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In the present work, residual stresses distribution in the gas nitrided AISI 4140 sample has been studied using finite element (FE) simulation. The nitrogen concentration profile is obtained from the diffusion-controlled compound layer growth model, and nitrogen concentration controls the material volume change through phase transformation and lattice interstitials which results in residual stresses. Such model is validated through residual stress measurement technique-micro-ring-core method, which is applied to the nitriding process to obtain the residual stresses profiles in both the compound and diffusion layer. The numerical and experimental results are in good agreement with each other; they both indicate significant stress variation in the compound layer, which was not captured in previous research works due to the resolution limit of the traditional methods. [ABSTRACT FROM AUTHOR]

The effects of TaON/LaON dual passivation interlayer on the interfacial and electrical properties of Ge metal-oxide-semiconductor (MOS) capacitor with HfO2 gate dielectric are investigated. As compared to its counterpart with only LaON as passivation interlayer, the formation of HfGeOx and LaHfOx, which would degrade the interfacial quality, is effectively suppressed due to the strong blocking role of the TaON barrier layer against Hf diffusion. As a result, excellent interfacial and electrical properties are achieved for the Ge MOS device with the TaON/LaON dual passivation interlayer: high k value (20.9), low interface-state density (5.32×1011cm-2eV-1) and oxide-charge density (-3.90×1012cm-2), low gate leakage current density (1.77×10-4 A/cm² at Vg=Vfb+1 V), and high reliability under high-field stress. [ABSTRACT FROM AUTHOR]

Confining pressure significantly influences the mechanical behavior of soil. Understanding geotechnical problems related to low confining pressures requires precise modeling of soil behavior at low confining stress. Yet laboratory tests, including element tests under low confining pressure, are so far quite limited. In this note, a series of element tests under low confining pressure (5-20 kPa) were carried out to investigate the effect of low confining pressure on the mechanical behavior of loose and medium dense Toyoura sand. Element tests include undrained cyclic loading tests, as well as drained and undrained strain-controlled monotonic loading tests. The results show that loose sand under low confining pressure behaves much like dense sand under higher pressure. Model tests of slope failure flow under microgravity, carried out to supplement the element test results, also confirmed the previously mentioned mechanical behavior. The results obtained in this paper provide a more fundamental understanding of geotechnical problems related to low confining stress. [ABSTRACT FROM AUTHOR]

An extension of Lahellec (2007) incremental variational approach to geomaterials is proposed. By using an implicit time-discretization scheme, the evolution equations describing the small strains constitutive behavior of the phases can be reduced to the minimization of an incremental energy function. This minimization problem is rigorously equivalent to a nonlinear thermoelastic problem with a transformation strain that is a heterogeneous field. The new approach proposed is for Callovo-Oxfordian argillites and considers the specific properties of geomaterials such as compressibility-dilatancy transition and influence of confining pressure. An isotropic, kinematic hardening effect is also considered for the more general cases. The accuracy of the model is assessed by comparison with FE and experimental results. [ABSTRACT FROM AUTHOR]

This study seeks a practical method for simulating the vertical bending fatigue test of the BANJO housing of a five-link rear axle. Linear static and transient dynamic finite element models are constructed for the rear axle in which the rubber bushings and the bearings of the axle shafts are reasonably modeled with solid and shell elements, respectively, for simplicity. The calculated results are compared with the measured strain histories, and the results indicate that the finite element models constructed are reasonable. The hypothesis of equal fatigue damage is applied to determine the Hainan proving ground driving life prediction that is equivalent to the constant amplitude fatigue life in the vertical bending fatigue test. [ABSTRACT FROM AUTHOR]

Evidence on the role of corrosion generated hydrogen in stress corrosion cracking of austenitic stainless steel in marine atmospheric environment is provided. The formation of corrosive solution film on the surface of steel was observed. Hydrogen permeation through the stainless steel membrane was measured. Slow strain rate tests showed that anodic and cathodic polarisations around the free corrosion potential can both increase the elongation. Thermal desorption spectroscopy measurement showed hydrogen concentration increase under cathodic potentials. The hydrogen concentration increase under deformation conditions was also confirmed. However, hydrogen accumulation at the tip of the prenotched specimens was not detected. [ABSTRACT FROM AUTHOR]

The compressive-deformation behavior of the ZrCuNiAl bulk metallic glass (BMG) was investigated over a wide strain-rate range at room temperature. The yield strength of the BMG studied is independent of the strain rates applied upon quasi-static loading; however, it decreases remarkably upon dynamic loading. Serrated flows and shear bands appear at low quasi-static strain rates; nevertheless, they vanish as the strain rate increases to 1.0 × 10 s. Cracks appearing on the side surface of the fractured sample after dynamic compression yield a strain-accommodation deformation mechanism upon dynamic loading. Scanning electron microscopy observations reveal that molten liquids increase on the fractured surfaces with increasing strain rate, indicating that adiabatic heating in the shear bands is enhanced as the strain rate increases. [ABSTRACT FROM AUTHOR]

Abstract: An analysis of the stability of circular cylindrical columns/beams composed of functionally graded materials is made where shear deformation is taken into account. In this study, a new approach is carried out. Different from the assumption of uniform shear stress at the cross-section adopted in the Timoshenko beam theory, proposed model provides a new approach for treating the problem. Based on the traction-free surface condition, two coupled governing equations for the deflection and rotation are derived, and a single governing equation is further obtained. A comparison of buckling loads derived from the proposed circular column model and the Timoshenko and Euler–Bernoulli theories of beams is made. Moreover, the effects of radial gradient on buckling loads of elastic columns with circular cross-section made of functionally graded materials are elucidated. Finally, the stability of double-walled carbon nanotubes is considered and critical stress is determined and compared with existing results. The results obtained by the proposed model show very good agreement with the results of the Timoshenko beam theory or Reddy–Bickford beam theory. [Copyright &y& Elsevier]

Susceptibility to stress corrosion cracking of X56 steel and its relationship with hydrogen permeation behaviour in atmospheric environment containing H2S was investigated by hydrogen permeation tests at a slow strain rate. The results show that: the fracture strain decreases with the decrease of strain rate under the same experimental conditions; the fracture strain also decreases with the increase of H2S concentration under the same strain rate, and the increased concentration of H2S has no significant effect on the hydrogen permeation in the first wet, etc. dry cycle, however has lead to increased hydrogen permeation in the later cycles. The SEM images of the fractured surfaces show clear evidences of enhanced stress corrosion cracking susceptibility by H2S. [ABSTRACT FROM AUTHOR]

Abstract: Current methodologies used for the inference of thin film stress through curvature measurement are strictly restricted to stress and curvature states that are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to a single layer of thin film deposited on a substrate subjected to the non-uniform misfit strain in the thin film. Such methodologies are further extended to multi-layer thin films deposited on a substrate in the present study. Each thin film may have its own non-uniform misfit strain. We derive relations between the stresses in each thin film and the change of system curvatures due to the deposition of each thin film. The interface shear stresses between the adjacent films and between the thin film and the substrate are also obtained from the system curvatures. This provides the basis for the experimental determination of thin film stresses in multi-layer thin films on a substrate. [Copyright &y& Elsevier]

Current methodologies used for the inference of thin film stress through curvature measurements are strictly restricted to uniform film stress and system curvature states over the entire system of a single thin film on a substrate. By considering a circular multilayer thin film/substrate system subjected to nonuniform temperature distributions, we derive relations between the stresses in each film and temperature, and between the system curvatures and temperature. These relations featured a "local" part that involves a direct dependence of the stress or curvature components on the temperature at the same point, and a "nonlocal" part, which reflects the effect of temperature of other points on the location of scrutiny. We also derive relations between the film stresses in each film and the system curvatures, which allow for the experimental inference of such stresses from. full-field curvature measurements in the presence of arbitrary nonuniformities. These relations also feature a "nonlocal" dependence on curvatures making full-field measurements of curvature a necessity for the correct inference of stress. The interfacial shear tractions between the films and between the film and substrate are proportional to the gradient of the first curvature invariant, and can also be inferred experimentally. [ABSTRACT FROM AUTHOR]

Abstract: Nix and Gao established an important relation between the microindentation hardness and indentation depth. It agrees well with the microindentation experiments for the Berkovich indenter. However, it is unclear whether it holds for other indenters with different indenter angles. We use the conventional theory of mechanism-based strain gradient plasticity established from the Taylor dislocation model to study the effect of indenter angles on the microindentation hardness. It is shown that the Nix–Gao relation between the microindentation hardness and indentation depth also holds for other indenter angles. The effect of friction is negligible for relatively flat indenters (e.g. Berkovich indenter), but may be significant for sharp indenters (e.g. cubic indenter). [Copyright &y& Elsevier]

Raman scattering (RS) spectroscopy is a popular measurement technique that uses inelastic scattering of monochromatic light to study vibrational characteristics of a material system. A typical application of RS is for material structure determination. This paper describes the application of RS for the characterization of the preferable growth direction of well-aligned nanocrystals (NCs) deposited on sapphire substrates. The results indicate that RS could become a powerful technique for the quick determination of the NCs orientation. The redshifts and asymmetric linewidth broadening of the Raman features of RuO2 NCs are analysed by a modified spatial correlation (MSC) model, which includes the factor of stress-induced shift. The usefulness of experimental RS together with the MSC model analysis as a nondestructive structural and residual stress characterization technique for NCs has been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: Debonding of particle/matrix interfaces can significantly affect the macroscopic behavior of composite material. We have used a nonlinear cohesive law for particle/matrix interfaces to study interface debonding and its effect on particulate composite materials subject to uniaxial tension. The dilute solution shows that, at a fixed particle volume fraction, small particles lead to hardening behavior of the composite while large particles yield softening behavior. Interface debonding of large particles is unstable since the interface opening (and sliding) displacement(s) may have a sudden jump as the applied strain increases, which is called the catastrophic debonding. A simple estimate is given for the critical particle radius that separates the hardening and softening behavior of the composite. [Copyright &y& Elsevier]

Fiber-reinforced polymer (FRP) composites have found increasingly wide applications in civil engineering due to their high strength-to-weight ratio and high corrosion resistance. One important application of FRP composites is as a confining material for concrete, particularly in the strengthening or seismic retrofit of existing reinforced concrete columns by the provision of a FRP jacket. FRP confinement can enhance both the compressive strength and the ultimate strain of concrete significantly. This paper presents a new stress–strain model for FRP-confined concrete in which the responses of the concrete core and the FRP jacket as well as their interaction are explicitly considered. Such a model is often referred to as an analysis-oriented model. The key novel feature of the proposed analysis-oriented model, compared to existing models of the same kind, is a more accurate and more widely applicable lateral strain equation based on a careful interpretation of the lateral deformation characteristics of unconfined, actively confined, and FRP-confined concrete. Through comparisons with independent test data, the proposed model is shown to be accurate not only for FRP-confined concrete but also for concrete confined with a steel tube, demonstrating the wide applicability of the model to concrete confined with different confining materials. The accuracy of the proposed model is also shown to be superior to existing analysis-oriented stress-strain models through comparisons with test data. [ABSTRACT FROM AUTHOR]

Recent experiments on particle-reinforced metal-matrix composite materials have shown particle size effects. Small particles tend to give larger plastic work hardening than large particles at the same particle volume fraction. Prior models used to study the particle size effect are based on the strain gradient plasticity theories, and these models are mainly axisymmetric models with vanishing lateral stress tractions in order to represent the uniaxial tension condition. However, the prior results fall short to agree with the experimental data. A three-dimensional (3D) unit-cell model is adopted in the present study. The periodic boundary conditions are imposed for the 3D unit cell to ensure the compatibility of the unit cell before and after the deformation. The particles are elastic, while the metal matrix is elastic-plastic and is characterized by the conventional theory of mechanism-based strain gradient plasticity, which is established from the Taylor dislocation model but does not involve the higher-order stress. It is shown that the 3D unit-cell model with the periodic boundary conditions gives better agreements with the experimental data than the unit-cell model with the traction-free boundary conditions on the lateral surfaces. [ABSTRACT FROM AUTHOR]

We reformulate the theory of mechanism-based strain gradient plasticity (MSG) [J. Mech. Phys. Solids 47 1239 (1999); ibid 48 99 (2000); J. Mater. Res. 15 1786 (2000)] that involves the third-order tensor of higher-order stress to a much simpler version within Fleck and Hutchinson's theoretical framework of strain gradient plasticity theory [J. Mech. Phys. Solids 49 2245 (2001)]. Similar to MSG, the new theory is also based on the Taylor dislocation model, but the higher-order stress is a vector (rather than a third-order tensor) and is the work conjugate of the gradient of plastic strain. The intrinsic material length in the new theory is still related to the shear modulus, yield stress and Burgers vector in the same way as in MSG, but the simplicity of the new theory makes it much easier to be implemented in the finite element analysis. We present a few examples that display strong size effects at the micron and submicron scales, including the shear of an infinite layer, torsion of thin wires, bending of thin beams and growth of microvoids. These examples show that this new strain gradient plasticity theory based on the Taylor dislocation model captures the strong size effect. [ABSTRACT FROM AUTHOR]

The Gurson model [J. Engrg. Mater. Technol. 99 (1977) 2] has been widely used to study the deformation and failure of metallic materials containing microvoids. The void volume fraction is the only parameter representing voids since the void size does not come into play in the Gurson model. Based on the Taylor dislocation model [Proc. R. Soc. (Lond.) A145 (1934) 362; J. Int. Metals 62 (1938) 307], we extend the Gurson model to account for the void size effect. It is shown that the yield surfaces for micron- and submicron-sized voids are significantly larger than that given by the Gurson model. For a voided, dilating material subject to uniaxial tension, the void size has essentially no effect on the stress–strain curve at small initial void volume fraction. However, as the initial void volume fraction increases, the void size effect may become significant. [Copyright &y& Elsevier]

In a remarkable series of experiments, Elssner et al. (1994) and Korn et al. (2002) observed cleavage cracking along a bimaterial interface between Nb and sapphire. The stress required for cleavage cracking is around the theoretical strength of the material. Classical plasticity models fall short to reach such a high stress level. We use the conventional theory of mechanism-based strain gradient plasticity (Huang et al., 2004) to investigate the stress field around the tip of an interface crack between Nb and sapphire. The tensile stress at a distance of 0.1 µm to the interface crack tip reaches 13.3δY, where cry is the yield stress of Nb. This stress is nearly 4 times of that predicted by classical plasticity theory (3.6δY) at the same distance to the crack tip, and is high enough to trigger cleavage cracking in materials and interfaces. This is consistent with Elssner et al.'s (1994) and Korn et al.'s (2002) experimental observations. [ABSTRACT FROM AUTHOR]

Texture and microstructure development during hot plane strain compression of Al–6Cu–0.4Zr has been examined using EBSD. Starting with a random texture in the cast condition, the material developed a typical β-fibre texture during the early stages of plane strain compression at a temperature of 375 °C. At strains higher than about 2, the “brass” texture component, {0 1 1} 〈2 1 1〉, began to dominate the texture. The development of such a texture has been observed previously in aluminium alloys, particularly when fine particles effecting Zener pinning of grain boundaries are present. In the present case, measurements indicate that grain boundary migration during deformation was responsible for the development of the strong “brass” texture. [Copyright &y& Elsevier]

Smart-Cut® is a recently established, advanced technology for fabricating high-quality silicon-on-insulator (SOI) systems and has found many other successful applications. It meets almost all the high requirements for processing and manufacturing SOI wafers, which provide the basis of ultra-large-scale integration device structures of modern microelectronic industry. In the present paper, we present a fundamental study on the basic mechanisms in the Smart-Cut technology from the viewpoints of mechanics and physics. First, a model for defect nucleation induced by hydrogen ion implantation is established based on the continuum mechanics theory accounting for the crystal structure of silicon. This model is used to provide an upper bound on the implantation dose of hydrogen ions, one of the most important process parameter in the Smart-Cut technology. An analytical formulation is derived to calculate the defect density as a function of the H-implantation dose and the temperature. Then, the splitting of SOI wafers in the Smart-Cut technology is analyzed using the elastic fracture mechanics theory. Accounting for the embrittlement and diffusion effects of hydrogen, a lower bound of the implantation dose of hydrogen ions is derived, which agrees reasonably with experimental observations. Furthermore, the effects of the handle wafer adopted in the Smart-Cut technique are examined on the splitting process. It is found that the handle wafer leads to uniform crack propagation and higher uniformity in the thickness of the final SOI systems, in comparison with conventional techniques to produce SOI substrates, and prohibits the blistering and flaking failure of an H-implanted wafer. This work provides not only a fundamental understanding to the physical mechanisms associated with the Smart-Cut technology but also a useful reference for determining the process parameters of SOI industrial production. [Copyright &y& Elsevier]

Recent molecular dynamics simulations of dynamic crack propagation have shown that there is a finite crack opening for a shear crack propagating at a sub-Rayleigh speed, but the crack opening becomes significantly smaller once the crack tip velocity exceeds the shear wave speed. To understand this difference between the crack opening for sub-Rayleigh and intersonic shear cracks, we develop in this paper a finite deformation continuum theory incorporating the linear harmonic potential to describe the deformation of a crack in a solid with triangular lattice structure. Using the asymptotic method developed by Knowles [Eng. Fract. Mech. 15 (1981) 469], we show that even after the geometric nonlinearity of finite deformation is accounted for, the intersonic shear cracks have a vanishing crack opening displacement. [Copyright &y& Elsevier]

There exist two frameworks of strain gradient plasticity theories to model size effects observed at the micron and sub-micron scales in experiments. The first framework involves the higher-order stress and therefore requires extra boundary conditions, such as the theory of mechanism-based strain gradient (MSG) plasticity [J Mech Phys Solids 47 (1999) 1239; J Mech Phys Solids 48 (2000) 99; J Mater Res 15 (2000) 1786] established from the Taylor dislocation model. The other framework does not involve the higher-order stress, and the strain gradient effect come into play via the incremental plastic moduli. A conventional theory of mechanism-based strain gradient plasticity is established in this paper. It is also based on the Taylor dislocation model, but it does not involve the higher-order stress and therefore falls into the second strain gradient plasticity framework that preserves the structure of conventional plasticity theories. The plastic strain gradient appears only in the constitutive model, and the equilibrium equations and boundary conditions are the same as the conventional continuum theories. It is shown that the difference between this theory and the higher-order MSG plasticity theory based on the same dislocation model is only significant within a thin boundary layer of the solid. [Copyright &y& Elsevier]

Metallic materials display strong size effect when the characteristic length associated with plastic deformation is on the order of microns. This size effect cannot be explained by classical plasticity theories since their constitutive relations do not have an intrinsic material length. Strain gradient plasticity has been developed to extend continuum plasticity to the micron or submicron regime. One major issue in strain gradient plasticity is the determination of the intrinsic material length that scales with strain gradients, and several microbend test specimens have been designed for this purpose. We have studied different microbend test specimens using the theory of strain gradient plasticity. The pure bending specimen, cantilever beam, and the microbend test specimen developed by Stolken and Evans (Stolken, J.S., Evans, A.G., 1998. A microbend test method for measuring the plasticity length scale Acta Mater. 46, 5109–5115) are found suitable for the determination of intrinsic material length in strain gradient plasticity. However, the double cantilever beam (both ends clamped) is unsuitable since its deformation is dominated by axial stretching. The strain gradient effects significantly increase the bending stiffness of a microbend test specimen. The deflection of a 10-μm thick beam is only a few percent of that estimated by classical plasticity. [Copyright &y& Elsevier]

Deals with a study which discussed the analytical derivation of a fundamental solution for mode-II intersonic shear crack propagation in an infinite solid material in applied mechanics. Details on the fundamental solution derived for the crack propagation; Relation between the crack-tip energy release rate and the stress intensity factor; Conclusions.

Presents information on a study which proposed a systematic approach to derive the governing equations and boundary conditions for strain gradient plasticity in plane-stress deformation. Plane-stress deformation in strain gradient plasticity; Equations for plane stress; Summary.

A mixed variational principle is suggested for electromechanical analysis, in which the displacements, the transverse stresses and the electric potential are taken as the primary variables, and a three-dimensional hybrid element approach is built on the principle. Two kinds of specific element, namely the bimaterial interface element and the surface element, are developed so that the interlayer traction-continuity and surface traction-free conditions of transverse stresses can be imposed exactly. Two numerical examples of intelligent laminates with piezoelectric layers bonded to the upper and lower surfaces are presented to demonstrate the efficiency of the present approach. [ABSTRACT FROM AUTHOR]

Presents an approach to stress analysis for printed circuit boards with highly populated small features. Use of an energy balance framework and a three-phase composite model; Stress components; Variation of in-plane effective modulus of the lumped board with area ratio of solder joints; Effective stress in solder joints.

The effects of stress and depolarization on current–voltage characteristics of ferroelectric field-effect transistor (FeFET) were investigated by Landau–Khalatnikov theory in conjunction with Pao and Sah's model. Output characteristics current increases under compressive stress but decreases under tensile stress. Transfer characteristics curve is enlarged by compressive stress but compressed by tensile stress, and it shifts to the negative voltage axis under compressive stress gradient while to the opposite direction under tensile stress gradient. Because of depolarization, output characteristics current is obviously affected, and transfer characteristics curve is seriously distorted. These results show that stress and depolarization should be considered in device design to prevent failure of FeFET. [ABSTRACT FROM PUBLISHER]

By reducing the testing temperatures down to the temperature well below the glassy transition temperature, the serrated flow behaviour during plastic deformation of a Zr-based metallic glass was experimentally investigated and the results were presented in Part I of the present paper. It shows that the yield strength, the plastic deformation ability, the density of shear bands of the metallic glass increase with decreasing temperature. In order to understand the mechanisms for the changes of the mechanical behaviour at low temperatures, in Part II of this study, the stress-time sequence in the plastic strain regime is characterized by a comprehensive dynamical and statistical analysis. The stress-time sequence is found to exhibit a chaotic state at high temperatures (>203 K), whereas a self-organized critical state is obtained at low temperatures (≤203 K) due to the freezing effect. The reasons for the transition between these two distinct spatio-temporal dynamical states are elucidated by investigating the effect of temperature on the deformation units (shear transformation zones) and the elastic interactions between neighbouring shear bands. The results demonstrate that the low temperatures results in an enhancement of the interactions between the elastic strain fields initiated by neighbouring shear bands, which is primarily responsible for the enhanced plasticity of the metallic glass and a dynamics transition. [ABSTRACT FROM AUTHOR]

One important aspect of stretchable electronics design is to shield the active devices from strains through insertion of a soft layer between devices and substrate. An analytical model is established, which gives linear dependence of strain isolation on the reciprocal of strain-isolation layer thickness, and the reciprocal of device and substrate stiffness. Strain isolation is also linearly proportional to the shear modulus of strain-isolation layer and square of device length. [ABSTRACT FROM AUTHOR]

Prior continuum models of van der Waals force between carbon nanotube walls assume that the pressures be either the same on the walls or inversely proportional to wall radius. A new continuum model is obtained analytically from the Lennard-Jones potential for van der Waals force, without the above assumptions. Buckling of a double-wall carbon nanotube under external pressure is studied, and the critical buckling pressure is much smaller than those models involving the above assumptions. [ABSTRACT FROM AUTHOR]

The discrete dislocation model is used in this note to investigate the source-limited dislocation generation and glide in nanoindentation. It is shown that once there are enough sources for dislocation generation, the material behavior becomes independent of the dislocation source distribution. [ABSTRACT FROM AUTHOR]

Proposes an alternative decomposition of the strain gradient tensor in order to ensure that the deviatoric strain gradient vanishes for an arbitrary volumetric strain field. Discussion on the Elastic-Plastic theory of mechanism-based strain gradient plasticity; Crack-tip singularity in mechanism-based strain gradient plasticity; Method used to investigate the crack-tip field.

Abstract: Nix and Gio [Nix, W.D., Gao, H.J., 1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. Journal of the Mechanics and Physics of Solids 46, 411–425] established an important relation between the micro-indentation hardness and indentation depth for axisymmetric indenters. For the Berkovich indenter, however, this relation requires an equivalent cone angle. Qin et al. [Qin, J., Huang, Y., Xiao, J., Hwang, K.C., 2009. The equivalence of axisymmetric indentation model for three-dimensional indentation hardness. Journal of Materials Research 24, 776–783] showed that the widely used equivalent cone angle from the criterion of equal base area leads to significant errors in micro-indentation, and proposed a new equivalence of equal cone angle for iridium. It is shown in this paper that this new equivalence holds for a wide range of plastic work hardening materials. In addition, the prior equal-base-area criterion does not hold because the Berkovich indenter gives much higher density of geometrically necessary dislocations than axisymmetric indenter. The equivalence of equal cone angle, however, does not hold for Vickers indenter. [Copyright &y& Elsevier]

Abstract: The effect of superimposed hydrostatic pressure on fracture in round bars under tension is studied numerically using the finite element method based on the Gurson damage model. It is demonstrated that while the superimposed hydrostatic pressure has no noticeable effect on necking, it increases the fracture strain due to the fact that a superimposed pressure delays or completely eliminates the nucleation, growth and coalescence of microvoids or microcracks. The experimentally observed transition of the fracture surface, from the cup-cone mode under atmospheric pressure to a slant structure under high pressure, is numerically reproduced. It is numerically proved that the superimposed hydrostatic pressure has no effect on necking for a damage-free round bar under tension. [Copyright &y& Elsevier]

Abstract: The stress distribution outside the contact-induced plastic zone can be estimated by the superposition of a Hertzian field and the field for an embedded center of dilatation (ECD) in a half-space, while the residual stress distribution can be estimated by the ECD field alone. This model has a simple closed-form analytical expression, matching with finite element results nearly perfectly. [Copyright &y& Elsevier]

Abstract: Two continuum mechanical models of crystal plasticity theory namely, conventional crystal plasticity theory and mechanism-based crystal plasticity theory, are used to perform a comparative study of stresses that are reached at and ahead of the crack tip of a bicrystal niobium/alumina specimen. Finite element analyses are done for a stationary crack tip and growing cracks using a cohesive modelling approach. Using mechanism-based strain gradient crystal plasticity theory the stresses reached ahead of the crack tip are found to be two times larger than the stresses obtained from conventional crystal plasticity theory. Results also show that strain gradient effects strongly depend on the intrinsic material length to the size of plastic zone ratio (l/R 0). It is found that the larger the (l/R 0) ratio, the higher the stresses reached using mechanism-based strain gradient crystal plasticity theory. An insight into the role of cohesive strength and work of adhesion in macroscopic fracture is also presented which can be used by experimentalists to design better bimaterials by varying cohesive strength and work of adhesion. [Copyright &y& Elsevier]

When deformed beyond their elastic limits, crystalline solids flow plastically via particle rearrangements localized around structural defects. Disordered solids also flow, but without obvious structural defects. We link structure to plasticity in disordered solids via a microscopic structural quantity, “softness,” designed by machine learning to be maximally predictive of rearrangements. Experimental results and computations enabled us to measure the spatial correlations and strain response of softness, as well as two measures of plasticity: the size of rearrangements and the yield strain. All four quantities maintained remarkable commonality in their values for disordered packings of objects ranging from atoms to grains, spanning seven orders of magnitude in diameter and 13 orders of magnitude in elastic modulus. These commonalities link the spatial correlations and strain response of softness to rearrangement size and yield strain, respectively. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the influence of the precipitate distribution on the microstructure and on the room and high temperature mechanical properties of an age-hardenable aluminium AA6082 alloy following severe straining by high-pressure torsion (HPT). With this goal, specimens in the as-cast and T6 peak-aged conditions were processed by HPT using 0.5, 1 and 5 turns at room temperature. At high strain levels (γ>100), similar saturation grain sizes (~250 nm), high-angle boundary fractions (~80%) and hardness values (Hv~160) were obtained for both initial conditions. Grain refinement led to significant strengthening and to good ductility values at room temperature. Analysis by TEM and EDS elemental mapping revealed that HPT processing of the as-cast condition led to fracture of the stable β-phase into many small precipitates located preferentially along grain boundaries and triple junctions. By contrast, HPT processing of the T6 peak-aged specimens revealed a partial dissolution of the needle-shaped nanoprecipitates. The different evolutions of the precipitate distributions following straining in the as-cast and peak-aged conditions gave rise to dramatic differences in the mechanical properties and the operative deformation mechanisms at warm temperatures. These results provide evidence that the high temperature mechanical behavior of age-hardenable Al alloys may be conveniently controlled by altering the precipitate distribution followed by severe straining. [ABSTRACT FROM AUTHOR]

Abstract: MgZnO/MgO strained multiple-quantum-wells (S-MQWs) with different structures are grown by pulsed laser deposition. The S-MQW films are composed of closely arranged, vertically oriented nanocolumns. Z-contrast scanning transmission electron microscopy observations and line-scan compositional analysis reveal that the nanocolumns are compositionally modulated along their length and have a MQW structure. A coherent epitaxial relationship with a sharp interface is established between MgZnO and MgO layers with large lattice mismatch. It is worth noting that the MgZnO layer undergoes a structural transition from hexagonal to cubic phase with its thickness decreasing. The calculations reveal that a large in-plane compressive stress dominates such an interesting phase transition process, stabilizes the low Mg-content MgZnO alloy in the anomalous cubic phase, and also leads to a broadening of the band gap. As a result, the wavelength-tunable deep-ultraviolet emission in the range of 261–314nm is obtained from these S-MQW nanocolumnar films. The 261nm is known to be the shortest emission wavelength ever reported for MgZnO material. [Copyright &y& Elsevier]

Abstract: An overview on microstructural and electronic properties of stoichiometric microcrystalline silicon carbide (μc-SiC) prepared by Hot-Wire Chemical Vapor Deposition (HWCVD) at low substrate temperatures will be given. The electronic properties are strongly dependent on crystalline phase, local bonding, strain, defects, impurities, etc. Therefore these quantities need to be carefully investigated in order to evaluate their influence and to develop strategies for material improvement. We will particularly address the validity of different experimental methods like Raman spectroscopy and IR spectroscopy to provide information on the crystalline volume fraction by comparing the results with Transmission Electron Microscopy (TEM) and X-Ray diffraction data. Finally the electronic properties as derived from optical absorption and transport measurements will be related to the microstructure. [Copyright &y& Elsevier]

Abstract: A batch of constitutive models for steel reinforcing bar, prestressing tendon, concrete and fiber-reinforced plastic are proposed for the nonlinear finite element analysis of reinforced concrete structures, prestressed concrete structures, reinforced concrete structures strengthened by fiber-reinforced plastics and prestressed concrete structures strengthened by fiber-reinforced plastics. These material models have been tested against series of experimental data and good agreements have been obtained, which justifies the validity and the usefulness of the proposed nonlinear constitutive models. [Copyright &y& Elsevier]

Based on the finite-deformation shell theory for carbon nanotubes established from the interatomic potential in Part I of this paper, we have studied the instability of carbon nanotubes subjected to different loadings (tension, compression, internal and external pressures, and torsion). Similar to the conventional shells, carbon nanotubes may undergo bifurcation under compression/torsion/external pressure. Our analysis, however shows that carbon nanotubes may also undergo bifurcation in tension and internal pressure, though the bifurcation modes for tension and compression are very different, and so are the modes for the internal and external pressures. The critical load for instability and bifurcation depends on the interatomic potential used. [ABSTRACT FROM AUTHOR]