Surface Stress Values Research Articles

Finite Element Analysis of the Effect of Femoral Prosthesis Varus and Valgus Angle Installation on the Lateral Compartment in Unicompartmental Knee Arthroplasty.

This study used finite element analysis (FEA) to investigate the effect of varus and valgus angle on the lateral compartment in unicompartmental knee arthroplasty (UKA). One patient who underwent UKA was enrolled as the subject. Thirteen working conditions of the femoral prosthesis were simulated at varus and valgus angles of 0°, 2°, 4°, 6°, 8°, 10°, and 12°. A load of 1,000 N was applied downward along the mechanical axis of the femur, and the highest stress values on the surface of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage in each model were recorded. The six highest points were used to calculate the mean value. The highest stress values on the surface of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage increased with an increase in the femoral prosthesis varus/valgus angle. As compared with the standard position of the femoral prosthesis, there was no significant difference in the surface stress values of the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus and tibial lateral plateau cartilage when the femoral prosthesis varus/valgus angle was less than 4° (p > 0.05). In addition, the stress magnitude on the polyethylene liner, cancellous bone under the tibial prosthesis, cartilage of femur lateral condyle, lateral meniscus, and tibial lateral plateau cartilage significantly increased when the femoral prosthesis varus/valgus angle was greater than 4° (p < 0.001). The optimal femoral prosthesis varus/valgus angle in UKA was less than 4°.

Wave propagation analysis in viscoelastic Timoshenko nanobeams under surface and magnetic field effects based on nonlocal strain gradient theory

In this work, wave propagation in viscoelastic Timoshenko nanobeam under surface stress and magnetic field effects is studied. The governing equations of the non-local strain gradient theory are reformulated incorporating the Kelvin-Voigt visco-elastic constitutive model under the effect of surface stress and longitudinal magnetic field. The effect of longitudinal magnetic field on the behavior of single walled carbon nanotubes is modeled using the Lorentz magnetic forces. Gurtin-Murdoch’s surface elasticity is used to account for the surface stresses. The closed-form solutions are developed for the reformulated governing equations. The results obtained agree well with the existing literature in the limiting case of no surface and magnetic field effects. It is observed that with the introduction of surface stress values, the damping ratio of both flexural and shear waves increases. The effect of magnetic field, non-locality and strain gradient on phase velocity of flexural and shear waves, threshold and blocking diameters of carbon nanotubes is also presented.

Evidence that uniform momentum zones originate from roughness sublayer structure interactions in fully rough channel turbulence

Fully rough wall-sheared turbulence is composed of an inner and outer layer, the former occupied by sinuous structures sustained by the well-known autonomous inner cycle, the latter occupied by inclined parcels of momentum deviations relative to the average. The outer-layer structures are also known as uniform momentum zones (UMZs), where the presence of successive UMZs manifests instantaneously with a distinct ‘staircase’ pattern in streamwise velocity. Direct numerical simulation (DNS) of fully rough channel turbulence was recently used to interpret UMZs as wakes originating from antecedent bluff-body-like interactions within the inner layer (Anderson &amp; Salesky, J. Fluid Mech., vol. 906, 2020, A8). Wake-scaling arguments agreed precisely with instantaneous results from DNS. Foremost among these results was evidence that the instantaneous wall-normal gradient of streamwise velocity exhibited scaling of ${\sim }x_3^{-1/2}$ , where $x_3$ is wall-normal location; this is in contrast to logarithmic scaling, which requires the wall-normal gradient of streamwise velocity to scale as ${\sim }x_3^{-1}$ . Herein, wake-scaling arguments have been advanced and compared against results from wall-modelled large-eddy simulation (LES). New results from the ‘bottom up’ wake-scaling arguments agree with LES results, such that the shear associated with the instantaneous staircase-like streamwise velocity follows a clear trend. We have leveraged conditional sampling during LES – predicated upon instantaneous low-frequency, high-magnitude surface stress values known to correspond to large-scale inertial-layer coherence – to further assess the predictive value of the wake-scaling arguments. Model results compare favourably.

A prediction model of residual stress for belt‐grinding blade based on geometrical characteristic and progressive wear of abrasive grains

AbstractThe formation mechanism of residual stress on the machined surface of belt grinding is sophisticated, and residual stress is an important factor affecting the fatigue life of aero‐engine blades. In this study, a prediction model of residual stress in a belt grinding blade is proposed with the geometrical characteristics and progressive wear of the grains as the research topic. By extracting the morphological features of abrasive belt, the residual stress based on different geometrical characteristics of grains (pyramidal, hexahedral, spherical, and conical belts) were investigated, and the optimal grain geometry was determined to be a uniformly arranged positive quadrilateral cone. Accordingly, a grinding experiment with a pyramidal belt was conducted to obtain an experienced model of the grain wear height. A numerical simulation model of the grain wear evolution under four wear states (no abrasion, early abrasion, middle abrasion, and late abrasion) was developed. Additionally, more detailed progressive wear of the abrasive grains was also applied to grind the entire profile of the complex curved blade. The residual stress on the blade surface was mainly compressive, and the surface stress values were distributed between −385 and −117 MPa with the service life of the pyramidal abrasive belt.

Surface stress calculations for nanoparticles and cavities in aluminum, silicon, and iron: influence of pressure and validity of the Young-Laplace equation

This study is dedicated to the determination of the surface energy and stress of nanoparticles and cavities in presence of pressure, and to the evaluation of the accuracy of the Young-Laplace equation for these systems. Procedures are proposed to extract those quantities from classical interatomic potentials calculations, carried out for three distinct materials: aluminum, silicon, and iron. Our investigations first reveal the increase of surface energy and stress of nanoparticles as a function of pressure. On the contrary we find a significant decrease for cavities, which can be correlated to the initiation of plastic deformation at high pressure. We show that the Young-Laplace equation should not be used for quantitative predictions when the Laplace pressure is computed with a constant surface energy value, as usually done in the literature. Instead, a significant improvement is obtained by using the diameter and pressure-dependent surface stress. In that case, the Young-Laplace equation can be used with a reasonable accuracy at low pressures for nanoparticles with diameters as low as 4 nm, and 2 nm for cavities. At lower sizes, or high pressures, a severely limiting factor is the challenge of extracting meaningful surface stress values.

Surface stress of gold nanoparticles revisited

The surface energy has been one of the topics of atomistic research for nanoparticles in the last decades. However, the physical role of surface stress and its quantification have been a lot less an object of research. Assumptions for the surface stress, going back to the thermodynamic basis of continua, have been popular. As an example the surface stress (state) follows as derivatives of the surface energy with a rather “classical” evolution equation for the deformation energy. The current concept introduces a combination of atomistic modelling and continuum mechanics for a core–shell system. Considering crystalline and amorphous gold nanoparticles with radii in the range of 1 nm to 12 nm, we are finally able to independently calculate the values of surface stress and surface energy, both slightly decreasing with the increasing particle radius. Surprisingly large values of surface stress are predicted for the case of amorphous nanoparticles.

Identyfikacja naprężeń powierzchniowych w rurze do układu wydechowego wykonanej technologią hydroformowania na podstawie pomiarów dyfraktometrycznych

In the work identificaton of surface stresses in the exhaust pipe made of Cr-Ni steel shaped with hydroforming technology. Stresses were determined by the non-destructive x-ray method sin2 ψ. A complex state of tensile stresses with values in the range of 69÷240 MPa for circumferential stresses and 26÷290 MPa for longitudinal stresses was found on the surface of the pipe. The distribution of stresses on the circumference and length of the pipe was analyzed on the basis of coefficients of variation and wall thickness. A relationship was found between the value of surface stress and the wall thickness of the pipe. The highest stresses occurred in the areas of the pipe where the thickness of the wall was reduced the most. In the central part of the pipe, where the wall thickness reduction was the smallest, the stresses were also the smallest, but they were characterized by the highest dispersion of value. The distribution of surface stresses determined by diffractometric method was compared with the model of deformation of the pipe generated numerically

Natural boundary conditions and nearsurface non-homogeneity in nonferromagnetic electro conductive half-space and layer

Within the framework of the local nonhomogeneous electroconductive solid model the regularities of near surface non-homogeneity in half-space and layer are studied. Two characteristic sizes are inherent to this non-homogeneity. It is shown that in a free of force load body the values of surface stress and surface, charge are uniquely defined by physical parameters of the material and the body. The electric double layer is the result of taking into account the structural non-homogeneity of material and the forces of Coulomb interaction.

Influence of Creep Model on Glass Tempering Process

In this paper, an in-depth research adopted a creep model has been conducted to focus on the stress during the process of glass tempering based on the finite element software ANSYS.During this research an simplified model of glass tempering has been established, and as a result the expected stress value of surface and mid-plane was achieved.The results show that using the creep model can also achieve the same simulation effect of glass tempering.

Special Section on Spectroscopy, Scattering, and Imaging Techniques for Nanostructured Materials

Special Section on Spectroscopy, Scattering, and Imaging Techniques for Nanostructured Materials

In Situ Deformation of Silicon Cantilever Under Constant Stress as a Function of Temperature

This research reports in situ creep properties of silicon microcantilevers at temperatures ranging from 25 °C to 100 °C under uniaxial compressive stress. Results reveal that in the stress range of 50–150 MPa, the strain rate of the silicon cantilever increases linearly as a function of applied stress. The strain rate (0.2–2.5 ×10-6s-1) was comparable to literature values for bulk silicon reported in the temperature range of 1100–1300 °C at one tenth of the reported stress level. The experiments quantify the extent of the effect of surface stress on uniaxial creep strain rate by measuring surface stress values during uniaxial temperature dependent creep.

Surface Cracks Analysis on Continuous Casting Slab Q345c during Hot Delivery and Hot Charging

The temperature field and stress field were simulated using the finite element software (ABAQUS) for Q345c continuous casting slab during cooling process. The hot ductility curve, high temperature tensile strength curve, and the surface stress value were obtained according to thermal simulation experiments. The results show that the temperature of brittleness zone is at 600-850°C, and the value of surface stress is larger than the high temperature tensile strength in the slab cooling process. The heat insulation device should be installed between the flame cutting machine and the heating furnace to avoid hot crack defects caused by excessive thermal stress on the surface in the process of hot slab delivery.

Remarkably high surface visco-elasticity of adsorption layers of triterpenoid saponins

Saponins are natural surfactants, with molecules composed of a hydrophobic steroid or triterpenoid group, and one or several hydrophilic oligosaccharide chains attached to this group. Saponins are used in cosmetic, food and pharmaceutical products, due to their excellent ability to stabilize emulsions and foams, and to solubilize bulky hydrophobic molecules. The foam and emulsion applications call for a better understanding of the surface properties of saponin adsorption layers, including their rheological properties. Of particular interest is the relation between the molecular structure of the various saponins and their surface properties. Here, we study a series of eight triterpenoid and three steroid saponins, with different numbers of oligosaccharide chains. The surface rheological properties of adsorption layers at the air–water interface, subjected to creep-recovery and oscillatory shear deformations, are investigated. The experiments showed that all steroid saponins exhibited no shear elasticity and had negligible surface viscosity. In contrast, most of the triterpenoid saponins showed complex visco-elastic behavior with extremely high elastic modulus (up to 1100 mN m−1) and viscosity (130 N s m−1). Although the magnitude of the surface modulus differed significantly for the various saponins, they all shared qualitatively similar rheological properties: (1) the elastic modulus was much higher than the viscous one. (2) Up to a certain critical value of surface stress, τC, the single master curve described the dependence of the creep compliance versus time. This rheological response was described well by the compound Voigt model. (3) On increasing the surface stress above τC, the compliance decreased with the applied stress, and eventually, all layers became purely viscous, indicating a loss in the layer structure, responsible for the elastic properties. The saponin extracts, showing the highest elastic moduli, were those of Escin, Tea saponins and Berry saponins, all containing predominantly monodesmosidic triterpenoid saponins. Similarly, a high surface modulus was measured for Ginsenosides extracts, containing bidesmosidic triterpenoid saponins with short sugar chains.

Correlation between Surface Stress and Apparent Young’s Modulus of Top-Down Silicon Nanowires

In this work, we report experimental evidence of surface stress effects on the mechanical properties of silicon nanostructures. As-fabricated, top-down silicon nanowires (SiNWs) are bent up without any applied force. This self-buckling is related to the surface relaxation that reaches an equilibrium with bulk deformation due to the material elasticity. We measure the SiNW self-deformation by atomic force microscopy (AFM), and we apply a simple physical model in order to give an estimation of the surface stress. If the equilibrium is altered by a nanoforce, applied by an AFM tip, nanowires find a new equilibrium condition bending down (mechanical bistability). In this work, for the first time, we report a clear and quantitative relationship between the SiNWs' apparent Young's modulus, measured by force-deflection spectroscopy, and the estimated value of surface stress, obtained by self-buckling measurements taking into account the Young's modulus of bulk silicon. This is an experimental confirmation that the surface stress is fundamental in determining mechanical properties of SiNWs, and that the elastic behavior of nanostructures strongly depends on their surfaces.

Aptamer Functionalized Microcantilever Sensors for Cocaine Detection

A cocaine-specific aptamer was used as a receptor molecule in a microcantilever-based surface stress sensor for detection of cocaine molecules. An interferometric technique that relies on measuring differential displacement between two microcantilevers (a sensing/reference pair) was utilized to measure the cocaine/aptamer binding induced surface stress changes. Sensing experiments were performed for different concentrations of cocaine from 25 to 500 μM in order to determine the sensor response as a function of cocaine concentration. In the lower concentration range from 25 to 100 μM, surface stress values increased proportionally to coverage of aptamer/cocaine complexes from 11 to 26 mN/m. However, as the cocaine concentration was increased beyond 100 μM, the surface stress values demonstrated a weaker dependence on the affinity complex surface coverage. On the basis of a sensitivity of 3 mN/m for the surface stress measurement, the lowest detectable threshold for the cocaine concentration is estimated to be 5 μM. Sensing cantilevers could be regenerated and reused because of reversible thermal denaturation of aptamer.

Water Molecule-Induced Stiffening in ZnO Nanobelts

We report the observation of remarkable water molecule-induced stiffening in ZnO nanobelts using atomic force microscopy three-point bending test. It was found that the elastic modulus of ZnO nanobelts could increase significantly from 40 GPa under ambient condition up to 88 GPa at the relative humidity level of 80%. The physical mechanism for this phenomenon was explained in terms of increasing surface stress induced by water molecule adsorption on ZnO nanobelt surface. Our first-principles density functional theory calculations revealed that the water molecules adsorbed on the ZnO surface would attract surface Zn atoms to move outward and hence increase the value of surface stress of ZnO surface.

Numerical Simulation of Inclined Multi-Seam Mining Subsidence of Considered the Impact by Faults

According to the complex mining geological condition of Shandong gentle inclined multi-seam mining, Use the three-dimensional finite element numerical analysis software to establish three-dimensional geological model under the different mining working conditions. Taking into account the impact of faults to calculate multi-seam roof strata movement and surface subsidence caused by the different mining working conditions. The level displacement &amp; subsidence distribution curve of the reference point of surface &amp; multi-seam roof strata under the different working conditions is shown. The maximum, minimum settlement, differential settlement and subsidence diagram is shown. And the principal stress, shear stress value of surface &amp; multi-seam roof strata after mining also is shown. The results showed that: little change of the biggest surface subsidence and differential settlement is caused by mining 3101&amp;3102 face or separate 3101 or 3102 face. And the largest subsidence, and the settlement difference of the surface is 520mm, 498mm, 515mm and 59mm, 78mm, 81mm, Respectively. It provides an reference for reasonable, safe, economic for the inclined multi-seam mining under similar conditions.

Mechanical stability of nanoporous metals with small ligament sizes

Digital samples of nanoporous gold with small ligament sizes were studied by atomistic simulation using different interatomic potentials that represent varying surface stress values. We predict a surface relaxation driven mechanical instability for these materials. Plastic deformation is induced by the surface stress without external load, related to the combination of the surface stress value and the surface to volume ratio.

Biocompatilibity‐related surface characteristics of oxidized NiTi

In the present study, we examined the effect of NiTi oxidation on material surface characteristics related to biocompatibility. Correspondence between electron work function (EWF) and adhesive force predicted by electron theory of adsorption as well as the effect of surface mechanical stress on the adhesive force were studied on the nonoxidized and oxidized at 350, 450, and 600 degrees C NiTi alloy for medical application. The adhesive force generated by the material surface towards the drops of alpha-minimal essential medium (alpha-MEM) was used as a characteristic of NiTi adsorption properties. The study showed that variations in EWF and mechanical stress caused by surface treatment were accompanied by variations in adhesive force. NiTi oxidation at all temperatures used gave rise to decrease in adhesive force and surface stress values in comparison to the nonoxidized state. In contrary, the EWF value revealed increase under the same condition. Variations in surface oxide layer thickness and its phase composition were also followed. The important role of oxide crystallite size in EWF values within the range of crystallite dimensions typical for NiTi surface oxide as an instrument for the fine regulation of NiTi adsorption properties was demonstrated. The comparative oxidation of pure titanium and NiTi showed that the effect of Ni on the EWF value of NiTi surface oxide is negligible.

Residual stress in thick low-pressure chemical-vapor deposited polycrystalline SiC coatings on Si substrates

Residual stress in thick coatings of polycrystalline chemical-vapor deposited SiC on Si substrates is a key variable that must be controlled if SiC is to be used in microelectromechanical systems. Studies have been conducted to characterize the residual stress level as a function of deposition temperature, Si wafer and SiC coating thickness, and the ratios of methyltrichlorosilane to hydrogen and hydrogen chloride. Wafer curvature was used to monitor residual stress in combination with a laminated plate analysis. Compressive intrinsic (growth) stresses were measured with magnitudes in the range of 200–300MPa; however, these can be balanced with the tensile stress due to the thermal-expansion mismatch to leave near-zero stress at room temperature. The magnitude of the compressive intrinsic stress is consistent with previously reported values of surface stress in combination with the competition between grain-boundary energy and elastic strain energy.