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Instrumented Taylor anvil-on-rod impact tests have been conducted on oxygen-free electronic copper to validate the accuracy of current strength models for predicting transient states during dynamic deformation events. The experiments coupled the use of high-speed digital photography to record the transient deformation states and laser interferometry to monitor the sample back (free surface) velocity as a measure of the elastic/plastic wave propagation through the sample length. Numerical continuum dynamics simulations of the impact and plastic wave propagation employing the Johnson-Cook [Proceedings of the Seventh International Symposium on Ballistics, 1983, The Netherlands (Am. Def. Prep. Assoc. (ADPA)), pp. 541–547], Zerilli-Armstrong [J. Appl. Phys. C1, 1816 (1987)], and Steinberg-Guinan [J. Appl. Phys. 51, 1498 (1980)] constitutive equations were used to generate transient deformation profiles and the free surface velocity traces. While these simulations showed good correlation with the measured free surface velocity traces and the final deformed sample shape, varying degrees of deviations were observed between the photographed and calculated specimen profiles at intermediate deformation states. The results illustrate the usefulness of the instrumented Taylor anvil-on-rod impact technique for validating constitutive equations that can describe the path-dependent deformation response and can therefore predict the transient and final deformation states. [ABSTRACT FROM AUTHOR]

In this work, we study the influence of capillary forces in combination with electrostatic and quantum vacuum generated forces on the pull-in voltage of microswitches having self-affine rough surfaces. This type of roughness is described by the rms roughness amplitude w, the in-plane correlation length ξ, and the roughness exponent H that quantifies the degree of surface irregularity at short length scales (<ξ). It is shown that an attractive capillary force decreases more the effective pull-in voltage when the plate surfaces are rougher. The latter corresponds to smaller roughness exponents H and/or larger long wavelength roughness ratios w/ξ. Notably, the capillary contribution increases the sensitivity of the effective pull-in voltage on the roughness exponent H. This behavior takes place for values of H close to its experimental accuracy. [ABSTRACT FROM AUTHOR]

A study of the interaction between a membrane and a submerged oscillating bubble is presented. Though the behavior of such a bubble near an elastic (relatively thick) boundary has been studied by several authors, much less attention is focused on the behavior of such a bubble near a (thin) elastic membrane. For membranes, it is the curvature and not the deflection that is responsible for a pressure buildup in the fluid close to the bubble. Due to this difference in physics, it is not a certainty if the dynamics of bubbles near a deformable elastic boundary vis-a-vis a membrane would exhibit any similarity. Our intent is a systematic study on the latter, which can be exploited in future work (e.g., in biomedical applications where elastic membranes are often involved). Experimental observations of transient bubble interaction with a thin elastic membrane are presented and the dynamics of the bubble in the vicinity of the membrane are compared to the boundary element method simulations. The bubble is generated using a very low voltage (only 55 V) in contrast to the relatively much higher voltages usually employed in reported works. This is very attractive from a safety viewpoint and accords great simplification of the setup. The comparisons show that the interaction between the transient bubble and the membrane induces a perturbation on the bubble surface that strengthens the bubble contraction and can lead to mushroom shape, bubble elongation, and bubble splitting. The influence of the two main parameters, namely, the distance between the bubble and the membrane and the elasticity of the membrane, are also discussed. [ABSTRACT FROM AUTHOR]

In this work, thermal transport in nanocrystalline materials is studied using large-scale equilibrium molecular dynamics simulation. Nanocrystalline materials with different grain sizes are studied to explore how and to what extent the size of nanograins affects the thermal conductivity and specific heat. Substantial thermal conductivity reduction is observed and the reduction is stronger for nanocrystalline materials with smaller grains. On the other hand, the specific heat of nanocrystalline materials shows little change with the grain size. Based on the calculated thermal conductivity, the thermal resistance at grain boundaries is calculated and found to be in the order of 10-9 m2 K/W. The simulation results are compared with the thermal transport in freestanding nanograins based on molecular dynamics simulation. Further discussions are provided to explain the fundamental physics behind the observed thermal phenomena in this work. [ABSTRACT FROM AUTHOR]

To examine pressure relationships in a mixed phase assemblage, we performed room temperature/high pressure radial x-ray diffraction measurements on a controlled-geometry bimaterial composite consisting of oriented Al2O3 fibers embedded in an aluminum matrix. Lattice strains of each material were measured as a function of orientation with respect to the fiber alignment, as a function of orientation with respect to the major principal stress axis of the diamond cell, and as a function of pressure of up to 15 GPa. The results show that Al and Al2O3 both support differential stresses, with Al supporting between -0.06(45) and 0.32(65) GPa and Al2O3 supporting between 1.4(3) and 4.9(9) GPa. The hydrostatic pressures determined from the average lattice strains of Al and Al2O3 are not in general equal, with the pressure of Al2O3 higher than that of Al by an average of 0.5(4) GPa throughout the measured range. The geometric relationship between the composite material and the principal stress axis of the diamond cell plays a role in establishing both the absolute and relative strain responses of the composite sample. A comparison of the two composite geometries under the same diamond cell compression shows that when the fibers are oriented vertically along the diamond cell axis, the differential stress supported by Al2O3 is 3.1(5) GPa, at a pressure of 9.35(42) GPa. The corresponding values for Al are much lower: 0.09(18) GPa (differential stress) and 8.67(04) GPa (hydrostatic pressure). When the fibers are oriented horizontally along the radial direction, the pressure supported by Al and Al2O3 is more similar: 9.63(15) vs 9.48(35) GPa. The differential stress supported by both materials is higher: 0.32(65) for Al and 4.9(9) for Al2O3. Understanding the strength and elastic behavior of an intermixed phase assemblage is vital for the interpretation of mineral behavior at high pressures and temperatures. Many in situ measurements of high pressure mineral phase stability and elasticity are performed using intermixed phases—the unknown and a reference marker. Measurement of properties relies on the assumptions that the reference material has an accurate and well-calibrated equation of state and that the pressures of the two materials are identical in the high pressure sample chamber. This latter assumption is clearly violated in our experiments. Therefore, it is important to account for potential pressure effects due to sample geometry when making in situ x-ray measurements of equations of state and phase transformations. [ABSTRACT FROM AUTHOR]

The neoclassical model for nematic elastomers, which displays soft elasticity, predicts striping in stretched sheets. Thus the experimental observation of striped domains has been suggested as evidence for soft elasticity. Here we show that the postulated director rotations and shears in the domain regions are also predicted by more general constitutive models that do not involve any notion of softness. Striping in nematic elastomers may therefore be a more general phenomenon that is not necessarily an indication of soft elasticity. Furthermore, constitutive models more general than the neoclassical model may also explain the behavior of some nematic elastomers that do not appear to exhibit striping. [ABSTRACT FROM AUTHOR]

A model based on the Burgers viscoelastic concept has been developed to describe the nanoindentation behaviors of polymeric materials. An analytical solution of displacement at the indenter tip has been derived based on the analog of the governing equation of elasticity in the time coordinate system to the governing equation of the viscoelastic model in Laplace transform coordinate system. The solution consists of the elastic, viscous, and plastic displacements during loading and unloading. Nanoindentation experiments have been conducted for poly(methyl methacrylate), polycarbonate, hydroxyethyl methacrylate copolymer, amorphous syndiotactic polystyrene, and fast-cure acrylic polymers to provide data for validating the model. The results show excellent agreement between experimental load-displacement data and model prediction for both the loading and unloading before the contact area decreases for all five polymers. The viscosity decreases but the hardness increases with increasing loading rate. Young’s moduli of the interior material obtained by the present study are close to those reported in the literature. Additional analysis showed that the prediction by both the Kelvin and Maxwell viscoelastic models does not agree with the experimental data generated in this study. [ABSTRACT FROM AUTHOR]

The magnetomechanical damping capacity of the giant magnetostrictive Tb0.36Dy0.64(Fe1-xTx)2 (x=0, 0.05, 0.10; T=Mn or Co) alloys has been calculated from quasistatic strain-stress hysteresis loops at room temperature. Stress ranges from 0 to 10, 20, 30, and 50 MPa were used in a series of applied fields between 0 and 3250 Oe. The largest damping capacities were obtained at zero field with values of 1.14 for Tb0.36Dy0.64Fe2, 1.62 for Tb0.36Dy0.64(Fe0.95Mn0.05)2, and 1.84 for Tb0.36Dy0.64(Fe0.90Co0.10)2, respectively. In low fields, the damping capacity ΔW/W decreases drastically with the applied stress and magnetic field. However, in higher fields, ΔW/W decreases slightly with the magnetic field but only increases slightly with the applied stress. The results show that both Mn and Co as substitutes for Fe are beneficial for obtaining higher damping capacity. [ABSTRACT FROM AUTHOR]

We have modified the Landau-Khalatnikov approach and shown that both the polar lattice and the screened charged defects determine the response of disordered ferroelectric semiconductors. This system exhibits the spatially inhomogeneous switching under the external field while the Landau-Khalatnikov model describes homogeneous switching with the sharp pyroelectric coefficient peak near the thermodynamic coercive field value. Our model gives more realistic pyroelectric hysteresis loop shape without any peaks near the coercive field and describes both qualitatively and quantitatively typical Pb(Zr,Ti)O3 and (Sr,Ba)Nb2O6 films pyroelectric hysteresis loops. [ABSTRACT FROM AUTHOR]

A survey of the elastic, mechanical, fragility, and thermodynamic properties of bulk metallic glasses (BMGs) and glass-forming liquids is presented. It is found that the elastic moduli of BMGs have correlations with the glass transition temperature, melting temperature, mechanical properties, and even liquid fragility. On the other hand, the elastic constants of available BMGs show a rough correlation with a weighted average of the elastic constants for the constituent elements. Although the theoretical and physical reasons for the correlations are to be clarified, these correlations could assist in understanding the long-standing issues of glass formation and the nature of glass and simulate the work of theorists. Based on the correlation, we show that the elastic moduli can assist in selecting alloying components for controlling the elastic properties and glass-forming ability of the BMGs and thus can guide BMG design. As case study, we report the formation of the families of rare-earth-based BMGs with controllable properties. [ABSTRACT FROM AUTHOR]

We present a model to study Young’s modulus and Poisson’s ratio of the composite material of amorphous nanowires. It is an extension of the model derived by two of us [da Fonseca and Galvão, Phys. Rev. Lett. 92, 175502 (2004)] to study the elastic properties of amorphous nanosprings. The model is based on twisting and tensioning a straight nanowire and we propose an experimental setup to obtain the elastic parameters of the nanowire. We used the Kirchhoff rod model to obtain the expressions for the elastic constants of the nanowire. [ABSTRACT FROM AUTHOR]

In this paper, a nonlocal Bernoulli-Euler beam model is established based on the theory of nonlocal elasticity. Frequency equations and modal shape functions of beam structures with some typical boundary conditions are derived based on the model. The corresponding dynamic properties are presented and discussed in detail, which are shown to be very different from those predicted by classic elasticity theory when nonlocal effects are significant. The results can be applied to modeling and characterization of size-dependent mechanical properties of micro- or nanoelectromechanical system (MEMS or NEMS) devices. [ABSTRACT FROM AUTHOR]

A ferroelectric crystal is known to exhibit the usual single hysteresis below its Curie point TC, but above this temperature its electric displacement D versus electric field E plot tends to form double loops. We first point out that there is a fundamental difference in the formation of double loops from the single one: the single loop is formed solely by polar reorientation, but in the double loops the right branch of its upper loop is formed by phase transition and only the left branch is formed by polar reorientation (the process is reversed for the lower loop). In this study we take the view that both cubic→tetragonal phase transition and the polar reorientation of ferroelectric domain are thermodynamics-driving process and use this concept to develop a micromechanics-based thermodynamic model to simulate the double hysteresis behavior of the crystal. We first derive the thermodynamic driving force for both spontaneous polarization and domain switch at a given level of temperature, stress, electric field, and new domain concentration c1 and then establish the kinetic equations for domain growth. A dual-phase homogenization theory is then introduced to calculate the overall electric displacement and mechanical strain of the crystal. This approach differs from the classical Landau-Ginzburg-Devonshire theory in at least two significant aspects: (i) it is developed with a micromechanics-based thermodynamics principle, and (ii) it can provide the evolution of new domain concentration. The developed theory is applied to a BaTiO3 crystal. The calculated results show a single loop below its TC and double loops above it but with a diminishing width at higher temperature. Furthermore, the longitudinal strain [variant_greek_epsilon] vs E loop is found to exhibit the usual butterfly-shape relation below TC, but above it the loop shows a new, overlapping double-well picture. Good agreement with available test data is also observed. [ABSTRACT FROM AUTHOR]

The glass-forming ability of Fe-based metallic glasses has a direct relationship with their metalloid content. A good glass-former usually needs a metalloid content of approximately 20 at. %. However, a high metalloid content causes deterioration not only in magnetic properties but also in elasticity and plasticity. Based on destabilization of the solid state we have developed a series of metalloid-free Fe-based metallic glasses of composition (Fe0.582Co0.418)100-x-yCrxZry (10<=x<=28 and 8<=y<=11). Via this destabilization the liquid state is stabilized, which results in a decreasing liquidus temperature. The mechanical and magnetic properties of the metalloid-free Fe-based metallic glass with the highest Fe and Co fractions were analyzed. The alloy of composition (Fe0.582Co0.418)80Cr10Zr10 exhibits bending elasticity and plasticity. Magnetization measurements reveal a saturation magnetization of up to 1.1 T and an inverted hysteresis. The origin of this inverted hysteresis presumably lies in the inclination to decompose in a ferromagnetic iron-rich α1 phase and an antiferromagnetic chromium-rich α2 phase. [ABSTRACT FROM AUTHOR]

Comparisons between adhesion hysteresis and friction at nanometer and micrometer length scales were investigated experimentally and theoretically. Nanoscale adhesion hysteresis was measured using the ultrasonic force microscopy (UFM) on mica, calcite, and a few metallic samples (Pt, Au, Cu, Zn, Ti, and Fe). Obtained adhesion hysteresis ranged between 4×10-19 and 4×10-18 J. At the microscale a similar setup with a nanoindenter was used and the same samples were investigated. Adhesion hysteresis measured at the microscale ranged between 8×10-17 and 14×10-17 J. Friction was investigated via lateral force microscopy, as well as by scratch tests done with the nanoindenter. Numerical simulations based on the UFM model as well as established theories of contact mechanics studied qualitative dependencies of adhesion hysteresis on experimental parameters. Quantitative relations between adhesion hysteresis and friction were obtained through an analytic model relying on elastic and adhesive properties of the contact. The model agreed with measurements and simulations. [ABSTRACT FROM AUTHOR]

We demonstrate that changes in electrolyte composition and applied potential during aqueous electrodeposition can be used to tune the magnetic hysteresis response of thin-film Fe3O4 (magnetite) on polycrystalline metal substrates. X-ray diffraction data confirmed that magnetite formation in electrolytes containing KCH3COO (0.04–2.0 M) and Fe(SO4)2(NH4)2 (0.01M) required temperatures between 60 and 85 °C, and deposition potentials between -0.300 and -0.575 V or galvanostatic current densities between 50 and 88 μA/cm2. Scanning electron microscopy studies show that magnetite crystallites tend to adopt different habits depending on the electrolyte composition. Room-temperature magnetic hysteresis responses (squareness and coercivity) are dependent upon the crystal habit of deposits, implying that the electrolyte’s acetate concentration influences the magnetic domain structure of the resulting magnetite deposits. Magnetite crystallites grown from electrolytes with low acetate concentrations showed pseudo-single-domain magnetic response, while magnetite grown from acetate-enriched electrolytes showed multidomain magnetic response. [ABSTRACT FROM AUTHOR]

The paper studies surface instability of a bilayer elastic film interacting with another flat rigid body through surface van der Waals forces under plane-strain conditions. The analysis is based on an approximate model which reduces the two-dimensional plane-strain problem of the bilayer elastic film to a one-dimensional problem on its surface. The critical value of the interaction coefficient for surface instability and the associated instability mode can be determined easily by identifying the minimum of the interaction coefficient as a function of the wavelength of the instability mode. Among others, the present analysis shows that a stiff bottom layer of a bilayer film can be approximately treated as a rigid substrate only when the surface compliance ratio of the top layer to the bottom layer exceeds a certain critical value. In contrast to a common assumption that nonequal Poisson ratios of the two layers have a minor effect, it is found that different Poisson ratio combinations could have a significant effect on the surface instability of a bilayer elastic film even when the thickness ratio and modulus ratio keep unchanged. In particular, the present study confirms that, unlike a single-layer elastic film which has only one instability mode, a bilayer elastic film can have two distinct surface instability modes when the top layer is more compliant and much thinner than the bottom layer. [ABSTRACT FROM AUTHOR]

The exchange-spring behavior found in Sm–Co (20 nm)/Fe epitaxial bilayer films was investigated by analyzing major hysteresis and recoil curves as a function of anneal conditions. The hard layer consists of nanocrystalline intermetallic Sm–Co hexagonal phases (majority phase Sm2Co7 with SmCo3 and SmCo5). Recoil curves, obtained from the successive removal to remanence and reapplication of an increasingly negative field from the major demagnetization curve, reveal the reversible and irreversible components of the magnetization. The Sm–Co thickness was fixed at 20 nm while the Fe thicknesses of 10 and 20 nm were studied, with ex situ annealing carried out in evacuated, sealed silica tubes at different temperatures. The peak in the recoil curve area is associated with the coercivity of the hard phase. The development of the soft component magnetization is revealed by the departure of the recoil area from zero with application of a reverse field. These two features together confirm that annealing stabilizes the 10 nm Fe bilayer sample against local magnetic reversal while it weakens the 20 nm bilayer sample. Furthermore, in both its as-deposited and annealed states the Sm–Co/Fe bilayer of 10 nm Fe thickness always displays a higher exchange field and smaller recoil loop areas than the bilayer of 20 nm Fe thickness, consistent with a stronger exchange response and more reversible magnetization in the former. [ABSTRACT FROM AUTHOR]

We have investigated an experimentally moderate bending of multiwalled carbon nanotubes (MWNTs) in the perpendicular direction from flat substrates. The tubes were in the diameter range of 3–13 nm and deposited over lithographically fabricated gold lines whose height determined the total bending. In our model for the bending profile we take into account the van der Waals attraction between the substrate and the MWNT and the opposing elastic bending force. With reasonable parameters for the competing forces we obtain an agreement between the model and the experimental data for the critical distance between two adjacent lines when the van der Waals attraction can no longer prevent elastic forces from straightening the tube to a suspended position between the lines. However, for the smallest nanotubes a simple classical model is clearly insufficient. [ABSTRACT FROM AUTHOR]

The elastic response of a [001]-oriented and -poled ferroelectric rhombohedral lead zinc niobate-lead titanate single crystal close to the morphotropic phase region is examined under thermal, electrical, and mechanical boundaries similar to those used in sound projectors. Resonance measurements yielded a monotonically decreasing Young’s modulus as a function of temperature in the ferroelectric rhombohedral state with a sudden stiffening near the ferroelectric rhombohedral (FR)-ferroelectric tetragonal (FT) transition. The quasistatic, zero-field stress-strain response revealed a FR instability under uniaxial compression. A dc bias field stabilized the FR state under compressive stress. Young’s modulus derived from the linear elastic response below instability agrees well with resonance data for FR. A larger modulus than expected for FT was observed above instabilities. The elastic response is analyzed in terms of ferroelectric-ferroelectric transitions as predicted by a high-order Devonshire theory. Implications for sound projectors are discussed. [ABSTRACT FROM AUTHOR]

Coplanar high-resolution x-ray diffraction has been used for the characterization of size, chemical composition, and strain of Ge/Si (001) islands in a three-dimensional island crystal grown using self-assembly on a prepatterned (001) Si substrate. The measured diffusely scattered intensity is simulated using the kinematical approximation and the parameters of model islands are fitted. These simulations require calculations of the strain fields within the islands and the spacer layers. For this purpose, an analytical approach to solve the continuum elasticity equations has been extended to a full three-dimensional calculation. The Ge content in the islands is found to be on the average 40%, and the island shape does not change dramatically during capping. [ABSTRACT FROM AUTHOR]

The microscopic superelastic behavior of thin-film NiTi is investigated by instrumented indentation experiments conducted at different temperatures. The indentation-induced superelastic effect is found to be persistent to about 100 K above the austenite transformation finish temperature (Af). In contrast, the upper temperature where superelastic effect exists is only around Af plus 40 K in uniaxial tension and compression tests, beyond which the plasticity of the austenite phase overwhelms the transformation-induced superelasticity. By combining the Clausius-Clapeyron equation and spherical cavity model for indentation, we show that the high hydrostatic pressure under the indenter is capable of elevating the transformation temperatures and increase the upper temperature limit of indentation-induced superelastic behavior. [ABSTRACT FROM AUTHOR]

Energy-dispersive powder diffraction as a function of pressure has been used to search for elastic interactions between CuCl nanocrystals embedded in NaCl and sample surfaces. Anomalous properties have been observed only for (200) reflexes of the NaCl matrix although crystallographic structure and imposed pressure are essentially isotropic. The material shows an initial compressive strain of S(200)=-0.002 which is large compared with the low concentration of CuCl but small compared with the accuracy achieved in a high-pressure apparatus. It was necessary to identify the influences of grain morphology, sample preparation, deformation of the sample cell, uniaxial pressure component, and nonlinear elasticity to obtain reliable results. The initial strain is accompanied by an elastic hardening of NaCl. The appearance of both effects is traced back to the influence of sample surfaces. This interpretation is verified by exciton spectroscopy studied in a thin optical plate. A comparison between experimental results and elastic continuum theory demonstrates that the theory describes correctly the observed phenomena but predicts effects which are significantly smaller than the measured values. The mechanisms which are able to amplify the impact of nanocrystals on the matrix are discussed. [ABSTRACT FROM AUTHOR]

Heteroepitaxial thin-film features that are lattice matched to the underlying substrate undergo elastic relaxation at the free edges of the feature. To characterize the degree of elastic relaxation, we employed synchrotron-based x-ray diffraction techniques to map the change in lattice spacing in the thin film at a submicron resolution. Measurements were conducted on 0.24-μm thick, heteroepitaxially grown SiGe strips of various widths on Si (001). A comparison of the SiGe diffraction peak positions across the features provides a real-space mapping of the extent of elastic relaxation as a function of linewidth. The resultant in-plane normal film stress measurements were compared to calculated values from several elastic mechanical models to assess their validity in predicting stress distributions within the features. [ABSTRACT FROM AUTHOR]

The hardness of nanocomposite (nc) films developed recently appears to reach the hardness of diamond. High hardness is commonly attributed to the granular structure of nanocomposites (Hall–Petch effect) [E. O. Hall, Proc. Phys. Soc. Lond. B 64, 747 (1951); N. J. Petch, J. Iron Steel Inst. 174, 25 (1953)]. However, grain size in nanocomposites is generally small (5–15 nm) and falls in the region where the Hall–Petch effect does not apply. The objective of the present study is to report the elastic properties of the superhard nanocomposites determined by means of surface Brillouin scattering (SBS), and to compare the results with those obtained by nanoindentation. Two types of nanocomposite films were studied: nc-TiN/a-Si3N4 and nc-TiN/a-BN. The SBS measurements presented yield values of Young’s modulus significantly larger than those obtained from the slope of unloading indentation curve. This discrepancy is attributed to the lack of the validity of the assumptions behind the Sneddon’s derivation of the formula used for the calculation of the Young’s modulus from the indentation data. [ABSTRACT FROM AUTHOR]

Here we present derivations of the force-displacement relationship for a rigid spherical inclusion embedded in homogeneous, isotropic, linear solids. Formulas are given for both the case of perfect interfacial bonding (no slip) and the case of a sliding contact (slip) between the medium and the inclusion. The formulas are applicable to both compressible and incompressible solids and are applicable for elastic media of finite extent. The results allow the determination of the elastic modulus of the medium from force-displacement measurements on the inclusion provided Poisson’s ratio is known. We find that, when the size of the medium is much larger than that of the inclusion, the inclusion displacement in response to an applied force is 50% larger when slip is present. [ABSTRACT FROM AUTHOR]

The plastic deformation of nanoporous Au under compressive stress was studied by depth-sensing nanoindentation combined with scanning electron microscope characterization. The nanoporous Au investigated in the current study exhibits a relative density of 42%, and a spongelike morphology of interconnecting ligaments on a length scale of ∼100 nm. The material is polycrystalline with a grain size on the order of 10–60 nm. Microstructural characterization of residual indentation impressions reveals a localized densification via ductile (plastic) deformation under compressive stress and demonstrates the ductile behavior of Au ligaments. A mean hardness of 145(±11) MPa and a Young’s modulus of 11.1(±0.9) GPa was obtained from the analysis of the load-displacement curves. The hardness of investigated np-Au is ∼10 times higher than the hardness predicted by scaling laws of open-cell foams thus potentially opening a door to a class of high yield strength—low-density materials. [ABSTRACT FROM AUTHOR]

A method is presented to describe the behavior of an oscillating bubble in a fluid near a second elastic (biological) fluid. The elasticity of the second fluid is modeled through a pressure term at the interface between the two fluids. The Laplace equation is assumed to be valid in each of the fluids, and a difference in the respective densities is allowed. A relationship between the two velocity potentials just above and below the fluid-fluid interface can be found. The boundary integral method is then used to solve for the unknown normal velocities at both the bubble interface and fluid-fluid interface. These said normal velocities are subsequently utilized to update the position of the interface(s) for the next time step. For bubbles oscillating near a second nonelastic fluid, the bubbles can develop a jet towards or away from the fluid-fluid interface (depending on the distance of the bubble from the fluid-fluid interface and the density ratios of the two fluids). This behavior can be greatly modified when the second fluid possesses some elastic properties. The elasticity causes a small perturbation to travel along the surface of the bubble. A complex interaction between this growing perturbation and the bubble in its collapse phase can lead to the bubble assuming a “mushroom” shape and/or even breakup into two smaller bubbles. These phenomena have not been observed when the elasticity is absent in the second fluid. Excellent agreement with experimental data was obtained for a wide range of parameters. [ABSTRACT FROM AUTHOR]

A well-known result due to Hill provides an exact expression for the bulk modulus of any multicomponent elastic composite whenever the constituents are isotropic and the shear modulus is uniform throughout. Although no precise analog of Hill’s result is available for the opposite case of uniform bulk modulus and varying shear modulus, it is shown here that some similar statements can be made for shear behavior of random polycrystals composed of laminates of isotropic materials. In particular, the Hashin-Shtrikman-type bounds of Peselnick, Meister, and Watt for random polycrystals composed of hexagonal (transversely isotropic) grains are applied to the problem of polycrystals of laminates. An exact product formula relating the Reuss estimate of bulk modulus and an effective shear modulus (of laminated grains composing the system) to products of the eigenvalues for quasicompressional and quasiuniaxial shear eigenvectors also plays an important role in the analysis of the overall shear behavior of the random polycrystal. When the bulk modulus is uniform in such a system, the equations are shown to reduce to a simple form that depends prominently on the uniaxial shear eigenvalue—as expected from physical arguments concerning the importance of uniaxial shear in these systems. Applications of the analytical results presented here include benchmarking of numerical procedures used for studying elastic behavior of complex composites, and estimating coefficients needed in upscaled equations for elasticity and/or poroelasticity of heterogeneous systems. [ABSTRACT FROM AUTHOR]

This paper presents a model describing the hysteresis in ferroelectric materials at moderate to high driving levels. Hysteresis and nonlinearities are attributed to the irreversible displacement of domain walls. The model, based on a simple mechanism related to the dry-friction concept, is developed to describe the hysteresis of polarization and strain under electric field and stress. Besides coefficients such as [variant_greek_epsilon]33 and d33 also exhibit large hysteresis loops under high electric and/or mechanic level. In this paper it is shown that modeling macroscopic quantities such as P or S hysteresis lead to a reasonable estimate of the coefficients since their behavior depends mainly on polarization. The proposed approach is developed, discussed, and compared with experimental results from Navy II piezoelectric transducer ceramic. Comparisons on hysteresis loops are given and are in good agreement for the polarization and strain versus electric field and, to a less extent, for the coefficients [variant_greek_epsilon]33 and d33. The linear and Rayleigh regime are deduced from the proposed approach. [ABSTRACT FROM AUTHOR]

We report a method—resonant-ultrasound microscopy—for measuring elastic-constant distribution over a solid’s surface. Applying an oscillating electric field to a rectangular-parallelepiped oscillator of langasite (La3Ga5SiO14) crystal by a surrounding solenoid coil, we generated and detected vibrations of the crystal without electrodes and without wires. Acoustic coupling of the specimen to the oscillator is only made at an antinodal vibration point on the crystal’s bottom surface. The crystal’s resonance-frequency shift reflects elastic constants of the specimen in the contacting area. Point-contact measurement permits sensitive, quantitative evaluation of a material’s local elastic constants. As an illustrating example, we measured the elastic-stiffness distribution of a Nb–Ti/Cu resin superconductive wire. We compared our measurements with both static-contact and dynamic-contact models. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A solute atmosphere forms around a dislocation at temperatures where the diffusion of solute atoms is comparable to or faster than the dislocation motion. The dynamic interactions between diffusive solutes and moving dislocations were studied using a phase-field model which takes into account both the chemical interactions in the solid solution and the elastic interactions among solutes and dislocations. The average velocity of dislocations as a function of solute concentration, solute mobility, dislocation mobility, and applied stresses was investigated. The dragging stress of a solute atmosphere and the solute flow around a moving dislocation are presented and analyzed. Some features of dynamic interactions between a single dislocation and its solute atmosphere are observed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The explosive molecular crystal cyclotetramethylene tetranitramine was studied in three orientations in a set of plate impact experiments; the orientations studied were {110}, {011}, and {010} in P21/n space group. The elastic–plastic shock response was measured using laser interferometry. The measured particle velocity profiles showed elastic precursor decay typical of a stress relaxing material. There is anisotropy in elastic shock strength and decay. The amount of precursor decay with propagation distance and stress relaxation behind the elastic shock varied among the orientations. The {010} orientation had larger elastic precursors than did the other two orientations; the {010} crystal does not have the regular plastic deformation mechanisms available to it. Elastic Hugoniots were obtained from the measurements. The inelastic deformation mechanisms may vary with orientation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Total and transport elastic scattering cross sections for positrons impinging on solid targets have been computed for energies in the range 10–10 000 eV. The phase shifts have been calculated by numerically solving the Schrödinger equation. The results have been discussed and compared where possible with other tabulations. Special attention has been given to the effect of the correlation potential. The latter was found to have much effect on the total elastic scattering cross sections while its effect on transport elastic scattering cross sections is more important when the positron energy is lowered. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The factors that control the stress–strain state of a polycrystal under differential stress depend on whether or not plastic deformation has occurred in the solid. If not, then the elastic properties with the constraints of the Reuss–Voigt bounds limit this relationship. If plastic deformation becomes important then the Taylor and Sachs models are relevant. These models assume that the plastic process is enabled by dislocation flow on specific lattice planes and specific Burger’s vectors. Then, the relationship between stress and strain is controlled by the orientation of an individual grain with respect to the stress field, von Mises criterion, and the critical resolved stress on the dislocation that is necessary for flow. We use a self-consistent model to predict the flow stress during the plastic deformation of polycrystalline MgO with a slip system of {110}<110>, {111}<110>, and {100}<011> at different critical resolved shear stress ratios for the different slip systems. The prediction of the models is correlated with the results of x-ray diffraction measurements. Uniaxial deformation experiments on polycrystalline and single-crystal MgO samples were conducted in situ using white x-ray diffraction with a multielement detector and multianvil high-pressure apparatus at a pressure up to 6 GPa and a temperature of 500 °C. A deformation DIA was used to generate pressure and control at a constant deformation rate. Elastic strains and plastic strains were monitored using x-ray diffraction spectra and x-ray imaging techniques, respectively. The correlation of the data and models suggests that the plastic models need to be used to describe the stress–strain observations with the presence of plasticity, while the Reuss and Voigt models are appropriate for the elastic region of deformation, before the onset of plastic deformation. The similarity of elastic strains among different lattice planes suggests that the {111} slip system is the most significant slip system in MgO at high pressure and high temperature. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Resonant-ultrasound microscopy evaluates local Young’s modulus of materials by the resonant-frequency shift of a vibrating oscillator. This study presents a dynamic-contact model to analyze free vibrations of an isotropic elastic-sphere oscillator contacting two semi-infinite viscoelastic solids, which sandwich the sphere. Assuming frictionless contacts and smaller vibrational amplitude, dynamic-contact pressure distributions are obtained with the linearized maximum contact pressure and contact radius. Combining the sphere oscillation and the solid motions through contact-displacement boundary conditions, resonant frequencies of the elastic sphere are obtained. Unlike the quasistatic model, this dynamic model agrees well with the measurements. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have measured the mechanical resonance of microscale quartz fibers to qualify the method of obtaining the Young’s modulus of nanowires from their resonance frequency and geometry. An equation for a circular beam with a linearly varying cross-section is derived and used to calculate the resonance frequency shift. We have established a model to discuss the boundary condition effect on the resonance frequency. The Young’s modulus of the quartz fibers has been determined by measuring the resonance frequency, and the geometry, and by applying the model that treats the influence of the type of clamp. The mean value from measurements of the fundamental resonance on 14 different microfibers is 70±6 GPa. This mean value is close to 72 GPa, the Young’s modulus of bulk fused quartz. Four resonance modes were observed in high vacuum and air. The mechanical resonance in high vacuum is linear at the fundamental vibration mode, and nonlinear for higher modes. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of surface energy on the effective elastic properties was analyzed for elastic composite materials containing spherical nanocavities at dilute concentration. Closed-form solutions of the effective shear modulus and bulk modulus were obtained, which turn out to be a function of the surface energy and size of the nanocavity. The dependence of the elastic response on size of the nanocavity in composite materials is different from the classic results obtained in the linear elasticity theory, suggesting the importance of the surface energy of the nanocavity in analyzing the deformation of nanoscale structures. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Periodic deformation arising as parallel stripes in super-twisted nematic displays are studied numerically. The role played by a surface tilt angle δ in their appearance and structure is determined. It is found that the stripes exist in a narrow voltage range between two thresholds. The lower threshold at which they arise is practically independent of the tilt angle. The higher threshold at which the homogeneous deformation occurs decreases with δ. For relatively small twist angles (e.g., 180°) the transition to the homogeneously deformed structure is continuous. If the twist angle is high (e.g., 270°) this transition becomes discontinuous. The stripes are eliminated if the tilt angle exceeds some critical value which increases with the twist angle and may be larger than 30°. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article presents studies on nanoindentation creep for polymeric materials at room temperature. A semi-empirical method has been established from a generalized Kelvin model. This model includes the elastic-viscoelastic-viscous effects on indentation creep. It is shown that this method can fit the experimental creep data well, to give the exact changes of creep behavior during nanoindentations for numbers of amorphous polymeric materials. A method has also been proposed to determine the elastic modulus based on this model; the elastic modulus determined from this method is independent of the holding and unloading processes of nanoindentations. Creep deformation is further used to derive creep compliance and retardation spectrums for the polymeric materials studied, which are very useful to predict other mechanical properties of polymeric materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Brillouin light scattering has been used to investigate elastic properties of a monocrystalline and of <111> textured polycrystalline 3C polytype silicon carbide films that have been deposited on silicon substrate by chemical vapor deposition. Taking advantage from the detection of different acoustic modes, a complete elastic characterization of the films has been achieved. The three unknown elastic constants of the monocrystalline 3C-SiC, namely, c[sub 11]=395 GPa, (c[sub 11]-c[sub 12])/2=136 GPa, and c[sub 44]=236 GPa have been selectively determined, respectively, from the frequency of the longitudinal and of the shear horizontal bulk modes traveling parallelly to the film surface. These determinations are in agreement with the frequency of the observed Rayleigh surface mode, of the pseudosurface mode, and of the bulk waves propagating at different angles from the normal of the single crystal film plane and consistent with existing theoretical calculations of β-SiC elastic constants. Finally, the calculated Voigt average values of the effective elastic constants for the <111> textured 3C-SiC polycrystalline film using the single crystal constants provides a good agreement with our experimental results (C[sub 11]=500 GPa, C[sub 33]=535 GPa, C[sub 44]=165 GPa, C[sub 66]=210 GPa, and C[sub 13]=50 GPa) and compare fairly well with the α-SiC published one. These results confirm that the elastic constants of silicon carbide are slightly influenced by the polytypism. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Defect profile induced by implantation of Li[sup +] ions with an energy of 175 keV and a fluence of 1×10[sup 17] ions/cm[sup 2] in MgO single crystals was characterized by Rutherford backscattering and optical absorption measurements. Several absorption bands at 5.0, 3.49, 2.16, and 1.27 eV, identical to those found in neutron irradiated crystals, were observed and have been previously associated with oxygen vacancies and higher-order point defects involving oxygen vacancies. Despite the high fluence of Li[sup +] ions, no evidence was found for the formation of Li nanocolloids during implantation. Nanoindentation experiments demonstrated that both the hardness and Young’s modulus were higher in the implanted layer than in the sample before implantation. The maximum values were H=(17.4±0.4) and E=(358±9) GPa, respectively, at a contact depth of ≈165 nm. Thermal annealings in flowing argon at increasing temperatures improved the crystalline quality of the implanted layer. After annealing at 500 K, two extinction bands at ≈2.75 and 3.80 eV emerged. These bands are attributed to Mie scattering from metallic lithium nanocolloids with either a face-centered- or a body-centered-cubic structure. The latter band was almost absent by 950 K. The former reached a maximum intensity after the thermal treatment at 1050 K and disappeared by 1250 K. The behavior of these bands can be satisfactorily explained by the Maxwell–Garnett theory. The decrease in hardening cannot be correlated with the thermal destruction of the absorption bands at 5.0, 3.49, 2.16, and 1.27 eV, but rather with the annihilation of both lithium and oxygen interstitials. Lithium outdiffusion from the implanted region takes place at temperatures of ≈1100 K. It is concluded that the hardening observed in the implanted region was primarily due to the extraordinarily large concentration of both lithium and oxygen interstitials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated how ambient humidity can affect quantitative measurements of elastic properties on the nanoscale. Using an emerging technique called atomic force acoustic microscopy (AFAM), two samples were examined: a thin film of fluorosilicate glass and a section of borosilicate glass. When experimental results were analyzed using a simple model of the atomic force microscope cantilever dynamics, values of the tip–sample contact stiffness k[sup *] increased approximately linearly with relative humidity. The effect is believed to be due to the presence of a humidity-dependent layer of water on the sample. To account for this, the data analysis model was extended to include viscoelastic damping between the tip and the sample. A damping term proportional to the relative humidity was used. The revised values for k[sup *] showed virtually no dependence on humidity. Thus, the subsequent calculations of the indentation modulus M from k[sup *] yielded similar values regardless of measurement humidity. These results indicate that environmental conditions can influence quantitative nanoscale measurements of elastic properties, at least in some materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ultrasonic methods were used to measure the room-temperature elastic moduli of polycrystalline LaSn[sub x]Ni[sub 5-x] compounds for 0<=x<=0.5. These materials are of great importance for their hydrogen storage properties. The samples, prepared by a hot isostatic pressing method, had near-theoretical densities with calculated porosities ranging from 0 to 1.5%. The porosity-corrected moduli decreased with increasing x. Poisson’s ratio was approximately constant at 0.314 for all the compounds. The Debye temperature, calculated from the RT polycrystalline moduli, decreased from 359 to 344 K as x increased from 0 to 0.5. The results were used to calculate the elastic interaction energy of an interstitial hydrogen atom with the strain fields of all the other interstitial hydrogen. This energy was in turn used to calculate the critical temperature below which phase separation occurs in LaM[sub x]Ni[sub 5-x]H[sub y] compounds (M=Sn or Al). It was found that the critical temperature decreases with increasing x, confirming in a more general way a conclusion drawn for a specific case from earlier thermodynamic measurements. It is suggested that the lowering of the critical temperature plays a role in limiting the width of the plateaus in pressure-composition isotherms for the two-phase regions of these compounds. This suggestion implies a relation between the elastic properties and the maximum hydrogen capacity. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A mechanics-based model is developed to examine the effects of clamping during wafer bonding processes. The model provides closed-form expressions that relate the initial geometry and elastic properties of the wafers to the final shape of the bonded pair and the strain energy release rate at the interface for two different clamping configurations. The results demonstrate that the curvature of bonded pairs may be controlled through the use of specific clamping arrangements during the bonding process. Furthermore, it is demonstrated that the strain energy release rate depends on the clamping configuration and that using applied loads usually leads to an undesirable increase in the strain energy release rate. The results are discussed in detail and implications for process development and bonding tool design are highlighted. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A model, based on the theory of nonlocal continuum mechanics, on the column buckling of multiwalled carbon nanotubes is presented. The present analysis considers that each of the nested concentric tubes is an individual column and that the deflection of all the columns is coupled together through the van der Waals interactions between adjacent tubes. Based on this description, a condition is derived in terms of the parameters that describe the van der Waals forces and the small internal length scale effects. In particular, an explicit expression is derived for the critical axial strain of a double walled carbon nanotube which clearly demonstrates that small scale effects contribute significantly to the mechanical behavior of multiwalled carbon nanotubes and cannot be ignored. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Active elasticity control has recently become a promising method used in acoustics to suppress the vibration of mechanical systems or to increase the noise transmission loss. The principle of this technique is based on the simultaneous utilization of both the direct and inverse piezoelectric effects, which is realized by connecting the piezoelectric sample to an external feed back circuit. The action of the feedback circuit results in an essential change of the vibrational response of the system, and a significant change of the resonant frequency in the mechanical system. This leads to the modification of the acoustic properties of the system. For that reason, this technique offers a very general approach to solve vibration and noise problems. To demonstrate this method, the design and theoretical analysis of an experimental realization of a sound absorbing system are presented. The system consists of a curved piezoelectric membrane and a passive sound absorber, which are attached to a rigid backing wall. The theoretical analysis of the system starts from the calculation of the absorption coefficient of an audible sound. This result is used for the determination of the optimal adjustment in the feedback control electronics. The efficiency and the frequency range of the active sound absorption, as well as aspects of the generalization of this method to solve other kinds of noise and vibration problem are discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article studies elastic anisotropy of chemical vapor deposition (CVD) polycrystalline diamond films using acoustic spectroscopy and micromechanics modeling. CVD diamond films often exhibit elastic anisotropy between the film-growth direction and in-plane direction and show five independent elastic constants. They are denoted by C[sub 11], C[sub 33], C[sub 13], C[sub 44], and C[sub 66] when the x[sub 3] axis lies along the film-growth direction. Measurements of thickness resonance frequencies and free-vibration resonance frequencies of the diamond film deduce four independent elastic constants among them, including C[sub 44] and C[sub 66], with which the elastic anisotropy is discussed. The anisotropy between the shear moduli is 5%–10%. The elastic constants are remarkably smaller than those of an isotropic polycrystalline diamond. We attribute the anisotropy and small elastic constants of the CVD diamond film to local incomplete cohesion. This view is supported by a micromechanics calculation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electromagnetic-resonance-ultrasound microscopy was applied to visualize Young’s-modulus distribution in SCS-6 SiC fiber/Ti-6Al-4V composite. Resonance of a piezoelectric langasite (La[sub 3]Ga[sub 5]SiO[sub 14]) crystal is excited and detected by a surrounding solenoid coil without any contact between them. Point contact with the specimen causes a shift in resonance frequency of the order of 10[sup -4], depending on the local elastic stiffness of the contacting material. Two-dimensional stepping on the specimen surface provides the image of Young’s-modulus distribution. Calibration measurements based on contact theory allow determination of Young’s moduli of the carbon core (150 GPa), SiC sheaths (180–505 GPa), and Ti-6Al-4V matrix (90 GPa). The radial variation of Young’s modulus depicts the concentric multi-phase layers in an SCS-6 fiber. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The models currently used to determine strains, stresses, and deflections in beams and plates made of magnetostrictive films deposited on nonmagnetic substrates are based on the assumption that the film is relatively thin compared to the substrate. Despite the lack of self-consistency and the limitations of these models, they can be used to calculate approximate strains and deflections when the ratio of the thickness of the film to the thickness of the substrate is smaller than about 0.001; even then they do not consistently predict stresses or energies. Unfortunately, the large deflections required in modern applications are only achievable with films that do not satisfy this assumption of relative film thinness, and the results obtained with the traditional models show large errors. In these circumstances it is necessary to introduce robust methods that can be applied regardless of the relative magnitude of the thickness of the film. In this article, one such method is presented. The method represents a self-consistent approach based on the minimization of the total internal energy of a film-substrate system, performed based on the assumption that the magnetostrictive strains can be modeled as anisotropic expansional strains. The expressions obtained using this approach can be used to calculate strains, stresses, deflections, and energies in an accurate way. The method is suitable for generalization to the cases in which the deformation of beams and plates is produced not only due to magnetostriction in the films, but may also include thermal, piezoelectric, or hygroscopic strains. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]