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The Journal of Materials Science awards the annual Robert W. Cahn Prize to recognize the best paper published in the journal each year. The winner of the 2023 Cahn Prize is a research paper titled "Molecular modelling of graphene nanoribbons on the effect of porosity and oxidation on the mechanical and thermal properties." The paper presents molecular simulation models of graphene nanoribbons and examines the impact of porosity and oxidation on their mechanical and thermal conductivity properties. The paper is well-written and provides valuable insights for researchers in this field. Two other papers were selected as runners-up for the prize. All the monthly finalists for the Cahn Prize can be downloaded for free on the journal's website. [Extracted from the article]

Twinning is an important deformation mechanism for magnesium alloys, which has a significant impact on the texture evolution and mechanical properties. Pre-twinning deformation has been considered as an effective method for texture regulation. For each twinning mode, there are six crystallographically equivalent variants. Properly identifying the activated twin and understanding its variant selection criteria are essential for the development of high-performance magnesium alloys. As summarized in this paper, the observed twin variant by the commonly employed electron backscatter diffraction technique can be identified by several approaches, including misorientation analysis, trace analysis and matrix method. Schmid factor analysis was commonly performed to explain the selection of twin variants. To broaden the application scope under complex stress state, a generalized Schmid factor was derived by introducing a stress tensor. The efficiency of Schmid criteria to assess twin variant selection was confirmed to be influenced by the type of the applied stress. To consider the local effect on twin activation, in particular twin-twin transfer and slip-induced twinning, displacement gradient tensor calculation and geometrical compatibility factor analysis have been employed. It was demonstrated that local strain accommodation played a critical role in selecting the variants of cross-boundary twins in magnesium alloys. Assisted with crystal plasticity finite element modeling, the resolved shear stress on twinning and a composite Schmid factor combining the global Schmid factor and geometrical compatibility factor were obtained to better explain the activated twin variants in magnesium alloys. All the above-mentioned Schmid law based criteria and some energy based criteria as well are summarized in this paper. Their applications in evaluating twin variant selection in magnesium alloys are critically reviewed and discussed. [ABSTRACT FROM AUTHOR]

Due to the machining-induced residual stress while processing, the machining distortion of thin-walled 7050 aluminum alloy parts occurs easily, which greatly affects the pass rate of the products. Herein, electromagnetic coupling treatment (EMCT) was proposed to relieve the residual stress of 7050 aluminum alloy. It was found that EMCT had a significant effect on residual stress relief (13.3–89.7%). The energy input by EMCT promoted the movement of dislocation, resulting in the uniform distribution of microplastic strain, the release of stored elastic strain energy, and the residual stress relief, ultimately. A numerical simulation method to visualize the evolution of the electromagnetic field, the stress, and the strain in the materials was proposed to explain the causes of microplastic strain. Specimen #5 with the optimal EMCT processing parameter (1.5 T, 1.5 V) was considered to be the most effective for both residual stress relief and mechanical property enhancement, in which the residual stress decreased by 85.1% and the tensile strength increased by 8.3%. In this paper, it is proposed that EMCT can be used as an effective method to reduce the residual stress of 7050 aluminum alloy. Moreover, it has certain technical reference value for the study of residual stress relief of other thin-walled part materials. [ABSTRACT FROM AUTHOR]

In the last years, a large number of new biocompatible materials for 3D printers have emerged. Due to their recent appearance and rapid growth, there is little information about their mechanical properties. The design and manufacturing of oral appliances made with 3D printing technologies require knowledge of the mechanical properties of the biocompatible material used to achieve optimal performance for each application. This paper focuses on analysing the mechanical behaviour of a wide range of biocompatible materials using different additive manufacturing technologies. To this end, tensile and bending tests on different types of recent biocompatible materials used with 3D printers were conducted to evaluate the influence of the material, 3D printing technology, and printing orientation on the fragile/ductile behaviour of the manufactured devices. A test bench was used to perform tensile tests according to ASTM D638 and bending tests according to ISO 178. The specimens were manufactured with nine different materials and five manufacturing technologies. Furthermore, specimens were created with different printing technologies, biocompatible materials, and printing orientations. The maximum allowable stress, rupture stress, flexural modulus, and deformation in each of the tested specimens were recorded. Results suggest that specimens manufactured with Stereolithography (SLA) and milling (polymethyl methacrylate PMMA) achieved high maximum allowable and rupture stress values. It was also observed that Polyjet printing and Selective Laser Sintering technologies led to load–displacement curves with low maximum stress and high deformation values. Specimens manufactured with Digital Light Processing technology showed intermediate and homogeneous performance. Finally, it was observed that the printing direction significantly influences the mechanical properties of the manufactured specimens in some cases. [ABSTRACT FROM AUTHOR]

To investigate the dynamic recrystallization (DRX) behavior of forged 42CrMoA steel during hot deformation, the hot deformation experiments of forged 42CrMoA steel under different deformation conditions (strain rate, temperature, and strain) were carried out in this paper. The hot deformation activation energy of forged 42CrMoA steel was determined to be 413627.2 J · mol - 1 . The constitutive model and DRX kinetic model of the steel were established. Analyzing the reconstructed parent phase grains reveals that when the strain is constant, as the deformation temperature increases and the strain rate decreases, the average size and DRX volume fraction of the parent phase grains gradually increase, and the peak stress gradually decreases. When the deformation temperature and strain rate are constant, as the strain increases, the average size of the parent phase grains gradually decreases, and the volume fraction of DRX gradually increases. Based on the cellular automaton theory model and considering the influence of grain deformation on the DRX process, a cellular automaton dynamic recrystallization (T-DRX-CA) model for forged 42CrMoA steel based on topological deformation technology was established, and the microstructure evolution under different deformation conditions was simulated. The microstructure evolution under different deformation conditions was simulated, which was compared with experimental results. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. The hot deformation behavior of forged 42CrMoA steel under different deformation conditions was investigated by a cellular automaton dynamic recrystallization (T-DRX-CA) model based on topological deformation technique. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. [ABSTRACT FROM AUTHOR]

During high-temperature applications, tensile stability is significantly important and urgent for the security of components. In this paper, the high-temperature tensile tests under different creep strain were performed and analyzed through scanning electron microscope (SEM) and transmission electron microscope (TEM) of TC11 titanium alloy. It is found that the creep strain, dynamic α precipitation and deformation modes have significant influence on the high-temperature tensile behavior of TC11 titanium alloy. An abnormal characteristic of high-temperature tensile stress plateau was observed with the increasing of the creep strain. Moreover, an increment of 100 MPa for yield strength was achieved when the creep strain increased from 0.075 to 0.21%. For low creep strain, sample was controlled by the dislocation slip. While at high creep strain, it promotes the precipitation of nano-sized α particles, and dislocation slip hardly transfers across the α/β interface. Then, dislocation tangles, deformation twins and stacking faults become dominated, which results in an obvious stress plateau in the stress–strain curve. [ABSTRACT FROM AUTHOR]

Some key structural parts made of welding titanium alloys usually serve in hydrogen environment in aerospace, ship building and chemical industries. To investigate the hydrogen embrittlement (HE) behaviors of the welded titanium alloy joints and the impact factors, the TC4 titanium alloy joints welded by laser welding method were first treated by ultrasonic surface rolling process (USRP). Then, slow-rate tensile tests were conducted under electrochemical hydrogen charging condition to compare the mechanical properties of the TC4 laser welded joints before and after USRP. On this basis, the HE behaviors and mechanisms of the USRP-treated TC4 laser welded joint and the USRP-untreated one were discussed in detail. The results show that USRP could significantly improve the anti-hydrogen embrittlement behaviors of the TC4 laser welded joint, which could be attributed to the grain refinement and residual compressive stress in the deformation layer induced by USRP. The results of this paper provide a theoretical basis for the design of anti-hydrogen embrittlement metal materials. [ABSTRACT FROM AUTHOR]

Haynes 282 is a γ ′ precipitation-strengthened nickel-based superalloy known for its exceptional high-temperature creep resistance and excellent fabricability. Recent advancements in powder-bed fusion-based additive manufacturing (PBF-AM) have enabled the fabrication of Haynes 282 with accurate, site-specific control of the grain orientation and morphology at the microscale. This ability opens up new avenues for microstructure design, to improve the material's fatigue crack resistance and service life. This paper investigates the fatigue crack growth behavior of hybrid microstructure Haynes 282 fabricated via PBF-AM. Previous experiments revealed a higher crack propagation rate in the coarse columnar-grained microstructural regions when compared against fine-grained areas. Here, a strain gradient crystal plasticity model was adapted to study the fracture-related mechanical fields at the crack tip in the two microstructures. The simulation results showed a consistent influence of grain structure and texture on crack propagation, as was seen in the experiment. The model analysis revealed higher crack propagation driving force along crack direction in the coarse-grained sharply textured microstructure and higher driving force for crack kinking in fine-grained more diffusely textured microstructure, which is ascribed to the combined effect of yield stress, hardening rate, texture and grain morphology. The presented modeling approach will facilitate the development of the AM-based accurate microstructure design by deepening the fundamental study in AM-specific microstructure-properties relations. [ABSTRACT FROM AUTHOR]

This article continues the work on dipolar thermoelastic materials, which are a special case of multipolar continuum mechanics. This theory allows a double-porous structure: a macro-porosity related to pores in the material and a microporosity, which shows fissures in the porous skeleton. This paper constructs a mathematical model for dipolar materials, which have a double-porosity structure by considering a fractional order Duhamel-Neumann stress-strain relation. The heat conduction is described by Cattaneo's equations. The results are the constitutive equations of the linear theory of thermoelasticity with fractional order strain. The equations are valid for anisotropic materials and are called the Duhamel-Neumann equations with fractional order. Finally, the isotropic case is considered under the conditions of plane strain in order to perform some numerical simulations for samples of porous copper. [ABSTRACT FROM AUTHOR]

A methodology that accurately simulates the brittle behavior of epoxy polymers initiating at the molecular level due to bond elongation and subsequent bond dissociation is presented in this paper. The system investigated in this study comprises a combination of crystalline carbon nanotubes (CNTs) dispersed in epoxy polymer molecules. Molecular dynamics (MD) simulations are performed with an appropriate bond order-based force field to capture deformation-induced bond dissociation between atoms within the simulation volume. During deformation, the thermal vibration of molecules causes the elongated bonds to re-equilibrate; thus, the effect of mechanical deformation on bond elongation and scission cannot be captured effectively. This issue is overcome by deforming the simulation volume at zero temperature-a technique adopted from the concept of quasi-continuum and demonstrated successfully in the authors' previous work. Results showed that a combination of MD deformation tests with ultra-high strain rates at near-zero temperatures provides a computationally efficient alternative for the study of bond dissociation phenomenon in amorphous epoxy polymer. In this paper, the ultra-high strain rate deformation approach is extended to the CNT-epoxy system at various CNT weight fractions and the corresponding bond disassociation energy extracted from the simulation volume is used as input to a low-fidelity continuum damage mechanics (CDM) model to demonstrate the bridging of length scales and to study matrix failure at the microscale. The material parameters for the classical CDM model are directly obtained from physics-based atomistic simulations, thus improving the accuracy of the multiscale approach. [ABSTRACT FROM AUTHOR]

It this paper, the comprehensive design process was carried out to fabricate selective, molecularly imprinted polymer (MIP). The material was used as a sorbent in the optimized analytical method, aimed at verifying the hypothesis that the conditions of an analytical process could convert 4-hydroxyphenylacetic acid to 4-hydro-3-nitrophenylacetic acid, comprising a series of novel studies. The design stage consisted of the analysis of specificity of the MIP, synthesized from the cross-linker and used five various functional monomers independently, in the presence of four different templates. The MIP from 1-vinylimidazole, imprinted by 4-hydroxyphenylacetic acid, revealed the highest specificity in relation to 4-hydro-3-nitrophenylacetic acid, with an affinity factor equal to 3, and the highest selectivity from a group of structurally similar and biologically important biomolecules. The theoretical analysis revealed that electrostatic interaction between the analyte and the polymer matrix enhanced selectivity. The physicochemical characterization showed the specific surface area of the MIP as being equal to 368.6 m2 g−1, and the presence of nitrogen atoms at the level of 6.80% wt., confirming the monomer residue in the material structure. The MIP was applied in the solid phase extraction protocol, allowing for the analysis of 4-hydroxy-3-nitrophenylacetic acid in a human urine sample. Finally, the conversion of 4-hydroxyphenylacetic acid in human urine in nitrate and nitrite salts at low pH conditions revealed an almost twofold increase in 4-hydro-3-nitrophenylacetic acid to 775 ± 81 ng L−1. The results also confirmed the applicability of the new MIP sorbent for the purpose of analysis of low levels of analyte, present in the complex sample. [ABSTRACT FROM AUTHOR]

The tension-tension fatigue behavior and damage mechanism of basalt fiber-reinforced epoxy polymer (BFRP) composites at different stress ratios are studied in this paper. The fatigue experiments were performed under stress ratios, R = σmin/σmax of 0.1 and 0.5, while the lifetime and the stiffness degradation were monitored and analyzed to investigate the effect of stress ratios. The damage propagation during fatigue loading was periodically monitored by using an in situ scanning electron microscope (SEM). The results show that the fatigue life decreases and the fatigue life degradation rate increases with the decrease of stress ratio for examined BFRP composites. The stiffness degradation is also sensitive to different stress ratios, showing a greater stiffness loss before failure at lower stress ratio. From the SEM images, it is indicated that the micro-damage mode shifts from interface debonding and matrix cracking into fiber breaking with decreasing stress ratios. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum well light-emitting diodes (LEDs) are conventionally grown on a sapphire substrate due to a lack of compatible substrates with a high compressive strain. This is a result of the relatively large lattice, and thermal expansion coefficient mismatches between GaN and sapphire. The compressive strain is considered to be a major obstacle to further improve next-generation high-performance GaN-based LEDs. In this paper, we have designed, electroplated, and tested an efficient substrate using a patterned copper (Cu) layer on the backside of sapphire to relax the compressive strain in a GaN epilayer. The patterned Cu layer has a significant function in that it supports the GaN/sapphire LEDs with an external tensile stress. The external tensile stress is capable of compensating for the compressive strain in the GaN/sapphire LEDs by controlling the curvature of the wafer bowing. This patterned Cu layer, when applied to the GaN/sapphire LEDs, suppresses the compressive strain by up to 0.28 GPa. The GaN-based LEDs on this innovative and effective sapphire/Cu substrate offer improved optical and electrical performance. [ABSTRACT FROM AUTHOR]

Some mean-field models are currently available for discontinuous dynamic recrystallization (DDRX). They offer an affordable way to predict the variation of averages altered by DDRX as flow stress, grain size and recrystallized fraction. They predict also a grain-size distribution, but it appears unrealistic, at least if a deterministic equation governs the migration of grain boundaries. The present paper exposes an extension to mean-field models which introduces some topological and stochastic features in the migration equation. This extension aims to bridge the gap between mean- and full-field models. It allows predicting realistic distributions of grain size by keeping the simplicity of mean-field approaches. The results obtained are consistent with experimental data on an 18% Cr-11% Ni stainless steel. [ABSTRACT FROM AUTHOR]

Polymer composite materials are being increasingly used in primary load-bearing structures in several advanced industrial fields such as aerospace vessels, railway wagons and mega-scaled wind turbines where detection of subcritical damage initiation can significantly reduce safety issues and maintenance costs. It is therefore crucial to inspect these composite structures in order to assess their structural health and to ensure their integrity. Non-destructive testing techniques (NDT) are used for this purpose, making it possible to monitor mechanical damage of composite materials under in situ or ex situ service conditions. This paper reviews the capabilities of the most common NDT techniques used to inspect the integrity of composite materials. Each technique has a detection potential and cannot allow a full diagnosis of the mechanical damage state of the material. Thus, depending on the occurring damage mechanism and the conditions of use, one technique will be preferred over another, or several techniques should be combined to improve the diagnosis of the damage state of the structures. [ABSTRACT FROM AUTHOR]

Stress rupture is an important failure phenomenon in composite overwrapped pressure vessels, which is highly unpredictable other than on a statistical basis. Even then, there are several statistical models, with varying bases in composite micromechanics and molecular failure mechanisms. Choosing among these models is not trivial, even when micromechanical details of the failure process are reasonably well appreciated, and one has available a reasonably large database of strength and lifetime data. As a result, there is little in the way of guidance to choose the most appropriate model. One important issue is that accurate predictions are desired at relatively low service loads compared to the strength, and low probabilities of failure that are far less, e.g., 10-6, than can be directly confirmed using the data itself. In essence, one needs a robust and accurate statistical model free of inconsistencies associated with such low stress levels and probabilities of failure. This paper performs an in-depth comparison of several current models, which have varying physical bases. The models compared differ in the number of parameters to be estimated from data. The results of this study, however, show that over a broad range of parameter values these models give surprisingly similar failure probability predictions. While practitioners may have a preference for one model over another, the basis for such a choice is not easily established, given the fidelity of typical data. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement is a complex phenomenon, involving several lengthand timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

The use of misfit strain to improve the electronic performance of semiconductor films is a common strategy in modern electronic and photonic device fabrication. However, pursuing a favorable higher strain could lead to mechanical instability, on which systematic and quantitative understandings are yet to be achieved. In this paper, we investigate the anisotropy effects on strain-induced thin-film surface roughening by phase field modeling coupled with elasticity. We find that compared with films grown along {111} and {100} surfaces, the instability of {110} film occurs at a much lower strain. Our simulations capture the evolution of interface morphology and stress distribution during the roughening process. Similar characterizations are performed for heteroepitaxial growth from a surface pit. Finally, from 3D simulations, we show that the surface roughening pattern on {110} film exhibits a clear in-plane orientation preference, consistent with experimental observations. [ABSTRACT FROM AUTHOR]

SrAlO:(Eu,Dy) is one of the most promising mechanoluminescence materials that have potential applications in stress sensing, lighting, imaging and energy conversion. However, the ML intensity decays with the afterglow time of SrAlO:(Eu,Dy), which hampers its application in the real world. Here, the mechanoluminescence property of SrAlO:(Eu,Dy) was investigated by impact of a load. A method was proposed to overcome the drawback of the mechanoluminescence decay behavior associated with the afterglow time. During the measurement of mechanoluminescence, continuous UV irradiation on SrAlO:(Eu,Dy) can effectively realize steady-state mechanoluminescence that is independent of the afterglow time. The underlying mechanism is discussed in this paper. [ABSTRACT FROM AUTHOR]

Metamagnetic shape memory alloys are a unique class of materials capable of large magnetic field-induced strain due to reverse martensitic phase transformation. A precondition for large shape change is martensite deformation, which heavily depends on microstructure. Elucidation of microstructure is therefore indispensable for strain control and deformation mechanics in such systems. The current paper reports on a self-accommodated martensitic microstructure in metamagnetic NiMnSn single crystal. The microstructure here is hierarchically organised at three distinct levels. On a large scale, martensite plate colonies, distinguished by intercolony boundaries, group individual martensitic plates. Plates are separated by interplate boundaries and deviate by 2.2° from an ideal twin relation. On the lower scale, plates are composed of subplate twins. Conjugation boundaries separating two pairs of twins arise in relation to a subplate microstructure. Modulation boundaries separating two variants with perpendicular modulation directions and with parallel c-axes also appear. Mechanical training frees larger plates from fine subplate microtwins bringing macro-lamellae into twin relation, what then permits further detwinning until a single variant state. [ABSTRACT FROM AUTHOR]

Strain wave propagation velocity in fibre materials is a primary consideration in the design of body armours for ballistic protection. In this paper, we compare the strain wave propagation (sonic) velocities and moduli of parallel and twisted ballistic fibre strands (yarns) derived from quasi-static tensile test and strain wave pulse test. In parallel multifilament yarns, the individual fibres behave independently from each other, and the yarn sonic velocities and moduli derived from the two test methods match each other very closely. In yarns with a twisted structure by twisting multifilament yarn or by spinning short fibres, fibres in the yarns are compressed against each other and fibre-to-fibre friction plays a significant role. Consequently, the yarn sonic velocities and moduli determined by the strain wave pulse method are significantly greater than that derived from the quasi-static tensile method. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue properties and deformation behavior of the T6-treated Mg-2.99Nd-0.18Zn-0.38Zr (NZ30K) and an AZ91D-T6 magnesium alloys with the same grain size. Compared with the AZ91-T6 alloy, the NZ30K-T6 alloy shows significant increases in mechanical properties, achieving 17 MPa in YS, 51 MPa in UTS, 2.4 % in elongation, and 15 MPa in FS, respectively. The NZ30K-T6 alloy also shows higher cyclic stress amplitudes in comparison with the AZ91-T6 alloy. This is attributed to increased matrix strength from the higher precipitate strengthening in the NZ30K-T6 alloy. The cyclic stress amplitude of the AZ91-T6 alloy increases with increasing the number of cycles. For the NZ30K-T6 alloy, the cyclic stress amplitude first increases and then decreases during cyclic deformation. Hysteresis loops were symmetrical at all total strain amplitudes due to the lessened extents of texture in these cast magnesium alloys and the absence of twinning-detwinning during cyclic deformation. For both AZ91-T6 and NZ30K-T6 alloys, the cracked slip bands initiate the fatigue cracks and also assist the crack propagation. The Coffin-Manson law and Basquin equation can be used to evaluate the fatigue parameters and predict the LCF lives of both AZ91-T6 and NZ30K-T6 alloys. The multi-scale fatigue (MSF) life models and the same model parameters were also used to predict the HCF lives of these alloys. [ABSTRACT FROM AUTHOR]

Manipulation of spin-flip is important in spintronics applications. In this paper, we report a simple manipulation of three Co-3 d spin states in the CoO spinel. From first principles calculations, we demonstrate that the spin state of Co atoms at octahedral sites (Co) of the CoO spinel can be manipulated through tensile stains. The magnetic moment of the Co changes from the ground non-magnetic (0 µ) state to the intermediate-spin state (2 μ) and high-spin state (4 μ) when 5 % (or higher) uniaxial tensile strain and 3 % (or higher) biaxial tensile strain are applied to the lattice, respectively. Moreover, the mechanism of the spin state transition of the Co-3 d electrons in CoO is discussed, and we show that the occurrence of spin-flip is a result of the competition between the cubic crystal field energy and the exchange correlation energy. These results open a new route to achieve and manipulate triple-spin states in spintronic devices. [ABSTRACT FROM AUTHOR]

Misfit strain relaxation-induced morphology instability is usually observed in epitaxial heterostructures at high temperatures. In this paper, we report that this morphology instability can occur even at room temperature in epitaxial ZnO/AZO (Al-doped ZnO) core-shell nanowires (NWs). As a result, densely distributed ZnO nanodots (NDs) were self-assembled on the NWs. The growth of NDs was slowed down during aging owing to the gradually reduced misfit strain. The final size and shape of the NDs were highly depended on the shell thickness and the doping ratio. It was proved that the morphology stability could be improved by surface passivation, thinning the shell thickness, or lowering the doping ratio. The results may provide instructive suggestions for the reliable design in strain and surface engineering of nanomaterials. [ABSTRACT FROM AUTHOR]

To obtain ultra-high strength with guaranteed ductility, stable nanolamellar austenite packed with high densities of dislocations and nanotwins is inserted into nanolamellar martensite. An ultra-high yield strengths of 1.6–2.2 GPa at room temperature and 1.94–2.5 GPa at liquid nitrogen temperature were obtained in the steel, which is combined with good uniform elongation of 4–9%. The designed steel is shaped with the combination of solid solution strengthening, lamellar boundary strengthening and dislocation strengthening. The nanostructure is stabilized by C distribution, and in this way the stress–strain carrying capacity of martensite and austenite is increased, thus ensuring ultra-high strength. In addition, the generation of TRIP effect at low temperatures ensures the realization of strain-hardening rate and uniform elongation at ultra-high strength. Therefore, the nanolamellar martenite-austenite microstructure and strong carbon partitioning through martensite and austenite is considered as a fundamental guarantee for the ultra-high strength and toughness. Our results provide an optional strategy for the development of new ultra-strong alloys for low-temperature applications. [ABSTRACT FROM AUTHOR]

The large deformation of difficult-to-deform metal under pulsed currents involves the coupling effect of grain refinement and electroplasticity, making it challenging to capture the flow behavior accurately during severe plastic deformation. To develop a highly accurate constitutive model that accounts for the coupling effect, a current-assisted plane strain compression (CAPSC) test of 30CrMnSiA was carried out, using a peak current density (Jp) range of 0–30 A mm−2 and duty ratio (d) of 0–20%. A microstructural observation was also performed via the EBSD test on the specimens after the CAPSC test. The result indicates that the true stress decreases significantly with increased Jp and d, descending to a stable value of 13% under high Jp and high d regions. Pulsed current accelerates grain refinement, promoting the transition from low-angle grain boundaries to high-angle grain boundaries through the recovery mechanism. Fine grain sizes increased from 31.7 to 45.5% in the pulsed-current condition compared to the non-current condition. Based on the above discovery, a physical-based constitutive model frame was proposed to characterize the independent evolution and transformation of dislocation density at the grain boundary and interior. Besides, the current density is also coupled into the model as an influence term of the material parameters to capture the influence of electroplasticity on grain refinement. Comparing the test stress to the predictive stress reveals that the model accurately predicts the CAPSC stress of 30CrMnSiA with a correlation coefficient of 0.974 and an average relative error of 4.56%. [ABSTRACT FROM AUTHOR]

To conquer the trade-off between strength and ductility, a new strategy for preparing heterostructured (HS) 2024Al alloys with various heterogeneity levels through introducing submicro-Al3Ti particles and adjusting partial remelting duration of powder thixoforming was proposed. The results indicate that the difference in volume fraction between soft and hard domains of the resultant HS alloys gradually decreases from 0.27 to 0.02, while that of microhardness also decreases from 1.58 to 1.17 GPa, i.e., the heterogeneity level gradually decreases with prolonging the remelting time. The excellent strength–ductility synergy is simultaneously achieved by a moderate heterogeneity level (the differences in microhardness of 1.23 GPa and volume fraction of 0.02) in the HS alloy thixoformed at the partial remelting time of 80 min. This is primarily ascribed to the largest strain gradient caused by the accumulation of the highest density dislocations at the boundary during deformation, which produces the highest heterodeformation-induced (HDI) strengthening and hardening. In addition, the dislocations emitted from the submicro-Al3Tip during the later deformation stage also improve the strain strengthening and hardening, further leading to the improvement in strength–ductility synergy. [ABSTRACT FROM AUTHOR]

The SA508-3 steel has been acknowledged as nuclear-grade steel used to manufacture power plant components owing to its high strength, good toughness, and low sensitivity to irradiation embrittlement. In this study, the dynamic mechanical properties of SA508-3 steel are investigated by the split Hopkinson pressure bar tests with a wide range of strain rates (0.0001–6000 s−1) and elevated temperatures (20–600 °C), and the corresponding flow stress curves are obtained. The results suggested that the dynamic stress–strain response of SA508-3 steel is dependent both on the strain rate and temperature, and the temperature sensitivity (na) is independent of the strain rate. Based on the experimental results, a constitutive model is built by Johnson–Cook (J-C) model to describe the dynamical property of SA508-3 steel, and the flow stresses predicted by the established J-C constitutive model at all the tested strain rates and temperatures are in good agreement with the experimental data. Furthermore, a successful finite element (FE) analysis of the milling process of SA508-3 steel at different cutting parameters is carried out by implementing the established J-C constitutive model into the third-wave-AdvantEdge software, and the predicted cutting forces are agreed well with the experimental results, which provides a strong support for the FE analysis of SA508-3 steel milling process. [ABSTRACT FROM AUTHOR]

Accurate and consistent constitutive model is required to characterize the material behavior in a variety of thermo-mechanical problems. Herein, widely used Johnson–Cook (J–C) model parameters are evaluated for Fe–30Mn–9Al–0.8C low-density steel to predict the flow stress in various forming applications. For this low-density steel prepared in our laboratory, the material compositions are optimally chosen to yield the best ductility (> 70%) with good tensile strength. Tensile tests have been performed at strain rates varying from 10–4 to 10–1 s−1 and at various temperatures such as 150 °C, 300 °C and 450 °C to determine the J–C parameters. Thereafter, genetic algorithm (GA) technique has been used to obtain optimum values of J–C parameters that best fit the experimental stress–strain data. The improved values of the J–C parameter are implemented in ABAQUS explicit software to replicate the experimentally observed tensile test data. It has been observed that the developed constitutive model can produce a fairly accurate and precise estimation of flow stress with a good correlation to experimental data under various strain rates and temperature conditions. [ABSTRACT FROM AUTHOR]

René 65 is a high strength cast & wrought (CW) Ni-base superalloy with thermomechanical performance tailored toward intermediate temperature and stress conditions (677 °C/690 MPa). René 65 Turbine disk rotor forgings are typically subject to a sub-solvus heat treatment utilized to retain a uniform and fine-grained microstructure that confers a high level of fatigue performance and strength at the expense of high-temperature creep resistance. However, the processing of René 65 via laser powder bed fusion (LPBF) can enable this material to exhibit intermediate or coarse-grained microstructures after heat treatment that possess improved creep resistance. The effect of the difference in the processing route in conjunction with heat treatment on the resulting microstructure is presented and correlated to the creep behavior (at 677 °C/690 MPa) and stress relaxation behavior (700 °C). A good correlation of relaxation and creep behaviors was found, with LPBF processed René 65 exhibiting overall improved resistance to high-temperature deformation. The primary factor with regards to microstructural difference toward the stress relaxation/creep behavior of René 65 has been identified to be the size and volume fraction of tertiary γ' present resulting from the chosen processing pathway. [ABSTRACT FROM AUTHOR]

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C. [ABSTRACT FROM AUTHOR]

Grain boundary engineering (GBE) has shown a promising application in improving resistance to intergranular corrosion (IGC) of polycrystalline metallic materials with low-stacking fault energy, such as austenitic stainless steels. However, the traditionally uniform plastic pre-straining methods, such as cold rolling, in thermomechanical processing are hard to implement on complicated surfaces. Here, we demonstrate a novel approach using gradient plastic strain induced by surface mechanical grinding treatment with a rotary tool and subsequent annealing to optimize grain boundary character distribution (GBCD) in the near-surface layer. The gradient plastic strain followed by long-time annealing (24–96 h) in 304 stainless steels achieved an optimized GBCD with over 75% frequency of coincidence site lattice (CSL) boundaries and disconnected random boundary network in the near-surface layer. The intergranular corrosion tests showed that the resulting 304 stainless steels with the optimized GBCD in the near-surface layer present an excellent resistance to IGC behavior due to a high fraction of Σ 3 n boundaries. During the annealing process, severe plastic strain near the surface results in small size grain clusters via strain recrystallization, while low-level plastic strain in the subsurface promotes the formation of high fraction of CSL boundaries and large size grain clusters via strain-induced boundary migration. After the complete depletion of gradient plastic strain, the directional growth of grain clusters promotes the further extension of surface GBE into interior region. Thus, the thickness of surface GBE region can be regulated by the annealing time. [ABSTRACT FROM AUTHOR]

Flexible low-dielectric constant (low-k, k < 4.0) SiCOH films were deposited onto ITO/PEN flexible substrates by plasma-enhanced chemical vapor deposition of tetrakis(trimethylsilyloxy)silane precursor at room temperature with plasma powers from 20 to 100 W. The pristine SiCOH films had a mechanical strength up to 9.1 GPa and a low k-value down to 2.00, and they were transparent, smooth, and hydrophobic. As the plasma power increased, there were an increase in the suboxide structure, increase in density, and decrease in the methyl group concentration. In the lower plasma power regime of 20–60 W, the k-value decreased as the plasma power increased due to the increased suboxide structure. In the higher plasma power regime of 60–100 W, the k-value increased as the plasma power increased due to the decreased methyl concentration and increased density. The mechanical properties increased as the plasma power increased. Upon repeated mechanical bending tests with bending cycles up to 10,000, the flexible SiCOH films maintained their transparency, smoothness, and hydrophobicity and showed a stable k-value below 4.0. There were no significant changes in the FTIR spectra and no cracks or delamination observed in the films. The SiCOH films showed stable physical, chemical, and electrical properties under the repeated mechanical bending. [ABSTRACT FROM AUTHOR]

The resistance to chloride-induced stress corrosion cracking was investigated on a high-strength CrNiMnMoN austenitic stainless steel in the hot-rolled and in different cold-drawn states. The resistance against chloride-induced stress corrosion cracking was determined by slow strain rate tests in different chloride containing solutions at elevated temperatures. A fracture analysis was carried out using scanning electron microscopy. Improved resistance is obtained by the formation of deformation-induced twins. In addition, synchrotron X-ray diffraction measurements show full austenite stability during all cold-drawing steps. [ABSTRACT FROM AUTHOR]

The true triaxial compression test was performed to further investigate the triaxial mechanical properties of coral concrete. Considering three concrete strength grades and nine stress ratios as variables, 100 mm × 100 mm × 100 mm cubic specimens were tested using a servo-controlled static-dynamic triaxial machine (TAWZ-5000/3000). The failure modes, stress–strain curves, peak stress, and peak deformation of coral concrete were obtained from the tests. The results showed that there are plate splitting and slant-shear in the failure modes of coral concrete. The stress and deformation were influenced by the concrete strength and stress ratio. The triaxial strength of coral concrete was significantly improved compared to the corresponding uniaxial strength. With the quadratic regression analysis, a functional relationship between material parameters and uniaxial compressive strength was established, which can accurately predict the meridian criterion of coral concrete for a certain strength grade. Moreover, comparing theoretical and experimental data, the failure criterion proposed by Wang for lightweight aggregate concrete was further verified to be applicable to coral concrete. [ABSTRACT FROM AUTHOR]

Thin sulfonated poly(ether ether ketone) films swell excessively in water. The extent of water-induced swelling is shown to be correlated with the optical anisotropy of the films, due to two distinct phenomena. Firstly, the optical anisotropy is directly related to the amount of water taken up from the surrounding ambient atmosphere, and thus to amount of water present in the material just prior to swelling. Secondly, the optical anisotropy corresponds to internal stresses in the film that affect the free energy of the film, and thus the potential of the film to swell. The anisotropy vanishes upon sorption of liquid water and returns when the water is desorbed. When the water is completely removed, the film changes from more or less colorless to an intense yellow color that can be attributed to molecular assembly of the aromatic rings in the polymer backbone. The color change is reversible and occurs immediately upon exposure to low humidity. For films prepared in the absence of water, the lack of hydration of the sulfonic acid groups affects the microphase separation behavior of the polymer. This is manifested by an apparent lower propensity to water-induced swelling. The possibility to affect the properties of sulfonated polymer films by varying the hydration state of the polymer during preparation can have important implications for applications of such films. [ABSTRACT FROM AUTHOR]

The effect of the evolution of phase transformation strain on the quasi-linear elastic deformation behavior for Nb/Ni50.3Ti49.7 composite was investigated on the basis of the theoretical analysis of martensitic transformation crystallography and in situ synchrotron X-ray diffraction experiment. The calculated and experimental results suggest that during the stress-induced martensitic (SIM) transformation, the B19′ martensitic variants 6 (V6) and 6′ (V6′) survived preferentially among 12 different B19′ martensitic variants due to their maximum phase transformation strains. Additionally, the phase transformation strains for the V6 and V6′ along the < 110 > B2 direction increase nonlinearly as the increase in macroscopic strain during deformation, which is mainly ascribed to the discrepancy in the change rates of the lattice parameters for the B2 parent phase and B19′ martensite. This increase in transformation strains for the V6 and V6′ during deformation is conducive to achieving the high quasi-linear elastic deforming capability (quasi-linear elasticity plus large recoverable strain) in Nb/Ni50.3Ti49.7 composite. [ABSTRACT FROM AUTHOR]

Two B2CO phases (oP8′ with sp2-sp3 hybridization coexist and mP16 with unitary sp3 hybridization) were predicted via structure searching and stability analysis. The study of formation enthalpy reveals that high pressure (HP) technology performed maybe an important method for synthesis. oP8′ and mP16 both have large mechanical modulus and they are typical materials with high hardness. Pressure has a positive correlation with its mechanical modulus. The simulated tensile stress–strain relationship reveals that the maximum stress that oP8′ can bear is 64.7 GPa in the direction [100], and the maximum tensile is 0.24. Among all isoelectronic with diamond (IED) B-C-O phases, oP8′ has the smallest gap and mP16 has the widest gap. With pressure increasing, for B2CO phases with high symmetry and composed of sp3 hybridization, their band gaps all increases monotonically; for B2CO phases composed by sp3-sp2 hybridization coexist or with low symmetry like mP16, their band gaps increased first and then decreased. [ABSTRACT FROM AUTHOR]

The high strain rate dynamic behavior of additively manufactured (AM) 316L stainless steel (SS) is investigated, and a dynamic deformation-induced microstructural evolution is examined in this study. First, the as-built microstructure feature is characterized. The grain morphology is revealed to be location-dependent and driven by the solidification process. A steep rise in the point-to-origin misorientation profile traversing a melt pool boundary is observed, quantitatively describing the influence of process-induced interface on the initial grain orientation state. The static and dynamic mechanical properties are then examined. Compared with conventional wrought 316L SS, AM 316L SS demonstrates an enhanced mechanical strength under quasi-static compression (with a ∼ 95 % increase in yield strength). Under dynamic shearing, strain rate-induced strength enhancement is observed in wrought 316L SS (with a ∼ 47 % increase in dynamic flow stress); AM 316L SS nevertheless demonstrates nearly rate-insensitive responses in its yield stress (with a ∼ 5 % increase in dynamic flow stress). Localized deformation in the form of an adiabatic shear band and the associated structural evolution are analyzed. Radical changes in crystallographic and structural features induced by high strain rate deformation are observed. Grain deformation and rotation lead to a remarkable difference in the grain orientation and spatial direction from the starting state driven by the solidification process. Upon dynamic shearing, the transmission of localized plastic deformation across melt pools is revealed, and the indication in grain rotations is discussed. The change in the geometrically necessary dislocation density is examined, hinting at the competition of the dislocation multiplication and annihilation under localized deformation. The current work enriches the understanding of the dynamic mechanical properties of AM materials at high strain rates. [ABSTRACT FROM AUTHOR]

The effect of the grain size on the mechanical properties of metallic materials has been a topic of significant interest for researchers and industry. For many decades, a relationship defining the mechanical strength proportional to the inverse of the square root of the grain size has been widely accepted despite some reports of deviations from this behavior. Nevertheless, the initial explanations for this relationship, based mainly on the activation of slip systems by dislocation pileups at grain boundaries, have provided essentially no predictive capability. Here, we show that a physically based model for grain boundary sliding predicts, in excellent agreement with experimental data, the flow stress for plastic deformation for a broad range of materials using the fundamental properties of each material over a wide range of grain sizes and testing conditions. This mechanism also successfully predicts the reported enhanced strain rate sensitivity in ultrafine and nanocrystalline materials at different temperatures. [ABSTRACT FROM AUTHOR]

This work proposes a structure which allows characterization of graphene monolayers under combined electric field and mechanical strain modulation. Our approach is based on a cantilever integrated into a two-dimensional graphene-based Field effect transistor (FET). This allows us to change graphene properties either separately or together via two methods. The first way involves electric field induced by the gate. The second is induction of mechanical strain caused by external force pushing the cantilever up or down. We fabricated devices using silicon-on-insulator wafer with practically zero value of residual stress and a high-quality dielectric layer which allowed us to precisely characterize structures using both mentioned stimuli. We used the electric field/strain interplay to control resistivity and position of the charge neutrality point often described as the Dirac point of graphene. Furthermore, values of mechanical stress can be obtained during the preparation of thin films, which enables the cantilever to bend after the structure is released. Our device demonstrates a novel method of tuning the physical properties of graphene in silicon and/or complementary metal-oxide-semiconductor technology and is thus promising for tunable physical or chemical sensors. [ABSTRACT FROM AUTHOR]

In this study, we investigate the temperature-dependent dielectric response of dabcoHBF4 molecular switchable dielectric materials. This compound made of polycrystals has been shaped into pellets under different controlled applied pressures [0.2–1 GPa]. The dielectric analysis carried out on these samples showed that the mechanical stresses induced by this shaping pressure had a significant effect on the value of the dielectric constant in both the ferroelectric and the paraelectric phase. However, the impact of this pressure remains secondary in the AC electrical conductivity, determined for the first time in these compounds. Thus, conductivity values around 2 × 10–7 S/cm in the ferroelectric phase and 2 × 10–6 S/cm in the paraelectric phase were found. The behavior of these compounds over wide frequency ranges [1–1 MHz] and temperature ramps [0.5–10 K/min] revealed that the frequency had no effect on the transition temperature at the difference of temperature rate as expected in most ferroelectric materials. When decreasing the frequency, the dielectric constant gains in value and can reach values higher than 50 in the ferroelectric phase and 1000 in the paraelectric phase with a frequency solicitation at 10 Hz. At lower frequencies, the Curie–Weiss law is lost in the paraelectric regime and an enhanced rise of the dielectric constant with increasing temperature probably reflects an interfacial polarization mechanism. Finally, this dielectric analysis in frequency, temperature (323–403 K) and along temperature ramps allowed to extract analytical laws of behavior associating some of these parameters. For example, one of these equations will be useful in the choice of the temperature ramp to be applied to optimize the switching time between a ferroelectric and a paraelectric state according to a condition on the value of the desired dielectric constant at the low and high states in the implementation of memories. [ABSTRACT FROM AUTHOR]

Bismuth has been proved a promising lead-free element that can mitigate whisker growth on Sn coatings. It is generally believed that the formation of the equiaxed crystal structure of Sn–Bi coating helps to relax the compressive stress uniformly. In this study, the Sn–xBi coatings with the columnar structure were prepared on the Al substrate. The addition of Bi promoted the whisker nucleation on the coatings but effectively mitigated the growth of whiskers. The density of geometrically necessary dislocations increased with the increase in Bi content, resulting in a high whisker density on the coatings. The reason why Bi inhibited whisker growth was proposed from the perspective of creep properties of the Sn–xBi coatings. The solution strengthening of Bi in Sn improved the creep resistance of the coatings. The creep stress exponent measured by nanoindentation indicated that the creep mechanism of the Sn–xBi coatings is dislocation climbing. The improvement of creep resistance led to insufficient dislocations in the coating leading to the limitation of Sn atomic diffusion for whisker growth. [ABSTRACT FROM AUTHOR]

Halloysite nanotubes (HNTs) were widely concerned in the research of electrode materials for supercapacitors because it had many advantages, such as abundant natural reserves, non-toxic, large specific surface area, and so on. The zero-dimensional Fe3O4 nanoparticles loaded onto the surface of one-dimensional HNTs (HNTs-O) could give HNT's excellent electrical properties and improve the specific capacitance. In our previous study, the HNTs were connected into three-dimensional interconnected nano-network (HCAs) by electrostatic interaction. It was found interesting phenomena in load transfer ability and increasing the specific surface area. Based on our previous studies, in this study, HNTs-O was compounded with the three-dimensional HCAs to prepare the composite aerogel (CA-O). The organic–inorganic hybrid aerogels (CA-OP) were prepared by loading conductive polymer polyaniline (PANI) onto the composite aerogel surface to form a two-dimensional PANI. The synergistic effect of inorganic HNTs-O and organic PANI had improved the conductivity and electrical properties of CA-OP. The results of the scanning electron microscope, Fourier transform infrared, N2 adsorption–desorption, stress–strain tests, and so on showed that the composite was successfully prepared and had the acceptable performance in specific surface area and mechanical properties. Cyclic voltammetry, electrochemical impedance spectroscopy, and other electrochemical tests suggested that the organic–inorganic hybrid aerogel had large capacitance and exciting cycle performance. [ABSTRACT FROM AUTHOR]

The small punch test (SPT) was developed for situations where source material is scarce, costly or otherwise difficult to acquire, and has been used for assessing components with variable, location-dependent material properties. Although lacking standardization, the SPT has been employed to assess material properties and verified using traditional testing. Several methods exist for equating SPT results with traditional stress–strain data. There are, however, areas of weakness, such as fracture and fatigue approaches. This document outlines the history and methodologies of SPT, reviewing the body of contemporary literature and presenting relevant findings and formulations for correlating SPT results with conventional tests. Analysis of literature is extended to evaluating the suitability of the SPT for use with additively manufactured (AM) materials. The suitability of this approach is shown through a parametric study using an approximation of the SPT via FEA, varying material properties as would be seen with varying AM process parameters. Equations describing the relationship between SPT results and conventional testing data are presented. Correlation constants dictating these relationships are determined using an accumulation of data from the literature reviewed here, along with novel experimental data. This includes AM materials to assess the fit of these and provide context for a wider view of the methodology and its interest to materials science and additive manufacturing. A case is made for the continued development of the small punch test, identifying strengths and knowledge gaps, showing need for standardization of this simple yet highly versatile method for expediting studies of material properties and optimization. [ABSTRACT FROM AUTHOR]

Thermal effect in absorbing composite is concerned gradually due to electromagnetic environment tends to high power, high frequency and wide bandwidth. Microstructure characteristics and some basic material properties of carbonyl iron powder/silicone rubber (CIP/SR) are obtained by experiments method. Complex permittivity and permeability of CIP/SR composite as an absorbing material is measured by the vector network analyzer. CIP/SR composite with 78 wt% particles filling exhibits excellent absorption performance in C and X band. A numerical model coupled with electromagnetic wave, heat transfer and mechanics theory is presented to study the thermal effect and mechanical damage of absorbing composite under microwave radiation. Microwave heating and attenuation mechanism of CIP/SR composite are discussed. Electric field, temperature, stress and deformation in CIP/SR composite are quantitatively characterized. The results indicate temperature distribution relates to electric polarization and hysteresis loss. Temperature of CIP/SR composite increases by 36 °C as microwave radiation lasts 2 s at 9.37 GHz. Thermal expansion and stress concentration will be aggravated as frequency increases. [ABSTRACT FROM AUTHOR]

The influence of uniaxial and biaxial strains on electronic and transport properties of phosphorene nanoribbons (PNRs) is investigated within the tight-binding Green's function theory by including an iterative procedure. For this purpose, we use tensile and compressive strains and employ the electronic band structure, effective mass and current-voltage curve, to explore the transport mechanism of PNR devices. Our results based on the band structure show that pseudogap in zigzag PNR (zPNR) is tunable under the strains. Hence, the tunneling transmission is controllable between two edge states of zPNRs. Obviously, we observe that the compressive strains can disturb the electron distributions leading to the induced charge polarization in armchair PNRs (aPNR). Also, in some particular cases there is massive-massless Dirac fermion transition in aPNRs. We found that the p-type zPNR devices can be designed under the compressive strains and the n-type aPNR devices can be modulated under the tensile strains. Our results show that the strains can be used as a way to control and improve the negative differential resistance phenomena in zPNRs. In aPNRs the current and threshold voltage under a finite bias can be changed several times with the uniaxial and biaxial strains. Thus, PNRs can be utilized for the development of flexible electronic and field effect transistor nanodevices. [ABSTRACT FROM AUTHOR]

To clarify the mechanism of irreversible dimensional changes due to the hygrothermal treatment of green wood, i.e., the hygrothermal recovery (HTR), the changes in vibrational properties of compression wood and normal wood were measured after hygrothermal treatment at 60 °C, 80 °C, and 100 °C. In addition, the relationship between those changes and HTR strains were discussed. The hygrothermal treatment induced an increase in mechanical loss tangent (tanδ) and decrease in specific dynamic Young’s modulus (E′/ρ). It seems that the changes in vibrational properties due to hygrothermal treatment had a time-temperature dependency: Higher temperatures and longer treatment durations induce larger increases in tanδ and larger decreases in E′/ρ. In contrast to the quenching effect, tanδ and E′/ρ did not recover to their original state even after 60 days of conditioning in water at 20 °C. For compression wood with a large microfibril angle (MFA), there was a clear relationship between the changes in vibrational properties and HTR strains. The tanδ increased and E′/ρ decreased with hygrothermal treatment, corresponding to dimensional changes in the L-direction. This suggests that structural changes in wood components are responsible for HTR. The most likely mechanism for HTR is that the hygrothermal treatment softens the lignin to release locked-in growth stress. Subsequently, irreversible structural changes in lignin induce both the changes in vibrational properties and HTR. For normal wood, because of the small MFA, the structural changes in lignin in the L-direction are possibly restricted by crystalline cellulose. As a result, the relationship between the changes in vibrational properties and HTR is uncertain. [ABSTRACT FROM AUTHOR]

The sensitivity toward mechanical stress of barium titanate-based positive temperature coefficient resistor material was investigated by determining the resistance change with application of uniaxial stress from room temperature to 200 °C, which is well above the Curie temperature TC. Using the Landau-Ginsburg-Devonshire theory the resistance increases in the paraelectric state, the negligible impact of stress close to TC and the observed increase in TC with increasing stress could be rationalized. For the ferroelectric state, the stress-related resistance increase was attributed to ferroelasticity, a change in bulk permittivity and interfacial stress inducing a piezoelectric potential. The obtained results are also discussed with respect to recent endeavors to tune properties of potential barriers in piezoelectric semiconductors by mechanical stress. [ABSTRACT FROM AUTHOR]

Compressional stability is an important mechanical factor that influences the overall performance of a fibre. Assessment of the compressive stability and internal-stress distribution of a fibre must be performed to determine the effect of stress-induced birefringence due to the high deformation gradients in an unstable fibre. The purpose of this study is to combine experimental and finite element investigations of stress evolution and large post-buckling fibre deformations. The results of this study show that stability is greatly influenced by the initial curvature of the fibre. Increasing the deformation of the fibre leads to post-buckling behaviour that results in a fibre taking a complex shape with altered stress-field components. The results are compared with the analytical relation given by Euler’s theory of a thin beam and show that the simple analytical formula cannot predict the complicated post-buckling states and stresses. [ABSTRACT FROM AUTHOR]