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Railway vehicle brake systems provides safely stopping, slowing and its movement at the appropriate speed. Mechanical braking is commonly performed by the effect of friction, and the use of brake discs is the only reliable option when railway vehicle is designed for high speed. The dimensions and weight of the brake discs, the area under the chassis, the service speed of the train, etc. varies as it is designed according to the parameters. The weight can be reduced by up to half, when different materials are used. During braking, mechanical energy is converted into heat. The air flowing between the ventilation vanes, which can be designed in various shapes and sizes, provides effective convective cooling in the disc. Locally overheated areas cause structural changes in the brake disc material, thermal crack formation and other damage. If these damages are not controlled and progress and turn into deep cracks, the disc becomes unusable over time. Lamellar, vermicular or spheroidal graphite cast iron is commonly and traditionally used in the manufacture of railway vehicle brake discs. Also cast irons with special compositions, as well as casting and forging steel. Various alloying elements can be added to the composition to increase the fracture toughness and wear resistance of steels to be used as brake disc material. There is also the use of composite materials especially aluminium or ceramic matrix composites thus, a train brake disc desired property and very light can be produced. In this study, information is given about brake disc structure and cooling vanes, heat generation and transfer in braking, heat gradients and problems in hot regions, thermal cracks, materials used and can be used in brake discs. [ABSTRACT FROM AUTHOR]

This study investigated the effects of abrasive type and particle size on the friction-wear characteristics of automotive brake friction materials. The Al2O3, SiC and B4C ceramic powders with different type and particle size were used as abrasive. Friction tests were performed on a Chase friction material testing machine according to the brake lining quality test procedure as per SAE J661. The composites were contained typical ingredients for commercial brake friction materials. The results showed that the highest and the lowest friction coefficients were recorded as 0.61 and 0.489 for Al2O3 containing A63 and SiC containing S63 coded samples. The B90 coded composite containing B4C showed the highest wear resistance. The friction coefficient of the composites increased and the specific wear rate decreased with increasing abrasive particle sizes. In order to reveal the wear behavior and mechanism, the worn surfaces of the composites as well as wear debris were examined under scanning electron microscopy. [ABSTRACT FROM AUTHOR]

A certain amount of research and studies has been done on the connections of the same kind of material such as aluminum to aluminum or steel to steel connections. However, as far as the connections of two different materials are concerned, there are no systematic works on the subject. In order to connect hot dip galvanized steel material with aluminum material, it is necessary to use high strength pre-loaded bolts. The use of weld is not possible because of the different properties of materials. The presented work is the result of the studies conducted on two different materials- aluminium and steel and their friction grip pre-loaded high strength bolted connections. For this reason, two different types of experiments have been done. These tests are the short-term and the long-term tests, performed on four different dimensions of thickness: 10.0 mm, 9.7 mm, 8.0 mm and 5.0 mm, and on three different aluminum alloys: AlMgSi1 (6082), AlMgSi0.5 (6063) and AlZn4.5Mg1 (7020). In each specimen two 10.9 M16 bolts have been used. In the first five tests of the short-term tests, friction surfaces are only treated oil-free and in the latter 9 test specimens are painted with alkali silicate zinc. In pre-loaded high strength bolted connections, the friction coefficient had been determined for the aluminum and steel specimens with oil-free contact surfaces and also for the alkali silicate zinc painted contact surfaces. For the above mentioned two different cases of treatment of the contact surface, loading-displacement diagrams are studied for shear loads and after it then, up to the occurrence of the rupture. After having subjected the bolts to preloading, the loss of pre-load had been studied for 30 min. prior to the beginning of the test. During the test under load, the specimen was monitored to determine whether a sudden loss in pre-load occurred. In the short-term tests after applying the pre-loading to the bolts, no big loss on the pre-load was noticed, because of the creep behavior of aluminum in time. In the short-term tests, when no paint on the friction surfaces was used, the number of the bolts necessary for the proper connections would be too high to be considered economical. In case of using the friction increasing alkali silicate zinc paint, the limit friction force of one bolt increases 3.5 times. A change of the thickness has no effect on the friction coefficient in short-term tests. When the aluminum alloy has lower yield stress than the steel, an indent under the washer will be observed. This observation is valid only for the AlMgSi0.5 (6063) alloy. That's why it is necessary to transfer the pre-load to a greater surface. To prevent the indent from happening, a thicker and wider washer could be used. After evaluating the short-term test results statistically, it has been noticed that the standard deviation of the distribution of friction coefficient does not exceed 10% limit. With the help of the results of fourteen short-term tests that were conducted, a longterm testing system was prepared and a total of fifteen long-term connection specimens in three different frames with 90 kN, 78 kN and 60 kN of continuous loading was monitored. The loading on each frame was determined so that the friction surface of each specimen was loaded with 75%, 65% and 50% ratios. To prepare the friction surfaces of long-term test specimens, all surfaces were treated with alkali silicate zinc paint. The long-term test had been carried out within one - year time span, during which the loading of each frame, the pre-loading on bolts and the slip between aluminum and steel plates were observed. The effect of small thickness on friction in the longterm tests causes the slip of contact surfaces in time. By using thinner aluminum plates, contact pressure was distributed on a smaller area of contact surface. This explains the earlier shear observed in the longterm tests under constant tension force. The thinner the specimen, the earlier the slip occurs. For the study of the long-term test results using constant distance separation - a method not found in the literature, an attempt has been made to predict the behavior of specimens within 50 years onwards. Inspecting of the 10 mm thick aluminum plate specimens after the period of one year shows that the predicted displacement in 50 years' time will be within the 0.30 mm slip limit range. The conclusion can be drawn that the alkali silicate zinc paint increases the friction coefficient of connections made of two different materials- aluminum and steel. [ABSTRACT FROM AUTHOR]

In recent years, researchers have modified masses, stiffness or damping in structures to control their vibration instead of using traditional method which provides dissipation of earthquake-induced energy by the inelastic response of the structural members. Damage due to this yielding action is usually repaired expensively or may be so serious that demolishing of building must be required. Here damping due to friction is considered as an energy dissipation method due to some advantages. Friction devices are generally capable of repeated cycles of displacement without loss of strength, stability or energy dissipation. In addition, since they are fabricated from traditional materials. They require little maintenance; their use in seismic design and retrofit applications appears to be very promising. The new significant feature in performance-based earthquake engineering is the selection of seismic performance level for a given earthquake ground motion. In this article, the effectiveness of friction dampers on reinforced concrete systems for immediate occupancy (IO) performance level is investigated considering the properties of the system and friction damper. A number of studies toward deriving a reasonable criterion for optimal design of frames with supplemental dampers have been reported. Some of them have defined performance indexes which evaluate the performance of the system as the ratio of suitable parameters calculated for the damped brace frame to that for the unbraced frame. The others have used the acceptability limits for the structural response as performance criteria to select appropriate damper properties. In this study, the selection of brace stiffness and slip displacement level of friction damper for SDOF RC systems having different period and strength ratio is made considering the peak response values for IO level obtained from the comprehensive nonlinear time history analyses. The reason of selecting IO performance level is that the structure is only slightly damaged and the capacities of force resisting systems have almost the same pre-earthquake ones in this level. Since both dynamic and inelastic response is modeled in nonlinear dynamic analysis permitted to be used for structures without any restrictions, this procedure is used for the evaluation.Nonlinear time history analyses are performed using the force displacement relationships of bare RC system and friction damped brace. Q-hyst model is considered for nonlinear dynamic response of RC system while elasto-plastic model is used to represent that of the damped brace here. Algorithm is developed to perform 14400 nonlinear dynamic analyses formed by 9 different periods (0.1s-0.9s), 2 strength ratios for bare RC system and 4 brace stiffness, 5 slip displacement values for friction damper using 40 earthquake records. The earthquake records are taken at stations whose closest distances are less than 15 km to the fault. The average peak ground acceleration of 20 unscaled earthquakes for each soil profile is 0.35 g. Peak values of displacements and shear forces are stored. The limit value for average peak displacement is considered as the yielding displacement of bare RC system. The damper properties are selected from the cases providing this limitation with low base shear. As a conclusion, ductility and base shear demand are strongly dependent on the brace to the frame stiffness ratio, the device slip to the frame yield displacement ratio and the soil profile. Generally base shear increases with the ratio of the brace stiffness to the frame stiffness and the device slip to the frame yield displacement. On the other hand, these conditions are opposite for the displacement demands. Although high brace stiffness ratio and slip displacement ratio warrant the displacement limitation, dissipated energy by friction damper decreases and the behavior of the system shows similarity with braced one without any dissipation feature. Higher brace stiffness causes greater decrement in displacement demand under the same slip load which can be obtained by using different brace stiffness and slip displacement ratio. For the period of bare RC system higher than 0.5s, required slip load level decreases for stiff soil profile while almost same load level is required for soft soil profile. In addition, lower slip load level is required to obtain performance objective for lower strength ratio of bare RC system. The results obtained are limited since only IO level is aimed for sites whose closest distances are less than 15 km. [ABSTRACT FROM AUTHOR]

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal 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.)

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal 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.)

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal 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.)

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal 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.)

Copyright of Teknoloji is the property of Engineering Science & Technology, an International Journal 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.)