends without and with SMA compatibilizer were prepared by an internal mixer and molded by compression molding. It was found that the dispersion of ABS phase and compatibility could not improve by using SMA compatibilizer in POM/ABS blends due to SMA can be miscible with ABS phase more than POM phase. The addition of ABS in a range of 10-30 wt% could improve the Young’s modulus of POM. Impact strength, tensile strength and percent strain at break of POM/ABS blends decreased with increasing ABS content. The addition of compatibilizer improved Young’s modulus of POM/ABS (60/40, 50/50) blends. The addition of ABS increased the degradation temperature of POM, while SMA compatibilizer did not improve the degradation of POM/ABS blends.

Novel Real-Time Nondestructive Technology for Chemical and Structural Health Management of Solid Rocket Propellants


 
 
 
 
 
 An innovative prognostics and chemical health management (CHM) technique was developed, for quantifying and characterizing health status of a CL-01 composite solid rocket propellant of tactical rocket motors. The technique is a cutting-edge real-time nondestructive technology approach which utilizes Near Infrared (NIR) spectra (M. Blanco, and I. Villarroya, 2002) emitted by microPHAZIRTM NIR miniature handheld platform, developed by Thermo Fisher Scientific. Benchtop high-performance liquid chromatography (HPLC) and ion chromatography (IC) were utilized as baseline reference techniques for correlation to TM microPHAZIR NIR measurements.To build a quantitative calibration model, near infrared spectra were acquired for twenty freshly manufactured mixes of CL-01 propellant formulae, which were iterated using a D-Optimal full-factorial design of experiment (DOE). Four-hundred eighty measurements were recorded and analyzed using Partial Least Squares (PLS) regression analysis for model building and method development (Schreyer, 2012). NIR results were correlated to spectra, which were produced using HPLC and IC reference techniques and were determined to be in precise agreement. All recorded measurements that were performed using microPHAZIRTM handheld platform were successfully validated with HPLC and IC measurements. An algorithm was developed for microPHAZIRTM NIR thus qualifying the platform as a real-time nondestructive test (NDT)/ nondestructive evaluation (NDE) tool for quantification of primary chemical constituents of CL-01 composite solid rocket propellant. Primary chemical constituents of CL-01 comprise a binder, oxidizer, plasticiser, and antioxidant/stabilizer.Data sets for Shore-A hardness of each of the twenty DOE mixes were collected and used to calculate elastic modulus, tensile strength and percent strain. Calculated results conformed to specification requirements for CL-01 solid rocket propellant, henceforth confirming use of Shore A hardness as a real-time nondestructive test technique for validation of structural health of a solid rocket propellant. This teaming effort between Raytheon Missile Systems (RMS), United Kingdom Ministry of Defence (UK MoD), Alliant Techsystems Launch systems (ATK LS), and Thermo Fisher Scientific demonstrated outstanding ability to utilize miniature cutting-edge technology to perform real- time NDT of CL-01 composite solid rocket propellant without generating chemical waste and residue and to ameliorate RMS technology base to capture incipient failures before the fact. The new technique will further be adapted for use to measure primary chemical constituents of other solid rocket propellants, liquid propellants, and composite explosives. The new technique will significantly reduce costs associated with surveillance and service life extension programs (SLEPs), which are often destructive and requires use of lengthy and expensive test techniques described in North Atlantic Treaty Organization (NATO) Standardization Agreement (ST ANAG)-4170 and Allied Ordnance Publication (AOP)-7 manuals.