Search results for: side friction

Authors: Hassan M. Alkomy, Hesham A. Elkaranshawy, Ahmed S. Ashour, Khaled T. Mohamed

Abstract:

For a rigid body sliding on a rough surface, a range of uncertainty or non-uniqueness of solution could be found, which is termed: Painlevé paradox. Painlevé paradox is the reason of a wide range of bouncing motion, observed during sliding of robotic manipulators on rough surfaces. In this research work, the existence of the paradox zone during the sliding motion of a two-link (P-R) robotic manipulator with a unilateral constraint is investigated. Parametric study is performed to investigate the effect of friction, link-length ratio, total height and link-mass ratio on the paradox zone.

Keywords: Dynamical system, friction, multibody system, Painlevé paradox, robotic systems, sliding robots, unilateral constraint.

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Authors: Hesham A. Elkaranshawy, Amr M. Abdelrazek, Hosam M. Ezzat

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The system of ordinary nonlinear differential equations describing sliding velocity during impact with friction for a three-dimensional rigid-multibody system is developed. No analytical solutions have been obtained before for this highly nonlinear system. Hence, a power series solution is proposed. Since the validity of this solution is limited to its convergence zone, a suitable time step is chosen and at the end of it a new series solution is constructed. For a case study, the trajectory of the sliding velocity using the proposed method is built using 6 time steps, which coincides with a Runge- Kutta solution using 38 time steps.

Keywords: Impact with friction, nonlinear ordinary differential equations, power series solutions, rough collision.

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Authors: Yu Chen, Weiwei Ren, Xiaojing Mu, Feng Zhang, Yi Xu

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The superhydrophobic surface is widely used to reduce friction for the flow inside micro-channel and can be used to control/manipulate fluid, cells and even proteins in lab-on-chip. Fabricating micro grooves on hydrophobic surfaces is a common method to obtain such superhydrophobic surface. This study utilized the numerical method to investigate the effect of eccentric micro-grooves on the friction of flow inside micro-channel. A detailed parametric study was conducted to reveal how the eccentricity of micro-grooves affects the micro-channel flow under different grooves sizes, channel heights, Reynolds number. The results showed that the superhydrophobic surface with eccentric micro-grooves induces less friction than the counter part with aligning micro-grooves, which means requiring less power for pumps.

Keywords: Superhydrophobic, transverse grooves, heat transfer, slip length, microfluidics.

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Authors: A. Lauvray, F. Poulhaon, P. Michaud, P. Joyot, E. Duc

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Additive Friction Stir Manufacturing, or AFSM, is a new industrial process that follows the emergence of friction-based processes. The AFSM process is a solid-state additive process using the energy produced by the friction at the interface between a rotating non-consumable tool and a substrate. Friction depends on various parameters like axial force, rotation speed or friction coefficient. The feeder material is a metallic rod that flows through a hole in the tool. There is still a lack in understanding of the physical phenomena taking place during the process. This research aims at a better AFSM process understanding and implementation, thanks to numerical simulation and experimental validation performed on a prototype effector. Such an approach is considered a promising way for studying the influence of the process parameters and to finally identify a process window that seems relevant. The deposition of material through the AFSM process takes place in several phases. In chronological order these phases are the docking phase, the dwell time phase, the deposition phase, and the removal phase. The present work focuses on the dwell time phase that enables the temperature rise of the system due to pure friction. An analytic modeling of heat generation based on friction considers as main parameters the rotational speed and the contact pressure. Another parameter considered influential is the friction coefficient assumed to be variable, due to the self-lubrication of the system with the rise in temperature or the materials in contact roughness smoothing over time. This study proposes through a numerical modeling followed by an experimental validation to question the influence of the various input parameters on the dwell time phase. Rotation speed, temperature, spindle torque and axial force are the main monitored parameters during experimentations and serve as reference data for the calibration of the numerical model. This research shows that the geometry of the tool as well as fluctuations of the input parameters like axial force and rotational speed are very influential on the temperature reached and/or the time required to reach the targeted temperature. The main outcome is the prediction of a process window which is a key result for a more efficient process implementation.

Keywords: numerical model, additive manufacturing, frictional heat generation, process

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Authors: Majid Tolouei-Rad, Peter Kalivitis

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Industrial robots become useless without end-effectors that for many instances are in the form of friction grippers. Commonly friction grippers apply frictional forces to different objects on the basis of programmers- experiences. This puts a limitation on the effectiveness of gripping force that may result in damaging the object. This paper describes various stages of design and development of a low cost sensor-based robotic gripper that would facilitate the task of applying right gripping forces to different objects. The gripper is also equipped with range sensors in order to avoid collisions of the gripper with objects. It is a fully functional automated pick and place gripper which can be used in many industrial applications. Yet it can also be altered or further developed in order to suit a larger number of industrial activities. The current design of gripper could lead to designing completely automated robot grippers able to improve the efficiency and productivity of industrial robots.

Keywords: Control system, end-effector, robot, sensor

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Authors: H. Ali, K. Hameed, N. Khan

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In DMVC, we have more than one options of sources available for construction of side information. The newer techniques make use of both the techniques simultaneously by constructing a bitmask that determines the source of every block or pixel of the side information. A lot of computation is done to determine each bit in the bitmask. In this paper, we have tried to define areas that can only be well predicted by temporal interpolation and not by multiview interpolation or synthesis. We predict that all such areas that are not covered by two cameras cannot be appropriately predicted by multiview synthesis and if we can identify such areas in the first place, we don-t need to go through the script of computations for all the pixels that lie in those areas. Moreover, this paper also defines a technique based on KLT to mark the above mentioned areas before any other processing is done on the side view.

Keywords: Side Information, Distributed Multiview Video Coding, Fusion, Early Decision.

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Authors: Gabi N. Nehme, Saeed Ghalambor

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The use of titanium fluoride and iron fluoride (TiF3/FeF3) catalysts in combination with polutetrafluoroethylene (PTFE) in plain zinc- dialkyldithiophosphate (ZDDP) oil is important for the study of engine tribocomponents and is increasingly a strategy to improve the formation of tribofilm and provide low friction and excellent wear protection in reduced phosphorus plain ZDDP oil. The influence of surface roughness and the concentration of TiF3/FeF3/PTFE were investigated using bearing steel samples dipped in lubricant solution at 100°C for two different heating time durations. This paper addresses the effects of water drop contact angle using different surface; finishes after treating them with different lubricant combination. The calculated water drop contact angles were analyzed using Design of Experiment software (DOE) and it was determined that a 0.05 μm Ra surface roughness would provide an excellent TiF3/FeF3/PTFE coating for antiwear resistance as reflected in the Scanning electron microscopy (SEM) images and the tribological testing under extreme pressure conditions. Both friction and wear performance depend greatly on the PTFE/and catalysts in plain ZDDP oil with 0.05 % phosphorous and on the surface finish of bearing steel. The friction and wear reducing effects, which was observed in the tribological tests, indicated a better micro lubrication effect of the 0.05 μm Ra surface roughness treated at 100°C for 24 hours when compared to the 0.1 μm Ra surface roughness with the same treatment.

Keywords: Scanning Electron Microscopy (SEM), ZDDP, catalysts, PTFE, friction, wear.

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Authors: M.Puviyarasan, C.Praveen

Abstract:

In this study, Friction Stir Processing (FSP) a recent grain refinement technique was employed to disperse micron-sized (2 *m) SiCp particles into aluminum alloy AA6063. The feasibility to fabricate bulk composites through FSP was analyzed and experiments were conducted at different traverse speeds and wider volumes of the specimens. Micro structural observation were carried out by employing optical microscopy test of the cross sections in both parallel and perpendicular to the tool traverse direction. Mechanical property including micro hardness was evaluated in detail at various regions on the specimen. The composites had an excellent bonding with aluminum alloy substrate and a significant increase of 30% in the micro hardness value of metal matrix composite (MMC) as to that of the base metal has observed. The observations clearly indicate that SiC particles were uniformly distributed within the aluminum matrix.

Keywords: Friction Stir Processing, Metal matrix composite, Bulk composite.

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Authors: Amer Ezoji, Mohammad Sedighi

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In the article, the wire winding process for the reinforcement of a pressure vessel frame has been studied. Firstly, the importance of the wire winding method has been explained. The main step in the design process is the methodology axial force control and wire winding process. The hot isostatic press and wire winding process introduce. With use the equilibrium term in the pressure vessel and frame, stresses in the frame wires analyzed. A case study frame was studied to control axial force in the hot isostatic press. Frame and them wires simulated then friction effect and wires effect in elastic yoke in the simulation model considered. Then theoretical and simulate resulted compare and vessel pressure import to frame because we assurance wire wounded not received to yielding point.   

Keywords: Wire winding, Frame, stress, friction.

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Authors: R. Ziaie Moayed , S. Tamassoki , E. Izadi

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Investigation of sandy clay behavior is important since urban development demands mean that sandy clay areas are increasingly encountered, especially for transportation infrastructures. This paper presents the results of the finite element analysis of the direct shear test (under three vertical loading 44, 96 and 192 kPa) and discusses the effects of different parameters such as cohesion, friction angle and Young's modulus on the shear strength of sandy clay. The numerical model was calibrated against the experimental results of large-scale direct shear tests. The results have shown that the shear strength was increased with increase in friction angle and cohesion. However, the shear strength was not influenced by raising the friction angle at normal stress of 44 kPa. Also, the effect of different young's modulus factors on stress-strain curve was investigated.

Keywords: Shear strength, Finite element analysis, Large direct shear test, Sandy clay.

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Authors: S. H. Teh, S. Malawaraarachci, W. P. Chan, A. Nassirharand

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The purpose of this paper is to present the design and instrumentation of a new benchmark multivariable nonlinear control laboratory. The mathematical model of this system may be used to test the applicability and performance of various nonlinear control procedures. The system is a two degree-of-freedom robotic arm with soft and hard (discontinuous) nonlinear terms. Two novel mechanisms are designed to allow the implementation of adjustable Coulomb friction and backlash.

Keywords: Nonlinear control, describing functions, AdjustableCoulomb friction, Adjustable backlash.

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Authors: Omid A. Zargar

Abstract:

In this project three type of tools, straight cylindrical, taper cylindrical and triangular tool all made of High speed steel (Wc-Co) used for the friction stir welding (FSW) aluminum alloy H20–H20 and the mechanical properties of the welded joint tested by tensile test and vicker hardness test. Besides, mentioned mechanical properties compared with each other to make conclusion. The result helped design of welding parameter optimization for different types of friction stir process like rotational speed, depth of welding, travel speed, type of material, type of joint, work piece dimension, joint dimension, tool material and tool geometry. Previous investigations in different types of materials work pieces; joint type, machining parameter and preheating temperature take placed. In this investigation 3 mentioned tool types that are popular in FSW tested and the results completed other aspects of the process. Hope this paper can open a new horizon in experimental investigation of mechanical properties for friction stir welded joint with other different type of tools like oval shape probe, paddle shape probe, three flat sided probe, and three sided re-entrant probe and other materials and alloys like titanium or steel in near future.

Keywords: Friction stir welding (FSW), tool, CNC milling machine, aluminum alloy H20, Vickers hardness test, tensile test, straight cylindrical tool, taper cylindrical tool, triangular tool.

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Authors: Raheleh Kholghi, Soheil Behnam Roudsari, Alireza Nemaney Pour

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Spam mails are unwanted mails sent to large number of users. Spam mails not only consume the network resources, but cause security threats as well. This paper proposes an efficient technique to detect, and to prevent spam mail in the sender side rather than the receiver side. This technique is based on a counter set on the sender server. When a mail is transmitted to the server, the mail server checks the number of the recipients based on its counter policy. The counter policy performed by the mail server is based on some pre-defined criteria. When the number of recipients exceeds the counter policy, the mail server discontinues the rest of the process, and sends a failure mail to sender of the mail; otherwise the mail is transmitted through the network. By using this technique, the usage of network resources such as bandwidth, and memory is preserved. The simulation results in real network show that when the counter is set on the sender side, the time required for spam mail detection is 100 times faster than the time the counter is set on the receiver side, and the network resources are preserved largely compared with other anti-spam mail techniques in the receiver side.

Keywords: Anti-spam, Mail server, Sender side, Spam mail

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Authors: Philip Baillie, Stuart W. Campbell, Alexander M. Galloway, Stephen R. Cater, Norman A. McPherson

Abstract:

This study compared the mechanical and microstructural properties produced during friction stir welding (FSW) of S275 structural steel in air and underwater. Post weld tests assessed the tensile strength, micro-hardness, distortion, Charpy impact toughness and fatigue performance in each case. The study showed that there was no significant difference in the strength, hardness or fatigue life of the air and underwater specimens. However, Charpy impact toughness was shown to decrease for the underwater specimens and was attributed to a lower degree of recrystallization caused by the higher rate of heat loss experienced when welding underwater. Reduced angular and longitudinal distortion was observed in the underwater welded plate compared to the plate welded in air.

Keywords: Charpy impact toughness, distortion, fatigue, friction stir welding (FSW), micro-hardness, underwater.

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Authors: Mohammad A. Khasawneh

Abstract:

The design of high pressure water jet based polishing equipment and its fabrication conducted in this study is reported herein, together with some preliminary test results for assessing its applicability for HMA surface polishing. This study also provides preliminary findings concerning the test variables, such as the rotational speed, the water jet pressure, the abrasive agent used, and the impact angel that were experimentally investigated in this study. The preliminary findings based on four trial tests (two on large slab specimens and two on small size gyratory compacted specimens), however, indicate that both friction and texture values tend to increase with the polishing durations for two combinations of pressure and rotation speed of the rotary deck. It seems that the more polishing action the specimen is subjected to; the aggregate edges are created such that the surface texture values are increased with the accompanied increase in friction values. It may be of interest (but which is outside the scope of this study) to investigate if the similar trend exist for HMA prepared with aggregate source that is sand and gravel.

Keywords: High-pressure, water jet, Friction, Texture, Polishing, Statistical Analysis.

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Authors: J. Vaseghi, S.Navaei, B. Navayinia, F. Roshantabari

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In This paper, the behavior of eccentric braced frame (EBF) is studied with replacing friction damper (FD) in confluence of these braces, in 5 and 10-storey steel frames. For FD system, the main step is to determine the slip load. For this reason, the performance indexes include roof displacement, base shear, dissipated energy and relative performance should be investigated. In nonlinear dynamic analysis, the response of structure to three earthquake records has been obtained and the values of roof displacement, base shear and column axial force for FD and EBF frames have been compared. The results demonstrate that use of the FD in frames, in comparison with the EBF, substantially reduces the roof displacement, column axial force and base shear. The obtained results show suitable performance of FD in higher storey structure in comparison with the EBF.

Keywords: Friction Damper (FD), Slip Load, Nonlinear Dynamic Analysis, Performance Index.

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Authors: Mohammad Heidari

Abstract:

Horizontal wells are proven to be better producers because they can be extended for a long distance in the pay zone. Engineers have the technical means to forecast the well productivity for a given horizontal length. However, experiences have shown that the actual production rate is often significantly less than that of forecasted. It is a difficult task, if not impossible to identify the real reason why a horizontal well is not producing what was forecasted. Often the source of problem lies in the drilling of horizontal section such as permeability reduction in the pay zone due to mud invasion or snaky well patterns created during drilling. Although drillers aim to drill a constant inclination hole in the pay zone, the more frequent outcome is a sinusoidal wellbore trajectory. The two factors, which play an important role in wellbore tortuosity, are the inclination and side force at bit. A constant inclination horizontal well can only be drilled if the bit face is maintained perpendicular to longitudinal axis of bottom hole assembly (BHA) while keeping the side force nil at the bit. This approach assumes that there exists no formation force at bit. Hence, an appropriate BHA can be designed if bit side force and bit tilt are determined accurately. The Artificial Neural Network (ANN) is superior to existing analytical techniques. In this study, the neural networks have been employed as a general approximation tool for estimation of the bit side forces. A number of samples are analyzed with ANN for parameters of bit side force and the results are compared with exact analysis. Back Propagation Neural network (BPN) is used to approximation of bit side forces. Resultant low relative error value of the test indicates the usability of the BPN in this area.

Keywords: Artificial Neural Network, BHA, Horizontal Well, Stabilizer.

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Authors: A. Al-Shyyab, A. F. Khadrawi

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The hydrodynamics behavior of fluid flow in microconverging plates is investigated analytically. Effects of Knudsen number (
) on the microchannel hydrodynamics behavior and the coefficient of friction are investigated. It is found that as
 increases the slip in the hydrodynamic boundary condition increases. Also, the coefficient of friction decreases as
 increases.

Keywords: Converging plates, hydrodynamic behavior, microplates, microchannel, slip velocity

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Authors: Emiliano Matta

Abstract:

Passive resonant vibration absorbers are among the most widely used dynamic control systems in civil engineering. They typically consist in a single-degree-of-freedom mechanical appendage of the main structure, tuned to one structural target mode through frequency and damping optimization. One classical scheme is the pendulum absorber, whose mass is constrained to move along a curved trajectory and is damped by viscous dashpots. Even though the principle is well known, the search for improved arrangements is still under way. In recent years this investigation inspired a type of bidirectional pendulum absorber (BPA), consisting of a mass constrained to move along an optimal three-dimensional (3D) concave surface. For such a BPA, the surface principal curvatures are designed to ensure a bidirectional tuning of the absorber to both principal modes of the main structure, while damping is produced either by horizontal viscous dashpots or by vertical friction dashpots, connecting the BPA to the main structure. In this paper, a variant of BPA is proposed, where damping originates from the variable tangential friction force which develops between the pendulum mass and the 3D surface as a result of a spatially-varying friction coefficient pattern. Namely, a friction coefficient is proposed that varies along the pendulum surface in proportion to the modulus of the 3D surface gradient. With such an assumption, the dissipative model of the absorber can be proven to be nonlinear homogeneous in the small displacement domain. The resulting homogeneous BPA (HBPA) has a fundamental advantage over conventional friction-type absorbers, because its equivalent damping ratio results independent on the amplitude of oscillations, and therefore its optimal performance does not depend on the excitation level. On the other hand, the HBPA is more compact than viscously damped BPAs because it does not need the installation of dampers. This paper presents the analytical model of the HBPA and an optimal methodology for its design. Numerical simulations of single- and multi-story building structures under wind and earthquake loads are presented to compare the HBPA with classical viscously damped BPAs. It is shown that the HBPA is a promising alternative to existing BPA types and that homogeneous tangential friction is an effective means to realize systems provided with amplitude-independent damping.

Keywords: Amplitude-independent damping, Homogeneous friction, Pendulum nonlinear dynamics, Structural control, Vibration resonant absorbers.

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Authors: Mukuna P. Mubiayi, Esther T. Akinlabi

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Friction Stir Welding is a solid state welding technique which can be used to produce sound welds between similar and dissimilar materials. Dissimilar welds which include welds between the different series of aluminium alloys, aluminium to magnesium, steel and titanium has been successfully produced by many researchers. This review covers the work conducted in the above mentioned materials and further concludes by showing the need to fully understand the FSW process in order to expand the latter industrially.

Keywords: aluminium, dissimilar materials, FSW, hardness, magnesium, microstructure, steel, tensile test, titanium

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Authors: R.K. Behera, S.Behera

Abstract:

In a wind power generator using doubly fed induction generator (DFIG), the three-phase pulse width modulation (PWM) voltage source converter (VSC) is used as grid side converter (GSC) and rotor side converter (RSC). The standard linear control laws proposed for GSC provides not only instablity against comparatively large-signal disturbances, but also the problem of stability due to uncertainty of load and variations in parameters. In this paper, a nonlinear controller is designed for grid side converter (GSC) of a DFIG for wind power application. The nonlinear controller is designed based on the input-output feedback linearization control method. The resulting closed-loop system ensures a sufficient stability region, make robust to variations in circuit parameters and also exhibits good transient response. Computer simulations and experimental results are presented to confirm the effectiveness of the proposed control strategy.

Keywords: Doubly fed Induction Generator, grid side converter, machine side converter, dc link, feedback linearization.

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Authors: M. Mojtahedpoor, M. M. Doustdar

Abstract:

A numerical study on the effect of side-dump angle on fuel droplets sizing and effective mass fraction have been investigated in present paper. The mass of fuel vapor inside the flammability limit is named as the effective mass fraction. In the first step we have considered a side-dump combustor with dump angle of 0o (acrossthe cylinder) and by increasing the entrance airflow velocity from 20 to 30, 40 and 50 (m/s) respectively, the mean diameter of fuel droplets sizing and effective mass fraction have been studied. After this step, we have changed the dump angle from 0o to 30o,45o and finally 60o in direction of cylinderand also we have increased the entrance airflow velocity from 20 up to 50 (m/s) with the amount of growth of 10(m/s) in each step, to examine its effects on fuel droplets sizing as well as effective mass fraction. With rise of entrance airflow velocity, these calculations are repeated in each step too. The results show, with growth of dump-angle the effective mass fraction has been decreased and the mean diameter of droplets sizing has been increased. To fulfill the calculations a modified version of KIVA-3V code which is a transient, three-dimensional, multiphase, multicomponent code for the analysis of chemically reacting flows with sprays, is used.

Keywords: Side-Dump combustor, Droplets sizing, Side-Dump angle, KIVA-3V

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Authors: F. Abdul Majeed, H. Karki, Y. Abdel Magid, M. Karkoub

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This paper analyses the non linear properties exhibited by a drill string system under various un balanced mass conditions. The drill string is affected by continuous friction in the form of drill bit and well bore hole interactions. This paper proves the origin of limit cycling and increase of non linearity with increase in speed of the drilling in the presence of friction. The spectrum of the frequency response is also studied to detect the presence of vibration abnormalities arising during the drilling process.

Keywords: Drill strings, Nonlinear, Spectrum analysis, Unbalanced mass

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Authors: Mohammad Javad Shariatzadeh, Dana Grecov

Abstract:

The tribological tests were performed on a new tribometer, in order to measure the coefficient of friction of a gland seal packing material on stainless steel shafts in presence of Cellulose Nanocrystal (CNC) suspension as a sustainable, environmentally friendly, water-based lubricant. To simulate the real situation from the slurry pumps, silica sands were used as slurry particles. The surface profiles after tests were measured by interferometer microscope to characterize the surface wear. Moreover, the coefficient of friction and surface wear were measured between stainless steel shaft and chrome steel ball to investigate the tribological effects of CNC in boundary lubrication region. Alignment of nanoparticles in the CNC suspensions are the main reason for friction and wear reduction. The homogeneous concentrated suspensions showed fingerprint patterns of a chiral nematic liquid crystal. These properties made CNC a very good lubricant additive in water.

Keywords: Gland seal, lubricant additives, nanocrystalline cellulose, water-based lubricants.

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Authors: Hamed Sanei, Mohammad Bagher Ayani

Abstract:

Optimizations of Plate Heat Exchangers (PHS) have received great attention in the past decade. In this study, heat transfer and pressure drop coefficients are compared for rectangular and circular PHS employing numerical simulations. Plates are designed to have equivalent areas. Simulations were implemented to investigate the efficiency of PHSs considering heat transfer, friction factor and pressure drop. Amount of heat transfer and pressure drop was obtained for different range of Reynolds numbers. These two parameters were compared with aim of F "weighting factor correlation". In this comparison, the minimum amount of F indicates higher efficiency. Results reveal that the F value for rectangular shape is less than circular plate, and hence using rectangular shape of PHS is more efficient than circular one. It was observed that, the amount of friction factor is correlated to the Reynolds numbers, such that friction factor decreased in both rectangular and circular plates with an increase in Reynolds number. Furthermore, such simulations revealed that the amount of heat transfer in rectangular plate is more than circular plate for different range of Reynolds numbers. The difference is more distinct for higher Reynolds number. However, amount of pressure drop in circular plate is less than rectangular plate for the same range of Reynolds numbers which is considered as a negative point for rectangular plate efficiency. It can be concluded that, while rectangular PHSs occupy more space than circular plate, the efficiency of rectangular plate is higher.

Keywords: Chevron corrugated-plate heat exchanger, heat transfer, friction factor, Reynolds numbers.

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Authors: J. K. Khare, Abhay Kumar Sharma, Ajay Tiwari, Amol A. Talankar

Abstract:

Powder metallurgy (P/M) is the only economic way to produce porous parts/products. P/M can produce near net shape parts hence reduces wastage of raw material and energy, avoids various machining operations. The most vital use of P/M is in production of metallic filters and self lubricating bush bearings and siding surfaces. The porosity of the part can be controlled by varying compaction pressure, sintering temperature and composition of metal powder mix. The present work is aimed for experimental analysis of friction and wear properties of self lubricating copper and tin bush bearing. Experimental results confirm that wear rate of sintered component is lesser for components having 10% tin by weight percentage. Wear rate increases for high tin percentage (experimented for 20% tin and 30% tin) at same sintering temperature. Experimental results also confirms that wear rate of sintered component is also dependent on sintering temperature, soaking period, composition of the preform, compacting pressure, powder particle shape and size. Interfacial friction between die and punch, between inter powder particles, between die face and powder particle depends on compaction pressure, powder particle size and shape, size and shape of component which decides size & shape of die & punch, material of die & punch and material of powder particles.

Keywords: Interfacial friction, porous bronze bearing, sintering temperature, wear rate.

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Authors: N. H. Othman, N. Udin, M. Ishak, L. H. Shah

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This study focuses on the effect of pin taper tool ratio on friction stir welding of magnesium alloy AZ31. Two pieces of AZ31 alloy with thickness of 6 mm were friction stir welded by using the conventional milling machine. The shoulder diameter used in this experiment is fixed at 18 mm. The taper pin ratio used are varied at 6:6, 6:5, 6:4, 6:3, 6:2 and 6:1. The rotational speeds that were used in this study were 500 rpm, 1000 rpm and 1500 rpm, respectively. The welding speeds used are 150 mm/min, 200 mm/min and 250 mm/min. Microstructure observation of welded area was studied by using optical microscope. Equiaxed grains were observed at the TMAZ and stir zone indicating fully plastic deformation. Tool pin diameter ratio 6/1 causes low heat input to the material because of small contact surface between tool surface and stirred materials compared to other tool pin diameter ratio. The grain size of stir zone increased with increasing of ratio of rotational speed to transverse speed due to higher heat input. It is observed that worm hole is produced when excessive heat input is applied. To evaluate the mechanical properties of this specimen, tensile test was used in this study. Welded specimens using taper pin ratio 6:1 shows higher tensile strength compared to other taper pin ratio up to 204 MPa. Moreover, specimens using taper pin ratio 6:1 showed better tensile strength with 500 rpm of rotational speed and 150mm/min welding speed.

Keywords: Friction stir welding, magnesium AZ31, cylindrical taper tool, taper pin ratio.

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Authors: Mohammad A. Khasawneh

Abstract:

Asphalt concrete pavements gradually lose their skid resistance causing safety problems especially under wet conditions and high driving speeds. In order to enact the actual field polishing and wearing process of asphalt pavement surfaces in a laboratory setting, several laboratory-scale accelerated polishing devices were developed by different agencies. To mimic the actual process, friction and texture measuring devices are needed to quantify surface deterioration at different polishing intervals that reflect different stages of the pavement life. The test could still be considered lengthy and to some extent labor-intensive. Therefore, there is a need to come up with another method that can assist in investigating the bituminous pavement surface characteristics in a practical and time-efficient test procedure.

The purpose of this paper is to utilize a well-developed image analysis technique to characterize asphalt pavement surfaces without the need to use conventional friction and texture measuring devices in an attempt to shorten and simplify the polishing procedure in the lab.

Promising findings showed the possibility of using image analysis in lieu of the labor-sensitive-variable-in-nature friction and texture measurements. It was found that the exposed aggregate surface area of asphalt specimens made from limestone and gravel aggregates produced solid evidence of the validity of this method in describing asphalt pavement surfaces. Image analysis results correlated well with the British Pendulum Numbers (BPN), Polish Values (PV) and Mean Texture Depth (MTD) values.

Keywords: Friction, Image Analysis, Polishing, Statistical Analysis, Texture.

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Authors: Santhosh K. S. Annayappa, Nupur Pruthi

Abstract:

The region of dentate nucleus is a common site for various pathologies like hematomas, tumours, etc. We aimed to study in detail the relationship of this region with the vermis, especially the pyramid using microscopic fibre dissection technique. To achieve this aim, 20 cerebellar hemispheres were studied from the 11 cerebellums. Dissection was performed using wooden spatulas and micro dissectors under a microscope following Klingler’s preservation technique. The relationship between the pyramid of vermis and the dentate nucleus was studied in detail. A similar relationship was studied on the MRI of randomly selected trigeminal neuralgia patients and correlated with anatomical findings. Results show the mean distance of the lateral margin of the dentate nucleus from the midline on anatomic specimens was 21.4 ± 1.8 mm (19-25 mm) and 23.4 ± 3.4 mm (15-29 mm) on right and left side, respectively. Similar measurements made on the MRI were 22.97 ± 2.0 mm (20.03-26.15 mm) on the right side and 23.98 ± 2.1 mm (21.47-27.67 mm) on the left side. The amount of white matter dissection required to reach the dentate nucleus at the pyramidal attachment area was 7.3 ± 1.0 mm (6-9 mm) on the right side and 6.8 ± 1.4 mm (5-10 mm) on the left side. It was concluded that the pyramid of vermis has a constant relationship with the dentate nucleus and can be used as an excellent landmark during surgery to localise the dentate nucleus on the suboccipital surface.

Keywords: Fiber dissection, micro neurosurgery, dentate nucleus of cerebellum, pyramid of vermis.

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Authors: S. Taghvamanesh, R. Ziaie Moayed

Abstract:

There are several methods for calculating the bearing capacity factors of foundations and retaining walls. In this paper, the bearing capacity factor Nγ (shape factor) for different types of foundation have been investigated. The formula for bearing capacity on c–φ–γ soil can still be expressed by Terzaghi’s equation except that the bearing capacity factor Nγ depends on the surcharge ratio, and friction angle φ. It is apparent that the value of Nγ increases irregularly with the friction angle of the subsoil, which leads to an excessive increment in Nγ of foundations with larger width. Also, the bearing capacity factor Nγ will significantly decrease with an increase in foundation`s width. It also should be highlighted that the effect of shape and dimension will be less noticeable with a decrease in the relative density of the soil. Hence, the bearing capacity factor Nγ relatively depends on foundation`s width, surcharge and roughness ratio. This paper presents the results of various studies conducted on the bearing capacity factor Nγ of: different types of shallow foundation and foundations with irregular geometry (ring footing, triangular footing, shell foundations and etc.) Further studies on the effect of bearing capacity factor Nγ on mat foundations and the characteristics of this factor with or without consideration for the presence of friction between soil and foundation are recommended.

Keywords: Bearing capacity, Bearing capacity factor, irregular foundation, shallow foundation.

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