Surface Elastic Properties Research Articles

Surface and size-dependent effects on the free vibration analysis of cylindrical shell based on Gurtin-Murdoch and nonlocal strain gradient theories

This paper investigates the free vibration analysis of a cylindrical shell based on first-order shear deformation theory (FSDT) and nonlocal strain gradient theory (NSGT). For the first time, the surface effects are taken into account for the proposed model. For this purpose, governing equations of motion are derived using Hamilton's principle and Gurtin-Murdoch surface elasticity model. Then, governing equations and corresponding boundary conditions are discretized by the generalized differential quadrature method and frequency responses are obtained. In the results section, differences between the obtained natural frequencies with and without considering the surface effects are reported to show their influence on results. Furthermore, the effects of each surface properties including surface elastic properties, residual surface stress, and surface mass density are investigated in different values of size-dependent parameters.

Near-surface Shear Velocity Structure Estimation using Ground-roll in Moran Area, Central Upper Assam Basin, India

Abstract The frequency dependent characteristics of Rayleigh-wave, which is considered to be noise during body-wave prospecting, can be utilized to infer near surface elastic properties. To generate the near surface VS profiles, initially spectral analysis of surface waves (SASW) was used, which has now been replaced by more sophisticated multi-channel analysis of surface waves (MASW). In the present study, MASW for impulsive source is applied to the seismic (impulsive source) datasets acquired in the Moran area of the central part of upper Assam basin to estimate the near-surface S-wave velocity (Vs) structure with the objective of its application to static correction during S-wave reflection data processing, and geotechnical and environmental studies in the area. Multichannel surface waves are extracted from conventional seismic record. The multichannel analysis includes construction of dispersion curves from observed Rayleigh-waves, and inversion of VS profile from calculated dispersion curves. The near surface 1D VS profiles, derived from the extracted ground roll vary from 200 m/sec (near the surface) to about 450 m/sec at 40m depth, and provides a good estimation of vertical shear velocity structure in the area. The 2D near surface shear velocity structure (VS) is generated by horizontal interpolation of individual vertical profiles. The results are in agreement with the available three component low velocity layer (3C-LVL) data.

Hierarchically Patterned Elastomeric and Thermoplastic Polymer Films through Nanoimprinting and Ultraviolet Light Exposure.

The surface relief structure of polymer films over large areas can be controlled by combining nanoscale imprinting and microscale ultraviolet–ozone (UVO) radiation, resulting in hierarchical structured surfaces. First, nanoscale patterns were formed by nanoimprinting elastomer [poly(dimethylsiloxane) (PDMS)] films with a pattern on a digital video disk. Micron-scale patterns were then superimposed on the nanoimprinted PDMS films by exposing them to ultraviolet radiation in oxygen (UVO) through a transmission electron microscopy grid mask having variable microscale patterning. UVO exposure leads to conversion and densification of PDMS to SiOx, leading to micron height relief features that follow a linear scaling relation with pattern dimension. Further, the pattern scopes are shown to collapse into a master curve by normalized feature values. Interestingly, these relief structures preserve the nanoscale features. In this paper, the influence of the self-limiting PDMS densification, wall stress at the boundary of micro-depression, and UVO exposure energy is studied in control of the micro-depression scale. This simple two-step imprinting process involving both nanoimprinting and UV radiation allows for facile fabrication of the dimension adjustable micro–nano hierarchically structures not only on elastomer films but also on thermoplastic polymer films. Coarse-grained molecular dynamics simulations were performed to correlate the surface tension and elastic properties of polymeric materials to the deformation of the pattern structure.

Influence of Surfactant Concentration and Temperature Gradients on Spreading of Crude-Oil at Sea*

Spreading kinetics measurements were carried out on crude oils at natural surfactant-containing sea water of well-controlled thermo elastic surface properties in laboratory conditions. It was found that oil lens expansion rates, predicted from the classical surface tension-driven spreading theory, were higher by a factor of 6-9 than those experimentally derived for natural seawater. Previously, in order to explain such a discrepancy, the initial spreading coefficient S0 - entering the lens radius vs time dependence was exchanged with the temporal one St dependent on the water phase surface viscoelasticity of (Boniewicz and Pogorzelski, 2008). Now, natural surfactant concentration and temperature gradients perpendicular to the surface were shown to drive a particular cell-like flow at the surface microlayer, as a result of the classic and thermal Marangoni phenomenon. The balance of interfacial forces was taken as: -µ∂Us/∂z=∂γ/∂T•∂T/∂x+∂γ/∂c•∂c/∂x where: µ is the dynamic viscosity, Us - the velocity, z and x axes oriented perpendicularly and horizontally to the main flow direction, T, γ, c are the temperature, surface tension and concentration of surfactants. Computations performed on original seawater (Baltic Sea) systems, shown that the natural surfactant concentration term ∂γ/∂c is several times lower than the thermal ∂γ/∂T one (Boniewicz and Pogorzelski, 2016). Such a surface tension gradients induce the Benard-Marangoni instability, for high enough the so-called Marangoni numbers that could significantly slow down the spreading process. On the basis of thermo-physical model liquids properties, the critical temperature difference ∆Tc required to initiate the process under an evaporative cooling condition was evaluated.

Wide range control in the elastic properties of PDMS polymer by ion beam (H+) irradiation

The effects of ion irradiation on the elastic and surface properties, nanostructure and the chemical changes of the widely used polydimethylsiloxane (PDMS) polymer were investigated as a function of the ion fluence, induced by high-energy ionizing radiation (2.0 MeV proton beam). The polymer was irradiated with different fluences of protons and then the chemical changes, the elastic modulus and surface roughness were investigated by infrared spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM). The FT-IR measurements showed very significant chemical changes in the material upon proton irradiation, such as detachment of methyl side groups first, then the starting of the main chain scissions, until the major silicatization of the PDMS by the formation of an inorganic silica like final product (SiOx). The AFM force curves were obtained by performing contact-mode point-spectroscopy. Their evaluation showed, that the surface elastic properties of PDMS can be controlled in the range of 240 MPa to 49 GPa (Young's modulus) with ion fluencies between 1.68 × 1013 ions/cm2 to 1.25 × 1016 ions/cm2, respectively. Compared to the 3–4 MPa of the reference material this indicates a more than four orders of magnitude increase in the elastic modulus of the material. The accompanying changes in the nanostructure of the polymer were characterized with AFM topography measurements and are also discussed in detail.

Improvements in Mechanical Properties of Spring Steel Through Surface Tempering and Hardening Assisted by SMAT

In this paper, the microstructural, mechanical properties of hardened and tempered spring steel altered by surface mechanical attrition treatment (SMAT) were investigated. The effect of SMAT on surface microstructure, phase constituents, hardness, elastic and plastic properties of the surface: Young’s Modulus, stiffness, YS, UTS were analyzed. The SMAT was carried out for different time periods such as 15, 30, 45, 60 and 75 min respectively. SMAT introduced severe plastic deformation (SPD) over the surface with case depth of about 200–300 µm. The SEM microstructure revealed the presence of tempered lath martensite in as received samples while SMAT had resulted in the formation of twinned martensite at SPD regions. Further, it was also found that fine carbides (Fe3C) started to precipitate and led to the formation of alternate layers of tempered martensite and Fe3C indicating stress relaxation/tempering by SMAT. The X-ray and EDX results also confirmed the presence of martensite in as received samples and precipitation of carbides by SMAT. However, in contrast to a thermal tempering, the surface hardness was found to be increasing due to the effects of SPD. The SMAT had altered the mechanical properties of the steel significantly. The stiffness of the leaf spring was 1452 and 2032 N mm−1 respectively for the samples before and after 15 min of SMAT. This could be attributed to the resistance to elastic deformation caused by surface composite layer. It was also interesting to note that the toughness of the hardened and tempered spring steel increased from 242.45 × 104 to 337.12 × 104 J m−3 by 75 min of SMAT.

Atomic force acoustic microscopy: Influence of the lateral contact stiffness on the elastic measurements

Atomic force acoustic microscopy is a dynamic technique where the resonances of a cantilever, that has its tip in contact with the sample, are used to quantify local elastic properties of surfaces. Since the contact resonance frequencies (CRFs) monotonically increase with the tip-sample contact stiffness, they are used to evaluate the local elastic properties of the surfaces through a suitable contact mechanical model. The CRFs depends on both, normal and lateral contact stiffness, kN and kS respectively, where the last one is taken either as constant (kS<1), or as zero, leading to uncertainty in the estimation of the elastic properties of composite materials. In this work, resonance spectra for free and contact vibration were used in a finite element analysis of cantilevers to show the influence of kS in the resonance curves due to changes in the kS/kN ratio. These curves have regions for the different vibrational modes that are both, strongly and weakly dependent on kS, and they can be used in a selective manner to obtain a precise mapping of elastic properties.

Effect of nanoimprint on the elastic modulus of PMMA: Comparison between standard and ultrafast thermal NIL

This paper is focused on the understanding of the effect of the nanoimprint lithography process on the elastic modulus of thin, thermoplastic films. In particular, we present the comparison between the standard and an ultrafast thermal NIL technology as well as the way both processes affect the top surface of poly(methyl methacrylate) (PMMA). The PeakForce QNM™ (Quantitative Nanomechanical Property Mapping) scanning probe technique was used to determine the Young's modulus of PMMA by comparison with a polystyrene standard. We demonstrate that imprinted PMMA, regardless of the used method, shows a 9-fold increase of Young's modulus compared to non-imprinted PMMA at least in the top 3–5nm thick surface layer. This important finding proves that the ultrafast process with much higher temperatures, but also with much shorter process times, leads to elastic surface properties that are comparable to those of PMMA imprinted with the standard process. We have confirmed that annealing alone does not significantly influence the Young's modulus.

Elastodynamic analysis of anisotropic elastic solid with multiple nanocavities

Abstract2D elastodynamic problem for a finite elastic anisotropic solid with nanosized cavities is worked out in this paper. The solid under plane strain conditions is subjected to time-harmonic load. The developed computational tool for the steady-state problem is boundary integral equation method based on frequency-dependent fundamental solutions for elastic anisotropic continuum obtained by Radon transform. Accuracy of the dynamic stress concentration factor and displacement components is proven by comparisons with existing in the literature analytical solution and with the results obtained using commercial finite element package. In addition, a parametric study is performed in order to examine the sensitivity of the dynamic stress concentration field to the geometrical configuration of multiple cavities, to the characteristics of the surface elastic properties, to the type of orthotropy and to the dynamic interaction between cavities.

Effect of surface energy on the dynamic response and instability of fluid-conveying nanobeams

Abstract A modified continuum model of fluid-conveying nanobeams is presented by incorporating the surface elasticity in this paper. The classical beam theory is adopted to model the bulk, while Gurtin and Murdoch's theory of surface elasticity is applied to model the surfaces. Based on the Timoshenko beam theory, the equation of motion for transverse vibrations of fluid-conveying nanobeams is formulated and the differential quadrature method is applied to solve this complex problem. Beams made from aluminum (Al) and silicon (Si) are chosen as examples. The surface effects on the vibrational characteristics are discussed for simply supported and clamped nanobeams. The results show that, due to the different surface elastic properties between Al and Si, the surface energies will increase the frequency and critical flow velocity of Al nanobeams but decrease those of Si beams. In addition, the frequency and critical flow velocity of Al and Si nanobeams obtained from the Timoshenko beam model are generally smaller than those from the Euler–Bernoulli beam model due to the effects of shear deformation and rotary inertia. However, when the cross-sectional size of the Si nanobeams is relatively small, their Timoshenko beam results are found to be close to the Euler–Bernoulli beam results.

Optical and mechanical properties of nanofibrillated cellulose: Toward a robust platform for next-generation green technologies

Nanofibrillated cellulose, a polymer that can be obtained from one of the most abundant biopolymers in nature, is being increasingly explored due to its outstanding properties for packaging and device applications. Still, open challenges in engineering its intrinsic properties remain to address. To elucidate the optical and mechanical stability of nanofibrillated cellulose as a standalone platform, herein we report on three main findings: (i) for the first time an experimental determination of the optical bandgap of nanofibrillated cellulose, important for future modeling purposes, based on the onset of the optical bandgap of the nanofibrillated cellulose film at Eg≈275nm (4.5eV), obtained using absorption and cathodoluminescence measurements. In addition, comparing this result with ab-initio calculations of the electronic structure the exciton binding energy is estimated to be Eex≈800meV; (ii) hydrostatic pressure experiments revealed that nanofibrillated cellulose is structurally stable at least up to 1.2GPa; and (iii) surface elastic properties with repeatability better than 5% were observed under moisture cycles with changes of the Young modulus as large as 65%. The results obtained show the precise determination of significant properties as elastic properties and interactions that are compared with similar works and, moreover, demonstrate that nanofibrillated cellulose properties can be reversibly controlled, supporting the extended potential of nanofibrillated cellulose as a robust platform for green-technology applications.

Interfacial Waves With Surface Elasticity

In this paper, we study the existence and uniqueness of interfacial waves in account of surface elasticity at the interface. A sufficient condition for the existence and uniqueness of a subsonic interfacial wave between two elastic half spaces is obtained for general anisotropic materials. Further, we explicitly calculate the dispersion relations of interfacial waves for interfaces between two solids and solid and fluid, and parametrically study the effects of surface elasticity on the dispersion relations. We observe that the dispersion relations of interfacial waves are nonlinear at the presence of surface elasticity and depend on surface elastic properties. This nonlinear feature can be used for probing the bulk and surface properties by acoustic measurements and designing waves’ guides or filters.

Nonlocal continuum-based modeling of breathing mode of nanowires including surface stress and surface inertia effects

Nonlocal and surface effects significantly influence the mechanical response of nanomaterials and nanostructures. In this work, the breathing mode of a circular nanowire is studied on the basis of the nonlocal continuum model. Both the surface elastic properties and surface inertia effect are included. Nanowires can be modeled as long cylindrical solid objects. The classical model is reformulated using the nonlocal differential constitutive relations of Eringen and Gurtin–Murdoch surface continuum elasticity formalism. A new frequency equation for the breathing mode of nanowires, including small scale effect, surface stress and surface inertia is presented by employing the Bessel functions. Numerical results are computed, and are compared to confirm the validity and accuracy of the proposed method. Furthermore, the model is used to elucidate the effect of nonlocal parameter, the surface stress, the surface inertia and the nanowire orientation on the breathing mode of several types of nanowires with size ranging from 0.5 to 4nm. Our results reveal that the combined surface and small scale effects are significant for nanowires with diameter smaller than 4nm.

Nanoparticle debonding strength: A comprehensive study on interfacial effects

The most appealing feature of nanofilled polymers is the perspective of obtaining surprisingly high mechanical properties at low nanofiller volume fractions. The knowledge of nanostructure–property relationships is however essential for the design of these materials.In the present work, a model for the critical hydrostatic tension related to nanoparticle debonding is presented. The model accounts for some important issues inherently related to the nanoscale with particular reference to surface elastic stresses on the nanoparticle periphery and the emergence of a zone of altered chemistry surrounding the nanoparticle. The analytical solution suggests that the range of nanoparticle radii where interfacial effects do affect the solution is limited to the nanometer scale. In more details, considering the interphase and surface elastic properties used in the analysis, it has been found that for stiff particles with radius between 10nm and 100nm (silica, alumina and other metal oxide nanoparticles) the prominent role is played by the interphase elastic properties. Surface elastic constants were found to have, instead, only a negligible effect.

Reflection and transmission of plane waves at surfaces carrying material properties and embedded in second-gradient materials

In this paper reflection and transmission of compression and shear waves at structured interfaces between second-gradient continua is investigated. Two semi-infinite spaces filled with the same second-gradient material are connected through an interface which is assumed to have its own material properties (mass density, elasticity and inertia). Using a variational principle, general balance equations are deduced for the bulk system, as well as jump duality conditions for the considered structured interfaces. The obtained equations include the effect of surface inertial and elastic properties on the motion of the overall system. In the first part of the paper general 3D equations accounting for all surface deformation modes (including bending) are introduced. The application to wave propagation presented in the second part of the paper, on the other hand, is based on a simplified 1D version of these equations, which we call “axial symmetric” case.

Tuning the Area Percentage of Reactive Surface ofTiO2by Strain Engineering

Surfaces with high reactivity usually have a low area percentage, which greatly limits the efficiency of surface reactivity. In this Letter we demonstrate a generic way of increasing the percentage of the highly reactive surface by using external strain. Bulk and surface elastic properties of TiO2 are studied via density functional theory calculations. The equilibrium shape of anatase TiO2 under applied strain is discussed based on the elastic properties. We find that when 5% compressive strain is applied biaxially along [100] and [010]; directions, the area percentage of the anatase (001) surface can be increased by ~5 times in comparison with the case when no strain is applied. Since the moderate strain does not introduce extrinsic defects into the material, we propose that it is an ideal way to increase the reactivity of titanium dioxide crystallites by applying biaxial compressive external strain along the a axis.

Investigation of phase morphology of polyetherimide-toughened epoxy resin by scanning probe microscopy

High resolution nanomechanical analysis in combination with high resolution topography imaging was used to investigate the phase morphology of a polyetherimide-toughened tetra-functional epoxy resin. A two-phase structure close to co-continuous morphology is observed. Here, polyetherimide and epoxy-rich regions can be clearly identified due to their different nanomechanical properties. Within the PEI-rich regions, the high resolution testing allows identification of polyetherimide-rich globules with a size between 50 nm and 500 nm, in addition to the well-known epoxy-rich rounded substructures with a diameter of about one micrometer. Etching influences the surface elastic properties and results in an increase of the epoxy surface modulus. Surface ageing results in a slight increase of the surface modulus.

Combined Effect of Polishing on Surface Morphology and Elastic Properties of a Commercial Dental Restorative Resin Composite

Combined Effect of Polishing on Surface Morphology and Elastic Properties of a Commercial Dental Restorative Resin Composite

Non-contact Measurement of Body Surface Elastic Properties in Scleroderma

Non-contact Measurement of Body Surface Elastic Properties in Scleroderma

Surface enthalpy and elastic properties of blood vessels

1. Blood vessels form one of the most complicated and important functional systems of humans and other mammals subjected to many risks and poorly amenable to medicinal treatment. The mathematical simulation of blood flow through the aorta, arteries, veins, peripheral vessels, and capillaries both sepa rately and as a whole still remains an important problem. At the same time, the published bloodflow models give no possibility to take into account the complex (composite and anisotropic) structure of walls of vessels. Moreover, the formulation itself of experiments on determining elastic characteristics of walls of ves sels is at the stage of development (see [1, 2] and the review of literature in monograph [3, sect. 8]). This study is devoted to derivation of certain relations for deformable bloodvessel walls on the basis of the conventional representation of their laminar structure (see, for example, [1, 4, 3]). By means of the dimensionreduction procedure and on the basis of the concept of surface enthalpy, we derived a simple formula for the effective elasticmodulus tensor. Contrary to the habitual formulation of the mathematical problem, the blood vessel is not beforehand assumed as a circular cylinder, and the occurrence of a variable curvature, which does not complicate principally the asymptotic analysis, enables us to investigate the deformation of walls of arteries due to damage, such as inhomogeneous calcification (hyalinosis or calcinosis), oblong atherosclerotic deposits (cholesterolplaques), or various surgical treatments (clipping, stenting, and stitching).