Development of a device for determining the coefficient of adhesion of a tire simulator with a flat support surface

To ensure optimal braking performance, i.e. minimum braking distance while maintaining the stability of the car at the limit of controllability, anti-lock systems are currently installed on cars. The relative fraction of the rest friction in the contact spot, which is used to form the longitudinal reaction of the support surface at the appropriate value of the slip coefficient, in relation to the total fraction of the rest friction in the contact spot is a constant value for any type and condition of the road surface. The coefficient of adhesion in physical essence is the coefficient of friction at rest. The proposed device for determining the coefficient of adhesion of a tire simulator with a flat horizontal support surface will simplify the design and increase the measurement accuracy. Keywords: coefficient of adhesion, a device for determining the coefficient of adhesion, a device

Numerical Analysis of the Heterogeneity Effect on Electroosmotic Micromixers Based on the Standard Deviation of Concentration and Mixing Entropy Index

One approach to achieve a homogeneous mixture in microfluidic systems in the quickest time and shortest possible length is to employ electroosmotic flow characteristics with heterogeneous surface properties. Mixing using electroosmotic flow inside microchannels with homogeneous walls is done primarily under the influence of molecular diffusion, which is not strong enough to mix the fluids thoroughly. However, surface chemistry technology can help create desired patterns on microchannel walls to generate significant rotational currents and improve mixing efficiency remarkably. This study analyzes the function of a heterogeneous zeta-potential patch located on a microchannel wall in creating mixing inside a microchannel affected by electroosmotic flow and determines the optimal length to achieve the desired mixing rate. The approximate Helmholtz–Smoluchowski model is suggested to reduce computational costs and simplify the solving process. The results show that the heterogeneity length and location of the zeta-potential patch affect the final mixing proficiency. It was also observed that the slip coefficient on the wall has a more significant effect than the Reynolds number change on improving the mixing efficiency of electroosmotic micromixers, benefiting the heterogeneous distribution of zeta-potential. In addition, using a channel with a heterogeneous zeta-potential patch covered by a slip surface did not lead to an adequate mixing in low Reynolds numbers. Therefore, a homogeneous channel without any heterogeneity would be a priority in such a range of Reynolds numbers. However, increasing the Reynolds number and the presence of a slip coefficient on the heterogeneous channel wall enhances the mixing efficiency relative to the homogeneous one. It should be noted, though, that increasing the slip coefficient will make the mixing efficiency decrease sharply in any situation, especially in high Reynolds numbers.

Water–copper nanofluid flow in flat and ribbed microchannels: numerical modeling and optimization

Purpose This paper aims to simulate the nanofluid forced convection in a microchannel. According to the results, at high Reynolds numbers and higher nanofluid volume fractions, an increase in the rib height and slip coefficient further improved the heat transfer rate. The ribs also affect the flow physics depending on the Reynolds number so that the slip velocity decreases with increasing the nanofluid volume fraction and rib height. Design/methodology/approach Forced heat transfer of the water–copper nanofluid is numerically studied in a two dimensional microchannel. The effects of the slip coefficient, Reynolds number, nanofluid volume fraction and rib height are investigated on the average Nusselt number, slip velocity on the microchannel wall and the performance evaluation criterion. Findings In contrast, the slip velocity increases with increasing the Reynolds number and slip coefficient. Afterwards, a non-parametric function estimation is performed relying on the artificial neural network. Originality/value Finally, the Genetic Algorithm was used to establish a set of optimal decision parameters for the problem

Experimental study on slip resistance performance of ASTM A1010 stainless steel bolted connections

The primary aim of this experimental research was to provide information on the slip coefficient performance of ASTM A1010 stainless steel material and to ascertain if its behaviour is comparable to that of 350W Structural Steel. In accomplishing this task, it was important to examine other parameters associated with slip resistance testing, such as (i) bolt relaxation and (ii) the effect of temperature variation and re-usability of high strength bolts. In the 2014 edition of the Canadian Highway Bridge Design Code, the slip coefficient for clean mill scale and hot dip galvanized surface condition for the 350W structural steel is specified as 0.35, whereas for blasted-clean surface condition is specified as 0.5. Although test results in this research showed lower values for tested structural steel plates, the slip coefficient of A1010 stainless steel material performed better than the 350W structural steel for each surface condition and at the same temperature range. Recommendations regarding the slip resistance test method and the methodology for achieving the required surface conditions in slip resistance connection were drawn.

Experimental study on slip resistance performance of ASTM A1010 stainless steel bolted connections

The primary aim of this experimental research was to provide information on the slip coefficient performance of ASTM A1010 stainless steel material and to ascertain if its behaviour is comparable to that of 350W Structural Steel. In accomplishing this task, it was important to examine other parameters associated with slip resistance testing, such as (i) bolt relaxation and (ii) the effect of temperature variation and re-usability of high strength bolts. In the 2014 edition of the Canadian Highway Bridge Design Code, the slip coefficient for clean mill scale and hot dip galvanized surface condition for the 350W structural steel is specified as 0.35, whereas for blasted-clean surface condition is specified as 0.5. Although test results in this research showed lower values for tested structural steel plates, the slip coefficient of A1010 stainless steel material performed better than the 350W structural steel for each surface condition and at the same temperature range. Recommendations regarding the slip resistance test method and the methodology for achieving the required surface conditions in slip resistance connection were drawn.

Slip Coefficient Testing of ASTM A709 Grade 50CR and Dissimilar Metal Bolted Connections

The purpose of this study was to conduct slip coefficient testing of bolted connections made from ASTM A709 Grade 50CR steel to determine how they fit into the current AASHTO LRFD Bridge Design Specifications surface condition classifications. At this time, Grade 50CR steel is not included in these classifications because it was not being used for bridges when the existing surface condition classifications were developed. The slip coefficient tests in this study were conducted according to the Research Council of Structural Connections. Some test specimens were made up entirely of Grade 50CR steel, while others were dissimilar metal connections, consisting of Grade 50CR steel and either weathering or galvanized steel. Dissimilar metal connections were included in the testing because their use is anticipated in which a bridge girder would be constructed using both Grade 50CR steel and other ASTM A709 bridge steels. Results showed that unblasted Grade 50CR steel has a slip coefficient value of at least 0.30, meeting the current AASHTO Class A surface condition for unblasted steel. Blast-cleaned Grade 50CR steel from either steel shot or garnet media has a slip coefficient value of 0.50, meeting the current AASHTO Class B surface condition for blast-cleaned steel. When dissimilar metal connections are made with Grade 50CR steel, the design slip coefficient value of the connection can be taken as equal to the smaller of the two slip coefficient values being joined.

Process of cutting vegetation by cutting machines of segment-finger mowers

The cutting machines of mowers are intended for mowing of natural or sown grasses, on the principle of operation they are divided into the devices of retaining and unpinning cutting. Because of this, the cutting machines are driven from the tractor's PTO or may have an individual hydraulic or electric drive. Depending on the technological process, the mowers may be equipped with an additional flatter or disc machine. The angle of inclination of the cutting machine forwards or backwards is regulated by the rotation of the movable frame relative to the stationary. The centering of the knife is carried out by changing the length of the connecting rod so that in its extreme positions the middle of the segments coincide with the middle of the fingers or do not reach the middle by 5 mm. When harvesting thick-stemmed crops (sunflower, corn), two supports adversely affect the slice. By cutting into a thick stem, the segments are wedged by incised stems, which leads to excessive effort when cutting. Therefore, it is advisable to use the fingers without sprouts in the cutting apparatus for collecting thick-stemmed plants. Segment-finger cutting devices cut plants at knife speed (cutting) 1.5 ... 3.0 m / s. They do not grind plants, require less energy compared to unpowered cutting devices. At the same time, the reciprocating movement of the knife causes considerable inertial forces, limiting the use of such mowers at higher operating speeds when collecting grasses. It is determined that the devices of the supporting cut are simple in structure and reliable in operation, mowers with such devices have lower energy costs per unit of collected area and metal-intensive, and the slip coefficient of the considered cutting apparatus is linearly dependent on the angle of installation of the blade and the position of the stalk axes of rotation of knives. It is established that the effect of the elderly and variable cutting increases, as the stem approaches, it cuts to the center of rotation.

KELLER-BOX SOLUTION OF THE STAGNATION POINT MICROPOLAR FLUID FLOW BETWEEN POROUS PLATES WITH INJECTION

The present study deals with the steady axisymmetric flow of micropolar fluid between two parallel porous plates when the fluid is injected through both walls at the same rate. The influence of velocity slip at the porous surface is analyzed. A detailed finite-difference solution is developed for the resulting non-linear coupled differential equations representing velocities and microrotation. The numerical computations are obtained for radial, axial velocities, and microrotation for varying injection Reynolds number, micropolar parameter, and slip coefficient. Further, a comparison of the results is given with those obtained in the literature with different methods as special cases.

Exploration of novel faying surface treatment for high-strength frictional bolted joints to enhance its after-slip performance

<p>Welded joints is adopted rather than bolted joints for megastructure’s connections because the former can carry large force. However, the former has several problems, such as quality control of welding in situ, which the latter can solve. By contrast, as the load transfer ratio of each bolt becomes uneven proportionally to the number of bolts, local slip around extreme bolts occurs before the whole slip. Extreme bolts to which a large shear force is applied will break before other bolts. For utilizing the strength of all bolts, the problem is solved by improving shear deformation capacity in faying surface with novel surface treatment. Here, the treatment concepts were explored, and the coating’s effectiveness was evaluated through friction tests. The deformation capacity can be twice or more than that of conventional treatment, and the slip coefficient doesn’t depend on contact pressure. These features have the advantage to give stable slip behaviour.</p>

Algorithm of anti-lock braking system for two-axle vehicles with one driving axle with adaptive redistribution of braking forces

The main purpose of active vehicle safety systems is to prevent an emergency situation. If such a situation arises, the system independently (without the participation of the driver) assesses the prob-able danger and, if necessary, prevents it by actively intervening in the driving process. One of the ways to increase the active safety of vehicles when braking is the use of anti-lock braking systems (ABS). The main problems in ensuring the operation of the ABS, built on different control principles and with different control parameters, are the impossibility of directly determining the vehicle speed and, as a result, the slip coefficient, as well as the inability to effectively respond to changing road conditions during braking. For example, when braking on a slippery supporting surface and trying to avoid an obstacle in front, there is a risk of losing traction and skidding. The algorithms of the ABS operation developed at present do not ensure the prevention of the occurrence and development of skidding under the conditions indicated above. The aim of the work is to increase the stability and controllability of two-axle vehicles with one driving axle during braking due to the adaptive redistribution of braking forces on the wheels. An algorithm for the operation of an anti-lock braking system with adaptive redistribution of braking forces on the wheels of a vehicle is proposed. Thanks to this algorithm, when braking on a slippery surface of a two-axle vehicle with one driving axle, the absence of wheel blocking and also skid re-sistance are ensured. The efficiency and effectiveness of the proposed algorithm when braking a two-axle vehicle with one driving axle on a slippery supporting surface were proved by the methods of simulation.