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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]

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]

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]

The working temperature of a bituminous pavement can typically range from 75 ∘ C to − 20 ∘ C. Bitumen shows a wide spectrum of mechanical behaviour in this temperature range and these include those of a viscoelastic fluid, a viscoelastic solid and an elastic solid. Due to the amorphous nature of the material, the transitions between such mechanical responses are gradual. This investigation focuses on the transition between the viscoelastic solid and the viscoelastic fluid state of a wide class of bitumens with regard to unaged and short-term aged conditions. An unmodified binder and three modified binders were subjected to temperature sweep and frequency sweep in the viscoelastic regime across a wide range of temperatures. Depending on the material and the post-processing method followed, one could discern a viscoelastic fluid and a viscoelastic solid regime and a frequency-dependent mixture regime consisting of a viscoelastic solid and a viscoelastic fluid, across the tested temperatures and frequencies. It is shown in this investigation that parameters such as G ′ –G ′′ crossover and frequency independence of tan δ cannot be used to estimate the temperatures corresponding to the onset of either fluid-like or solid-like behaviour of the body as the temperature varies. It is also shown that the time–temperature superposition principle does not hold good in the temperature regime tested (75–25 ∘ C) due to the viscoelastic transitions exhibited by bitumen and modified bitumen. [ABSTRACT FROM AUTHOR]

This paper presents an experimental method to investigate the effect of nanomagnetic particle on mechanics performance of magneto-rheological (MR) fluid, including the normal force and shear torque. Under different currents, the mechanics performance of a series of MR fluids with different quantities of nanomagnetic particles (0%, 4%, 7%, 12%, and 16% respectively) are measured by the plate-on-plate shearing test rig. The experimental results indicate that, with an increasing quality percentage of nanomagnetic particles, in a small range of currents (0-1.5 A), the mechanics performances are increasing, but their increment is no longer obvious when the current is above 1.5 A. [ABSTRACT FROM AUTHOR]

This paper proposes a tactile display providing both shear and normal feedback to the fingertip for generating three-axis tactile feedback during teleoperation of a surgical robot. The display is composed of five balloons actuated by controlling the pneumatic pressure. The implemented display is 18?mm?×?18?mm?×?15?mm. This size is suitable for mounting the display onto the master controls of a surgical robot. The maximum normal and shear displacements are 2 and 1.3?mm, respectively. The proposed tactile display may provide perceivable stimuli to a human finger pad in all five directions: normal, distal, proximal, radial, and ulnar. This paper also reports on the results of psychophysical measurement of the minimum perceivable movement of the developed tactile display for each of the five directions. [ABSTRACT FROM AUTHOR]

A set of model polypropylene (PP) and talc-filled PP with various lubricants were prepared to study the effects of normal force on the scratch hardness of polymers. The effects of additives and annealing treatment on the scratch behavior of neat and talc-filled PP systems were investigated using a multiple-finger scratch test with focus on the influence of applied normal force on the scratch hardness. A way to revise the scratch hardness test method based on ASTM G171-03 (standard test method for scratch hardness of materials using a diamond stylus; ASTM International; West Conshohocken, PA) and ASTM D7027-05 (standard test method for evaluation of scratch resistance of polymeric coatings and plastics using an instrumented scratch machine; ASTM International; West Conshohocken, PA) is given. Differential scanning calorimetry and optical microscopy were used to characterize crystallinity, morphology, and scratch deformation mechanisms in the PP systems. It was found that the scratch hardness is related to the applied normal loads, the friction coefficient, and the fracture features generated during the scratch process. The talc-filled impact copolymer polypropylene (ICPP) exhibited higher scratch hardness than the neat ICPP. Homo-PP exhibited superior scratch resistance and less susceptibility to scratch deformation than ICPP. The addition of lubricant and annealing treatment improved the scratch resistance of both neat and the talc-filled PP systems. [ABSTRACT FROM PUBLISHER]

Piezoelectric ceramics, constituting an active element, make a stator vibrate generating a rotational force in ultrasonic motors. In the drive of ultrasonic motors, many factors exist that can affect the resonance characteristics of piezoelectric ceramics. For example, those factors are the bonding conditions with the elastic body, the magnitude of the electric field, the normal force for the frictional drive, the emission of heat due to vibration and friction, and so on. Therefore, it is important to properly research the inclination for variation of piezoelectric ceramics in the circumstance where complex elements are involved. In this paper, we focus on the analysis of the resonance characteristics of an ultrasonic motor due to the magnitude of the input voltage and normal force. [ABSTRACT FROM AUTHOR]

We reexamine the interpretation of the normal force measured with a cone-and-plate rheometer for nematic liquid crystals. We point out the fact that the quite widespread belief that the normal force is directly related to the well-known rheological function N1 (i.e., the first normal stress difference) fails for these complex fluids. After a brief presentation of the theoretical bases leading to the general expression of the normal force, this new approach is applied to nematic liquid crystals within the framework of Leslie-Ericksen theory. In order to avoid heavy numerical computations the full Leslie-Ericksen equations describing the three-dimensional flow within the cone-and-plate cell are reduced, thanks to reasonable approximations, to an effective one-dimensional problem (i.e., a system of partial differential equations with spatial derivatives with respect to one single coordinate). Results for low molecular weight liquid crystals are presented and discussed. The main feature evidenced in this work is the notable difference between the normal force calculated in this way and the N1 function, in particular the normal force function becomes negative for high shear rate while N1 stays positive. [ABSTRACT FROM AUTHOR]

An analytical method is applied in the calculations of ball contact angles varying with the position angle of a ball bearing with a centrifugal force. This is further extended to investigate the thermal slipping behavior occurring at the contact surface of the inner raceway. The sliding velocities at the contact area are analyzed in the present study by the ball bearing contact mechanisms. The shear stress created at this contact surface is evaluated by considering the temperature-pressure dependence of the lubricant viscosity. The contact temperature of a ball and the inner raceway is obtained if the frictional heat created by the shear stress is available. Under the condition of controlling the outer raceway temperature, the thermal deformations of all components of a ball bearing are taken into account in the evaluation of bearing performance. Comparisons are made for several parameters, including the normal load, linear slip velocity, and linear traction force, between the results of considering the thermal effect or ignoring it. The friction torque evaluated by taking the thermal effect into account is higher than the torque evaluated when ignoring the thermal effect. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the static friction properties between human palmar skin and five grabrail materials (chrome, stainless steel, power-coated steel, textured aluminium and knurled steel) for dry, wet and soapy hands. Thirty subjects (15 female, 15 male) participated in this study, their ages ranging from 19 to 45 years with a mean age of 28 years. The normal force, friction force, and coefficient of static friction were determined by measuring three-dimensional forces while slipping the palm of the hand over the surface of a grabrail. A repeated measures ANOVA indicated that gender, age, hand size and trial effect had no significant influence (p >0.05) on these results. The coefficient of friction (p <0.001) and friction force (p <0.001) were significantly lower when the hand was soapy than when it was dry or wet. The normal force applied when the hand was soapy was significantly greater (p <0.001) than when it was dry or wet. No significant difference was found between dry and wet hands. The two textured materials displayed superior friction properties when the hand was soapy, while the smooth materials performed best when the hand was dry. [ABSTRACT FROM AUTHOR]