Quantum dissipation and friction attributed to plasmons

In this paper, we computed quantum friction of two parallel metal plates separated by a small distance moving with constant relative velocity [Formula: see text]. The plasmons as the internal degrees of freedom living on the two plates are coupled to a vacuum field in the gap between the two plates. We got the in–out quantum action which contained all the dynamical information of the system. Furthermore, we associated the imaginary part of the in–out quantum action with dissipation and frictional force. For the case of dispersionless plasmons, the imaginary part of the in–out quantum action is strongly suppressed as [Formula: see text]. The frictional force exhibits the same feature as [Formula: see text]. The difference is that the frictional force increases as [Formula: see text] and decreases as [Formula: see text]. For the case of dispersive plasmons, there is a threshold for the imaginary part of the in–out quantum action and the frictional force, that is, there is no dissipation when the relative velocity [Formula: see text] is not big enough. We gave a classical argument of the existence of the threshold, and this argument matched the mathematical results.

Optimal design of the disc vents for high-speed railway vehicles using thermal-structural coupled analysis with genetic algorithm

Braking devices are devices that convert kinetic energy into thermal energy using frictional force. A disc-type brake uses the frictional force to brake and can be used in a wide range of applications, such as automobiles, railway vehicles, and aircraft. However, heat dissipation of the disc has been considered a major problem. High temperatures during the braking process cause thermal stress and deformation problems of the disc because the physical properties of metal composing the disc change drastically with temperature. In this study, vents were applied on the disc surface to increase their heat dissipation performance. In general, vents are structurally susceptible to stress and deformation. However, heat dissipation is essential because the disc surface rises to high temperatures. Therefore, a thermal-structural coupled analysis was performed using the computational fluid dynamics and finite element method methods. Five different rotational speeds and surface temperatures of the disc were considered. Design of experiments was used to determine an optimized design utilizing the data from the coupled analysis, and Latin hypercube sampling was used to generate samples from a set of N regions. And the genetic algorithm was used to conduct a sensitivity analysis of the design parameters. The optimized design was determined for harsh conditions. The diameters of vents were selected 6.87 mm, 6.12 mm, and 5.99 mm in a radial direction through the optimization. Thermal stress and deformation acting on the disc were reduced in the optimally designed disc. The optimized disc model experiences a 7.01% decrease in maximum equivalent stress when compared to the original disc. The model also decreased by 7.63% in maximum equivalent elastic strain. So, through enhanced convection-induced heat dissipation, the vents can be considered as a new way to prevent problems with the thermal stress and deformation that were apparent at high temperatures.

Study on the Distribution of Frictional Forces on Z-Yarn Continuous Implanted Preforms and Its Application

In order to improve the quality and efficiency of the Z-directional 3D preform forming, the Z-yarn friction force distribution model of the preform and its wear mechanism were investigated. Designed the tensile force measuring device of the replacement guide sleeves,the measured tensile force is equivalent to the Z-yarn friction force. Found that the frictional force was proportional to the number of preform layers, the frictional force applied to the one preform decreased from the corner, edge, sub-edge and middle in order. Established BP neural network model to predict the friction at different positions of preform with different layers, the error is within1.9%. The wear of Z-yarn was studied at different frictional positions and after different times of successive implantation into the preform, showed that with the increase of the number of Z-yarn implantation and the friction force, the amount of carbon fiber bundle hairiness gradually increase, and the tensile fracture strength damage of the fiber is increasingly affected by the friction force,and in the corner position of the preform, when the number of implantation is 25 times, the fiber fracture strength will occur non-linearly and substantially decreased, in order to avoid fiber fracture in the implantation process, the Z-yarn needs to be replaced in time after 20~25 times of continuous

Experimental Modal Analysis of a Linear Reciprocating Tribometer for Maximum Reciprocating Frequency

This work demonstrates estimation of critical reciprocating frequency of a fabricated linear pin-on-reciprocating plate tribometer by modal analysis. Experimental investigation by impact testing and numerical analysis using ANSYS Work bench 14 were performed to extract the modal parameters of individual subsystems. The authors could not find reported literature on of estimation of critical reciprocating frequency of pin-on-reciprocating plate tribometer. Authors developed a pin-onreciprocating plate tribometer that can simulate friction and wear under reciprocating sliding conditions for stroke lengths up to 150 mm. The developed pinon- reciprocating plate tribometer had a loading sub system, transmission subsystem and measurement subsystem. From experimental and numerical estimation of modal parameters, transmission subsystem found to had the lowest modal frequency of 18 Hz. Maximum frequency of reciprocation then fixed at 30% of the lowest modal frequency of 18 Hz that is 5 Hz. Confirmatory friction tests were then conducted on the tribometer and found that identification of maximum frictional force was difficult when the reciprocating frequency of plate of tribometer exceeded 4 Hz due to vibrations in measuring system and agreed with the reported literature. This work addresses the need of methodology for establishing critical reciprocating frequency of tribometer. This paper elaborates the modal analysis of a fabricated linear reciprocating tribometer. Resonance of subsystems in reciprocating tribometer affects experimental estimate of coefficient of friction (CoF). Subsystems have their own individual modal frequencies. Hence, modal analysis of all subsystems becomes obligatory. Tribometer developed for this study can simulate reciprocating friction and wear for stroke lengths up to 150 mm. Experimental and numerical analysis utilized to identify modal frequency of individual subsystems. Tests identified that transmission subsystem had the lowest modal frequency of 18 Hz. Maximum frequency of reciprocation then fixed at 4Hz. This is 25% of the lowest modal frequency of 18 Hz as delineated in literature. Confirmatory friction tests then conducted on the tribometer. Resolving maximum frictional force along the stroke length was impossible over 4 Hz of reciprocating frequency. This is 25% of the lowest modal frequency of structure and agreed with the reported literature. Authors sincerely hope the methodology used in this paper will guide fellow researchers for modal analysis of reciprocating tribometer.

Tribology of The Sock-Skin Interface – The Influence of Different Fabric Parameters On Sock Friction

The purpose of this parametric design of experiments was to identify and summarize how the influence of knit structure (single jersey vs. terry), fiber composition (polyester vs. cotton), fiber linear density (30/1 Ne vs. 18/1 Ne & 1/150/34 vs. 2/150/34), and yarn type (filament vs. spun) affected the frictional profile across the sock-skin interface, and then relate these factors to friction blister incidence. Friction testing trials were completed against both a polypropylene probe and a synthetic skin material (Lorica soft®) to determine if there was a difference in friction based on interface interaction. Friction testing was completed by sliding a probe across the inside bottom surface of the sock (the part that is usually in-contact with the bottom of the foot) while instantaneously measuring the frictional force every tenth of a second. For both trials (plastic probe and synthetic skin), in the dry condition, knit structure was found to be the most prominate fabric parameter affecting the frictional force experienced at the sock-skin interface. It was also determined that fiber linear density, and yarn type are tertiary factors affecting the frictional force measured at the sock-skin interface. Finally, in the dry state, it was determined that fiber composition had seemingly no effect on the frictional force experienced at the sock-skin interface.

Influence of the movement of involute profile gears along the off-line of action on the gear tooth position along the line of action direction

When gears change their distance along the off-line of action (OLOA) direction, this affects the distance between the working surfaces of the meshing teeth along the line of action (LOA). This effect is usually neglected in studies. To include this effect precise equations are derived for spur gears. The analysis is carried out for the general case of spur gears with shifted profiles frequently used in the industry. The influence of OLOA gear displacement on LOA direction is also a function of gears parameters. An analysis is conducted, and the impact of parameters such as module, pressure angle, gear ratio, and the number of teeth is determined. As an example, a simulation of a 12 DOF analytical model is presented. The movement of gears along OLOA is caused by a frictional force that can be high during tooth degradation e.g. scuffing. Results show that when the movement of gears along the OLOA direction is significant, its influence on the distance between the mating teeth should not be neglected.

EFFECT OF CYCLE OF LOADING ON SUBBASE FRICTION CHARISARITICS UNDER RIGID PAVEMENT

The coefficient of friction is a measurement of the frictional force between two objects. As the temperature of the pavement changes, it might slide against the resistance of the supporting subbase. In order for pavement to perform as anticipated, this resistance must be calculated. Concrete cracking does not occur when the pavement is joined. A membrane layer is positioned between the subbase and the plate in joint plain concrete pavements to smooth the interface. The displacement of concrete caused by temperature differences is less resistant on a smooth surface. For subbase conditions, two stages of the push-off test were performed (smooth and rough) to show the effects of movement cycles. Based on the results of the friction tests, the friction properties of the concrete and subbase were investigated. The parameters that influence the coefficient of friction and displacement are (interface state, movement rate, thickness number of movement cycles), changing the interface condition from smooth to rough leads to an increase the FRF of (6, 9 and 12 cm/hr) by (194.7, 194.4 and 189.8 %) respectively. Finally, once the applied force reaches a stable state, the frictional force increases dramatically. The most important influence on this force is the interface state, which is accompanied by movement rate and thickness. The variation of the relationship curves with number of cycles tends to be insignificant after the third to fourth cycle of slab movement.