Search

During the braking process, frictional heat generated between a disc and a pad can lead to high temperatures. The location of friction blocks on the brake pad can lead directly to differences in friction contact time and friction speed at each point on the brake disc surface, this can lead to non-uniform temperature distribution on the brake disc surface. In this paper, the optimum design for friction blocks on a brake pad is investigated using the design of experiments (DOE) of Taguchi approach and response surface method (RSM) with an aim to minimize the deviation in the rate of friction heating in each area along the radial direction of brake disc. 18 design variables on 2 levels are adjusted. A table of orthogonal arrays, L32 (218), is used. Finite element analysis (FEA) is performed to analyze the mean squared error (MSE) values in the temperature deviations from frictional heat, the disc's thermo-mechanical characteristics are taken into account. Analysis of variance (ANOVA) is carried out using the data gathered from the DOE stage, we find 7 significant factors among the design variables. A meta-model using RSM is proposed for reduction of temperature deviations over the brake disc. An optimized brake pad is analyzed in terms of the temperature and thermal stress imparted on the brake disc, this optimized pad is then compared with the original pad. The maximum temperatures of the optimized pad and original pad were 399.8 °C and 480.6 °C, respectively. The thermal stress of the optimized pad and original pad were 640.4 MPa and 721.4 MPa, respectively. In the optimized model, the size of the hot band on the disc is larger than that from the original model, so the thermal stress distribution on the disc is smaller. Finally, the optimized pad was found to give significant performance benefits with a 16.8 % decrease in maximum temperature and 11.2 % decrease in thermal stress. [ABSTRACT FROM AUTHOR]

The threaded fasteners are typical machine components in tightening of the machine parts and structures. In addition, as threaded fasteners are easy to maintenance, these are used extensively from large structures to small electronic devices. However, after the clamping, if repetitive load is applied to the bolt/screw, loosening of the screw occurs. In this study, clamping analysis and loosening analysis are carried out for the M12 bolts which are used for the wheels of commercial vehicles. Since it is difficult to carry out test and finite element analysis (FEA) for the wheels of commercial vehicles, we propose a complex structure to deal with these problems. Through the test and FEA, the clamping force and the loosening load of bolt are derived. Not only the reduction of clamping force but also displacement of the complex structure subjected to load can indicate the loosening of the bolt. Three equivalent models are proposed to replace a detailed model for reduction of the analysis time and cost. Then, the three equivalent models are forms of rigid beam — beam — pretension (RBP), shell — beam — pretension (SBP) and shell — beam — temperature (SBT), respectively. Among these forms, the SBT model is most similar with analysis results of the detailed model. The difference between the analysis results of the detailed model and the SBT model was only 5 %. Based on the SBT model and the detailed model, it is applied to the wheel of the commercial vehicles to be verified. Then, the changes in the clamping force of the detailed model and the SBT model are identified as similar, proving the validity of the equivalent. [ABSTRACT FROM AUTHOR]

The structure of a brake disc is coupled to the axle and rotates together with the wheel. A brake disc is a friction-type device that presses the pad on both sides of the disc. As more of its surface area becomes exposed to the air, it has better heat dissipation than the drum disc. It also has low fade phenomenon or vapor lock phenomenon despite frequent brake operation. In addition, it has the advantage of enabling precise control. But the braking force is obtained by the disc brake system by using the frictional force between the disc and the pad, and the pad is subjected to wear. For high-speed railway vehicles in particular, the wear and tear of the pad occurs more rapidly. This not only shortens the replacement cycle of the pad, but also has the disadvantage of reducing braking efficiency due to the rise in temperature during the initial braking process. Moreover, the heat that occurs will cause thermal distortion, which leads to the occurrence of a hot spot. This results in a reduction of the disc life. Looking comprehensively at the research trends to date it appears that thermal behavior analysis has only been performed thus far in terms of frictional thermal energy between the disc and the pad. Thermomechanical contact characteristics, on the other hand, have yet to be considered. The thermal behavior of the disc is analyzed experimentally using an infrared camera, and the causes of the hot band and hotspot are suggested. This analytical approach can shorten the analysis time, but it can only confirm the temperature distribution achieved by a single braking. While there is a significant difference in temperature distribution according to the actual braking, the analytical approach has solely focused on the hotspot generation mechanism. Therefore, in this study, the authors will use both a dynamometer and a thermographic camera to analyze BPs through a repetitive braking process, and will attempt to verify the cause of thermomechanical movement and BP occurrence through contact analysis of the disc and the pad. [ABSTRACT FROM AUTHOR]

One of the primary interests in the railway field is to improve speed as well as to secure the safety of railway vehicles at a high speed. In light of this, the demand for braking systems that offer improved performance and safety has also been growing consistently. The braking system is a critical element directly connected with safety. In order to secure reliability and establish the maintenance standard for the braking system, it is necessary to secure an accurate evaluation technology. As the braking disc of the braking system is very sensitive to safety and maintenance, a method to evaluate thermal cracking must be developed. Because the brake disc goes through a repeated process of heating and cooling due to the friction energy and the heat convection, respectively, in every braking action, it is subject to thermal fatigue. As well, the partial contact area caused by friction between disc and pad during the braking process results in thermal distortion, causing a hot band and a hot spot. This thermal distortion may also cause thermal cracking on the friction surface. The aim of this research was to find the cause of thermal cracking through a thermo-mechanical friction analysis of disc and pad, and to verify the analysis model through the dynamo machine. [ABSTRACT FROM AUTHOR]

This study aimed to dynamically analyze a simulated bimodal tram by determining the motion equations for computer-aided analysis with Newton-Euler equations of motion, which algebraically represent motion. We utilized the multi-body dynamics analysis program, MSC.Adams, to evaluate the equations of motion, running stability, curving performance, and ride comfort of the simulated bimodal tram in comparison with single fleet and double fleet trams. For the double fleet tram, the characteristic equation was deduced to control the all-wheel steering mechanism by independently moving all the wheels characterizing an articulated vehicle. Our study aimed to design a double fleet bimodal tram. We confirmed that domestic and international standards were satisfied via the design and analysis of the simulation. Steering control equations are the significant preliminary data for coupling device research and development for double fleet bimodal trams. [ABSTRACT FROM AUTHOR]

The histidine-rich Ca-binding protein (HRC) is located in the lumen of the sarcoplasmic reticulum (SR) and exhibits high-capacity Ca-binding properties. Overexpression of HRC in the heart resulted in impaired SR Ca uptake and depressed relaxation through its interaction with SERCA2a. However, the functional significance of HRC in overall regulation of calcium cycling and contractility is not currently well defined. To further elucidate the role of HRC in vivo under physiological and pathophysiological conditions, we generated and characterized HRC-knockout (KO) mice. The KO mice were morphologically and histologically normal compared to wild-type (WT) mice. At the cellular level, ablation of HRC resulted in significantly enhanced contractility, Ca transients, and maximal SR Ca uptake rates in the heart. However, after-contractions were developed in 50 % of HRC-KO cardiomyocytes, compared to 11 % in WT mice under stress conditions of high-frequency stimulation (5 Hz) and isoproterenol application. A parallel examination of the electrical activity revealed significant increases in the occurrence of Ca spontaneous SR Ca release and delayed afterdepolarizations with ISO in HRC-KO, compared to WT cells. The frequency of Ca sparks was also significantly higher in HRC-KO cells with ISO, consistent with the elevated SR Ca load in the KO cells. Furthermore, HRC-KO cardiomyocytes showed significantly deteriorated cell contractility and Ca-cycling caused possibly by depressed SERCA2a expression after transverse-aortic constriction (TAC). Also HRC-null mice exhibited severe cardiac hypertrophy, fibrosis, pulmonary edema and decreased survival after TAC. Our results indicate that ablation of HRC is associated with poorly regulated SR Ca-cycling, and severe pathology under pressure-overload stress, suggesting an essential role of HRC in maintaining the integrity of cardiac function. [ABSTRACT FROM AUTHOR]

Metabolic profiling of the fecal extracts of male mice was carried out to assess the effects of probiotics on colonic inflammation using 1H NMR spectroscopy coupled with multivariate data analysis. The control group (n = 5) was administered phosphate buffered saline for 14 days. Acute colitis was induced with dextran sulfate sodium (DSS) for 7 days following administration of phosphate buffered saline for 7 days (DSS-treated group, n = 5). LAB + DSS-treated group (n = 5) was administered lactic acid bacteria (LAB) daily for 7 days followed by treatment with DSS for 7 days to investigate protective effect of LAB against DSS-inducible colitis. Histological damage, myeloperoxidase activity, and malondialdehyde content of colon tissue were reduced, whereas colon length increased in LAB + DSS-treated mice compared to those in DSS-treated mice. DSS treatment was associated with fecal excretion of amino acids, short chain fatty acids, and nucleotides, revealing significant decreases of threonine, alanine, glutamate, glutamine, aspartate, lysine, glycine, butyrate, uracil, and hypoxanthine together with increases of monosaccharides, glucose, and trimethylamine in the feces of mice with DSS-induced colitis. Increased levels of acetate, butyrate, and glutamine and decreased levels of trimethylamine were found in the feces of LAB + DSS-treated mice compared to DSS-treated mice alone. The increased short chain fatty acids levels in the feces of mice fed with LAB indicate that the probiotics have protective effects against DSS-induced colitis via modulation of the gut microbiota. This work highlights the possibility for alternative approach of metabonomics in feces for assessing the probiotic effect in an animal model of inflammatory bowel disease. [ABSTRACT FROM AUTHOR]

To investigate the mechanisms of the preventive activity of lactic acid bacteria in colitis, the inhibitory effect of Bifidobacterium longum HY8004, which potently inhibited lipid peroxidation in vitro, was examined in 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitic mice. We measured the ability of lactic acid bacteria (LAB) to inhibit lipid peroxidation in vitro and to inhibit colitis outcomes, colon shortening, and myeloperoxidase activity in TNBS-induced colitis in C3H/HeN and C3H/HeJ mice. We also measured levels of the inflammatory markers interleukin (IL)-1β and tumor necrosis factor (TNF)-α and their transcription factor, NF-κB, in the colon by enzyme-linked immunosorbent assay and immunoblot analysis. Among the LAB tested, B. logum HY8004 most potently inhibited lipid peroxidation in vitro but did not inhibit TLR-4-linked NF-κB activation in HEK cells. Oral administration of HY8004 inhibited TNBS-induced colon shortening and myeloperoxidase activity in the colon of C3H/HeN and C3H/HeJ mice as well as IL-1β and TNF-α expression. B. longum HY8004 also inhibited TNBS-induced lipid peroxidation, TLR-4 expression, and NF-κB activation in the colon of C3H/HeN and C3H/HeJ mice. B. longum HY8004 can improve colitis via the inhibition of lipid peroxidation as well as NF-κB activation. [ABSTRACT FROM AUTHOR]

To evaluate the anti-colitic effect of lactic acid bacteria by cDNA microarray analysis, a lactic acid bacteria mixture (LM) consisting of Lactobacillus brevis HY7401, L. suntoryeus HY7801 and Bifidobacterium longum HY8004 was orally administered to dextran sulfate (DSS)-induced colitic mice and the expression profile of numerous genes was assessed. DSS treatment caused colitic outcomes such as inflammation and colon shortening. DSS also up-regulated the expression of inflammation-related genes: pro-inflammatory and chemotactic cytokines, including IL-1β, TNF-α, IL-6, CCL2, CCL4, CCL7, CCL24, CXCL1, CXCL2, CXCL5, CXCL9 and CXCL10, and their receptors CCR3 and CCR7, and other colitis-related genes such as COX-2, PAP, MMP family, S100a8, S100a9 and DEFA1. LM treatment inhibited the mRNA expression of inflammation-related and tissue remodeling genes induced by DSS as well as the colitic symptoms. LM inhibition for the DSS-induced expression of the representative inflammatory markers, IL-1β, TNF-α and COX-2, was supported by quantitative real-time polymerase chain reaction analysis. These findings suggest that LM ameliorates DSS-induced colitis by regulating inflammatory-related cytokines as well as tissue remodeling genes. [ABSTRACT FROM AUTHOR]

The Korean Railroad Research Institute (KRRI) developed the rubber-tired AGT system (Model: K-AGT) between 1999 and 2005. The K-AGT is a light rail transit system does not require a driver and generally operates on an elevated railroad for transporting passengers. Accidents caused by driverless vehicles can severely affect social confidence, safety and economy. Therefore, it is very important to minimize the occurrences of such faults, and to accurately perform detailed maintenance tasks and thoroughly investigate the cause of any repeated failures. This research develops the web-based reliability centered maintenance (RCM) system for the K-AGT train system. The framework of the RCM system is based on performing a failure mode and effects analyses (FMEA) procedure on all the sub-systems in the K-AGT system. Out of the devices that have a low reliability, the high failure ranked devices are included high on the list for performing the overall maintenance plans. Through registration of historical failure data and the reliability indexes, the results of the FMEA can be updated. Such a process is repeated continuously and can achieve very accurate predictions for device operational lifetimes and failure rates. Also, the RCM system is designed so that workers can refer to the expert system for the latest procedures to perform the required diagnosis and repair of any failure. The overall RCM system consists of a failure/task management system, a preventive maintenance system, an expert system, a material management system, and an approval system. This research describes the development of the preventive maintenance system and the expert system that have been produced because these are the main functions for the RCM system. [ABSTRACT FROM AUTHOR]