Search

This paper investigates the squeezing action of hybridized nanofluid flow that takes place in the mechanism of truck brakes, dampers, polymer manufacturing, power transportation, oiling structure, and food production. The modeling technique relied on a set of partial differential equations to direct the fluid, taking into consideration external factors like the magnetized force and the time-dependent source of heat and thermal radiation. The hybridized nanofluid consists of copper and aluminum oxide nanoparticles that are dispersed in the machine oil. Entropic thermodynamic analysis is also examined to evaluate its role in the thermal examination of the system. The optimal homotopy asymptotic and Adomian decomposition methods were used to solve the problem. The study examined the changes in the rate of entropy formation and the characteristics of fluid velocities, heat transference rate, and performance based on the kind and concentration of nanoparticles and external thermal impacts. The results are presented in many key components, including a notable 30% increase in heat conductivity when using a combination of nanoparticles. The use of hybridized nanofluids manages to reduce surface frictional force, whereas the employment of a combination of particles results in an increase in friction owing to the heightened viscosity of the mixture. [ABSTRACT FROM AUTHOR]

Sharp curves are vulnerable sections for rollover accidents. This study was conducted to investigate the effects of transition curve and superelevation on the critical speed and critical braking distance of truck rollovers. Using different transition types (spiral, Bloss and Grabowski curve) and different superelevation values (6%, 120 m transition length and 8%, 160 m) as variables, experiments of constant speed driving and hard braking were simulated and conducted by Trucksim. Conclusions regarding the influence of these road design factors on the stability of vehicles were then proposed. Grabowski curve allowed for the maximum critical rollover speed. The difference in critical rollover speed between different transition types was only determined by the length of the transition section. Simply extending the length of the transition section increased the critical rollover speed of spiral curve, at the same time decreasing the critical speed of Bloss and Grabowski curve. Hard braking experiments showed completely different characteristics. As the initial speed increased, only spiral curve became safer. Increasing superelevation made the braking behaviour of the vehicle more dangerous and fraught with uncertainties due to different target speed, starting curvature and changing superelevation. Based on these findings, a number of useful recommendations for drivers and road designers were put forward. [ABSTRACT FROM AUTHOR]

During the braking manoeuvre of a vehicle on a pavement, the mechanics associated with load transfer is complex due to the presence of slip, load shift between the front and rear axles, and development of longitudinal forces. The road profiles, braking intensity, truck mass, and speed during braking play a critical role here. This investigation reports an attempt to collect such data. A unique Hardware-in-Loop set-up was integrated with vehicle dynamics software, TruckMaker, to perform a realistic braking manoeuvre. Three truck loadings were chosen from the axle load survey conducted in the field (unladen, laden, and overloaded). Three ISO road profiles (A, B, C) generated using the power spectral density approach, three initial speeds (30, 50, and 80 km/h), and three braking intensities (Partial (10%), Partial (45%), and Complete (100%)) were chosen for the simulation. In total 81 simulations were performed considering all the above-said factors. From the analysis of wheel slip values, it was identified that the wheels of unladen trucks lock during complete braking, irrespective of the speeds and road profiles. The complete braking manoeuvre for all vehicle types showed more load shift from the rear axle to the front axle compared to partial braking manoeuvres. Also, the unladen trucks were found to transfer more percentage (>50%) of their rear axle load to the front axle during braking. The maximum longitudinal force developed at the tyre-pavement interface was found to be independent of the loading conditions during complete braking. [ABSTRACT FROM AUTHOR]

Routine checkup of security vehicle, together with drivers' complaints of abnormal vibrations during the braking process, indicated a severe damage of brake disks in terms of radial macro-crack and heavily micro-cracks on the friction surfaces. This failure occurred after a short period of service (less than 15000 km) and significant damage was also noticed in the brake disk that was removed after 6000 km. Although the characteristics driving in such vehicle are accompanied by high speed with high g-deceleration frequently, it is still an abnormal failure. The inquiry process indicates that some modifications had been made which considerably increased the total mass of the vehicle. This change significantly affects the forces acting on the brake disk and accordingly on the temperature evolution during the braking process. This change did not involve any adjustment to the braking system. Comprehensive microscopic examination (metallographic, fractographic together with chemical analysis and mechanical testing) of the gray iron brake disks enables to point out some additional sources which lead to this precursory failure. Possible solutions were suggested to prevent such damage which can be hazardous to the proper functionality of this safety component. Firstly, to replace the brake disk more often based on the fatigue crack initiation study. Secondly, to consider using new structural material such as AISI 4330 with a higher fatigue endurance limit and with great resistance to thermal fatigue crack initiation. [ABSTRACT FROM AUTHOR]

Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fluid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented. Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions. [ABSTRACT FROM AUTHOR]

To reduce the probability of secondary accidents caused by the direction deviation, body rollover, and excessive deceleration of runaway vehicles during braking on a truck escape ramp (TER), the safety of the occupants and the vehicles must be ensured. Based on the momentum theorem, an intelligent control method for a TER is proposed. In the method, a slope aggregate with a small rolling resistance coefficient is used on the original escape lane, and the information acquisition, braking device control, and braking modules are established. Through these modules, the operation parameters and control parameters of the out-of-control vehicle are obtained in advance, to control the operation state of the runaway vehicle. Achieve the purpose of reducing the braking effect of the slope bed aggregate and ensuring maximum utilization of the braking ramp. Finally, the proposed control method is simulated on the MATLAB/Simulink simulation platform. The results show that the control method can realize safe braking of an out-of-control vehicle at various speeds and different mass conditions, and it can play a highly significant role in the braking of high-speed and heavy-duty vehicles. [ABSTRACT FROM AUTHOR]

This paper deals with the coupled thermal structural analysis developed in Volvo heavy truck disc brake as a function of disc thickness and braking time. A ventilated type of disc brake was employed by having vents (holes) on its surface, which needs a cooling system. When the brake pedal is applied, the friction between the disc and pad tremendously increases due to the heat generated in this system. This heat was partitioned into two contacting bodies (disc rotor and pad). Both analytical and numerical approaches were used to carry out the analysis. Analytically, the transient temperature obtained by the partial solution approach and the stress field were evaluated by the elastic von Mises criterion. In the numerical approach, temperature and stress response were analyzed by the explicit standard ABAQUS. From both results, high thermal gradient and von Mises stress distribution were observed at the sharp edges of the disc, which causes a decrement in braking efficiency and an overall drop in braking performance. [ABSTRACT FROM AUTHOR]

In the present work, the study of fatigue failure of the disc brake of Volvo truck under thermomechanical effects across the disc thickness is reported. Both analytical and numerical approaches have been used. In the analytical approach, flat rigid asymmetric punch contact behavior was assumed at surface interaction, while in the numerical approach, the 3D finite element model of the vented disc type is subjected to thermomechanical cycles using ABAQUS software. Linear elastic material models were used to simulate the material's behavior under the applied pad pressure on the disc. Surface-to-surface type of contact was used for bodies that have arbitrary shapes with relatively large contact areas at disc pad interfaces. The crack initiated due to hydraulic pressure of 1.47 MPa on the disc was analyzed under mixedmode (mode I and II) conditions. This analysis has shown that the crack propagated up to critical length of 6.02 mm and finally, failure of the disc brake was observed. [ABSTRACT FROM AUTHOR]

The long-steep downgrade sections of expressways are characterized by a large elevation difference, poor horizontal and vertical alignment, and the easy failure of brakes on large trucks. They are sections with a high overall operation safety risk. It is necessary to strengthen the research on traffic risk evaluation. In order to study the traffic safety risks of long-steep downgrade parts of expressways, the fuzzy hierarchical comprehensive evaluation method is used to establish the calculation model. First, an evaluation index system including the target level, rule level, first-level index level and second-level index level is established. The qualitative and quantitative indicators are processed by the set value statistical method and the linear standard method, respectively, so that all indicators can be quantitatively evaluated together. Then, each indicator is assigned a score and divided into five risk levels, and a ridge-shaped fuzzy distribution is used to constitute a membership function for each level. A hierarchical structure model is established with the analytic hierarchy process to determine the affiliation between the upper and lower levels, and the relative weight of each level to the upper level also can be obtained. Finally, according to the hierarchical relevance of each evaluation indicator, a three-level fuzzy comprehensive evaluation model is constructed. The traffic risk evaluation level for long-steep downgrade sections can be obtained, and the probability of the corresponding risk evaluation level can be calculated. Through the risk evaluation of the long-steep downgrade sections of the Fuzhou Yinchuan Expressway in China, this shows that the risk evaluation conclusion obtained by using this evaluation method is consistent with the actual traffic safety situation, which shows that the traffic safety risk evaluation model based on a fuzzy hierarchy comprehensive evaluation is operable. [ABSTRACT FROM AUTHOR]

The paper addresses the driving dynamics of emergency fire trucks. It focuses on the issues of braking, measuring real braking distances and calculating adhesion coefficients. It presents the results of measuring the real braking distances for firefighting vehicles - type water tenders. Measurements were taken on dry asphalt and depending on the vehicle's speed of travel. Experiments were conducted on five types of firefighting vehicles. The results of measurements are mainly used by fire protection units to the drivers’ self-education to improve safety when driving to intervene. [ABSTRACT FROM AUTHOR]

In order to study the effect of interface modifications combination of multiple friction blocks on truck brake squeal, a field test was carried out in this study. In the test, the vibration acceleration and the noise signals of the truck braking system were collected. The test results showed that the high-frequency squeal noise during braking resulted from the frictional vibration of the braking system. A simplified finite element model of the heavy truck braking system was established to investigate the effect of slotting and chamfering of friction block on brake squeal. The results of complex eigenvalue analysis indicate that the interface modifications have a great influence on truck brake squeal. A proper combination of slotting and chamfering of friction blocks is useful for the reduction of brake squeal tendency. This study can provide guidance for the design and optimization of silent braking system. [ABSTRACT FROM AUTHOR]

Under adverse weather conditions, visibility and the available pavement friction are reduced. The improper selection of speed on curved road sections leads to an unreasonable distribution of longitudinal and lateral friction, which is likely to cause rear-end collisions and lateral instability accidents. This study considers the combined braking and turning maneuvers to obtain the permitted vehicle speed under rainy conditions. First, a braking distance computation model was established by simplifying the relationship curve between brake pedal force, vehicle braking deceleration, and braking time. Different from the visibility commonly used in the meteorological field, this paper defines "driver's sight distance based on real road scenarios" as a threshold to measure the longitudinal safety of the vehicle. Furthermore, the lateral friction and rollover margin is defined to characterize the vehicle's lateral stability. The corresponding relationship between rainfall intensity-water film thickness-road friction is established to better predict the safe speed based on the information issued by the weather station. It should be noted that since the road friction factor of the wet pavement not only determined the safe vehicle speed but also be determined by the vehicle speed, so we adopt Ferrari's method to solve the quartic equation about permitted vehicle speed. Finally, the braking and turning maneuvers are considered comprehensively based on the principle of friction ellipse. The results of the TruckSim simulation show that for a single-unit truck, running at the computed permitted speed, both lateral and longitudinal stability meet the requirements. The proposed permitted vehicle speed model on horizontal curves can provide driving guidance for drivers on curves under rainy weather or as a decision-making basis for road managers. [ABSTRACT FROM AUTHOR]

The failure of grey cast iron drum brake is mainly caused by thermal fatigue crack running through the top along the axial direction, which has the characteristics of regional failure. By using the advantages of laser fabrication technology, the single models with five different angles combined with the anti-crack ring were designed. The optical microscope, scanning electron microscope and X-ray diffraction were used to characterize the microstructure and phase of the drum brake material grey cast iron and the bionic coupling unit. Both single models and double combination models were tested for thermal fatigue and wear after thermal fatigue, respectively. The effects of angle on the thermal fatigue and wear resistance of the bionic coupling models were investigated. Experimental results show that the microstructure of the unit was better than that of the base grey cast iron due to the appearance of ledeburite, martensite and residual austenite after laser treatment. Besides, thermal fatigue crack has a great influence on wear performance. The thermal fatigue crack and wear loss weight are the least in the model with anti-crack ring + 45°angle, the main crack length is the shortest. The service life of the drum brake with the double combination bionic coupling model is increased by 50% compared with that of the untreated drum brake in bench test. [ABSTRACT FROM AUTHOR]

Inverted asphalt pavement is an innovative pavement structure where the unbound aggregate base (UAB) is sandwiched between the asphalt concrete (AC) layer and cement-treated base (CTB). This structure has the potential to improve rutting resistance of pavement and prevent propagation of reflective cracks. However, its implementation has been limited due to the lack of experience. In addition, the braking condition of the vehicle applied on the pavement surface plays a significant role on the pavement responses, thereby affecting its service life. This study conducted a simulation using finite layer method to investigate the effects of heavy truck braking on inverted asphalt pavement considering vehicle dynamics. The results indicated that truck braking would generate a significant horizontal load and change the magnitude of the vertical load at each axle. Furthermore, the impact of vertical load on mechanical responses would gradually enhance and eventually dominate with increasing pavement depth. It was also observed that when the truck was treated as a whole, vehicle braking would result in a 3.2% to 10.2% increase in critical responses, but cause a 0.023% and 31.7% decrease in predicted rutting and life respectively. Among three truck axles, the effect of driving axle was close to that of the entire truck, but the effect of other axles was greater or lower than that of the entire truck. A comparison of three inverted pavements found that a thick AC layer could effectively reduce the critical responses and extend the pavement life. Furthermore, a thick CTB layer could also achieve most of the above purposes due to higher integral stiffness of pavement. • Loads of each wheel of heavy truck with different braking conditions were determined. • Finite layer method incorporating vehicle dynamics was used to perform simulations. • Effect of truck braking on responses and life of inverted pavement was evaluated. [ABSTRACT FROM AUTHOR]

The microstructure, the phase composition, the microhardness and the wear resistance of hypoeutectic white cast irons with different contents of chromium are studied. It is shown that the wear resistance of the iron depends substantially on the type of the carbide phase and on the morphology of the ledeburitic eutectic, which is determined in its turn by the content of chromium. [ABSTRACT FROM AUTHOR]

During the fire extinguishing process, the motion stability of the fire ladder truck can be affected by the jet reaction forces of the fire water monitor, lengths, vertical angles and horizontal angles of the fire ladder. This paper presents a virtual prototype method and its analysis of the effects of the aforementioned parameters on the motion stability of fire ladder truck under different working conditions during the braking process. An experiment analyzing fire water monitor jet reaction forces is established in this paper to obtain the forces under working conditions as the boundary conditions for the subsequent simulation analysis. During the simulation, two vertical pitch angles and three horizontal angles of the fire ladder are selected in this paper as the boundary conditions for the fire ladder truck motion stability simulations. The judgment standard of the motion stability of fire ladder truck is based on design criteria that the vehicle can maintain stability under braking operating working conditions if the maximum vertical pressure forces of all tires range from 0 N to 100,000 N. Thus, the findings based on the analysis results of this study can provide a theoretical foundation for the stability design of a fire ladder truck. [ABSTRACT FROM AUTHOR]

The design dimensions of the executive hydraulic cylinders of the brake system of heavy-duty mining dump trucks cause high fluid flow during the braking process. Therefore, dimensions of the anti-blocking system modulator spool pair require unique electromagnets or hydraulic amplifiers to control. These solutions do not allow the required modulator performance. Thus, a modulator scheme with a division of the flow of fluid from the source to the brake cylinders was developed. This scheme allows during emergency braking passing, an additional amount of fluid to cylinders through the valve, installed parallel to the main valve upon pressure increase phase and controlled by the pressure difference. The task is to develop a method for calculating the main structural dimensions of a modulator. The calculation of the valve of the second cascade, installed in parallel to the main stage, is carried out for the emergency braking mode with the maximum flow rate to ensure the required performance of the braking system. The balance of fluid flows equations is compiled at the key points. The flow rate of the fluid through each of the valves is determined by the Torricelli formula, and the pressure difference across the valves is assuned equal. The obtained relations allows building a family of Q-p curves, which can be used to select the diameter and stroke of the additional valve depending on the flow rate in the brake system. [ABSTRACT FROM AUTHOR]

When a dump truck brakes, it is difficult to effectively absorb the braking energy due to the transient mutation of braking energy. At the same time, braking energy production is too high to store easily. Focusing on these problems, this paper proposes a new type of two-stage series supercapacitor and battery (SP&B) hybrid energy storage system (ESS). Using the characteristics of supercapacitors, which can charge and discharge quickly with large currents, the system combines the supercapacitors with a battery with a high energy storage capacity. This allows sudden large currents to be absorbed and released rapidly, while large amounts of energy can be stored. This system can also reduce the charge and discharge times of the SP&B to meet the working requirements of dump truck braking while improving the service life of the system. After completion of the research and implementation of the proposed SP&B hybrid ESS, a laboratory dynamic model was set up as an experimental platform and vehicle operation experiments were performed. The obtained results show that the energy recovery efficiency of the hybrid ESS can reach 53.5%, which can realize both security and stability for dump truck braking energy recovery and utilization (BER&U) systems. [ABSTRACT FROM AUTHOR]

Some recent accident reports involving large vessels in mooring operations or breaking away from their moorings conclude that brakes of mooring winches do not render before line parts. As the potential loss of life is high, the utmost attention on-board must be paid to minimise this inherent risk. When the load on the mooring lines becomes overloaded beyond the pre-set levels, mooring winches band brakes have the safety function of rendering and allowing the line to shed this load before its potential breaking and the subsequent snap-back. As a preventive measure against breaking, the pre-set level, known as Brake Holding Capacity (BHC), must be below the Minimum Breaking Load (MBL) of the line. In this paper, the authors analyse concerns that can arise from those with conventional screw manually-applied band brakes regarding their BHC reliability. Thus, in order to improve safety, the advantages of the spring-applied band brakes with manual setting and release or with hydraulic release are highlighted. Finally, the paper shows a typical procedure using a hydraulic jack for brake testing the winch of a Liquefied Natural Gas (LNG) ship to fix their BHC in order to hold 60% of the MBL of the mooring line. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, 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.)

The milled fly ash (MFA) was attained by mechanical ball milling of raw fly ash (RFA) and was characterized for changes in particles morphology, size, and specific surface area (SSA). The RFA and MFA, varying in wt% from 20 to 35, were exclusively used for composite fabrication using compression molding machine. The milled fly ash composite (MFC) specimens were assessed for the tribo‐performance in comparison with raw fly ash composite (RFC) and commercial truck brake composite (CTBC) specimens under the loads ranging from 125 to 200 N at 3.3 and 5 m/s of sliding velocity. The characterization study showed that the glassy and spherical RFA particles of average size 86 μm changed to rough and irregular size of 15 μm, after ball milling. The SSA per unit bulk volume was found to increase from 138.2 to 1009 m2/m3. The tribo‐study revealed that the fly ash milling significantly improved the friction coefficient of MFC specimens, especially at 35 wt% of MFA, as compared to RFC and CTBC specimens. The increase in fly ash content (raw as well as milled) to 35 wt% greatly increased the specific wear rate (SWR) at both the sliding velocities. The worn surfaces of RFC specimens were found to be more damaged than the MFC specimens as revealed from SEM results. The appreciable frictional characteristics of MFC specimens encourage the use of MFA in brake friction composites; however, the changes in the friction formulation are required from SWR point of view. [ABSTRACT FROM AUTHOR]

This article focuses on generating a monobloc fingered hub (top-hat) disc design, aiming at reducing disc mass but maintaining rotor thermal capacity, while also improving heat dissipation characteristics. The analyses and tests demonstrated that such a design is possible to achieve, with mass reduction of just over 9%. The activities included research into cast iron modelling, which gave very important insights into the limits of mechanical performance under bending. Initial finite element analyses enabled considerable progress to be made towards establishing a baseline design, but only through shape optimization and topology optimization procedures was the full potential of the design accomplished. Shape optimization facilitated the reduction of maximum principal stress by 32%, considerably improving disc torsional strength with practically no increase in mass. The safety factor in torsion achieved a value of 3.57. Topology optimization provided further, although small, mass reduction (1.5%) while maintaining low stress levels. [ABSTRACT FROM AUTHOR]