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The mechanical contact properties of M50 aviation bearing steel surfaces by using ultrasonic-assisted electrolytic in-process dressing (UA-ELID) grinding greatly influence the machined surface's quality. However, in wet grinding conditions, there are three contact forms on the grinding surface: the micro-cutting contact between the diamond abrasive particles of the grinding wheel and the workpiece surface, the sliding contact between the oxide film asperities on the grinding wheel surface and the asperities on the workpiece surface, and the hydrodynamic liquid film contact of the electrolytic grinding solution. The existing research on the mechanical behaviour of the grinding contact surfaces mainly focuses on the influence of one of the contact forms on the normal force. Therefore, calculation models of the dynamic solid-liquid mixing normal force of the UA-ELID grinding contact surfaces that with three contact forms are constructed in this paper to accurately understand the mechanical contact properties of the grinding surface. The relationship between the three contact forms under different process conditions, such as wheel speed, feed depth, and feed speed, and their influence on the normal force of the grinding contact surfaces are revealed. Finally, the accuracy and versatility of the calculation models in this paper are verified through comparative analysis with other normal force calculation model and experimental measurement. [Display omitted] • The contact mechanical models of grinding surfaces under the action of three contact forms were constructed. • The normal force generated by abrasive micro cutting is about 60% of the sliding contact of the asperities. • It reveals the shortcomings of the grinding specific energy normal force calculation model in the application process. [ABSTRACT FROM AUTHOR]

Nowadays, many scholars have been studied the normal force of MRF in the uniform magnetic field. However, the research on the normal force of MRF in the non-uniform magnetic field is relatively limited. The non-uniform magnetic field can cause the MRF to generate normal force of different sizes and directions to cope with different working conditions, thus the normal force generated in the non-uniform magnetic field require more attention. In this paper, a theoretical model of the normal force of MRF in the non-uniform magnetic field was developed based on the enhanced magnetic dipole model. The normal force of MRF within a unit area can be calculated based on this theoretical model. However, the magnetic induction intensity is different at different locations of the non-uniform magnetic field, which leads to the normal force generated by the MRF are not accurately calculated. Therefore, it is necessary to use COMSOL to establish the material model of the MCR-302 plate rheometer and MRF to verify the accuracy of the proposed model. Then a flat-plate rheometer was used to test the static normal force of the MRF in the non-uniform magnetic field. Finally, the simulation and experimental data were compared. The results show that the simulation result with the experimental data is a good agreement, which verifies the reliability of the theoretical model. The static normal force of the MRF increases with the increase of volume fraction and magnetic field intensity. [ABSTRACT FROM AUTHOR]

• Normal force oscillation in single-wheel testbeds adds artifacts to timeseries data. • Normal force oscillation does not significantly affect average experimental results. • Acceleration related to vertical wheel motion cannot explain normal force variation. • Normal force oscillations are mainly caused by friction in vertical sliders. • A 4-bar mechanism essentially removes normal force oscillation. This work reviews wheel load application methods in single-wheel testbeds (SWTBs), used widely to study terramechanics. Normal force oscillations have been reported in SWTBs, and visible in time-series data when provided. This has usually been attributed to grousers, but is also visible for wheels without grousers suggesting other system dynamics (e.g. friction in the vertical axis) are the cause. Furthermore, accelerations related to periodic vertical displacements of the wheel (whether caused by grousers or otherwise) cannot explain more than a small fraction of the amplitude of normal force variations. In this work, a 4-bar mechanism was developed that balances the normal load and ensures that a constant (not oscillating) normal force is achieved throughout terramechanics experiments. System behaviour with and without the 4-bar mechanism was assessed, highlighting the need for a 4-bar mechanism or other method of balancing normal loads if a constant normal force is desired. No significant effects on average experimental results were observed due to normal force oscillation, but artifacts were observed in the time-series data. Comparisons of results with a system where wheel load is applied pneumatically and characterization of friction in each testbed provide further support to the conclusion that normal force oscillations are mainly caused by friction in the vertical axis. [ABSTRACT FROM AUTHOR]

The effect of contact forces on rail uneven longitudinal wear was investigated using three series of rolling tests, including tests with the same tangential force and varying normal force, tests with the same normal force and varying tangential force, and tests with varying tangential and normal forces. Results indicated that the effect of tangential force on rail uneven longitudinal wear was greater than that of normal force. When the tangential force was the same, rail uneven longitudinal wear occurred under the small normal force condition. As the normal force increased, the wear rate decreased. With the same normal force, rail uneven longitudinal wear occurred under the large tangential force condition. The main damage of the unevenly worn rail was oxidative wear and fatigue wear. The oxidative wear and ploughing were more severe at the crest. Plastic deformation, the degree of grain refinement and fatigue cracks were more severe at the trough. More severe fatigue cracks at the trough lead to more severe wear and then the aggravation of rail uneven longitudinal wear. • The influence of normal force and tangential force on rail uneven longitudinal wear was studied. • The effect of contact forces on rail uneven longitudinal wear was quantified. • The wear and rolling contact fatigue behaviors of rail were investigated in detail. • The damage mechanism of rail uneven longitudinal wear was proposed. [ABSTRACT FROM AUTHOR]

During the last decades, the use of connectors in electrical devices for automotive has significantly increased. This raise in the number of electrical and electronic devices on board has led to a growing number of breakdowns. Indeed, this connectors need to keep a low and stable electrical contact resistance (ECR) but due to engine vibrations, fretting wear damage occur. Characterized by small oscillatory motions, fretting induces wear and oxide debris layer (third body) decaying the electrical contact resistance. The aim of this work is to study the effects of two main factors, which are the normal contact force and the displacement amplitude. In this study, a silver-plated contact (2 µm of thickness) was investigated applying various loading parameters: 2 N < P < 6 N and ±3 µm < δ* < ±20 µm. Results show that the ECR endurance decreases when the displacement amplitude increases regardless of the normal force. However, a non-monotonic evolution is found regarding normal force effect. Indeed, for a given displacement amplitude, a rise of the normal force tends to increase the contact pressure but at the same time induces a reduction of the effective sliding amplitude due a larger tangential accommodation. Hence, by coupling a friction energy density approach with a basic compliance description, the synergic effect of the normal force and the displacement amplitude is described and the ECR endurance predicted. • The influence of the normal force on the electrical endurance was clarified. • Reduction of the sliding amplitude when the normal force increases (accommodation). • Fretting maps of endurance and friction energy were developed. • The higher the friction dissipation, the lower the electrical endurance. • Prediction of the electrical endurance based on a friction density approach. [ABSTRACT FROM AUTHOR]

Abstract Wind tunnel experiments were performed at Re = 6.5 × 104 to measure the mean drag and normal forces, mean bending moment, and vortex shedding frequency for surface-mounted finite-height cylinders. The cylinder aspect ratio was varied in small increments between AR = 0.5 and 11, and two different boundary layer thicknesses were used, δ / D = 0.6 and 1.9. Small increments in AR and use of a single Re helped clarify some AR effects for finite cylinders. The data allowed a more precise definition of the familiar critical aspect ratio to be set, based on the behaviour of the mean aerodynamic forces and the point of action of the mean drag force. A second change in behaviour of the aerodynamic forces with AR was also identified; this transition was related to changes in the vortex formation length, the development of the near-wake recirculation zone, and the influence of the two main near-wake vortex structures, with AR. The general effects of increasing δ / D are to lower the force and moment coefficients and Strouhal number, increase the critical AR, and increase the AR where the second transition occurs. Highlights • Exploration of how C D , C N , C My , and St behave with AR and δ / D for surface-mounted finite-height cylinders. • The critical AR can be defined based on the behaviour of the aerodynamic forces and the point of action of the drag force. • A second change in the behaviour of the forces with AR may be attributed to changes in the near-wake recirculation zone. [ABSTRACT FROM AUTHOR]

For understanding the long term fretting mechanism, the effect of normal force on the fretting wear behavior of 690 TT heat transfer tube against 304 stainless steel (SS) ball in simulated secondary water with 10 6 total fretting cycles was studied. The changes of the friction coefficients can be divided into five stages: small and slowly increase stage, sharply increase to a peak point, dramatically decrease to a steady value, steady stage, and continuously increase stage. And the friction coefficient decreases with the increase of the normal force. The morphologies of the worn scars under different normal forces are quite different. A stratified layer structure is formed on the 690 TT surface during the fretting wear process when the normal force is 60N. [ABSTRACT FROM AUTHOR]

In this paper the new semi-analytical solution for the moving mass problem, published by the author of this paper, is extended to account for the non-homogeneous initial conditions. Derivations are presented for infinite homogeneous beams placed on a two-parameter visco-elastic foundation. Methods of integral transforms and contour integration are exploited to obtain the final closed-form solution, which is presented in form of a sum of the truly steady-state part, mass induced harmonic part, initial conditions induced harmonic part and transient vibration. Except for the transient part that is obtained by numerical integration, full evolution of the transversal vibrations can be quickly and accurately obtained by simple evaluation of the presented closed-form results. Newly derived formulas for infinite beams are validated by analysis of long finite beams, where the problem is solved by the eigenmode expansion method. Excellent agreement between the results is obtained validating the new formulas. [ABSTRACT FROM AUTHOR]

The friction between an elastomer and a rigid substrate may depend on a large number of system and loading parameters. Based on a general structure of the law of friction, we propose a generalized master curve procedure for elastomer friction where the significant governing parameter – indentation depth (or normal force) was taken into account. Unlike the generation of the classical master curve by horizontal shifting of dependence “friction - logarithm of velocity” for different temperatures, in the case of various indentation depth the shifting in both horizontal and vertical direction is required. We experimentally investigated coefficient of friction of elastomer on sliding velocity for different indentation depths and temperatures, and generated a ‘master curve’ according to this hypothesis. [ABSTRACT FROM AUTHOR]

The frictional performances of surgical sutures have been found to play a vital role in their functionality. The purpose of this paper is to understand the frictional performance of multifilament surgical sutures interacting with skin substitute, by means of a penetration friction apparatus (PFA). The influence of the size of the surgical suture was investigated. The relationship between the friction force and normal force was considered, in order to evaluate the friction performance of a surgical suture penetrating a skin substitute. The friction force was measured by PFA. The normal force applied to the surgical suture was estimated based on a Hertzian contact model, a finite element model (FEM), and a uniaxial deformation model (UDM). The results indicated that the penetration friction force increased as the size of the multifilament surgical suture increased. In addition, when the normal force was predicted by UDM, it was found that the ratio between the friction force and normal force decreased as the normal force increased. A comparison of the results suggested that the UDM was appropriate in predicting the frictional behavior of surgical suturing. [ABSTRACT FROM AUTHOR]

At present, researches about surface roughness mainly focus on the measurement methods and the relation between wood surface roughness and adhesion strength as well. It is well known that some sanding parameters are considerably key factors for analyzing the cause of surface roughness. However, only a few research studied the relations among surface roughness, sanding parameters, sanding pressure and wood texture direction. Back-propagation network ( BP network) system was applied to simulate and predict the surface roughness value during the sanding process. The aim of this study was to determine the effects of sanding parameters on surface roughness of pinus koraiensis and the relation between sanding pressure and surface roughness, and finally establish the model of surface roughness combined with wood texture characteristic of pinus koraiensis through neural network system. The results showed that All values of surface roughness had a “vacuum belt” when λ  = 0° and λ  = 45°, but it did not appear when λ  = 90° ( λ refers to the angle between the feeding direction and the wood grain). The confidence of the fitting surface roughness results was 97% by BP network model and the average error was 5.8%, which can simply and successfully predict surface roughness during sanding process. [ABSTRACT FROM AUTHOR]

This paper presents the theoretical modeling and numerical simulation of the probe tip based nanochannel scratching. According to the scratching depth, the probe tip is modeled as a spherical capped conical tip or a spherical capped regular three side pyramid tip to calculate the normal force needed for the nanochannel scratching. In order to further investigate the impact of scratching speed, scratching depth and scratching direction on the scratching process, the scratching simulation is implemented in LS-DYNA software, and a mesh-less method called smooth particle hydrodynamics (SPH) is used for the sample construction. Based on the theoretical and simulated analyses, the increase of the scratching speed, the scratching depth and the face angle will result in an increase in the normal force. At the same scratching depth, the normal forces of the spherical capped regular three side pyramid tip model are different in different scratching directions, which are in agreement with the theoretical calculations in the d 3 and d 4 directions. Moreover, the errors between the theoretical and simulated normal forces increase as the face angle increases. [ABSTRACT FROM AUTHOR]

In this paper a new semi-analytical solution for the moving mass problem is presented. Firstly, the problem of a mass traversing a finite beam on an elastic foundation is reviewed and some new aspects are added. Then, the new semi-analytical solution is deduced for an infinite beam. The semi-analytical solution of the displacement under the mass is derived with the help of integral transforms and the full deflection shape is obtained by linking together two semi-infinite beams. An iterative procedure is suggested for the determination of the frequency of the oscillation induced by the moving mass. Results deduced for infinite beams are confirmed by analysis of long finite beams, with the help of derivations given in the first part of this paper. Convergence analysis on finite beams is also presented, and, in addition, the effects of the normal force, of the harmonic component of the vertical force and of the foundation damping are discussed. [ABSTRACT FROM AUTHOR]

Although there are evidences that most, if not all, soil physical and mechanical processes on larger scales have their origin in processes and properties at the microscale, the range of methods to investigate micro-scaled soil behavior directly is limited. One method to detect flow and deformation behavior under steady and transient stresses is rheometry. This method is well established by means of the amplitude sweep test (AST) to detect viscoelastic properties of soils, i.e. stress-strain relationships under transient stresses that occur due to wheeling or trampling. This test is based upon a soil sample positioned between two parallel plates, where the upper plate rotates in an oscillatory manner with increasing stress or strain amplitude, and the lower plate is fixed. Depending on the retardation of the sample's shear stress reaction, viscous and elastic strain proportions are defined with the help of storage and loss modulus (G′ and G″), and their ratio (tan δ). However, the AST is strongly susceptible to sample preparation and the vertical force of the upper plate. Either a low force (e.g. 1 N) was applied or samples with forces beyond a critical limit (e.g. 12–15 N) were excluded. We used controlled force of 1, 3 and 10 N, equivalent to compressive stresses of 2.04, 6.11 and 20.37 kPa, to find the optimum settings to run the AST. The selected forces/stresses are either low, intermediate or high compared to those observed under undefined conditions in two South Brazilian soils (A and B horizon of a Typic Hapludox – Oxisol, and an Oxyaquic Hapluderts – Vertisol). Furthermore, field density and a common (high) density were applied to the homogenized soil material. The variability of the results generally decreased with increasing compressive stress level, and at highest stress variability was lower than under variable force/stress. The microaggregation of the Oxisol based upon iron oxides and hydroxides (pseudosand) and high kaolinite content in the B horizon resulted in a smaller range of recoverable elasticity than in the Vertisol. However, at large strains the elasticity was higher in the Oxisol, while the Vertisol exhibited alignment of the soil particles. The Oxisol generally showed a brittle rupture by means of a maximum shear stress; while in the Vertisol yielding occurred due to expandable clay. High compressive force and density simultaneously reduced the share of elastic deformation and promoted plastic yielding. The results do not allow yet defining an optimum compressive stress. Thus, we suggest investigating further force or stress levels and to test more soils, e.g. of high soil organic matter content and/or high or low clay, silt or sand content. [ABSTRACT FROM AUTHOR]

A newly magnetorheological fluid based honing process is developed for internal surface finishing of ferromagnetic cylindrical workpiece as existing magnetorheological fluid based finishing processes are not found suitable to finish the ferromagnetic internal surfaces. The performance of the present developed finishing process in terms of reduce wear and improve the functional application of cylindrical components, mainly depends on the normal force acting on abrasive particles due to magnetic behavior of carbonyl iron particles in magnetorheological polishing fluid. Also, it depends on shear force acting on surface by abrasive particles due to translational and rotational motion of tool as similar to the honing operation. For the newly developed finishing process, the modeling of surface roughness with the effect of induced magnetic field and magnetic normal force for different finishing cycles have been proposed. To validate the model and understand the wear mechanism during finishing, the experiments have been performed on the internal surface of cylindrical ferromagnetic workpiece with the three different sets of finishing cycles. The surface roughness of cylindrical workpiece has experimentally measured with Mitutoyo SJ-400 surftest. Also, to understand wear mechanism during finishing, the scanning electron microscopy has been performed. The theoretical calculated values of surface roughness with number of finishing cycles are validated with experimentally obtained surface roughness values for the same number of finishing cycles and conditions. Both were found in close agreement within 5.88%. Thus, the present developed finishing process is found suitable to reduce wear on internal surface of cylindrical components which leads to saving in service, energy consumption, maintenance costs, and improves its functional applications as compared to traditional finishing techniques. [ABSTRACT FROM AUTHOR]

This paper describes the development and precise positioning control of a thin and compact linear switched reluctance motor (LSRM). The LSRM that has been developed has a mover that is easy to fabricate and can be disposable. The mover can be easily separated from the stator, allowing it to be changed frequently or discarded in a hazardous application. The prototyped LSRM mover is only 0.128 mm thick with the stator measuring 2.0 mm at its thickest point. These features are highly desirable for space savings while being cost-effective. However, the LSRM has a strong nonlinear driving characteristic that presents a challenge with respect to precision control. In order to overcome this problem and achieve precision positioning, a linearizer unit was designed and integrated into the controller to compensate for the nonlinear relationships among the effective thrust force, mover position, and excitation current. The usefulness of the designed controller was examined experimentally. The experimental positioning results show that the steady-state errors were all less than 1 μm in the working range of the LSRM. In addition, the redesign for the improvement of thrust characteristic and easy fabrication of the LSRM is explained. [ABSTRACT FROM AUTHOR]

Magnetic Field Assisted Abrasive Finishing (MFAAF) process is one of the advanced fine finishing process which uses a flexible multipoint cutting tool to finish the workpiece. The knowledge of finishing forces acting during the MFAAF process is essential to understand the nature of surface finish produced. This paper presents the effect of process parameters like voltage supplied to the electromagnet, machining gap, rotational speed of electromagnet, abrasive size and feed rate on finishing forces during MFAAF process. The work material selected was SS316L material. The experiments were carried out as per Taguchi L 27 orthogonal array. Kistler cutting force dynamometer (Model 9257B) and charge amplifier (Model 5070A) were utilised to measure the normal and tangential forces. From the experimental results, it was found that higher voltage (22 V) and lower machining gap (1.5 mm) resulted in maximum magnitude of the normal and tangential forces to 33.92 N and 14.16 N respectively. Also it was observed that the voltage supplied to the electromagnet and the machining gap have significant effect in determining the normal and tangential cutting forces. [ABSTRACT FROM AUTHOR]

Fretting wear experiments have been performed in high temperature water with a range of normal forces to investigate the wear behavior of Alloy 690TT tube sections oscillating against stainless steel Type 304 plates. Alloy 690TT is a Ni-based alloy containing Fe, Cr, and other minor additions. Results of tests conducted in an autoclave chamber in pressurized 288 °C water, indicated that fretting wear processes mainly consisted of adhesive wear, abrasive wear, delamination, material transfer, and oxidation. As normal force increased, the initial contact area also increased, resulting in the increase of wear area as well as wear depth. Fretting wear promoted the oxidation of fresh material, and the mechanism corresponded in certain aspects to static oxidation. That is, the outermost surface layer consisted of an Fe-rich spinel, while Cr 2 O 3 existed in the inner layer after fresh materials were exposed to the testing environment. [ABSTRACT FROM AUTHOR]

Initially uncracked push-off specimens were tested to investigate shear transfer in recycled aggregate concrete with concrete grade, normal force and the replacement level of recycled aggregates being the variables. A marginal increase in normalized shear strength was noted when the natural coarse aggregates were replaced with the recycled aggregates. Normal force and concrete grade had the most significant effect on the measured strengths and predictions obtained from modified Zia failure criterion were in good agreement with the experimental results of the natural as well as the recycled aggregate concretes. Selected shear strength models in the literature have been reviewed for their predictive efficacy and in the context of design, the PCI code gave reasonably accurate and conservative predictions of the measured shear strengths of both the concrete types. [ABSTRACT FROM AUTHOR]

The normal force of magnetorheological (MR) fluids in porous foam metal was investigated in this paper. The dynamic repulsive normal force was studied using an advanced commercial rheometer under oscillatory shear modes. In the presence of magnetic fields, the influences of time, strain amplitude, frequency and shear rate on the normal force of MR fluids drawn from the porous foam metal were systematically analysed. The experimental results indicated that the magnetic field had the greatest effect on the normal force, and the effect increased incrementally with the magnetic field. Increasing the magnetic field produced a step-wise increase in the shear gap. However, other factors in the presence of a constant magnetic field only had weak effects on the normal force. This behaviour can be regarded as a magnetic field-enhanced normal force, as increases in the magnetic field resulted in more MR fluids being released from the porous foam metal, and the chain-like magnetic particles in the MR fluids becoming more elongated with aggregates spanning the gap between the shear plates. [ABSTRACT FROM AUTHOR]

This paper presents the normal force phenomena for static and steady shear mode in magnetorheological (MR) fluid. The results of the study show that, in the static mode, with the magnetic flux density increasing, the normal force will increase until the maximum, and then reduce to a steady value, and during the increasing stage, it can be expressed as F N =4667* B 2.48 approximately; however, in the steady shear mode, only when the magnetic flux density achieves a certain value, the normal force phenomena will be observed clearly, and with the increasing of magnetic field, the normal force reaches the maximum, and then also decreases to a steady value. Besides, by defining the time parameters of dynamic response, the dynamic response of normal force is studied. If the shear plate is stationary, from the magnetic field on to a stable normal force produced, the response time is about 25.11 ms. [ABSTRACT FROM AUTHOR]

A novel design for a flexible tactile force sensor, which is called conductive elastic silicon tactile (CEST) sensor, is proposed in this paper. The flexible tactile force sensor is fabricated using a molding process of a composite material, which is a mixture of two components: conductive ink and silicon elastomer. The composite material is poured into a mold, which contains an array of cavities with desired shapes. After curing at room temperature, the solidified part is ejected out of the mold and attached to a designed flexible printed circuit board film. Five tactile sensing elements in the fabricated CEST sensor layer enable independent detection of the external normal force. The efficacy of this sensor is tested when a 0–5 N normal force is applied. Good linearity of 0.93, high selectivity in real-time measurement, and good repeatability of 98.67% are observed. By comparing the characteristics of CEST with those of one of the most used force-sensitive resistor sensor, the CEST sensor achieved competitive sensitivity with better repeatability, high selectivity, and extremely low cost. [ABSTRACT FROM AUTHOR]

• A mechanical model of monocrystalline silicon modified-substrate layer structure based on two-dimensional green's function was established. • The correctness of the mechanical model is proved by the nanoindentation-scratch experiment combined with the phase transition of monocrystalline silicon. • Using this mechanical model to draw the stress component contour diagram and interface stress distribution diagram of monocrystalline silicon modified-substrate layer structure, the internal stress state of the material when the surface is stressed is obtained. It provides a reference for the formulation of process parameters of chemical mechanical micro-grinding process. The application and demand of monocrystalline silicon components are becoming more and more urgent for many advanced applications like solar cells. Chemical-mechanical micro-grinding is one of the effective methods for processing such components. However, the theory of chemical-mechanical micro-grinding of monocrystalline silicon has not been fully established, and the mechanism of material removal is still unclear. In this paper, the monocrystalline surface is modified by catalytic modification, resulting in a modified-substrate layer region. A model is proposed to study and analyze force conditions based on Green's function for modified-substrate layer region under the action of normal force and tangential force. The nanoindentation, XPS, and Raman spectroscopy have been done to verify the theoretical model and explore the phase change process of monocrystalline silicon. The results showed that the established mechanical model can predict the stress distribution at the interface between the surface modification layer of the monocrystalline silicon material and the substrate layer. Furthermore, the internal stress distribution of the surface of the monocrystalline silicon material that has undergone surface chemical modification under load can be obtained. Therefore, the recent paper provides a theoretical basis for the optimization of the process of chemical-mechanical micro-grinding of monocrystalline silicon. [Display omitted] [ABSTRACT FROM AUTHOR]

• Exploration of the mean pressure distribution on the free end of a finite-height square prism. • Systematic changes are made in aspect ratio (AR) and incidence angle (α), and results are shown for two different boundary layer thickness (δ / D). • The locations of the conical delta-wing vortices, as well as the value of the mean normal force coefficient due to pressure, are sensitive to AR, α , and δ / D. In this experimental study, the mean pressure distribution was measured on the free end of a surface-mounted finite-height square prism for different aspect ratios, incidence angles, and boundary layer thicknesses. The Reynolds number based on the width of the prism was kept constant at Re = 6.5 × 104, the aspect ratio of the prism was changed from AR = 1 to 11, and the incidence angle was varied in small increments from α = 0° to 45°. The thickness of the boundary layer on the ground plane relative to the prism width was either δ / D = 0.8 or δ / D = 2.6, representing a thin or thick boundary layer. When the prism was oriented at α = 0°, distinct mean pressure distributions were observed for prisms nearly or completely immersed in the boundary layer, and also for the very slender high-aspect ratio prisms. The mean normal force coefficient steadily increased with the aspect ratio but its value decreased in the presence of the thicker boundary layer. When the prism was oriented at α = 45°, strong pressure gradients were encountered near the leading edges for prisms nearly or completely immersed in the boundary layer, and the conical vortex angles increased with aspect ratio. For intermediate aspect ratios, these pressure gradients weakened and the vortex angles became insensitive to AR. When the incidence angle was between 0° and 45°, the asymmetric mean pressure distribution meant that the conical vortices were located at different angles. The position of the conical vortex located more centrally above the free end was more sensitive to changes in aspect ratio. The influence of the boundary layer on the vortex angles was more pronounced for smaller aspect ratios. In addition, the behaviour of the normal force coefficient with incidence became more complex for higher aspect ratios. [ABSTRACT FROM AUTHOR]

This paper studies the tribocorrosion behaviour of Ti-6Al-4 V in phosphate buffered saline under reciprocating frequencies of 1, 5, 10, 15, 20, and 25 Hz at different normal forces of 3.5, 6, 10.8, and 17.5 N using a customised ball-on-disk test set-up. The tribocorroded scars were then post-assessed by scanning electron microscopy and energy dispersive x-ray spectroscopy, atomic force microscopy, profilometry, and confocal microscopy. The results demonstrated a unique pattern for the total volume loss versus frequency such that the loss was maximum at 5 Hz with a subsequent reduction from 5 to 15 Hz, and a final stabilisation beyond 15 Hz. Compared to the total and chemical losses, mechanical volume loss showed more significant variations with frequency. The results indicated complex interactions between the normal force and frequency in relation to the total material loss from the alloy. These findings challenge the general understanding of an increase in the total loss with increasing frequency. • Tribocorrosion of Ti-6Al-4 V was studied under various normal forces and frequencies. • Variations in total material loss with frequency with a maximum occurring at 5 Hz. • Mechanical part of total material loss was more sensitive to changes in frequency. • Complex interactions between normal force and frequency determined the total loss. [ABSTRACT FROM AUTHOR]

While there is a major body of literature relating the non-linear response of both elastomers and polymer melts with the molecular structure and topology of the chains, the same cannot be said of the non-linear response, especially that below the yield point, for polymer glasses. Here we take an approach that uses ideas of finite deformation elasticity and apply them to the isochronal response of glassy polymers in torsional deformations. We find that, while the torsional (shear) responses are similar for different molecular structures, there seems to be a strong effect of side group relaxations on the normal forces. The results are discussed in terms of the strain energy density function and the opportunities for future research. [ABSTRACT FROM AUTHOR]

Lugs (i.e., grousers) are routinely attached to the surfaces of wheels/tracks of mobile robots to enhance their ability to traverse loose sandy terrain. Much previous work has focused on how lug shape, e.g., height, affects performance; however, the goal of this study is to experimentally confirm the effects of lug motion on lug-soil forces. We measured normal and tangential forces acting on a single lug as functions of inclination angle, moving direction angle, sinkage length, horizontal displacement, and traveling speed. The experimental results were mathematically fitted by using least square method to facilitate quantitative analyses on effects of changes in these motion parameters. Moreover, we compared the measured tangential forces to values calculated from a conventional tangential force model to evaluate the effects of the lug-tip surface, which is generally ignored in existing terramechanics models. The conclusions from this study would be useful for estimating the traveling performance of locomotive mechanisms equipped with lugs, modeling interaction mechanics between lugged wheels and soil, etc. [ABSTRACT FROM AUTHOR]

This paper starts with a short tribute to the scientific legacy of Peter Kralchevsky and his role in the collaboration with the research group of Kuniaki Nagayama in Japan. Next it presents an overview of the lateral capillary forces, studied jointly by both authors and their groups. Analogies with some other forces in nature are highlighted where relevant. The lateral capillary forces emerge between objects dispersed at a liquid interface or in liquid film and act in direction parallel to the liquid interface, being caused by the liquid surface tension. The lateral capillary forces depend on the size of the objects and the wetting of the particle by the liquid and can be either attractive or repulsive. For fine particles the force–distance relationship follows an inverse-linear law. Their effect is seen in our everyday experience that dust particles and bubbles tend to aggregate on the water surface. These forces are universally acting between any objects regardless of scale and are described by equations similar to those describing the gravitational and electric forces in the two-dimensional (2D) world. The current KN & PK review article provides a didactic overview that is easy to digest as a 2D model of gravity in general relativity, because the origin of the latter force, namely the space distortion, can be clearly visualized. [ABSTRACT FROM AUTHOR]

Highlights: [•] Tribological surface affected friction coefficient. [•] Normal force and gap height fluctuation were affected by instrument parameters. [•] A data screening protocol was developed to mitigate variations in normal force. [•] Proper selection of measurement parameters is critical to obtain reproducible data. [ABSTRACT FROM AUTHOR]

Abstract: Railways can inevitably cause railway rolling noise, which is induced by both wheel and rail roughness. Due to the deformation and wear between the wheel/rail at the contact patch, the rail roughness may grow in amplitude after a number of wheelset passages. This results in increasing railway rolling noise. Rail roughness is a common aspect in all transit systems and much research has been pursued to predict and mitigate its growth on track but prediction of resultant noise growth has not been a focus. This paper provides the experimental validation of the modified Railway Rolling Noise Prediction Software (RRNPS) model for the prediction of rail roughness growth and corresponding noise growth. The model is a new framework to enable noise growth predictions due to rail roughness growth mechanics. It is validated by means of several experiments that have been performed along a straight railway line. Through comparisons between predictions and measurements, it is shown that the RRNPS model gives reliable predictions on rail roughness growth and corresponding noise growth. Subsequently this model is used to predict how speed, normal force, wheelset traffic and ballast vertical stiffness affect rail roughness growth and corresponding noise growth. [Copyright &y& Elsevier]

Abstract: This paper aims to investigate the dynamic contact stiffness characteristics of a double-nut ball screw operating at high speeds. The present study first established a proper transformed coordinate system according to the ball screw mechanism, then a variable contact angle is now considered as a function of the position angle of balls to reflect their dependence on the distribution in the raceway. It goes further to derive a contact stiffness matrix to capture the dynamic behavior of ball screws, which is based on the quasi-static method. The obtained numerical results are validated by experiment. Finally, the 5-dof dynamic model is employed to investigate the distribution of contact angles and normal force varying with the ball screw position angle under different operation condition and structure parameters, and the relation between dynamic contact stiffness and operation condition and structure parameters. [Copyright &y& Elsevier]

Abstract: The tribocorrosion of a Stellite 21 type alloy sliding against alumina in sulfuric acid was investigated in order to identify relevant degradation mechanisms. Tribocorrosion tests were performed using a reciprocating motion pin-on-plate system operating under potentiostatic conditions as well as open circuit potential under different loadings. Scanning electron microscopy, optical microscopy, laser profilometry and focus ion beam (FIB) were used for characterizing wear pattern and subsurface deformation. Results show that the prevailing electrochemical conditions, and in particular the presence or not of a passive film, crucially affect the tribocorrosion behavior of this alloy. The passive film was found to significantly enhance tribocorrosion damage and this for two reasons: (i) abrasion of the passive film induces wear accelerated corrosion, (ii) the presence of the passive film significantly increases subsurface deformation in the metal and thus mechanical wear. The effect of electrode potential and normal load on the overall degradation by tribocorrosion could be accurately described by the Archard's wear law (taking into consideration the effect of the passive film) and existing models for wear accelerated corrosion. [Copyright &y& Elsevier]

Abstract: The magnetorheological (MR) fluid based finishing process is a deterministic process for finishing of flat, curved and freeform surfaces. In case of finishing, the knowledge of forces acting on the curved workpiece surface in different conditions improves the understanding of the process. An experimental investigation is carried out to measure the forces on the freeform surface in real time. The effects of the process parameters such as angle of curvature of the workpiece, rotational speed of the tool and feed rate on normal, tangential and axial forces, are studied. The normal force is found to be more dominant compared to other forces. A theoretical model of normal force and tangential force acting on the workpiece is also proposed to improve the understanding of the workpiece–abrasive particles interaction in the MR fluid based finishing process. A comparison of theoretical and experimental results is carried out to validate the proposed models, which show that the trends are in good agreement. [Copyright &y& Elsevier]

Abstract: The need for calibration is important as ancient humankind at B.C. age pioneered calibration for measurable items such as length, weight, frequency and other basic measurement. In the robotic application, the precision of movement and the sensitivity of reaction also based on the calibration of its sensors and actuators. Therefore it is vital for a newly developed sensor to be calibrated thoroughly before it can be used. In this paper, the authors proposed a calibration of a new optical based silicone tactile sensor developed in our lab. Measurable item which is normal force is relates to the blob area of image recorded in the inner side of optical based silicone tactile sensor. The normal force acquired from digital force sensor in experiment conducted. The experiment produced 9 images. The 9 images acquired is processed in WiT 8.2 image processing software to find the area of the specific spot as known as blob image. A blob area VS normal force graph is plotted using experimental data. The graph is then interpolated using suitable curve fitting technique to get the optimum relationship. The result shows that the quadratic plot is the best suit for the data with the force range from 0 to 3.79N. [Copyright &y& Elsevier]

Abstract: The normal forces of magnetorheological fluids under oscillatory shear are investigated by a commercial magneto-rheometer with plate–plate geometry. At the constant strain amplitude and frequency, the normal forces almost keep a steady value with the testing time if the strain amplitude is smaller than the critical value. When a larger strain is applied, they will fluctuate periodically. Under the strain sweep mode, the relationships between normal forces and strain amplitude can be divided into three regions: linear viscoelastic region, nonlinear viscoelastic region and the viscoplastic region. Under the frequency sweep method, it is found that the angular frequency show little influence on the normal forces. At last, the normal forces increase with increasing of the temperature under a low magnetic field, while they decrease under a high magnetic field. [Copyright &y& Elsevier]

Abstract: Magnetorheological (MR) fluid based finishing process is a nano finishing process applicable to a large variety of materials. A theoretical model of forces (normal and tangential) acting on the workpiece is proposed to improve the in-depth understanding of the mechanism of material removal during MR fluid based finishing process. Two different theories are proposed to model the effect of abrasive particles concentration in the MR fluid. A normal and tangential squeeze force model is also proposed based on the theory of rolling process. A comparison of theoretical and experimental results is carried out to validate the proposed models which show their trends in good agreement. [Copyright &y& Elsevier]

Abstract: Temperature field model for aluminum-stainless steel composite conductor rail (stainless steel)/collector shoe (metal impregnation carbon) under the coupling of contact resistor-friction thermal was established by FE software ANSYS. The temperature field distribution model of the friction pair was simulated and the maximum coupled temperature changing with different normal force was researched. The results show that the maximum coupled temperatures decrease firstly and then rise with the increasing of normal force under the constant displacement, current and relative sliding speed. There is an optimal normal force making the maximum coupled temperature to be the lowest for the friction pair of the metal impregnation carbon and stainless steel. The normal force can be used as the working normal force in order to reduce the abrasion induced by temperature rising. [Copyright &y& Elsevier]

Abstract: Self healing is known as a built-in property of bitumen, which can help bitumen and asphalt concrete to recover its strength after damage. Healing can also extend the service life of asphalt pavements. A two-piece healing (TPH) test was developed to investigate the self healing behaviour of pure bitumen using the Dynamic Shear Rheometer (DSR). During the TPH test, a healing process was directly simulated by pressing the two pieces of bitumen together under a parallel-plate system. Two phases can be distinguished from the TPH healing test, the initial healing phase due to gap closure, and the time dependent healing phase. The results are summarised as following. (1) Initial healing phase: The initial healing phase has a three-stage complex modulus increase with the closure of the gap thickness. A rapid increase of the complex modulus is observed in the second stage of the initial healing curve due to a 0.5mm gap reduction. (2) Time dependent healing phase: The time dependent healing results show a distinctive difference between the gap constant control mode and the normal force constant control mode. The normal force control healing can be decomposed into the time dependent healing during a gap constant mode and additional healing by compression. It was indicated that the compressive normal force strongly promotes healing development. (3) It was also demonstrated that many factors can influence the complex modulus measurement results by using the DSR parallel-plate geometry. [Copyright &y& Elsevier]

Abstract: The nanotribology mechanism of alkanethiol self-assembled monolayers (SAM) chemisorbed on a gold surface under a non-flat contact by a tilt plane was studied using molecular dynamics (MD) simulations. The molecular trajectories, tilt angles, normal forces, shear forces, and frictional coefficient of the SAM were evaluated during the friction and relaxation processes for various parameters, including the tilt angle of the slider, interference magnitude, and SAM length. At the nanoscale, the magnitude of interface interactional forces is strongly dependent on the magnitude of the contact area, not on the surface geometry. The contact area and the exerted normal force of the SAM increase with decreasing the tilt angle of the slider at the same contact interference. In contrast, the periods in both normal force and shear force are gradually delayed as the tilt angle of the slider increases. Once the contact interference increases, the normal force and shear force increase together. During the sliding friction process with a smaller tilt slider angle, SAM molecules can maintain a better collective ordered structure. Short SAM molecules are more sensitive to a compressive loading and react to a larger normal force under the same contact interference due to the deformation of a larger tilt angle and decrease in chain length. The friction coefficient of SAM is significantly more dependent on the tilt angle of the slider than the contact interference. [ABSTRACT FROM AUTHOR]

Abstract: This study compares the force sensing properties of polyvinylidenefluoride (PVDF) and ElectroMechanical Film (EMFi) sensor materials. The PVDF material has solid structure whereas the structure of the EMFi material is cellular. Due to the structural differences, some of the material properties differ. The sensor operation is evaluated here with force sensitivity measurements. The sensitivity is measured in directions related to the length, width and thickness of the sensor. The EMFi material is sensitive to dynamic forces exerted normal to its surface, and the sensitivity in that direction ((58.7±16.5) mV/N) was found to be about five-fold when compared to the corresponding value of the PVDF material ((12.6±0.8) mV/N). The PVDF material also detects the forces related to its length and width while the EMFi material has very low sensitivity to these force components. [ABSTRACT FROM AUTHOR]

The use of vertical-axis turbines in marine-current applications for electric energy generation is still in early developments, and one of the key factors for assessing the applicability of such technology is the power coefficient. To contribute towards the highly competitive market of renewable energy conversions, the turbine system requires good outcomes in terms of energy yield. In this scenario, one of the main challenges regarding the design process to improve the blade performance is to find the best trade-off between the maximization of the power output and the minimization of the structural loadings. In the current work, the influence of blade pitch angles on the hydrodynamics of a vertical-axis five-blade water turbine has been studied. The pitch angles from −5° to +5° were investigated using Computational Fluid Dynamics (CFD). The simulations were validated against experimental data for the power coefficient collected in a river. Overall, a good agreement was found in terms of computed power between simulations and experiments for a wide range of tip speed ratios. The CFD model was proven to be suitable for exploratory analyses and an optimized design was found, providing a 2.3% higher power coefficient by adopting a pitch angle of +2° compared to the zero-referenced pitch angle. Besides validating with the experiment, the CFD simulations were compared with the results of a vortex model. The effect of different pitch angles on the performance prediction and on the blade and turbine loadings was also discussed. It is becoming vital to develop an understanding of the complex interaction of vertical-axis turbines, especially in tidal-current areas where there is a lack of detailed experimental data. • Numerical investigation of the influence of the blade pitch on power conversion for a VAMT. • Validation of two-dimensional CFD simulations from field-testing experimental data. • Power enhancement up to 2.3% for positive pitch angles compared to a reference zero pitch. • Significant effect on blade and turbine loadings by the fixed pitch angle. • Accuracy evaluation of numerical approaches with different fidelity level. [ABSTRACT FROM AUTHOR]

Abstract: A method for measuring the coefficient of friction between sliding solid bodies has been developed. In the proposed method, both frictional and normal forces are measured as inertial forces acting on masses. Two pneumatic linear bearings, one placed horizontally and the other vertically, are used to realize a linear motion with a sufficiently small friction acting on the masses, i.e., the moving parts of the linear bearings. The inertial force acting on each mass is calculated from the velocity of the mass; this velocity is determined with a high accuracy by measuring the Doppler shift frequency of a laser light beam that is reflected off the mass using an optical interferometer. The performance of the proposed method is demonstrated by measuring the coefficient of friction between a car wiper blade and a glass surface. [Copyright &y& Elsevier]

Abstract: This paper introduces a model for short-range fibre–fibre interaction and combines it with the Shaqfeh–Fredrickson result for long-range hydrodynamic interactions. The short-range interactions are assumed to be localised, such that the interaction forces may be taken to act at points on the fibre axes. Only interactions of viscous Newtonian character are explored in this work; the approach, however, may be used to treat more general nonlinear interactions, such as non-Newtonian vicous forces or friction. To simulate the orientation evolution, a convective discretisation technique combined with a modification of the Folgar–Tucker rotary diffusion model is proposed. The rotational parallel-plate geometry is analysed, and transient as well as steady state responses are computed. Experiments are performed on suspensions of polyamide fibres in silicon oil, using a rotational parallel-plate rheometer. It is demonstrated that the effect of fibre volume fraction and aspect ratio are well captured by this theory. Normal force as well as torque is adequately predicted. Other effects, however, such as shear thinning and effect of absolute particle size, are not predicted by the linear theory. [Copyright &y& Elsevier]

The fluid flow in cluster magnetorheological-porous foam finishing method (CMRFF) was studied for planner finishing in this study. A normal force model composed by magnetic and hydrodynamic force was established for CMRFF. The normal force is generated by the integral of pressure distribution on workpiece surface and the average relative error between theoretical and experimental results is less than 5.737%. CMRFF can achieve much higher normal force compared with traditional cluster magnetorheological finishing method (CMRF). In the finishing processes of silicon wafer, the surface roughness reduced from 49.66 nm to 16.991 nm in CMRFF in 45 min, compared with 50.559 nm–22.891 nm in CMRF, which indicates the effectiveness of CMRFF in improving surface finishing rate and quality. • A normal force model composed by magnetic and hydrodynamic force is built for CMRFF. • Fluid flow of MRPF in porous foam enhances the normal force in CMRFF process. • Porous foam reduces the adverse effect of centrifugal force on MRPF. • Shear elastic layer thickness considers magnetic field and centrifugal effect. • CMRFF effectively improve the surface finishing rate and quality compared to CMRF. [ABSTRACT FROM AUTHOR]

• A mechanical system of the asphalt pavement on curved bridge deck was established in the computation. • The mechanical response of asphalt bridge deck pavement were explored using a 3D FEM. • The most unfavorable load positions were analyzed under the different factors. • The sensitivity of the factors that affect the mechanical response of bridge deck pavement was graded. Curved concrete bridges with small radii and large longitudinal slopes are important parts of viaduct ramp, on which the asphalt pavement plays an important role in resisting and dispersing traffic loads. Due to the complexity of curved concrete bridge structures with small radii and large longitudinal slopes, the asphalt pavement is subjected to complex mechanical action under loading. This study investigated the mechanical response of the asphalt pavement on a concrete deck under complex load conditions through a three-dimensional finite element model. The effects of different curvature radii, inside and outside wheel groups, driving speeds and temperature fields on the mechanical response of asphalt pavement were analyzed. The results show that in the process of driving on curved bridge deck, the inside and outside wheels of a vehicle produce different normal forces and longitudinal shear forces due to the influence of centrifugal force and radial force moment. With the decrease of the curvature radius and the increase of the driving speed, nonuniform loads are produced on the bridge deck pavement, which would eventually contribute to nonuniform damages. Under different temperature fields, the bridge deck pavement can undergo different failure modes. Besides, temperature fields have the greatest impact on the damage of bridge deck pavement, followed by driving speeds and curvature radii. [ABSTRACT FROM AUTHOR]

Abstract: The influence of shear deformation on the normal force of magnetorheological elastomer was investigated. In quasi-static shear, the normal force decreases with increasing shear strain at low magnetic field, while increases with increasing shear strain when the magnetic field exceeds 452mT. In oscillatory shear, the normal force shows similar trend. However, it decreases sharply when the strain amplitude exceeds 7%. A microstructure based theory was proposed to investigate this phenomenon. Under shearing, the elastic modulus decreases while the magnetic torque increases, which lead to the different trends of normal force at different magnetic fields. This mechanism agrees well with the experimental results. [Copyright &y& Elsevier]

An increasing number of vertical-axis wind turbine prototypes have reached the step in which the theoretically predicted performance needs to be validated in order to move to the next steps of a real commercial project. This step often faces the significant challenges posed by their airfoil aerodynamics that are more complex than those of conventional horizontal-axis wind turbines, and it has also to deal with the lack of fundamental experimental data for robust validation. In this context, an accurate prediction of the real turbine operation is important and the use of computational fluid dynamics (CFD) is imposing itself as the most suitable tool to characterize the unsteady phenomena that are difficult to detect by means of experimental measurements. In the current work, two-dimensional numerical simulations of an H-type three-blade Darrieus turbine have been performed in a wide range of tip-speed ratios (TSRs) from TSR ​= ​1.8 to TSR ​= ​5.0. Unsteady CFD simulations were compared with unique experimental data collected in the field in terms of normal aerodynamic forces acting on the blades during the revolution. Generally, nice agreement was found between simulations and experiments, especially at medium-high tip-speed ratios. The influence of operating conditions on the performance prediction capability of the numerical model was also discussed. This is one of the key points of study since the lack of detailed experimental data often makes numerical analyses doubtful or scarcely effective. Finally, the simulation results were exploited in order to analyze the phenomena occurring during the revolution and to correlate them with the experimental findings. • 2D CFD results compared with revolution-resolved experimental force data. • Unsteady open-site aerodynamics of Darrieus turbine. • Tip-speed ratio affected significantly aerodynamic performance. • Reliable estimation of downwind physical phenomena. [ABSTRACT FROM AUTHOR]

As fretting wear has become one of the main failure mode of Alloy 690 tube in steam generators and is significantly affected by normal force and displacement, the fretting wear behavior of Alloy 690 with different normal force and displacement is studied in high temperature pressurized water. The coefficient of friction, wear volume and maximum wear depth decrease with the increasing of the normal force, while they increase with the increasing of displacement. In addition, the wear mechanism and wear damage are also significantly affected by the applied normal force and displacement. Wear coefficient and energy wear coefficient are calculated respectively. Energy wear coefficient may be a more precise parameter than wear coefficient to describe the fretting wear process. • Fretting wear between Alloy 690 and 405 SS with 1.08×107 cycles is studied in HTP water. • Coefficient of friction and wear volume change significantly under different normal force and displacement. • Wear mechanism and wear damages are significantly affected by the applied normal force and displacement. • Both wear coefficient and energy wear coefficient are calculated. [ABSTRACT FROM AUTHOR]