Surface Elastic Modulus Research Articles

Nanomechanical Behaviour and Surface Roughness of New Generation Dental Fissure Sealants

The aim of this study is the comparative evaluation of surface roughness, elastic modulus and hardness values of some new generation fissure sealants using nanoindentation method and triboindenter. In this study, we have tested five dierent materials of dental fissure sealant in five groups with six specimens in each. Tested specimens were prepared from the following materials; Fuji Triage as a glass ionomer, Glass Seal as a glass carbomer, Ultra Seal XT Hydro, Teethmate F-1 and Defence Chroma as three resin composites. In the study, Hysitron Triboindenter TI 950 machine was used for nanohardness measurements. This machine has load resolution of less than 1 nN and displacement resolution of 0.04 nm. Data were statistically analysed using one-way analysis of variance (ANOVA) and Kolmogorov-Smirnov Z tests. Hardness values of Fuji Triage, Glass Seal, Ultra Seal XT Hydro were fairly close. Same situation was seen between Teethmate F-1 and Defence Chroma. However, hardness values of the Teethmate F-1 and Defence Chroma was lower than in other examined materials. We can also say that the Defence Chroma has the lowest elastic modulus and Fuji Triage has the highest one among the examined materials. Surface of Teethmate F-1 was the roughest. On the other hand, Ultra Seal XT Hydro has the smoothest surface.

Thermocycling effect on mechanical and tribological characterization of two indirect dental restorative materials

The purpose of this study is to evaluate the effects of aging by thermocycling on the mechanical and tribological properties of two indirect filling commercial resin-based restorative composite materials. The studied composites are referenced by the capital letters: A and B. The commercial trade names are omitted, to avoid commercial references. Forty specimens of each material were produced and divided into three groups: a control group not subjected to aging, and two groups, T1 and T2 submitted to different thermocycling conditions. The studied properties were surface roughness, elastic modulus (determined dynamically by impulse excitation of vibration, and statically by four-point bending test), flexural strength and work of fracture (four-point bending test), micro-hardness (Vickers micro-indentation) and coefficient of friction (scratch test). From this study, it was possible to conclude that Composite A, in addition to having better mechanical properties, is less affected by thermocycling than Composite B, which suggests that it will better withstand the stresses, both mechanical and thermal, which it is subjected to. It is also possible to infer that the thermocycling regimen proposed by Standard ISO 11405 (Dental materials—testing of adhesion to tooth structure, 2003) is not sufficient to adequately simulate the degradation caused by the oral environment on current commercial resin-based restorative composites.

Eigenstress model for electrochemistry of solid surfaces.

Thermodynamic analysis and molecular dynamics simulations were conducted to systematically study the size-dependent electrochemical response of solids. By combining the generalized Young-Laplace equation with the popular Butler-Volmer formulation, the direct influence of surface stress on solid film electrochemical reactions was isolated. A series of thermodynamic formulas were developed to describe the size-dependent electrochemical properties of the solid surface. These formulas include intrinsic surface elastic parameters, such as surface eigenstress and surface elastic modulus. Metallic films of Au, Pt, Ni, Cu and Fe were studied as examples. The anodic current density of the metal film increased, while the equilibrium potential decreased with increasing solid film thickness.

Simultaneous co-deposition of SiC and CNT into the Ni coating

Various researches are carried out to investigate the properties of Ni-SiC and Ni-CNT composite coatings. The simultaneous effect of carbon nanotube (CNT) and silicon carbide (SiC) is not addressed in the literature. Hence, Ni-SiC and Ni-SiC-CNT nanocomposite coatings were electrodeposited on aluminium substrate in this paper. Surface hardness and elastic modulus of the coatings were measured by atomic force microscope, and X-ray diffraction technique was used to evaluate the grain size of the coatings. Pin-on-disk wear test was carried out and the frictional surfaces along with the morphology of the coatings were investigated using scanning electron microscope. Both hardness and elastic modulus of the coating increased after CNT was introduced. The results indicate that CNT improved the wear behaviour of the coating by preventing the detachment of strengthening particles from the coating and consequently decreasing its abrasive wear.

Thermo-oxidative induced shrinkage in Organic Matrix Composites for High Temperature Applications: Effect of fibre arrangement and oxygen pressure

The present paper focuses on thermo-oxidative induced chemical shrinkage in HTS/TACTIX carbon/epoxy Organic Matrix Composites for High Temperature Applications, providing an insight on the effect of the fibre arrangement and of the oxygen pressure as an accelerating parameter. In particular, measurement of matrix shrinkage in composites surface is carried out by Interferometric Microscopy for virgin samples (initial state) and for samples aged under oxygen pressure and air at atmospheric pressure: some discussion about the “structural” effect (arrangement of fibres, fibre volume fraction) on matrix shrinkage development of unidirectional composites is provided; a link between the measured surface matrix shrinkage and the evolution of the surface elastic indentation modulus measured in pure resin samples can be clearly established: moreover, it is shown that matrix shrinkage development in composites can be conveniently accelerated by the employment of oxygen pressure, as in pure resin systems.

Microstructure and mechanical properties of nanostructured and microstructured TiO2 films

In this study, we present results of comparative studies on the microstructure and mechanical properties of nanostructured and microstructured titanium dioxide (TiO2) films formed on titanium substrates by electrochemical anodization at different electrolytes. Nanostructured TiO2 film was prepared in 1% HF solution for 30min. Microstructured TiO2 films were anodized in two different electrolytes (1M H2SO4 and 1.4M H3PO4) for 10min. The phase structures, surface morphologies and surface topographies of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscopy (AFM), respectively. The surface hardness and elastic modulus of the TiO2 films were studied using nanoindentation technique. The results showed that the electrolyte type and applied voltage have a strong influence on the morphology and crystalline structure of the TiO2 films. It was found that hardness and elastic modulus of the nanostructured TiO2 film were much lower than the microstructured TiO2 films.

The Deposition of Silicon-Carbon Coatings in Plasma Based Nonself-Sustained Arc Discharge with Heated Cathode

Silicon-carbon coatings on silicon substrates were deposited in plasma based nonself-sustained arc discharge with heated cathode by plasma polymerization of silicon organic agent such as polyphenyl methylsiloxane (PPhMS). Silicon-carbon coatings were deposited at PPhMS flow rate of 0.012 ml/min, argon pressure of 0-0.1 Pa, discharge current of 5-8 A, discharge voltage of 130-150 V, and filament current of 68 A. Bipolar pulsed bias voltage was supplied on the substrate during coating deposition. Surface morphology, hardness and elastic modulus of silicon-carbon films were investigated after the deposition. The film surface is very smooth with root-mean-square roughness of 0.579 nm. Maximum hardness of coatings was 11 GPa, and maximum elastic modulus was 142 GPa.

In situ plasma fabrication of ceramic‐like structure on polymeric implant with enhanced surface hardness, cytocompatibility and antibacterial capability

Polymeric materials are commonly found in orthopedic implants due to their unique mechanical properties and biocompatibility but the poor surface hardness and bacterial infection hamper many biomedical applications. In this study, a ceramic-like surface structure doped with silver is produced by successive plasma implantation of silicon (Si) and silver (Ag) into the polyamine 66 (PA66) substrate. Not only the surface hardness and elastic modulus are greatly enhanced due to the partial surface carbonization and the ceramic-like structure produced by the reaction between energetic Si and the carbon chain of PA66, but also the antibacterial activity is improved because of the combined effects rendered by Ag and SiC structure. Furthermore, the modified materials which exhibit good cytocompatibility upregulate bone-related genes and proteins expressions of the contacted bone mesenchymal stem cells (BMSCs). For the first time, it explores out that BMSCs osteogenesis on the antibacterial ceramic-like structure is mediated via the iNOS and nNOS signal pathways. The results reveal that in situ plasma fabrication of an antibacterial ceramic-like structure can endow PA66 with excellent surface hardness, cytocompatibility, as well as antibacterial capability.

Mechanical properties investigation of bilayer graphene/poly(methyl methacrylate) thin films at macro, micro and nanoscale

Mechanical properties of bilayer graphene/poly(methyl methacrylate) (GR/PMMA) and reference PMMA thin films are investigated using various macro, micro and nano mechanical test methods. The GR/PMMA bilayer film consists of the CVD graphene layer (1 nm thick) spin coated with 1 μm thick PMMA layer. Small punch test, Berkovich nanoindentation, AFM nanoindentation, AFM nanoscratch, and spherical-conical stylus nanoscratch are used as mechanical characterization techniques. The freestanding films behave as 2D-membranes and high stretching is achieved at slower tests due to the dissipation of energy during elongation. The bilayer film is more brittle with lower fracture strength, strain and toughness than the PMMA film, due to interfacial delamination between the GR and the PMMA layers at large strain. The surface elastic modulus is higher than the bulk tensile modulus due to the scale effect. The graphene layer contributes to the improvements of hardness and resistance to scratch for both freestanding and supported GR/PMMA films. Critical normal force of adhesive failure of the bilayer films is identified as an important parameter characterizing intrinsic adhesion properties of the graphene/PMMA interfaces. The GR/PMMA thin films have potential in future shielding applications for protection of electronic devices.

Effects of UV Intensity, Line-speed, and Light Distribution on Conversion and Surface Elastic Modulus of Roll-to-roll UV-cured Film

Effects of UV Intensity, Line-speed, and Light Distribution on Conversion and Surface Elastic Modulus of Roll-to-roll UV-cured Film

Electropolishing parameters optimization for enhanced performance of nickel coating electroplated on mild steel

Abstract The purpose of this work is to investigate the influence of electropolishing process on performance parameters of nickel coating electroplating on Q235A mild steel as substrate, including the surface roughness, thickness, elastic modulus and hardness. The contribution of magnetic stirring was first studied. On the basis of this, we explored the effect rules of electropolishing parameters on nickel coating using orthogonal test. The result showed that nickel coating became smoother and thicker by magnetic stirring in electropolishing process. The current density in electropolishing process significantly influenced the thickness, elastic modulus and hardness of Ni coating, while it showed little influence on the coating surface roughness. The above three parameters were also affected by polishing time and the temperature of polishing slurry. With the other condition remaining the same, elastic modulus and hardness of nickel coating reached their peaks after electropolishing with a current density of 30 A/dm 2 in electrolyte at 65 °C for 15 min.

Surface elasticity revisited in the context of second strain gradient theory

Surface/interface stresses, when notable, are closely associated with a surface/interface layer in which the interatomic bond lengths and charge density distribution differ remarkably from those of the bulk. The presence of such topographical defects as edges and corners amplifies the noted phenomena by large amounts. If the principal features of interest are such studies as the physics and mechanics of evolving microscopic-/nanoscopic-interfaces and the behavior of nano-sized structures which have a very large surface-to-volume ratio, traditional continuum theories cease to hold. It is for the treatment of such problems that augmented continuum approaches like second strain gradient and surface elasticity theories have been developed by Mindlin (1965) and Gurtin and Murdoch (1975), respectively. In the mathematical framework of the former theory, the surface effect is explicitly revealed through surface characteristic length and modulus of cohesion, whereas within the latter theory, which views the bulk material and its complementary surface as separate interacting entities, the critical role of surfaces/interfaces is directly incorporated through the introduction of the notions of tangential surface strain tensor, surface stress tensor, and surface elastic modulus tensor into the formulation. In the realm of the experimentations, evaluation of the above-mentioned surface parameters poses serious difficulties. One of the objectives of the current study is to provide a remedy as how to calculate, not only these parameters, but also Mindlin’s bulk characteristic lengths as well as Lame constants with the aids of first principles density functional theory (DFT). To this end, surface elasticity is reformulated by maintaining the first and second gradients of the strain tensor for the bulk; as a result two new key equations are obtained. One of these equations is an expression for the net surface stress, needed to relate the surface parameters in surface elasticity to the Mindlin’s second gradient theory parameters. The other equation is for the total elastic energy which is utilized to find an analytical expression for the surface energy. The available data on surface relaxation obtained experimentally and computationally are in good correspondence with the results of the current theory. Moreover, employing the present theory, an estimate for the effective elastic constants of films with infinite extension is provided.

Size-dependent free vibration analysis of nanoshells based on the surface stress elasticity

Based upon the Gurtin–Murdoch elasticity theory capturing the surface stress effect, a size-dependent continuum model is developed to investigate the free vibrations of nanoscale cylindrical shells. The equations of motion including the surface stress effect are derived based on the first-order shear deformation theory (FSDT) and using Hamilton's principle. A Galerkin-based closed-form solution technique together with modal beam functions is also utilized to solve the problem. Comprehensive results for the size-dependent vibration behavior of nanoshells under various boundary conditions are given. The results from the present analysis, where possible, are shown to be in very good agreement with the existing data from the literature. A comparison is also made between the predictions of surface stress model and those of its classical counterpart, and it is revealed that the surface stress has a significant influence on the resonant frequency of very thin nanoshells. Moreover, the effects of surface properties including surface elastic moduli, surface residual tension and surface mass density on the vibration characteristics of nanoshells are studied.

Assessing the Local Nanomechanical Properties of Self-Assembled Block Copolymer Thin Films by Peak Force Tapping.

The mechanical properties of several types of block copolymer (BCP) thin films have been investigated using PeakForce quantitative nanomechanical mapping. The samples consisted of polystyrene/poly(methylmethacrylate) (PS/PMMA)-based BCP thin films with different pitches both randomly oriented and self-assembled. The measured films have a critical thickness below 50 nm and present features to be resolved of less than 22 nm. Beyond measuring and discriminate surface elastic modulus and adhesion forces of the different phases, we tuned the peak force parameters in order to reliably image those samples, avoiding plastic deformation. The method is able to detect the changes in mechanical response associated with the orientation of the PMMA cylinders with respect to the substrate (parallel versus vertical). The nanomechanical investigation is also capable of recognizing local stiffening due to the preferential growth of alumina deposited by atomic layer deposition on BCP samples, opening up new possibilities in the field of hard mask materials characterization.

Analytical Solution for Thermomechanical Vibration of Double-Viscoelastic Nanoplate-Systems Made of Functionally Graded Materials

In this article, based on the nonlocal elasticity theory of Eringen, dynamic characteristics of a double-FGM viscoelastic nanoplates-system subjected to temperature change with considering surface effects (surface elasticity, tension and density) is studied. Two Kirchhoff nanoplates are coupled by an internal Kelvin–Voigt viscoelastic medium and also are limited to the external Pasternak elastic foundation. The material properties of the simply supported functionally graded nanoplates are assumed to follow power law distribution in the thickness direction. The governing equations of motion for three cases (out-of-phase vibration, in-phase vibration and one nanoplate fixed) are derived from Hamilton's principle. The analytical approach is employed to determine explicit closed-form expression for complex natural frequencies of the system. Numerical results are presented to show variations of the frequency of double-FGM viscoelastic nanoplates corresponding to various values of the nonlocal parameter, temperature change, power law index, aspect ratio and transverse and shear stiffness coefficients of the Pasternak elastic foundation. Moreover, influence of higher order modes, viscoelastic structural damping and damping coefficient of the viscoelastic medium on vibration characteristics are investigated. Numerical results show that natural frequency is greatly influenced by surface elastic modulus and residual surface stress.

Analysis and Measurement of Volume Change by Transformation of Crystal Between Hf and HfOx Thin Film During Oxidation Using Nanoindenter.

In this study, nanomechanical properties were analyzed using a nanotribology method. The nanoindenter system is the main analysis method in nanotribology. The nanoindenter can measure the induced stresses, elastic modulus, and stabilities of Hf and HfO2 thin film surfaces as a function of the annealing temperature. The surface hardness and elastic modulus decreased, except at 600 °C, from 8.1 to 6.22 GPa and from 143.87 to 93.68 GPa, respectively, as the annealing temperature was increased from the as-deposited state to 800 °C. These results were related to the surface oxidation of the Hf thin film or the formation of a HfO2 monoclinic crystal. The change in the crystal structure caused an increase in volume that subsequently induced a compressive stress.

A Nonlinear Shear Deformable Nanoplate Model Including Surface Effects for Large Amplitude Vibrations of Rectangular Nanoplates with Various Boundary Conditions

In this paper, a geometrically nonlinear first-order shear deformable nanoplate model is developed to investigate the size-dependent geometrically nonlinear free vibrations of rectangular nanoplates considering surface stress effects. For this purpose, according to the Gurtin–Murdoch elasticity theory and Hamilton's principle, the governing equations of motion and associated boundary conditions of nanoplates are derived first. Afterwards, the set of obtained nonlinear equations is discretized using the generalized differential quadrature (GDQ) method and then solved by a numerical Galerkin scheme and pseudo arc-length continuation method. Finally, the effects of important model parameters including surface elastic modulus, residual surface stress, surface density, thickness and boundary conditions on the vibration characteristics of rectangular nanoplates are thoroughly investigated. It is found that with the increase of the thickness, nanoplates can experience different vibrational behavior depending on the type of boundary conditions.

Effect of Surface Elastic on the Response of Microcantilevers Under Photothermal Excitation

Surface elasticity often plays a significant role in the physical properties of micro and nanosized materials and structures. In this paper the effect of surface elastic modulus on the bending of a microcantilever, which was excited with a frequency-modulated laser, is studied by incorporating the effect of the surface elastic modulus into the equation of motion. The deflection of microcantilever with surface elastic effect was obtained analytically and shown graphically. It was found that the surface elastic modulus had distinct effect on the deflection and resonance frequencies of microcantilever. The present study might be helpful for the design and application of microcantilever device.

Effects of aging procedures on the molecular, biochemical, morphological, and mechanical properties of vacuum-formed retainers

The influence of intraoral exposure procedures on the physical characteristics of thermoplastic vacuum-formed retainers (VFRs) is still unclear. The effects of thermoforming and intraoral use on the molecular, chemical, morphological, and mechanical properties of thermoplastic VFRs were investigated. VFRs with a 0.8-mm-thick thermoplastic PETG sheet acquired from 48 patients were investigated with two aging procedures, including vacuum forming and intraoral exposure, for 2-week and 6-month. Eight evaluating sites for thermoplastic VFRs were assessed with seven analytical techniques. LM, SEM, and AFM microscopic findings showed that the surface characteristics increased with increasing in vivo exposure time (a four-fold increase) and varied depending on the sites evaluated (an occlusal surface). Raman and EDX spectroscopic findings showed that aging procedures led to a significant change in the molecular composition of VFRs, leading to a decrease in the composition rate of carbon (C) and the presence of silicon (Si), phosphorus (P), and calcium (Ca). Compressive strength and tensile tests showed that aging procedures led to a significant increase (P<0.01) in ultimate tensile strength, elastic modulus, the stored energy at a 6-mm deflection (u6mm), and the compressed load at a 3-mm deflection (σ3mm). Thermoforming led to a smoother surface and no crystallization of PETG sheets. Intraoral exposure accelerated changes in surface morphology, tensile strength, and elastic modulus of VFRs. This change was site-specific and enhanced with an increase in intraoral exposure time. Therefore, thermoforming and in vivo oral exposure procedures led to the molecular, morphological, and mechanical properties of thermoplastic VFRs.

Nanoindentation of soft solids by a flat punch

Measuring the surface tension and elastic modulus of soft materials and biological tissues under different physiological and pathological conditions is of significance for understanding various phenomena associated with deformation. In this paper, the nanoindentation of a circular flat punch on a soft solid is analyzed with the influence of surface tension. By solving the corresponding singular integral equation, the relation between load and indent depth is obtained. When the radius of the flat punch shrinks to the same order as the ratio of surface tension to elastic modulus, surface tension significantly affects the indentation load–depth relation, which provides a facile method to measure surface tension in soft solids and biological tissues. The nanoindentation of a circular flat punch on a soft solid is analyzed with the influence of surface tension. By solving the corresponding singular integral equation, the relation between load and indent depth is obtained. When the radius of a flat punch shrinks to the same order as the ratio of surface tension to elastic modulus, surface tension significantly affects the indentation load–depth relation, which provides a facile method to measure surface tension in soft solids and biological tissues.