Range Of Normal Forces Research Articles

Ion nitriding of a face-centered cubic high-entropy alloy: Nitriding kinetics, the effect of temperature and contact stress on tribological behavior

Face-centered cubic (FCC) high-entropy alloys (HEAs) have good mechanical properties, but their low hardness makes it difficult to meet the wear resistance required by actual working conditions. Therefore, the effect of ion nitriding on the microstructure, mechanical properties and tribological properties of Fe40Mn20Cr20Ni20 FCC HEA was investigated in this work. It was found that the activation energy of ionic nitriding of Fe40Mn20Cr20Ni20 FCC HEA was 41.388 kJ/mol, which was lower than that of CoCrFeMnNi HEA (64.034 kJ/mol). When nitriding at 400 °C, the nitrided layer was mainly expanded FCC phase; above 400 °C, the expanded FCC phase began to decompose into CrN and γ phase, the generation of γ phase and the growth of CrN caused the hardness of the nitrided layer to decrease with the increase of temperature. After evaluating the hardness, brittleness and nitriding growth kinetics of the nitrided layer obtained from different nitriding processes, the nitrided layer obtained from the nitriding process with the nitriding temperature of 550 °C and the nitriding time of 5 h was selected for the friction and wear test under different normal forces and temperatures. It was demonstrated that at 20–400 °C, the wear resistance of the nitrided alloy was relatively stable over a wide range of normal forces and was substantially improved over the matrix alloy. At 500–600 °C, due to a certain degree of softening of the surface of the nitrided layer, the wear rate increased slightly, but it was still much lower than that of the matrix alloy.

Biomechanics of the finger pad in response to torsion.

Surface skin deformation of the finger pad during partial slippage at finger-object interfaces elicits firing of the tactile sensory afferents. A torque around the contact normal is often present during object manipulation, which can cause partial rotational slippage. Until now, studies of surface skin deformation have used stimuli sliding rectilinearly and tangentially to the skin. Here, we study surface skin dynamics under pure torsion of the right index finger of seven adult participants (four males). A custom robotic platform stimulated the finger pad with a flat clean glass surface, controlling the normal forces and rotation speeds applied while monitoring the contact interface using optical imaging. We tested normal forces between 0.5 N and 10 N at a fixed angular velocity of 20° s-1 and angular velocities between 5° s-1 and 100° s-1 at a fixed normal force of 2 N. We observe the characteristic pattern by which partial slips develop, starting at the periphery of the contact and propagating towards its centre, and the resulting surface strains. The 20-fold range of normal forces and angular velocities used highlights the effect of those parameters on the resulting torque and skin strains. Increasing normal force increases the contact area, the generated torque, strains and the twist angle required to reach full slip. On the other hand, increasing angular velocity causes more loss of contact at the periphery and higher strain rates (although it has no impact on resulting strains after the full rotation). We also discuss the surprisingly large inter-individual variability in skin biomechanics, notably observed in the twist angle the stimulus needs to rotate before reaching full slip.

Study of Influence of Metal-sealing Additive on Operating Characteristics of Machine Power Plants

. The article considers the issues of creating a lubricating composition which is an internal complex salt and possesses anticorrosive properties along with thermal oxidative stability. Antifriction and anti-wear properties of the additive were investigated, the wear of parts in friction units was reduced by 3.2-7.5 times within the normal force range of 73.15-115.15 kgf.

Frictional contacts between individual woody biomass particles under wet and dry conditions

Friction between wood particles can be a critical property when designing processing equipment for creating cellulosic biofuels and similar natural products. Also, as wood processing is likely to occur year-round, understanding the friction between wet as well as dry wood particles can help design and model equipment, such as screw feeders. Here, a tribo-rheometry method was developed using a commercial rheometer that measured the torque required to rotate two contacting millimeter-scale wood chip particles. First, a range of normal forces were used to find the limits of the experimental method. Torque values were measured for seven pairs of wood chip particles at 1 N normal force under both dry and wet conditions, at both ambient conditions and in a humidity-controlled chamber. The torque required to rotate the wet particles was consistently higher than that of the dry particles, although differences were not quite statistically significant when measurements were performed at ambient conditions. Using humidity control resulted in torque values for wet particles of 1900 μNm and 900 μNm for dry particles. Finally, the friction coefficient was calculated as 0.23 for wet particles and 0.11 for dry particles when humidity was controlled. These frictions coefficients agreed with values for wood reported in the literature. Overall, controlling humidity is strongly recommended to quantify the range of friction for particles that uptake water, including granular systems from biomass to food to powders. Friction higher for wet vs dry wood particles at constant humidity from bar graph on left. On right parallel plate rheomter shown with two wood particles between the plates and axial force pushing plates/particles together and shear force rotating bottom plate. • Tribo-rheometric method developed for controlled moisture friction experiments. • Individual particle friction measured for millimeter-scale wood particles. • Friction coefficients higher for wet versus dry wood particles.

The Tribocorrosion Behaviour of Ti-6Al-4 V Alloy: The Role of Both Normal Force and Electrochemical Potential

The tribocorrosion behaviour of Ti-6Al-4 V exposed to phosphate buffered saline was investigated under a range of normal forces in both cathodic and anodic regions to provide a basis for properly deriving the tribological constants of this alloy. To achieve this, a new customised tribotester was designed and manufactured to rub the Ti-6Al-4 V disks against zirconia balls. The tests were conducted at a sliding frequency of 1 Hz and a sliding distance of 4.8 mm under various normal forces and potentials as 17.5, 10.8, 6, 3.5 N, and − 1.2, − 0.6, 0, 0.4, 0.8 V/VAg/AgCl, respectively. The damaged surfaces were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy, profilometer, and micro-hardness tester. The post analyses confirmed the appearance of some minor cracks together with third-body wear particles. No significant changes in the hardness were detected after the tribocorrosion tests. The results of profilometry and electrochemical current indicated that in the anodic region the chemical losses accounted for a significant proportion (up to 36%) of the total loss. The proportional chemical loss increased with the potential; however, neither direct nor reverse relationship was found with the normal force. Overall, in the anodic domain, the material loss increased with the potential level due to the formation of oxide layer which may induce more shear cutting. In the cathodic domain, hydrogen embrittlement changed the properties of the interface and thus, the amount of material loss. Both the mechanical and chemical wear were described by an existing tribocorrosion theory; thereby, the theory was equipped with its tribocorrosive constants for future analyses on the tribocorrosion of this alloy extensively used in various applications including biomedical implants.

A comparative study on fretting wear and frictional heating behavior of PEEK composites for artificial joint applications

Fretting wear becomes one of most concerning issues in the clinical applications of artificial joints. Polyetheretherketone (PEEK) and PEEK-based composites are promising alternative materials for polymer-on-metal joints. In this study, an experimental investigation is conducted to evaluate the fretting wear behavior and the frictional heating behavior of PEEK and three kinds of PEEK-based composites under the dry sliding and water lubricated conditions. The composite filled with carbon fibers shows excellent fretting wear resistance under a range of normal forces, while the composite filled with PTFE, carbon fibers, and graphite demonstrates different wear mechanisms under small and large normal forces. The temperature increase due to the frictional heating for these four materials is insignificant under the fretting wear loading conditions. The water lubrication reduces the coefficients of friction for all four materials.

How to Measure the Area of Real Contact of Skin on Glass.

The contact between the fingertip and an object is formed by a collection of micro-scale junctions, which collectively constitute the real contact area. This real area of contact is only a fraction of the apparent area of contact and is directly linked to the frictional strength of the contact (i.e., the lateral force at which the finger starts sliding). As a consequence, a measure of this area of real contact can help probe into the mechanism behind the friction of skin on glass. In this article, we present two methods to measure the variations of contact area; one that improves upon a tried-and-true fingertip imaging technique to provide ground truth, and the other that relies on the absorption and reflection of acoustic energy. To achieve precise measurements, the ultrasonic method exploits a recently developed model of the interaction that incorporates the non-linearity of squeeze film levitation. The two methods are in good agreement ($\rho =0.94$) over a large range of normal forces and vibration amplitudes. Since the real area of contact fundamentally underlies fingertip friction, the methods described in the article have importance for studying human grasping, understanding friction perception, and controlling surface-haptic devices.

The role of charge distribution on the friction coefficients of epitaxial graphene grown on the Si-terminated and C-terminated faces of SiC

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients.

Horizontal Normal Force on Buried Rigid Pipelines in Fluctuant Liquefied Silty Soil

The submarine pipelines that are buried in the Yellow River subaqueous delta can be subject to fluctuant local-liquefied soil caused by storm wave action, possibly causing pipeline damage. An experimental investigation was carried out in a wave flume to study the horizontal normal force on buried rigid pipelines in fluctuant liquefied soil. In this experiment, the soil bed was made of silt from the Yellow River Delta, whereas a steel pipe served as pipeline. Under the experimental conditions, the normal force range on the pipeline in fluctuant liquefied soil was several times higher than that in stable soil, specifically on the side of the pipeline exposed to the wave direction. The resultant force of the horizontal normal forces on the buried pipeline grew by about one order of magnitude after soil liquefaction.

Experimental research on frictional resistance of smart isolation tool during maintenance operation in offshore pipeline

PurposePipeline maintenance technology using smart isolation tool is becoming more widely used in the global scope. This paper aims to investigate the effects of parameters on the frictional resistance between the slip and pipeline and the frictional characteristics under different lubrication films.Design/methodology/approachAn experimental platform consisting of slip, pipeline and data acquisition system was developed, wherein the slip slips on the pipeline under different normal forces and velocities. In addition, three lubrication conditions, namely, dry wall, oil liquid and black powder on the wall, were investigated to study the effects of lubrications on the frictional coefficient and characteristics.FindingsResearch results indicate that the frictional force and coefficient were sensitive to normal force. The crude oil affected the frictional coefficient within a certain range of normal force, and the black powder enhanced the surface roughness in the natural gas pipeline. However, velocity had no effect on them. In addition, different contact behaviors could be observed from the frictional coefficient curves.Originality/valueIn this paper, the effects of normal force and velocity on frictional resistance of sliding slip during decelerating process in pipeline were investigated, and the effects of lubrication films on frictional characteristics were also revealed. The research results are of great value to improve the prediction accuracy of smart isolation tool, and also provide a guiding significance for the development of maintenance operation in pipelines.

Effect of normal force on fretting wear behavior and mechanism of Alloy 690TT in high temperature water

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 Cr2O3 existed in the inner layer after fresh materials were exposed to the testing environment.

Assessment of the contact behavior of a soft hemispherical finger tip in curved profile grasping

Abstract This paper presents a finite element study on the contact parameters of a soft hemispherical finger tip pressed against curved surface. The variation in magnitudes of contact radius, contact pressure and vertical displacement are estimated using two-dimensional finite element models. The special effects of geometry using a wide range of normal force on soft finger tips are presented with the aid of a dimensionless parameter, curve factor (R/a). It addresses the effects of the load–contact relationship for ten different fingertip combinations. From close observations it can be concluded that a higher magnitude of contact radius can be obtained with a lower curve factor and vice-versa. Also, it is evident that the radius of contact is higher for a curved object when compared with a flat one for a particular combination. However, there is a significant reduction in the magnitudes of vertical depression and contact pressure.

The frequency response of dynamic friction: Enhanced rate-and-state models

The prediction and control of friction-induced vibration requires a sufficiently accurate constitutive law for dynamic friction at the sliding interface: for linearised stability analysis, this requirement takes the form of a frictional frequency response function. Systematic measurements of this frictional frequency response function are presented for small samples of nylon and polycarbonate sliding against a glass disc. Previous efforts to explain such measurements from a theoretical model have failed, but an enhanced rate-and-state model is presented which is shown to match the measurements remarkably well. The tested parameter space covers a range of normal forces (10–50N), of sliding speeds (1–10mm/s) and frequencies (100–2000Hz). The key new ingredient in the model is the inclusion of contact stiffness to take into account elastic deformations near the interface. A systematic methodology is presented to discriminate among possible variants of the model, and then to identify the model parameter values.

Evidence of Superposition between Grooving Abrasion and Rolling Abrasion

In ball-cratering wear tests, two abrasive wear modes are commonly observed, grooving abrasion and rolling abrasion, which act in distinct areas. Observing this tendency, the aim of this article is to discuss the characterization of an intermediate condition, in which the superposition of the grooving and the rolling abrasive wear modes is observed. This phenomenon is referred to as microrolling abrasion due to the following particular characteristic: the rolling abrasion was found to act on the grooving abrasion. Additionally, in a defined sliding distance range and normal force range, microrolling abrasion is qualitatively observed to be proportional to the sliding distance and inversely proportional to the normal force.

Micro-mechanical Experimental Investigation of Grain-to-Grain Sliding Stiffness of Quartz Minerals

The study presents micro-mechanical tests at the contacts of quartz soil grains exploring the inter-particle sliding (tangential) stiffness through tests of a force-controlled type. The experiments are conducted in a custom-built micromechanical apparatus which is capable to study the particle contact response at relatively low confining forces. This makes its configuration more appropriate for soil mechanics purposes. The experimental data indicated a dependency of particle-contact sliding stiffness (KT0) on the level of normal force (FN) with almost a linear increase of KT0 with FN for the range of normal forces of the study. The results of the research work could be incorporated directly as input in numerical simulations that use the discrete element method for a more realistic representation of the behavior at soil grain contacts.

Finite element assessment of the temperature field couple under joule heat and friction heat between a third rail and collector shoe

Based on the finite element software COMSOL Multiphysics 4.3b, a temperature field model for an aluminium/stainless steel composite third rail and a copper impregnated carbon collector shoe contact with coupling of joule heat and friction heat was established. A method of coupling the two kinds of heat was developed, the temperature fields were calculated, and the maximum coupled temperature change under different electric current, normal forces, sliding velocities and sliding distances were studied. The results show that the temperature distribution expands around the contact area in a descending tendency at positions closer to the electric contact area and the temperature gradients are higher; the maximum coupled temperature increases with an increase of electric current; with an increase of normal force, the maximum coupled temperature initially decreases then increases; the maximum coupled temperature increases initially then gradually becomes stable with an increase of sliding distance; an optimal normal force range exists in frictional sliding with an electric current, at which the maximum coupled temperature is at its lowest; joule heat and friction heat are competitive with each other. When normal force is lower, the joule heat becomes the main heat source, but when normal force is greater, mechanical friction heat becomes the main heat source.

Flexible three-axial force sensor for soft and highly sensitive artificial touch.

A soft tactile sensor able to detect both normal and tangential forces is fabricated with a simple method using conductive textile. Owing to the multi-layered architecture, the capacitive-based tactile sensor is highly sensitive (less than 10 mg and 8 μm, for minimal detectable weight and displacement, respectively) within a wide normal force range (potentially up to 27 N (400 kPa)) and natural touch-like tangential force ranges (from about 0.5 N to 1.8 N). Being flexible, soft, and low cost, this sensor represents an original approach in the emulation of natural touch.

Test–retest reliability and validity of normative cut-offs of the two devices measuring touch threshold: Weinstein Enhanced Sensory Test and Pressure-Specified Sensory Device

Introduction Touch threshold screening instruments must accurately distinguish normal versus abnormal sensation to screen nerve pathology. This study was conducted to find out whether two touch threshold measuring devices (i.e. Weinstein Enhanced Sensory Test (WEST) and Pressure-Specified Sensory Device (PSSD) provide consistent results and indicators of “normal” sensation, and secondarily what rules best define normality. Methods The study design was a cross-sectional reliability and validity assessment with 23 healthy participants. Instruments were applied in random order on the pulp of the middle and little fingers of both hands; with five applications on each digit. Cut-offs of 3, 4, and 5 correct responses were used to classify the response as being normal. Weighted kappa and percent agreement were used to indicate test–retest reliability of the WEST, and validity was determined by calculating the percentage of normal controls that achieved a normal score. The Bland–Altman method was used to characterize the retest reliability of PSSD, and validity was determined by whether the mean of the score is different from the normative scores. Results The agreement between test and retest of WEST (detection level = 3/5) was almost perfect ( k = 1). The average percentages of normal detection of the WEST on two test/retest were 93% and 97% (detection level = 4/5) and 82% and 85% (detection level = 5/5). All mean PSSD tests values were found within the predetermined normal range. The Bland–Altman plot demonstrated a minimal mean difference between test occasions and similar limits of agreement across the four test locations. Discussion The study found that more than 90% of the tests with healthy young participants were reliable and valid in relation to their ability to detect a normal WEST filament or PSSD within a normal force range. Our study was limited by a small sample with healthy participants.

Dry sliding wear behavior of AM50B magnesium alloy

Wear behaviour of AM50B magnesium alloy was tested using pin-on-disc configuration with carbon steel discs as counterpart on dry-sliding conditions. Wear rates and friction coefficients were measured in a sliding velocity range of 0.1–1 m s−1 and normal force range of 10–250 N. Worn surfaces were analysed using Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectrometer (EDS) to define the main wear mechanisms. Abrasion, adhesion, delamination, oxidation, and plastic and severe plastic deformation were observed. Wear mechanism map was proposed. Oxidation and abrasion mechanisms dominated at the lowest sliding velocities and loads. Increasing load and speed led to a combination of oxidation, delamination and adhesion. Plastic deformation and severe plastic deformation were detected for the highest applied load and sliding speeds.

An analysis of the physiologic parameters of intraoral wear: a review

This paper reviews the conditions of in vivo mastication and describes a novel method of measuring in vitro wear. Methods: parameters of intraoral wear are reviewed in this analysis, including chewing force, tooth sliding distance, food abrasivity, saliva lubrication, and antagonist properties. Results: clinical measurement of mastication forces indicates a range of normal forces between 20 and 140 N for a single molar. During the sliding phase of mastication, horizontal movement has been measured between 0.9 and 2.86 mm. In vivo wear occurs by three-body abrasion when food particles are interposed between teeth and by two-body abrasion after food clearance. Analysis of food particles used in wear testing reveals that food particles are softer than enamel and large enough to separate enamel and restoration surfaces and act as a solid lubricant. In two-body wear, saliva acts as a boundary lubricant with a viscosity of 3 cP. Enamel is the most relevant antagonist material for wear testing. The shape of a palatal cusp has been estimated as a 0.6 mm diameter ball and the hardest region of a tooth is its enamel surface. pH values and temperatures have been shown to range between 2–7 and 5–55 °C in intraoral fluids, respectively. These intraoral parameters have been used to modify the Alabama wear testing method.