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Hypothesis: Sample-spanning particle networks are used to induce structure and a yield stress, necessary for 3D printing of porous ceramics and paints. In capillary suspensions, a small quantity of immiscible secondary fluid is incorporated into a suspension. By further adding nanoparticles with a range of hydrophobicities, the structure of the bridges and microparticle-microparticle contacts is expected to be modified, resulting in a tunable yield stress and shear moduli. Moreover, the compressibility of these samples, important in many processing and application steps, is expected to be sensitive to these changes. Experiment: The nanoparticle hydrophobicity was altered and their position relative to the microparticles and the bridges was examined using confocal microscopy where the correlation between bridge size and network structure was observed. A step-wise uniaxial compression test on the confocal was conducted to monitor the microparticle movement and structural changes between capillary suspension networks with and without nanoparticles. Findings: Our observation suggests that nanoparticles induce the formation of thin liquid films on the surface of the microparticles, mitigating contact line pinning and promoting internal liquid exchange. Additionally, nanoparticles at microparticle contact regions further diminish Hertzian contact, enhancing the capacity for rearrangement. These effects enhance microparticle movement, narrowing the bridge size distribution. Nanoparticles added to capillary suspensions : The nanoparticles either homogeneously aggregate around the microparticles or stabilize the liquid-liquid interface. These capillary nanosuspensions readily rearrange and compress, opening new opportunities for tunable design of porous ceramics, printed electronics, and low-fat spreadable chocolate. • Nanoparticles in capillary suspensions aggregate on microparticles or stabilize interfaces depending on the wettability. • Nanoparticles induce thin layers of liquid films, promoting internal liquid exchange, and reducing Hertzian contacts. • Capillary nanosuspensions demonstrate a reduction in elastic moduli and less pronounced peak in the viscous modulus. • The structures of capillary nanosuspensions rearrange more easily when subjected to compression. [ABSTRACT FROM AUTHOR]

The raceway damage of the bearing restricts the operation stability of the system. Therefore, in the case of damage, simulating vibration response and predicting the performance of the shaft-cylindrical roller-bearing-pedestal system have high research value. According to the structural characteristics and the force transfer relationship, a dynamic model of the shaft-cylindrical roller-bearing-pedestal system is established in this paper. Then, the vibration response of the system is simulated by Runge–Kutta algorithm and measured by experiment. Finally, the effects of load and speed, damage size, and radial clearance on the dynamic performance are investigated. The simulation and measurement results indicate that the load F and the speed N can promote the enhancement of the vibration acceleration signal. As the damage length continues to increase, the ring in the Poincaré map begins to break, and the system transits from quasi-periodic to chaotic motion. The vibration signal is more affected by the damage size than by the damage location. When the radial clearance increases from 5 × 10−6 m to 15 × 10−6 m, the PTP value increases from 23.83 m·s−2 to 61.36 m·s−2. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We derive the compliance of an elastic cylinder submitted to a line Hertzian contact. The cylinder is maintained in static equilibrium by bulk forces that are proportional to rigid body motions. Displacements are measured by setting integral gauges that amount to prescribing zero net linear and angular momentum, if the problem were to depend upon time. Various cases are covered, representing either infinitesimal or finite contact displacements, including partial slip. The developments are illustrated by revisiting a classical example in what could be called The heavy cylinder on a vibrating soil. The four contact resonances and forced response of the system are given in closed form in the quasi-static approximation, and compared against a reference numerical solution. The formulae can also be used as building blocks to assemble the compliance matrix of a system comprising several cylinders. [ABSTRACT FROM AUTHOR]

We design a one-dimensional granular container in the form of a granular chain to reduce the force transmitted to a fixed barrier at its boundary. The granular chain considered is composed of ordered "heavy" and "light" beads (granules), and possesses strongly nonlinear acoustics due to Hertzian interactions, as well as zero tensile strength resulting in bead separations and subsequent collisions. We find the relationship between the transmitted force and the mass ratio of light beads to heavy beads and the relationship between the transmitted force and the number of beads in each subchain. We obtain an optimal design to minimize the transmitted force under the condition of a fixed total length of the chain. Computational predictions are validated by experiments, wherein we also estimate (i) the value of the damping between beads and (ii) the linear stiffness between the end bead and the barrier at the boundary of the granular chain. Transient, propagating localized oscillations are found in this system in both simulations and experiments, which result due to the strong nonlinearity of the granular chain. These results offer the possibility of systematically designing granular shock absorbers of enhanced performance compared to their linear counterparts. [ABSTRACT FROM AUTHOR]

The dynamic behaviour of a railway vehicle is mainly depending on how the interaction of wheel and rail is taking place in running operation and what is the accuracy and efficiency of the applied contact models. Contact mechanics of railway vehicle is keyed with the history of the wheel-rail contact mechanics. For a designer of braking and traction control systems, it is essential to go through the fundamental knowledge of forces produced due to contact of wheel-rail and geometric constraints as well as moments to assess the wheel-rail wear and to evaluate the ride performance indices. This article gives a brief review to the evolution and present scenario of the previously published contact theories to get rid of the wheel-rail contact problems. The key theories which have most attention to solve normal contact problems are Hertzian contact theory as well as non-Hertzian contact theory, whereas, to tackle the problems related to tangential contact, linear as well as non-linear theories proposed by Kalker, theory proposed by Polach, FASTSIM, CONTACT etc are considered in this paper. This paper reviews the state-of-the-art of past studies based on experiments to study various contact models. [ABSTRACT FROM AUTHOR]

Copyright of Revista Iberoamericana de Ingeniería Mecánica is the property of Editorial UNED and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Locating bearing track rollers are used, for example, in monorail transport systems to enable relative movement between the rail and the shuttle. Due to the two-point contact, both radial and axial forces can be transmitted simultaneously. Since friction is involved, the state of the art does not provide any calculation rules for the dimensioning and design. The development of a calculation model with sophisticated commercial software brings its difficulties since no plausibility check is possible using existing models. For this reason, a model based on analytical descriptions including the Hertzian and the elastic half space theories is presented in this paper. It bridges the gap between very simple approaches and widely developed commercial software. With this model, the contact forces, friction forces, surface tensions, relative velocities and subsurface stresses can be calculated for both free and driven rolling. The main advantages are that the model is easy to apply, and thus comparisons between different track roller designs can be made quickly.

Knowledge of creep forces at wheel-rail interface when high power is applied to the locomotive wheels has been the subject of many recent studies. The common wheel-rail interaction methods are generally divided by two theories – Hertzian and non-Hertzian. The first method uses Hertzian contact for the normal problem and the tangential problem is divided into two algorithms – Polach's theory and the Simplified theory-based algorithm referred to as Modified Fastsim. Kalker's original Fastsim-based method shows a better accuracy for these two Hertzian-based algorithms. The second method is based on the non-Hertzian theory, and it uses the Exact theory also developed by Kalker and implemented in the Extended Contact library to calculate forces at the wheel-rail interface. Considering that the second method is more accurate, this paper aims to present an adaptive simulation and integration method (ASIM) which is positioned in the middle between the two common methods and is designed to introduce a transition from the non-Hertzian to Hertzian contact in the normal problem with the application of the Modified Fastsim for the calculation of contact forces at the wheel-rail interface. The proposed method is aimed to be used in vehicle system dynamics studies performed in multibody software packages. A specially developed wheel-rail coupling incorporating geometrical, normal, and tangential modules is integrated into Gensys multibody software and benchmarked with the standard Extended Contact based wheel-rail coupling by means of locomotive traction tests that use a full mechatronic model of a high adhesion locomotive. The computational performance and accuracy of the proposed method are assessed and discussed. [ABSTRACT FROM AUTHOR]

The objective of this paper is to elucidate the response to contact stresses of Polymer Infiltrated Ceramic Network (PICN) using the microscopic viscoplastic finite elements, validated by clinically relevant in vitro tests. A feldspathic ceramic material, namely Vita Mark II, is an interconnected structure infiltrated with the polymer (PMMA). Axisymmetric finite element microstructure models are reconstructed from two-dimensional images of a PICN microstructure. Viscoplastic finite element analysis (FEA) with various degrees of microscopic damages occurring over contact is performed. The force-displacement responses obtained from FEA are validated with Hertzian contact tests. Finite element results for force-displacement, stresses and strains in each phase are discussed. We hypothesize that the resistance to fracture of PICN can be further improved by microstructural tailoring. The experimental evidence suggests that a composite material is both more resistant to displacement under load and more resistant to crack initiation and propagation, as hypothesized. Further parametric study on the effects of various volume fractions of two phases in PICN is done to provide some insight on increased contact damage resistance of PICN as well as potential optimization of microstructures. [ABSTRACT FROM AUTHOR]

Optimising the performance of materials requires, among other things, the characterisation of residual stresses during the design stage. Raman spectroscopy offers access to these residual stresses at the micrometre scale when this inelastic light scattering is active in these materials. In this case, the relationship between the Raman mode shift and the pressure must be known. High-pressure cells with diamond anvils or bending instruments coupled to Raman spectrometers are habitually used to determine this relationship. In this article, we propose a new method that involves a Hertzian contact to obtain this relationship. A device that compresses an alumina ball against a transparent glass plane is connected to a Raman spectrometer. Under these conditions, the contact pressure can be as high as 1.5 GPa. The contact between the glass plane and the ball is observed through a diaphragm. Several hundred Raman spectra are recorded depending on the contact diameter. The spectral profiles obtained represent the shift in the Raman modes of alumina and glass along the contact diameter. Hertz's theory accurately describes the pressure profile as a function of position for elastic materials. Therefore, the contact diameter can be measured by fitting the spectral profile with a function identical to the Hertz profile. We then deduce the maximum pressure. Next, the calculated pressure profile along the contact diameter is correlated with the spectral profile. We obtain a pressure dependence of the Raman mode with a coefficient equal to 2.07 cm − 1 /GPa for the Eg modes of alumina at 417 cm − 1 , which is in good agreement with the literature. In the case of glass, we refine the measurement of the Q3 mode shift at 1096 cm − 1 in the studied pressure range compared to the literature. We find a coefficient of 4.31 cm − 1 /GPa. This work on static contacts opens up promising prospects for investigations into dynamic contacts in tribology. [ABSTRACT FROM AUTHOR]

The traditional solution for the stresses below an elliptical Hertzian contact expresses the results in terms of incomplete Legendre elliptic integrals, so are necessarily based on the length of the semi-major axis a and the axis ratio k. The result is to produce completely different equations for the stresses in the x and y directions; and although these equations are now well-known, their derivation from the fundamental, symmetric, integrals is far from simple. When instead Carlson elliptic integrals are used, they immediately match the fundamental integrals, allowing the equations for the stresses to treat the two semi-axes equally, and so providing a single equation where two were needed before. The numerical evaluation of the Carlson integrals is simple and rapid, so the result is that more convenient answers are obtained more conveniently. A bonus is that the temptation to record the depth of the critical stresses as a fraction of the length of the semi-major axis is removed. Thomas and Hoersch's method of finding all the stresses along the axis of symmetry has been extended to determine the full set of stresses in a principal plane. The stress patterns are displayed, and a comparison between the answers for the planes of the major and minor semiaxes is made. The results are unchanged from those found from equations given by Sackfield and Hills, but not previously evaluated. The present equations are simpler, not only in the simpler elliptic integrals, but also for the "tail" of elementary functions. [ABSTRACT FROM AUTHOR]

A Rowe cell type compression-breakthrough-bender element column (CBB column) was developed to simulate and monitor the internal erosion process of glass bead (GB) and salt grain (GB-NaCl) mixtures with salt contents of 5% and 34% by weight. Dry samples of GB-NaCl mixtures were compressed up to 100 kPa and were then flushed with de-ionized water. Salt dissolution left voids within the GB pore space, which facilitated the transportation of solid particles in an internal erosion scenario. Shear wave velocities (Vs) in three orthogonal directions (vh, hh, and hv) of GB-NaCl mixtures were measured with bender elements. A salt content of 34% yielded a Vs of 430–500 m/s for the GB-NaCl mixture, which is significantly higher than that of pure GB (160–205 m/s). A major drop of Vs occurred before the 1st pore volume (PV) of de-ionized water, after which only a minor reduction of Vs occurred until a stable value, ranging from 75 to 250 m/s, was reached. From an empirical equation by a previous study which is based on the pore fluid concentration and the undissolved salt mass in the samples, 8.9% and 38.7% of the total salt were flushed away at the end of the 1st PV for GB mixtures with 34% and 5% salt content, respectively. The presence of salt grains induced cone-to-plane contact in the GB-salt mixtures during compression. As salt dissolved completely, Hertzian contacts were observed in hh and hv directions as suggested by the β coefficient (ranging from 0.16 to 0.19), and a more complicated contact pattern in direction vh was postulated. [ABSTRACT FROM AUTHOR]

Locating bearing track rollers are used, for example, in monorail transport systems to enable relative movement between the rail and the shuttle. Due to the two-point contact, both radial and axial forces can be transmitted simultaneously. Since friction is involved, the state of the art does not provide any calculation rules for the dimensioning and design. The development of a calculation model with sophisticated commercial software brings its difficulties since no plausibility check is possible using existing models. For this reason, a model based on analytical descriptions including the Hertzian and the elastic half space theories is presented in this paper. It bridges the gap between very simple approaches and widely developed commercial software. With this model, the contact forces, friction forces, surface tensions, relative velocities and subsurface stresses can be calculated for both free and driven rolling. The main advantages are that the model is easy to apply, and thus comparisons between different track roller designs can be made quickly. [ABSTRACT FROM AUTHOR]

The calculation of the wheel–rail contact forces is one of the most difficult yet time-consuming processes in multibody system (MBS) simulations for a vehicle-track interaction system. The classical combination of the Hertzian model with the FASTSIM algorithm is the most widely used model in MBS code for railway application and the 'exact' solver CONTACT is seldom used due to its high computational cost. A trade-off solution between accuracy and computational efficiency is the simplified and approximate non-Hertzian approach. This paper attempts to compare the influence on MBS simulation for rail vehicle system dynamics of the varied combinations of the classical contact models (i.e. Hertz model and FASTSIM), well-known simplified non-Hertzian model (Kik–Piotrowski model) recently developed improved simplified non-Hertzian models i.e. Extended Kik–Piotrowski and Kalker Book of Tables for Non-Hertzian contact (KBTNH), and the CONTACT algorithm. The results show that all non-Hertzian approaches deviate from the classical Hertzian solutions in both local contact and global dynamics and the KBTNH model provides better agreement with CONTACT than the FASTSIM algorithm for non-elliptic contact conditions considered in this study. A detailed analysis of the causes and influences of the difference due to varied contact models is presented. [ABSTRACT FROM AUTHOR]

For the design of ship equipment and crew training, it would be useful to develop software for the three-dimensional simulation of a totally enclosed lifeboat. To improve the simulation accuracy and immersion of the software, we present a multibody dynamics model for a lifeboat lowered from a ship, accounting for the coupled motion among the ship, lifeboat slings, a cable-pulley system, and the lifeboat. The equations of the whole system are formulated using Kane's method. The model of ship manoeuvring mathematical group is used to calculate the forces and moments acting on the hull of the ship. The hydrodynamic and wind loads on the boat are modeled using the strip theory. The impact force between the ship and the boat colliding is estimated using the contact theory of Hertz and an elastoplastic model. The method of lumped mass is used to model the lifeboat slings. For the cable-pulley system, we present an efficient model for the dynamics of the pay-out/reel-in process based on the framework of Kane's method. The local load of each cable segment between two pulleys is calculated by the model of a linear spring on the basis of the amount of cable passages over pulleys and the variation of the pulley positions, conversely, the cable segment exerts force and moment on the pulleys. The motion equations of the whole system are solved using fourth-order Runge-Kutta. The model can simulate the lowering of the lifeboat, and obtain the three-dimensional motion parameters of the ship, the lifeboat, slings and pulleys, and the local tension load of the cable. The results show that the simulation curves are near the ones of the model experiment, and their trends are coincident. Thus, it can be concluded that our model is feasible. According to our model, the motion of the ship has a significant effect on the magnitude of the lifeboat's oscillation when the sea state is above level 4; it is safe when the initial clear distance is greater than 1.5 times the width of the boat and the sea conditions are below level 5. Finally, the model is applied to the software for three-dimensional simulation.

The filling behavior of Fe-Ni-Mo steel powder for sintered machine parts is simulated using our original DEM (Discrete Element Method) code based on FDPS (Framework for Developing Particle Simulator). The difference between the simulated and experimental apparent densities after self-weight filling is only -6.7%, which is a significantly higher prediction accuracy than the prior study. This result is obtained by only calculating the repulsive force, viscous damping, friction force and gravity using the actual Young's modulus. This is due to using the experimental friction coefficients and the upper limit setting of the distance between the particle surfaces based on the experimental study. This method can be used to simulate the porosity, especially the low density region, in the actual filling process.

Optimising the performance of materials requires, among other things, the characterisation of residual stresses during the design stage. Raman spectroscopy offers access to these residual stresses at the micrometre scale when this inelastic light scattering is active in these materials. In this case, the relationship between the Raman mode shift and the pressure must be known. High-pressure cells with diamond anvils or bending instruments coupled to Raman spectrometers are habitually used to determine this relationship. In this article, we propose a new method that involves a Hertzian contact to obtain this relationship. A device that compresses an alumina ball against a transparent glass plane is connected to a Raman spectrometer. Under these conditions, the contact pressure can be as high as 1.5 GPa. The contact between the glass plane and the ball is observed through a diaphragm. Several hundred Raman spectra are recorded depending on the contact diameter. The spectral profiles obtained represent the shift in the Raman modes of alumina and glass along the contact diameter. Hertz’s theory accurately describes the pressure profile as a function of position for elastic materials. Therefore, the contact diameter can be measured by fitting the spectral profile with a function identical to the Hertz profile. We then deduce the maximum pressure. Next, the calculated pressure profile along the contact diameter is correlated with the spectral profile. We obtain a pressure dependence of the Raman mode with a coefficient equal to 2.07 cm−1/GPa for the Eg modes of alumina at 417 cm−1, which is in good agreement with the literature. In the case of glass, we refine the measurement of the Q3 mode shift at 1096 cm−1 in the studied pressure range compared to the literature. We find a coefficient of 4.31 cm−1/GPa. This work on static contacts opens up promising prospects for investigations into dynamic contacts in tribology.

Copyright of Tribologie und Schmierungstechnik is the property of Narr Francke Attempto Verlag GmbH & Co.KG and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Electrical capacitance method has been applied in measuring the elasto-hydrodynamic lubrication film thickness in rolling element bearings since 1970s, due to its feasibility of measuring film thickness directly in metallic components and its simple theory. In the current article, a summary on the evolution of the method and the corresponding issues relating to the film thickness measurements is given. The evolution of electrical capacitance method and other developed electrical capacitance methods in measuring the film thickness are discussed. Especially, the two existing methods of converting measured capacitance into film thickness are highlighted. One is to calculate the capacitance in the Hertzian contact area and the dielectric constant of the lubricant. The other is to apply calibration tests which are then used to transfer the measured capacitances into film thicknesses. The strengths and weaknesses of the two methods are also explored and discussed based on published researches. [ABSTRACT FROM AUTHOR]

In this article, a semianalytical method of solution is developed for the nanocontact problem of elastic half-space indented by a rigid cylindrical roller. The mechanical formulation is based on the complete version of Steigmann–Ogden surface elasticity theory. Surface tension, surface tensile stiffness and surface flexural rigidity of the half-space boundary are all taken into consideration. Fourier integral transform method converts the governing equations and displacement boundary conditions of the nanocontact problem into a singular integral equation. Gauss–Chebyshev quadrature and an iterative algorithm numerically solve this integral equation and the force equilibrium condition. The developed semianalytical solution is general in the sense that it can reduce to a few simplified theories. These include classical solution, considering only a single surface material parameter, and Gurtin–Murdoch surface elasticity theory, for which analytical kernel functions of the singular integral equation are presented. Dimension analysis demonstrates that the effects of Steigmann–Ogden surface elasticity on the two-dimensional Hertzian nanocontact properties are up to three dimensionless ratios among surface material parameters, shear modulus and the size of nanocontact. Moreover, least-squares regression analysis suggests that, in the presence of surface effects, an elliptic arc less than a half can represent the nanocontact pressure. When compared with their classical counterparts, lower maximum contact pressure and nonzero minimum pressure are found. Parametric experiments further show that surface tension and surface flexural rigidity significantly affect contact length, contact pressure, contact stiffness as well as displacements and stresses near the half-space boundary. In contrast, the effects of surface membrane stiffness are of secondary importance. In general, smaller indenters and larger surface constants lead to higher load-carrying capabilities of half-space and thus better mechanical responses. [ABSTRACT FROM AUTHOR]

Copyright of Advanced Engineering Science / Gongcheng Kexue Yu Jishu is the property of Advanced Engineering Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dental ceramics made from Yttria stabilized tetragonal Zirconia polycrystalline (Y-TZP) with feldspathic porcelain veneers have similar mechanical and aesthetic response to natural tooth. However, cases of early failure, such as chipping or fracture in the veneering have been reported after short periods of use. The present study evaluated the feldspathic porcelain (VITA-VM9) with addition of 0.5 and 2.5 wt% Alumina-Zirconia as reinforcing agents. Hardness, fracture toughness, contact resistance and color variations were evaluated finding better mechanical performance on the new formulations.

Tilting pad journal bearings (TPJB) are used in turbomachinery for their stability at high speeds. For design purposes, it is necessary to preliminarily investigate the turbomachine rotor dynamic behavior by simulation. The dynamic characteristics of all components must be known as precisely as possible and experimental validation of each single model is required. While a lot of work has been carried out on bearings, the ball-and-socket stiffness is still estimated by means of Hertzian formulas. Recently, some authors have used the finite element method, but it seems that nothing has been done experimentally to date. This paper describes the test rig designed to determine the stiffness of a TPJB ball-and-socket pivot by equipping the grippers of a tensile universal testing machine with specifically designed interfaces. A methodology for evaluating the stiffness from the experimental results is reported. Preliminary compression results are presented and compared with the analytical ones obtained using Hertz’s formula showing significant differences for the ball-and-socket conformal contact.

Ball-in-socket metal on metal (MOM) contacts were analysed using the Abaqus Finite Element package to simulate dry contact between the acetabular cup and the femoral head. Different cup thicknesses of 4, 6, 8, and 10 mm were considered using a polyurethane foam block support system. Elastohydrodynamic lubrication (EHL) analyses were developed for the contacts using three different approaches to specify the contact. These were (i) A simple model based on the radii of relative curvature, (ii) An equivalent contact model developed so that its dry contact area and maximum pressure replicated the values obtained from the FE analysis, and (iii) A modified version of (ii) that also ensured equivalence of the gap shape outside the contact area. Published in vivo information for the hip joint contact forces over the walking cycle was used to specify the operating conditions for the EHL analysis. The analysis method was found to be effective for all points of the walking cycle for cases where the cup thickness exceeded 5 mm and modelling approach (ii) was identified as satisfactory. For a cup thickness of 4 mm, membrane action began to emerge in the FE analyses so that such contacts behaved in a different way. [ABSTRACT FROM AUTHOR]

The drop test of a Boeing-737 fuselage section is modelled using a multibody (MB) with spatial plastic hinge method. The test is simulated in MADYMO to evaluate the structural interaction of the cabin with a stiff auxiliary fuel tank underneath the floor, in a severe but survivable impact condition. The fuselage ribs, cargo door frame, cargo door, and passenger floor with spar webs are modelled using a large number of bodies and universal joints with directional properties to allow for appropriate torsional and bending deformations. The contacts for the fuselage section are modelled using a Hertzian-based contact force model with dissipative damping. The simulation results from the MB approach show reasonably good agreement with those from the experimental test and from a detailed finite element (FE) model. This MB approach then could be a viable tool in modelling occupant and structural deformations for aircraft crashworthiness problems. [ABSTRACT FROM AUTHOR]

Dental ceramics made from Yttria stabilized tetragonal Zirconia polycrystalline (Y-TZP) with feldspathic porcelain veneers have similar mechanical and aesthetic response to natural tooth. However, cases of early failure, such as chipping or fracture in the veneering have been reported after short periods of use. The present study evaluated the feldspathic porcelain (VITA-VM9) with addition of 0.5 and 2.5 wt% Alumina-Zirconia as reinforcing agents. Hardness, fracture toughness, contact resistance and color variations were evaluated finding better mechanical performance on the new formulations. [ABSTRACT FROM AUTHOR]

Copyright of Tribologie und Schmierungstechnik is the property of Narr Francke Attempto Verlag GmbH & Co.KG and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A symmetric axial-torsional stiffness matrix for metallic strands is proposed. • The terms of the stiffness matrix are remarkably compact and simple. • Contraction of the wires helix radius due to contact and Poisson effect is accounted. • The expressions are accurate for many strand constructions and loading conditions. • The lay angles range for which the effect of wire contact is essential is identified. A new formulation for the evaluation of the axial-torsional response of single-layer metallic strands is presented. The proposed model fully accounts for the contraction of the helix radius of the external wires due to both the Poisson effect and the local deformation (flattening) of the internal contact surfaces. Closed form equations are found for the coefficients of the cross sectional elastic stiffness matrix of the strand. Differently from other models of the literature that include the effects of the radial contraction of the wire helices, the proposed stiffness matrix is symmetric. The proposed expressions for the terms of the stiffness matrix are remarkably compact and simple, making them an attractive tool for analytical developments and design calculations. Extensive comparisons with experimental, analytical and Finite Element results of the literature show that the proposed expressions are accurate over a wide range of strand constructions and within a loading range sufficiently extended to cover most practical service conditions. [ABSTRACT FROM AUTHOR]

Summary: The discrete element method (DEM) typically uses an explicit numerical integration scheme to solve the equations of motion. However, like all explicit schemes, the scheme is only conditionally stable, with the stability determined by the size of the time step. Currently, there are no comprehensive techniques for estimating appropriate DEM time steps when a nonlinear contact interaction is used. It is common practice to apply a large factor of safety to these estimates to ensure stability, which unnecessarily increases the computational cost of these simulations. This work introduces an alternative framework for selecting a stable time step for nonlinear contact laws, specifically for the Hertz‐Mindlin contact law. This approach uses the fact that the discretised equations of motion take the form of a nonlinear map and can be analysed as such. Using this framework, we analyse the effects of both system damping and the initial relative velocity of collision on the critical time step for a Hertz‐Mindlin contact event between spherical particles. [ABSTRACT FROM AUTHOR]

Zone of influence has been defined as a region beyond which stresses due to loads applied on an elastic half-space are below a given fraction of the peak stress. These zones are significant since the half-space assumption is valid if the width of contacting body is beyond these zones of influence, while it may need correction if the width is less than the zone width. Further, the half-space solution for stresses needs revision at certain depths since they do not integrate up to the corresponding applied loads within the finite body width, thus violating equilibrium. This paper presents analytical solutions for zones of influence for different stresses and peak percentages and the revised stress distribution at various depths of the contacting body, for Hertzian contacts under: (a) normal loading only; and (b) full-sliding condition. They are found to match with solutions from finite element analysis. [ABSTRACT FROM AUTHOR]

In the present research work, we intend to evaluate the effect of aging of CL (contact lenses) on friction and, in case there are alterations in the value of the coefficient of friction after aging, to understand which modifications in the material incite these variations. For this, a simulation of the aging process to which the CL are subject in vivo is carried out and the friction and stiffness of the CL are characterized, before and after aging. The aging procedure of SCLs (soft contact lenses) was simulated by a cycling process considering that the main parameter influencing the material surface is the transition between the closed and open eye and the exposure to environmental aggressions, particularly ultraviolet radiation. The values of the coefficient of friction and elastic modulus before and after the aging process were compared and was verified the increase of both parameters for all contact lenses. The hydrogel lens was the least affected by aging and the silicone - hydrogel lens based on delefilcon A was the one that showed the least stability of properties. [ABSTRACT FROM AUTHOR]