جستجوی مقالات مرتبط با کلیدواژه « coefficient of friction » در نشریات گروه « فنی و مهندسی »

In Iran and some other countries, elastomer bearings in seat-type bridges are used with no sole/masonry plates and there is no positive connection between superstructure and substructure. Different codes have diverse provisions regarding the coefficient of friction (μ) between elastomer bearing and superstructure/substructure and also the design strength of shear keys (Vsk). Developing a finite element model for bearing slip, this paper investigates how different assumptions for μ and Vsk could affect the seismic performance. Incremental dynamic analysis is used to investigate the probability of unseating, residual displacement and nonlinear deformation in the substructure on a prototype three-span bridge. While performance during past earthquakes is fairly good, evaluating response using codes’ recommended value, i.e., μ=0.2, leads to an unacceptably high probability of unseating. Regarding design strength of shear keys, it is shown that design for weak shear keys could lead to relatively large transverse displacement during small to large earthquakes, and on the other hand, strong shear keys does not provide better protection against large transverse displacement during intense ground shakings.

Hybrid composites consisting of AA6061 matrix reinforced with TiB2 (2, 4, 6, and 8 wt. %), Al2O3 (2 wt. %) particles were produced by the sintering process. In comparison to the base material AA6061, the composite produced had improved mechanical properties. The sintered composites' mechanical properties, such as tensile strength and hardness, are measured and compared to the wear-tested specimen. Optical micrographs reveal that composites were riddled with defects like blowholes, pinholes, and improper bonding between the particulates before sintering. However, the post-sintered optical micrograph showed that the defects were greatly suppressed. Micrographic images revealed the changes in surface characteristics before and after wear. Until a sliding distance of 260 m, the wear rate of the hybrid composites was kept lower than that of the base material. The coefficient of all the composite materials produced for this study was noted to be less than that of the base material. The results reveal that the hardness of hybrid composites having 4 wt. % and 6 wt. % of TiB2 particulates increased by 5.98 % and 1.35 %. Because of the frictional heating during the wear test, the tensile properties lowered by up to 49.6%. It is concluded that the hybrid composites having 4 wt. % and 6 wt. % of TiB2 particulates exhibited less wear rate for extended sliding distance, good hardness, moderate tensile strength, and decent elongation percentage compared to its counterparts.

This paper reports the wear behavior of Cu, high Cu-Sn alloy, high Cu-Pb alloy and high Cu-Sn-Pb alloy under dry sliding at ambient conditions. These four materials were chosen for the wear resistance characterization of SnPb-solder affected old/scraped copper (high Cu-Sn-Pb alloy) to explore its reusing potentials. Wear tests were conducted using a pin-on-disk tribometer with the applied load of 20N for the sliding distance up to 2772 m at the sliding speed of 0.513 ms-1. The applied load was also changed to observe its effect. The investigation reveals that the presence of a little amount of Sn increased the hardness and improved the wear resistance of Cu, while a similar amount of Pb in Cu reduced the hardness but improved the wear resistance. The general perception of ‘the harder the wear resistant’ was found to match partially with the results of Cu, Cu-Sn alloy and Cu-Sn-Pb alloy. Coefficient of friction (COF) values revealed non-linearly gradual increasing trends at the initial stage and after a certain sliding distance COF values of all four sample materials became almost steady. SnPb-solder affected Cu demonstrated its COF to be in between that of Cu-Pb alloy and Cu-Sn alloy with the maximum COF value of 0.533.

Seat-type bridges compose a large portion of bridge inventories in different countries. There is evidence of excellent performance of these bridges in Iran during past earthquakes, that could be attributed to the slip of elastomeric bearings. This study investigates how the coefficient of friction between elastomeric bearing and its support and skew angle of the bridge could affect the performance of seat-type bridges. This assessment is done using incremental dynamic analyses on a three-span model bridge. The finite element model accounts for the slip of bearings, backfill passive resistance, and plastic deformation of columns. The results show that while the skew angle predominantly affects the required seat width in different codes, the correlation between the required seat width and coefficient of friction is much stronger. It is also established that, considering the mean response, there is no possibility of unseating even for maximum considered level ground motion. At the same time, the possibility of a loss of access due to abutment displacement is quite probable even for a design-basis earthquake. Furthermore, it is shown that the slip of the bearings significantly reduces seismic demand on the substructure. The findings show the paramount importance of modeling bearing slip in any seismic assessment of these bridge types

Friction stir welding (FSW) is a solid state bonding process in which the parts are joined together at the temperature below the melting point. In present study, a modified model was developed based on the partial sticking/sliding assumption in the tool-workpiece interface and the dependence of the thermal energy equations on the temperature-dependent yield stress to determine heat generation in FSW process that is independent from coefficient of friction. So to eliminate the dependence of the final equations on the coefficient of friction, an equation was used which the coefficient of friction was expressed as a function of workpiece yield stress. To validate the model, the FSW process was simulated by the finite element package ABAQUS and two subroutines of DFLUX and USDFLD and then the simulation results were compared with the experimental ones. The results showed that the modified model is appropriately capable of predicting the temperature and the residual stresses in the different zones of welded section.

Finite element analysis has been carried out to investigate the effect of various parameters on axisymmetric hot extrusion process using aluminum alloy. The objective of the present work is to investigate the effect of friction coefficient, die angle, die-profile radius and predefined temperature of workpiece through FEM simulation of extrusion process. Nodal temperature distribution, heat flux, peak temperature at nodes and peak flux induced are identified as the output variables to assess the thermo-mechanical deformation behavior of aluminum alloy. Mesh sensitivity analysis is performed for the evaluation of mesh convergence as well as depicts the accuracy of present FEM model. Higher will be the coefficient of friction between interacting surfaces of die-billet assembly, more will be the increment in nodal temperature in billet. Higher will be the coefficient of friction, higher will be the generation of heat flux within billet, as this is achieved for highest coefficient of friction. Peak nodal temperature diminishes with increase in die profile radius nearly by 17 %.Maximum heat flux diminishes non-linearly by 30% with increase in die profile radius. Maximum nodal temperature increases nearly linearly by 14% with increment in predefined temperature of billet. Maximum heat flux decreases non-linearly by 5 % with increment in the initial temperature of workpiece. Validation of present numerical model is established on the basis of deformation behavior in terms of evolution of nodal temperature distribution upon comparison with previous studies available in literature.