Search

AbstractIntroductionMaterial and MethodsResults and discussionConclusion\nIMPLICATION FOR REHABILITATIONMost people with a spinal cord injury are concerned by pressure injuries (PrI). Since dynamic activities may involve distributions of forces over time that are different from static and given the significant impact of PrIs on healthcare costs, it is, important to study these sitting forces. We aim to investigate sitting forces (overall normal, shear forces and Peak Pressure Index (PPI)) assessed in both able-bodied and wheelchair users (WCU) under static and dynamic conditions. Our hypothesis is that wheelchair sitting forces encountered by able-bodied participants are significantly different from those of WCUs.An experimental seat and a pressure mapping system were used to investigate forces in two different populations, 102 able-bodied and 15 WCUs, in static conditions and during synchronised hand-cycling. The analysis includes statistical comparisons of the sitting conditions (static/dynamic) and of the populations (able-bodied/WCUs).Significant differences in normal forces and PPI were observed between able-bodied and WCUs; conversely, differences in shear forces were non-significant. This suggests that contrary to shear forces, no conclusion on normal forces drawn from trials with healthy participants can directly be applied to WCUs. Secondly, the present results indicate significant reduced averaged: normal force, PPI, and shear forces for able-bodied performing a dynamic activity compared to static sitting. WCUs experienced non-significant lower averaged normal force and PPI but significant lower averaged shear forces.While the present results seem to indicate lower forces for able-bodied performing a dynamic activity compared to static sitting, due to reduced averaged forces, this conclusion is less clear-cut for WCUs.The present observational study can help understand the specific characteristics of wheelchair users concerning the biomechanical sitting load in rest and during propulsive activity: the shear forces are reduced during activity compared to static conditions.From the data collected in the present study, it seems that no conclusion on normal sitting forces drawn from trials with healthy participants can directly be applied to wheelchair users.The present observational study can help understand the specific characteristics of wheelchair users concerning the biomechanical sitting load in rest and during propulsive activity: the shear forces are reduced during activity compared to static conditions.From the data collected in the present study, it seems that no conclusion on normal sitting forces drawn from trials with healthy participants can directly be applied to wheelchair users. [ABSTRACT FROM AUTHOR]

Isotropic and anisotropic magnetorheological elastomers (MRE) were prepared using spherical carbonyl iron (CI) particles and electrolyte non-spherical iron (EI) particles having a 60% weight fraction in silicon rubber. The pre-structured MREs were prepared under a constant magnetic field of 0.3 Tesla. A parallel-plate MR rheometer with a magneto-rheological cell was used to conduct dynamic measurements under different normal forces. All the data were recorded under 1 Hz frequency and strain amplitude of 0.1% (in the linear viscoelastic region), and normal force was varied from 1N to 10 N. Results show that the magnetic-induced shear modulus increases in both MREs with normal force for isotropic as well as anisotropic samples. However, in CIP-based MRE, the MR effect increases with a pre-structured sample, whereas for EIP-based pre-structured MRE, the MR effect decreases compared to isotropic samples. Nevertheless, the relative MR (RMR) effect decreases with normal force in both cases. The rate of decrease is different in CIP- and EIP-based MREs. A possible mechanism for the same is discussed in the paper. [ABSTRACT FROM AUTHOR]

Abstract The attractive specifications of vertical axis wind turbine (VAWT) are its operating with low noise and wind in various directions. To achieve a higher performance of these turbines, modeling of a curved‐blade VAWT by the modified double multiple streamtube (DMST) method and optimizing this wind turbine are performed. The power coefficient and the total normal force acting on blades were selected as two objective functions. Minimizing the normal force acting on turbine blades as the second objective function was not observed in the open literature. The amount of normal force is crucial in the structural design of VAWT because it generates both the bending moment on blades and forces on supporting arms of VAWT. Another innovation of this study is to consider the shape coefficient parameter that determines the shape of the rotor geometry as a design variable in optimization procedure. A 3 m height curved‐blade VAWT type was optimized by this multi‐objective optimization technique. The optimum values of the design variables obtained by the Genetic Algorithm were selecting an elliptical rotor geometry, pitch angle −1.4°, diameter/height 1.3, blade aspect ratio 19.8, tip speed ratio 4.3 and selecting three blades which could provide a power coefficient of 0.49 and a normal force of 158.7 N.

Multi-wire swing reciprocating sawing technology is the main machining method used to cut sapphire crystal bars into wafer substrates, while normal force is an important index that reflects the processing stability. In this paper, the normal force（\begin{document}$ {F}_{\mathrm{n}} $\end{document}）during multi-wire swing reciprocating wire saw cutting sapphire crystal bars was measured, and the change in normal force at different positions and cutting depths of the sapphire crystal bars was tracked. The influence of various process parameters on the stability of the machining process was tracked by using the rangeability of normal force（\begin{document}$ \mathrm{\Delta }{F}_{\mathrm{n}} $\end{document}）as the index. The experimental results show that \begin{document}$ {F}_{\mathrm{n}} $\end{document} is closely correlated with the reciprocating motion of the wire saw and the rocking motion of the workpiece, and Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document} in the front of the sapphire crystal bar is significantly different from that in the middle and back. Process parameters such as the wire saw speed（Vs）, maximum swing angle (θmax), single piece wire consumption (Md), tensioning force (Fw), and total cutting time (T) have different effects on Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document}. The fluctuation degree of Δ\begin{document}$ {F}_{\mathrm{n}} $\end{document} is closely related to the wear of the wire saw.

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]

The attractive specifications of vertical axis wind turbine (VAWT) are its operating with low noise and wind in various directions. To achieve a higher performance of these turbines, modeling of a curved‐blade VAWT by the modified double multiple streamtube (DMST) method and optimizing this wind turbine are performed. The power coefficient and the total normal force acting on blades were selected as two objective functions. Minimizing the normal force acting on turbine blades as the second objective function was not observed in the open literature. The amount of normal force is crucial in the structural design of VAWT because it generates both the bending moment on blades and forces on supporting arms of VAWT. Another innovation of this study is to consider the shape coefficient parameter that determines the shape of the rotor geometry as a design variable in optimization procedure. A 3 m height curved‐blade VAWT type was optimized by this multi‐objective optimization technique. The optimum values of the design variables obtained by the Genetic Algorithm were selecting an elliptical rotor geometry, pitch angle −1.4°, diameter/height 1.3, blade aspect ratio 19.8, tip speed ratio 4.3 and selecting three blades which could provide a power coefficient of 0.49 and a normal force of 158.7 N. [ABSTRACT FROM AUTHOR]

In industries including aerospace, automotive, and marine, a machined component's surface integrity is essential since it improves the corrosion resistance and fatigue life. Hastelloy C-276 is a superalloy based on nickel that is used in the chemical and petrochemical sectors due to its high hot strength, high heat resistance, and high corrosion resistance. In the present work, modelling and simulation of UAMAF process is done on flat work piece with the help of ANSYS Maxwell 16.0 software. The experimental setup for flat work piece on milling machine is modelled according to the dimensions of the experiment. These models are then simulated in ANSYS Maxwell 16.0. After validating the model, the obtained results of analysis were matched with the experimental output. If it is found that the simulation and experiment results vary within the acceptable range, then simulation models are accepted. [ABSTRACT FROM AUTHOR]

Copyright of Diamond & Abrasives Engineering is the property of Zhengzhou Research Institute for Abrasives & Grinding 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.)

Copyright of Electric Drive for Locomotives is the property of Electric Drive for Locomotives 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.)

Knowledge of the Coulomb dynamic coefficient of friction of snow is a vital input parameter for the estimation of run-out distance, velocity, forces, and lateral spread of the snow avalanches in the hilly regions. This parameter is defined as the ratio of the wall shear force to the normal force components of an avalanche. Avalanches are one of the most devastating natural hazards. So, the proper understanding of avalanche flow parameters is vital for the people and the infrastructure in the mountainous regions of the world. Notwithstanding the utmost significance of the Coulomb friction parameter, a few measurements are available for this parameter. In the present work, based on 32 measurements carried out from 2017 to 2020, a new database for the shear force and normal force components of the avalanches and derived values of the dynamic coefficient of friction between the chute steel surface and the flowing snow are presented. The measurements were carried out using a three-component piezoelectric load cells-based dynamometer which in turn was installed on the 12° slope of a 61-m long snow chute, located in the Pir Panjal Himalayan range of India. Based on all the measurements, the average value of the dynamic coefficient of friction for snow-steel surface is estimated to be 0.113 with a standard deviation of 0.032. The results have been exhibited to be in accordance with the published literature. It is expected that the present database will be highly significant for the validation and improvement of avalanche dynamics models especially for high-density wet snow conditions. Further, shear force and normal force components data may be useful for the designing of snow sheds in mountainous regions.

The main core of the semi-active friction damper is the control unit of normal force, which often comprises a piezoelectric actuator with a high dynamic response frequency. However, the telescopic range of the piezoelectric actuator is very limited, so the magnitude of the normal force generated by this actuator is also limited. Moreover, the actuator is sensitive to abrasion and deformation of the friction surface, which affects the friction accuracy of such dampers. To ameliorate these problems, this study proposes a modified semi-active friction damper with a new control mechanism for normal force. The aim is to improve the controllability of the friction damper and reduce its sensitivity to the abrasion, deformation, temperature and speed of the friction surface. Test results show that the three characteristics of this proposed control mechanism are as follows: (1) The internal strain energy is not transformed when the normal force is changed. Therefore, this proposed mechanism can operate without an energy supply; (2) It has flexibility, allows abrasion and deformation of the friction surface, and can still maintain good accuracy; (3) This proposed mechanism provides a closed loop driver and high control accuracy. [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.)

The effect of normal force on fretting corrosion of Alloy 690 TT tube in high temperature high pressure water was investigated. Increasing the normal force accelerates the wear behaviour of the tube. The small normal force has a larger coefficient of friction. The wear mechanism changes from the dominant form of abrasive wear to delamination wear. The increase in normal force not only causes the wear debris layer (WDL) and the tribologically transformed structure to become thicker and more refined, but also affects the oxidation and corrosion behaviour of the tube and changes the composition of the WDL.

The objective is to solve the college physics problem of a block sliding down a movable smooth wedge without friction anywhere using a spatial-numeric perspective. The drawing method used the sum of the normal force and weight of the block to find the wedge acceleration. The drawing method results are equivalent to the algebra method results within drawing accuracy. The result of a geometric construction with regular drawing uncertainly was shown for the case without any horizontal applied force. For the case of a given horizontal applied force, an additional numeric graphing method was shown with additional drawing uncertainty in the result. The geometric construction without graphing resuted in solving the horizontal applied force case via scaling in the concept of modified gravity experienced by the block on the wedge’s slant edge, assuming a pre-requisite knowledge of algebra and trigonometry. The presented spatial numeric method and results imply a Physics First pedagogy of using the spatial numeric abilities, with the inclusion of the pre-projectile problem, pre-traffic-light problem, and post-collision problem in a one-semester syllabus.

The mechanical and hydrodynamic phenomena occurring in the refining zones of disc refiners cause fibres to undergo fibrillation. This paper presents a study of the changes occurring during fibre fibrillation as expressed in terms of the fibrillation index when refining pulp with a 10%, 15%, and 20% consistency. The influences of the tangential force of a circular bar and a straight bar on fibre fibrillation were compared. The changes in the tangential force are shown to depend on the angle between the tangent to the cutting edge and the radius from the centre of the disk to the tangency point. Increasing the angle between the tangent to the cutting edge and the radius from the centre of the disk to the tangency point gives higher fibrillation index values. The study revealed a relationship between fibre fibrillation and the strength characteristics of handsheets.

In order to investigate the influence of sepiolite minerals on the normal force of magnetorheological grease (MRG), a mixed sample (ALCH) on the basis of preparing an aluminum–lithium-based magnetorheological grease (base sample ALC), containing sepiolite was further prepared. The field-dependent normal force of the two samples was tested using a rotational rheometer, considering conditions such as magnetic field, time, strain amplitude, frequency, and temperature, and the results were compared. The results indicate that sepiolite limits the field dependent normal force of the magnetorheological grease under steady state shear, and is unaffected by magnetic field, time, temperature, and shear rate. Sepiolite has minimal impact on the transient response of the magnetorheological grease. Under oscillatory shear, the magnetic field is an important factor influencing the field-dependent normal force response of the sepiolite-magnetorheological grease (ALCH). At low magnetic fields, the field-dependent normal force of the sepiolite-containing sample (ALCH) is greater than that of the base sample (ALC), while this relationship is reversed at high magnetic fields, unaffected by other factors. Under long-term shear conditions, both samples exhibit good shear stability, as well as consistency at different frequencies and strain amplitudes. However, an increase in shear rate reduces the normal force, and temperature also affects the field-dependent normal force. The patterns of variation in steady-state and oscillatory shear modes are not entirely the same, but both exhibit a characteristic decrease with increasing temperature under high magnetic field intensities. Sepiolite can reduce the temperature sensitivity of the normal force of the magnetorheological grease. In conclusion, the introduction of sepiolite is beneficial for the application of magnetorheology in high-precision devices. [ABSTRACT FROM AUTHOR]

The mechanical and hydrodynamic phenomena occurring in the refining zones of disc refiners cause fibres to undergo fibrillation. This paper presents a study of the changes occurring during fibre fibrillation as expressed in terms of the fibrillation index when refining pulp with a 10%, 15%, and 20% consistency. The influences of the tangential force of a circular bar and a straight bar on fibre fibrillation were compared. The changes in the tangential force are shown to depend on the angle between the tangent to the cutting edge and the radius from the centre of the disk to the tangency point. Increasing the angle between the tangent to the cutting edge and the radius from the centre of the disk to the tangency point gives higher fibrillation index values. The study revealed a relationship between fibre fibrillation and the strength characteristics of handsheets. [ABSTRACT FROM AUTHOR]

Robot-assisted minimally invasive surgery enables surgeons to tele-perform elaborate surgical operations to patients with less damage and pain. Besides force feedback provided by the surgical robot to the surgeon, touching sensations are also important for the surgeon to acquire the complete conditions of the patient. Thus, tactile display devices are crucial elements in surgical robots. Meanwhile, various sensations of magnetorheological (MR) fluid can be provided to human fingers because its stiffness, elasticity, and viscosity can be controlled by applied magnetic field. Therefore, in this paper, a new tactile display device based on MR fluid is proposed. This device has high magnetic conduction efficiency, less magnetic leakage, no MR fluid leakage, and overcomes the major drawbacks of the existing tactile display devices based on MR fluid in literatures. Firstly, the design of the tactile display device is described in detail, followed by its fabrication and assembling methods. Secondly, the working current range of the tactile display device is determined by using electromagnetic finite element method (FEM) simulation. Thirdly, the mathematical model to characterize the compression and shear behaviors of the tactile display device is developed. Then, the tactile display device is tested in terms of normal and shear contact forces, followed by its elastic and shear moduli analysis. Finally, the unknown parameters in the mathematical model are figured out, and the model is validated by using structural FEM simulation. The experimental results show that the elastic and shear modulus range of the proposed tactile display device are respectively 3–7.5 kPa and 1.4–5.0 kPa, which can cover the mechanical properties of various human viscera. [ABSTRACT FROM AUTHOR]

Magnetorheological elastomer (MRE), which is capable of exhibiting magnetostriction in the presence of a magnetic field, has a great potential to be used for the development of sensor devices. Unfortunately, to date, many works focused on studying low modulus of MRE (less than 100 kPa) which can hamper their potential application in sensors due to short lifespan and low durability. Thus, in this work, MRE with storage modulus above 300 kPa is to be developed to enhance magnetostriction magnitude and reaction force (normal force). To achieve this goal, MREs are prepared with various compositions of carbonyl iron particles (CIPs), in particular, MRE with 60, 70 and 80 wt.% of CIP. It is shown that both the magnetostriction percentage and normal force increment are achieved as the concentration of CIPs increases. The highest magnetostriction magnitude of 0.075% is obtained with 80 wt.% of CIP, and this increment is higher than that of moderate stiffness MRE developed in the previous works. Therefore, the midrange range modulus MRE developed in this work can copiously produce the required magnetostriction value and potentially be implemented for the design of forefront sensor technology. [ABSTRACT FROM AUTHOR]

The aim of the study was to characterize raw aqueous extracts from Plantago ovata husk in terms of molecular chain mass, osmotic, hydrodynamic, and rheological properties. The raw extracts used in this study have not been yet investigated in the indicated research area. Determination of the molecular weight of the chains present in the extract was performed by gel permeation chromatography (GPC). Osmotic properties were characterized using membrane osmometry. Rheological properties were investigated via classical rotational rheology with normal force measurements, as well as less common but equally important measurements of extensional viscosity. Two types of chains with an average molecular mass of 200 and 1780 kDa were found. The values of the first virial coefficient (B2) indicate the predominance of biopolymer-biopolymer interactions. The hydrodynamic radius established at 25 and 30 °C was 74 and 67 nm, respectively, and lower than at 40 °C (>600 nm). The first critical concentration was determined: c * = 0.11   g · dL − 1 . The dominance of negative normal force values resulting from the formation of a pseudo-gel structure of the heteroxylates was demonstrated. Extensional viscosity measurement results revealed that the studied extracts cannot be treated as simple shear-thinning fluids, as indicated by shear flow, but should be considered as viscoelastic fluids. [ABSTRACT FROM AUTHOR]

Wood friction welding is a green and pollution-free wood processing technology. Research on wood friction welding mainly focuses on the influence of wood type, welding process, and welding interface additives on welding interface strength. However, studies on the tribological properties of wood friction welded interface and its effect on the strength of the welded interface are few. In this article, chemical additives in wood were added to the interface. The frictional force, normal force, microstructure, and chemical composition of the welding interface, and their effects on the strength of the welding interface were studied. In the rotating friction welding of wood, frictional force increased gradually with friction welding. Approximately 2 s after welding, the frictional force achieved a stable state. Normal force increased and then gradually decreased. No considerable changes in frictional force and interface strength were observed and interface strength increased with normal force. The interface strength of glucose and rosin increased, whereas that of N2 protection showed little change. The interface strength of tung oil, cellulose, and guaiac decreased. This study provides a basic reference for the further industrial application of wood friction welding technology. [ABSTRACT FROM AUTHOR]

To solve the problem of springback in traditional multi-point forming (MPF), a new multi-point forming process, namely, multi-point forming with individually controlled force–displacement (MPF-ICFD), is proposed. In this manuscript, traditional MPF and MPF-ICFD are compared. Taking the cylindrical surface as the research object, the change in the springback of a plate is analysed by experiments, and the distribution of the strain and wall thickness of the plate is analysed by numerical simulation. Theoretical analysis is used to calculate the forming window for the MPF-ICFD process, and the results from theoretical analysis are verified by experiments and numerical simulation. The results show that the springback of 1060 aluminium alloy and Q295 for MPF-ICFD can be decreased by 73.8% and 45.5%, respectively, compared with traditional MPF. In traditional MPF, the strain uniformity of the plate is poor, and the maximum thinning rate is 4.5%. For MPF-ICFD, the strain is relatively uniform, and the maximum thinning rate is 0.25%. For an aluminium alloy sheet with a wall thickness of 1.5–3 mm, the upper and lower limits of the forming force for a single head are observed to change linearly from 6.3 to 12.6 kN and from 0.5 to 1 kN, respectively. [ABSTRACT FROM AUTHOR]

Cutting using an abrasive water jet is a complex process involving several physical phenomena. This research studies some of them, mostly the influence of selected variables on the measured forces and vibrations. The traverse speed represents one of the key parameters when cutting using the AWJ. In the presented research, a set of experiments was performed on twelve different metal samples, while the force sensor measured the exerted forces and accelerometers measured the vibrations. Ten different types of steel samples of the same dimensions were cut applying five different traverse speeds. The data obtained during these measurements show that an increase in the traverse speed leads to an increase in the measured forces and vibrations. An analogous experiment performed on bronze and duralumin samples of the same dimensions, having applied higher speeds to compensate for the difference in the material structure and properties, completes the presented data. The most important results of the research are that exerted forces in the z-axis are higher than those in the x-axis, whereas measured vibrations are higher in the x-axis. According to our research, the elemental structure, especially the carbide formation, affects the measured forces and vibrations substantially. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of sepiolite minerals on the normal force of magnetorheological grease (MRG), a mixed sample (ALCH) on the basis of preparing an aluminum–lithium-based magnetorheological grease (base sample ALC), containing sepiolite was further prepared. The field-dependent normal force of the two samples was tested using a rotational rheometer, considering conditions such as magnetic field, time, strain amplitude, frequency, and temperature, and the results were compared. The results indicate that sepiolite limits the field dependent normal force of the magnetorheological grease under steady state shear, and is unaffected by magnetic field, time, temperature, and shear rate. Sepiolite has minimal impact on the transient response of the magnetorheological grease. Under oscillatory shear, the magnetic field is an important factor influencing the field-dependent normal force response of the sepiolite-magnetorheological grease (ALCH). At low magnetic fields, the field-dependent normal force of the sepiolite-containing sample (ALCH) is greater than that of the base sample (ALC), while this relationship is reversed at high magnetic fields, unaffected by other factors. Under long-term shear conditions, both samples exhibit good shear stability, as well as consistency at different frequencies and strain amplitudes. However, an increase in shear rate reduces the normal force, and temperature also affects the field-dependent normal force. The patterns of variation in steady-state and oscillatory shear modes are not entirely the same, but both exhibit a characteristic decrease with increasing temperature under high magnetic field intensities. Sepiolite can reduce the temperature sensitivity of the normal force of the magnetorheological grease. In conclusion, the introduction of sepiolite is beneficial for the application of magnetorheology in high-precision devices.

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. [ABSTRACT FROM AUTHOR]

This paper describes a bio-inspired gait generation mechanism for quadruped robots. The gait generation mechanism is an adaptation of one the authors previously developed. Our previous work focused on how a quadruped robot system can generate gaits using pulse-type hardware neuron models (P-HNMs), which have functions similar to the biological neurons. A microcontroller mounted on the robot changed the joints' angle each time the P-HNMs output a pulse. The joints' angular velocity changed by the pulse period's variation according to the toes' pressure. In this paper, the authors imported the previously developed robot's body into a dynamic simulator and implemented the bio-inspired gait generation mechanism. The robot model's mechanical properties are the same as the previously developed robot. The degrees of freedom are excluded except for the legs. Each leg has two joints and a force sensor at the end of the leg. The gait generation mechanism separately controls the legs using each toe's normal force. Instead of using the P-HNMs' pulse period variation, the authors defined a simple mathematical formula in which the joints' angular velocity corresponds to the normal force. The authors confirmed that the robot model could actively generate animals' gaits due to dynamic simulations. The robot model generated the walk gait and the trot gait according to the locomotion speed. These results show that we can generate gaits for quadruped robots by a straightforward method. [ABSTRACT FROM AUTHOR]

In this paper, we develop an adaptation of the LuGre friction model so as to allow the development of the friction force and its application in any directions on systems subjected to varying normal forces. This is achieved by projecting a modified LuGre model adapted to varying normal forces in 3D along an arbitrary orthogonal system. Consequently, the direction of the friction force is automatically oriented in the correct direction, thus stick, stick-slip, and slip behavior can be represented in all directions. The projected friction model has the following friction features: stick-slip, presliding displacement, frictional lag, varying break-away force, viscous friction, Stribeck effect, and is adapted to varying normal forces. The equivalence of this projected LuGre model with the modified one is proven analytically. The friction model is then applied to simulate the friction on two mechanical systems. The first system consists of a cube sliding on a plane with a transition from stick to slip due to varying normal forces and with a pulling force oriented in multiples directions of the contact plane. The second one is a more complex system consisting of three turbine blades that uses friction to damp their resonance. The results obtained for both systems are consistent with literature. [ABSTRACT FROM AUTHOR]

In this paper, a kind of magnetorheological fluid, containing nano‐Fe3O4, was prepared in order to study the influence of nano‐Fe3O4 content on its normal force characteristics. Firstly, the microscopic force model is constructed and the microscopic static analysis is carried out. Secondly, the force of the magnetic chain under impacted is simulated by using the numerical simulation method of ANSYS finite element analysis and a plate‐to‐plate shear test system is established. The results show that the normal force of the magnetic chain is enhanced by the supporting force of the nano iron powder embedded in the magnetic chain. At the same magnetic induction intensity, the normal force of the magnetorheological fluid gradually increases with the increase of the mass fraction of nano‐particles. When the mass fraction of the nanoparticles is 7 %, the normal force reaches the maximum. [ABSTRACT FROM AUTHOR]

How to reduce the friction resistance between two planes is a difficult problem that has been studied in the field of tribology. Aiming at this problem, the concept of reducing the friction resistance by exciting the periodic change of normal force between the planes is proposed. A calculation model of the displacement amplitude distribution of the plate is established based on the principle of reciprocity of work, and the influence of the periodic change of normal force on sliding friction between the planes is studied. Additionally, an experimental device for analysis of friction between the planes under the periodic change of normal force is established. The calculation model of the plate's displacement amplitude distribution considering the change frequency of normal force is verified and modified by experiments. The research results mainly show two aspects. On the one hand, the calculation model of the displacement amplitude distribution of the plate is in good agreement with the experimental results, which can effectively help to study the effect of periodic change of normal force on sliding friction between the planes. On the other hand, the change of amplitude and frequency of the normal force have an influence on the sliding friction between the planes. That is, the latter decreases with the increase of the former. The above conclusions have great reference significance for the study of vibration drag reduction in engineering production. [ABSTRACT FROM AUTHOR]

The aim of the present work was measuring the effect of varying normal forces on frictional forces applied to different bracket types in combination with archwires made of NiTi and stainless steel of variable cross section. The measurements were carried out in artificial saliva. Three-way ANOVA and Bonferroni post-hoc tests (α=0.05) were applied. Except for one subgroup the combination of normal force, bracket system and wire dimension had significant effect on friction (p<0.001) as friction increased with increasing normal forces. Only moderately tied ligatures or passive self-ligating brackets generate low friction forces. There was a statistically significant order (0.016"x0.022"<0.018"x0.025"<0.019"x0.025") for stainless steel wire material. Finite element modeling simulation showed the increasing effect of active clip force on friction especially for 0.025" wire profiles. If compared to NiTi wires, stainless steel archwires delivered higher friction. Combinations between wire-type and ligation should be chosen carefully for the intended treatment step. [ABSTRACT FROM AUTHOR]

This purpose was to investigate developed seat-cover assemblies' effect on decreasing the fluctuation of the shear force exerted onto the buttocks as the factors causing decubitus ulcers when the back-support was inclined. The participants were 10 wheelchair users. The force plate was used to measure the horizontal force as the shear force. The back-support was inclined at increasing angles, starting from the upright position (IUP), then proceeding to a fully reclined position (FRP), and returning to the upright position (RUP). The experimental conditions were two conditions; the seat-cover assembly conditions and without the seat-cover assembly as the control conditions. The average values in the seat-cover assembly condition were 14.4 ± 3.3, 13.9 ± 2.3, and 17.3 ± 3.3% body weight in the IUP, FRP, and RUP, respectively. The average values in the control condition were 14.8 ± 2.6, 11.4 ± 1.7, and 24.0 ± 6.7% body weight in the IUP, FRP, and RUP, respectively. In the FUP and the RUP, there were significant differences between two conditions (p <.01). These results suggested that the shear force exerted onto the buttocks may to be decreased by using novel seat-cover assembly. It is possible to decrease the fluctuations in the shear force by moving the body up and down according the novel seat-cover assembly attached the back-support incline. Disabled, older individuals can be provided with a comfortable life on a reclining wheelchair while preventing decubitus ulcers. [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]

Magnetorheological elastomer (MRE), which is capable of exhibiting magnetostriction in the presence of a magnetic field, has a great potential to be used for the development of sensor devices. Unfortunately, to date, many works focused on studying low modulus of MRE (less than 100 kPa) which can hamper their potential application in sensors due to short lifespan and low durability. Thus, in this work, MRE with storage modulus above 300 kPa is to be developed to enhance magnetostriction magnitude and reaction force (normal force). To achieve this goal, MREs are prepared with various compositions of carbonyl iron particles (CIPs), in particular, MRE with 60, 70 and 80 wt.% of CIP. It is shown that both the magnetostriction percentage and normal force increment are achieved as the concentration of CIPs increases. The highest magnetostriction magnitude of 0.075% is obtained with 80 wt.% of CIP, and this increment is higher than that of moderate stiffness MRE developed in the previous works. Therefore, the midrange range modulus MRE developed in this work can copiously produce the required magnetostriction value and potentially be implemented for the design of forefront sensor technology.

As one of the most important mechanical parameters of magnetorheological fluids (MRF), the normal force has been studied by a large number of researchers using various experimental equipment and methods. However, it is difficult to reveal the effects of particle microstructure characteristics on the normal force of MRF by experimental methods, especially for such factor as the particle size distribution. To advance this research area, a numerical method for calculating the normal force of MRF is proposed in this study. The accuracy of the simulation model is verified with the experimental results measured by a plate-plate magnetorheometer. The results show that the simulated values agree well with the experimental data, which indicates the feasibility of calculating the normal force of MRF using numerical methods and provides a new research idea for a more intuitive and comprehensive analysis of the normal force characteristics of MRF. Besides, the simulated data show that the increase in magnetic field intensity and particle volume fraction will sufficiently enhance the normal force of MRF and improve the response time of MRF. For the MRF with the same particle volume fraction, a decline in the average particle diameter will increase the normal force. Moreover, increasing the dispersion of particle size of MRF particles can also improve its normal force.

• 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]

This work evaluated several electrode designs in a capacitive tactile sensor (CTS) to provide an optimized solution that shows the maximized sensitivity in shear force detection. In addition to shear angle derivation procedure, identical overlapping areas between the paired electrodes in capacitors were assigned for fair comparison on detection sensitivity of normal force. The theoretical calculation, numerical simulation, practical fabrication, analysis, and discussion were comprehensively conducted in this work with a typical CTS that showed square electrodes as a reference. Results indicated that when the number of legs in a polygon electrode is small, the detection sensitivity in shear force application is high. Furthermore, because the operating principle was unaltered, all designs exhibited compatible detection capability on shear angle in terms of resolution and accuracy. Although only two extreme cases of CTSs with triangular and circular electrodes were demonstrated as proofs-of-concept in this work, the universal solution is also eligible to other designs with polygon electrodes. [ABSTRACT FROM AUTHOR]

The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, a metamaterial is engineered that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, it is shown that the system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre‐compression applied prior to torsion. The work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots, and actuators to engineering biological tissues, implants, and prosthetic devices functioning under compression and torsion. [ABSTRACT FROM AUTHOR]

We report the real time characterization and measurement results of a new tri-axial capacitive sensing array. Each unit cell of the Kapton based sensor has an overlapping electrode geometry that allows for the measurement of normal and shear force magnitudes, and the estimation of the 2D and 3D angle of the shear force. The use of a patterned Ecoflex dielectric layer further improves the shear force response and the tunability of the sensor. A custom readout circuit was developed to selectively read the differential capacitances in the sensor array. The local (unit cell) and global (array) force response of the sensor was characterized using a tilt stage, allowing us to determine both the normal and the shear response at different angles in the range of 0-20N. The results show that the Unit Cell response is uniform in the linear range of 0-10N for normal forces (4.6fF/N for all four differential capacitances) and shows good sensitivity for shear forces (1.4 fF/N difference between the right and left differential capacitances at the minimum) and low cross talk. Similar results were seen when a global force was applied across the sensor array. 2D and 3D models were developed to extrapolate the shear force angle from the capacitance data. We also characterized the flexible patterned dielectric layer to understand the effect of its structural dimensions on the effective relative permittivity and developed an analytical model to easily calculate the effective relative permittivity, which showed excellent correlation with the experimentally obtained results. [2020-0382] [ABSTRACT FROM AUTHOR]

Copyright of Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department 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.)

Abstract The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, a metamaterial is engineered that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, it is shown that the system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre‐compression applied prior to torsion. The work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots, and actuators to engineering biological tissues, implants, and prosthetic devices functioning under compression and torsion.

Cutting using an abrasive water jet is a complex process involving several physical phenomena. This research studies some of them, mostly the influence of selected variables on the measured forces and vibrations. The traverse speed represents one of the key parameters when cutting using the AWJ. In the presented research, a set of experiments was performed on twelve different metal samples, while the force sensor measured the exerted forces and accelerometers measured the vibrations. Ten different types of steel samples of the same dimensions were cut applying five different traverse speeds. The data obtained during these measurements show that an increase in the traverse speed leads to an increase in the measured forces and vibrations. An analogous experiment performed on bronze and duralumin samples of the same dimensions, having applied higher speeds to compensate for the difference in the material structure and properties, completes the presented data. The most important results of the research are that exerted forces in the z-axis are higher than those in the x-axis, whereas measured vibrations are higher in the x-axis. According to our research, the elemental structure, especially the carbide formation, affects the measured forces and vibrations substantially.