Air-Bearing Shear Force in the Head–Disk Interface of Hard Disk

The air-bearing shear force in the head–disk interface (HDI) of hard disk drives is a dominant factor determining the motion and instability of the lubricant layer, which plays an important role in drive reliability. In this communication, an analytical formula, which is applicable to the flow of an arbitrarily rarefied gas in the HDI and is more general than that based on the first-order slip theory, is presented based on the Boltzmann equation. When a hard sphere model is used for the air molecules, the formula reduces to that based on the first-order slip theory, and it thus validates previous studies based on the latter formula.     

Temperature Effect on a HDD Slider’s Flying Performance at Steady State

The temperature inside modern hard disk drives (HDDs) can become as high as 100°C during operation. The effects of such high temperatures on the slider’s flying attitude and the shear forces on the slider and the disk are investigated in this paper. General formulae for the shear forces are derived, and the generalized Reynolds equation is modified to take into account the temperature effect on the mean free path of air as well as the air viscosity. Numerical results are obtained for two different air bearing surface designs. It is shown that the temperature changes result in non-negligible changes in the slider’s flying height and the shear forces. These changes could further induce changes in the deformation and instability of the lubricant layer and thereby affect the reliability of the HDDs.     

Extreme Pressure Lubricant Additives Interacting on the Surface of Steel- and Tungsten Carbide–Doped Diamond-Like Carbon

Certain diamond-like carbon (DLC) coatings offer excellent tribological properties under both dry and oil-lubricated sliding conditions. However, the underlying mechanisms under lubricated conditions are generally not fully understood, especially when performance depends on strong tribochemical interactions with lubricant additives. The aim of the present work is to explore the friction and wear performance of steel and tungsten carbide (WC)-doped DLC (WC-DLC) surfaces in the presence of different types of extreme pressure (EP) and nitrogen–sulfur-based (NS) additives. Tribological tests were performed on a ball-on-disc test rig, and X-ray photoelectron spectroscopy (XPS) was used for physical and chemical characterization of the tribofilms. It was observed that EP and NS additives significantly reduced the wear of WC-DLC surfaces in comparison with tests conducted on steel surfaces. XPS indicated that the additive interactions on the WC-DLC surface formed a distinctive tribofilm that promoted better friction and wear performance. The higher concentration of carbon compounds and lower concentration of oxygen compounds in the tribofilm significantly improved friction and wear characteristics.     

Flow dynamics at the minimum starting condition of a supersonic diffuser to simulate a rocket’s high altitude performance on the ground

A numerical analysis was conducted to investigate and characterize the unsteadiness of the flow structure and oscillatory vacuum pressure inside of a supersonic diffuser equipped to simulate high-altitude rocket performance on the ground. A physical model including a rocket motor, vacuum chamber, and diffuser, which have axisymmetric configurations was employed. Emphasis was placed on investigating the physical phenomena of very complex and oscillatory flow evolutions in the diffuser operating very close to the starting condition, i.e. at a minimum starting condition, which is one of the major important parameters from a diffuser design point of view. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park Hyo-Won Yeom received a B.S. degree in the department of Aerospace & Mechanical Engineering from Korea Aerospace University in 2007. He is currently a master candidate at the school of Aerospace & Mechanical Engi-neering at Korea Aerospace Uni-versity in Goyang-city, Korea. His research interests are in the area of numerical analysis for High-speed propulsion system. Sangkyu Yoon received a B.S. degree in the department of Aerospace & Mechanical Engineering from Korea Aerospace University in 2006 and M.S. degrees in the school of Aerospace & Mecha-nical Engineering from Korea Aerospace University in 2008. He currently works in Hanwha Corporation R&D Center. Hong-Gye Sung received a B.S. degree in the department of Aerospace Engineering from Inha University in 1984 and Ph.D. degree in Nuclear and Mechanical Engineering from The Pennsylvania State University in 1999. Dr. Sung has various research experiences in the fields of high-speed propulsion and rocket propulsion in Agency for Defense Development for 22 years (1984–2006). He is currently a professor at the School of Aerospace and Mechanical Engineering of Korea Aerospace University in Goyang, Korea. Dr. Sung’s research interests are in the area of propulsion, combustion, and its control.     

Influence of Spindle Wobble in a Lathe on the Tool’s Deformational-Displacement Trajectory

Attention focuses here on the conversion of the trajectory of spindle-group wobble in a lathe into deformational displacement of the tool and the associated modification of the shaping trajectory. This process depends on the change in dynamic properties of the system due to the wobble. On the basis of simulation and digital experiments, it may be concluded that the wobble changes the stability of the trajectories and that various attractive sets are formed in the system (such as limit cycles, invariant tori, and chaotic attractors). The wobble does not change the shaping trajectory directly, but rather through the formation of attractive deformational-displacement sets. Therefore, the attractive sets affect the geometric topology of the workpiece surface and the limiting feasible manufacturing precision.     

Finding the maximally inscribed rectangle in a robot’s workspace

In this paper we formulate an optimization based approach to determining the maximally inscribed rectangle in a robot’s workspace. The size and location of the maximally inscribed rectangle is an effective index for evaluating the size and quality of a robot’s workspace. Such information is useful for, e. g., optimal worktable placement, and the placement of cooperating robots. For general robot workspaces we show how the problem can be formulated as a constrained nonlinear optimization problem possessing a special structure, to which standard numerical algorithms can be applied. Key to the rapid convergence of these algorithms is the choice of a starting point; in this paper we develop an efficient computational geometric algorithm for rapidly obtaining an approximate solution suitable as an initial starting point. We also develop an improved version of the algorithm of Haug et al. for calculating a robot’s workspace boundary.     

Measurement and evaluation of the apparent modulus of elasticity of apple based on Hooke’s,Hertz’s and Boussinesq’s theories

Awareness on the mechanical properties of agricultural products is necessary in order to estimate and predict the deformation of viscoelastic materials under external loads for system design, transport, processing and packaging. The aim of this study was to evaluate three theories (i.e. Hooke, Hertz and Boussinesq) on the apparent modulus of elasticity of some apple varieties i.e. Golden Delicious, Red Delicious and Granny Smith. The theoretical results were analyzed in a factorial experiment with completely randomized design with 9 treatments and 15 replicates. The results showed the practical usability of Hertz’s theory with better prediction accuracy whilst the Boussinesq’s theory showed a significant difference of predicted modulus of elasticity compared to other theories and the values reported in some publications. Although, the Hook’s theory enables the identification of a bio-yield point on its force–deformation curve, but Hertz’s theory was recommended as the most appropriate method due to easiness of working on a cylindrical sample of apple and the closer agreement with reality. Based on the results of this study, Golden Delicious and Granny Smith varieties had the lowest and the highest modulus of elasticity as 2.211 MPa and 3.431 MPa, respectively. This difference shows the firmness of apple varieties and different tissue responses to external loads and forces accordingly.     

A study on the modeling and analysis of a helicopter’s occupant seat belt for crashworthiness

Abstrac  In this paper, a method of modeling a seat belt on a crew seat during a dynamic seat testing was studied. The body segments of the occupant were modeled with joints that consisted of various stiffness, damping, and friction. Three types of seat belt restraint systems were investigated and an analysis on the injury assessment of the helicopter’s crew under a drop impact was conducted. The effectiveness of the seat belt system for crashworthiness and safety was likewise evaluated. From the impact analysis results, it was determined that the head, neck, and spine of the crew body can be easily damaged in the vertical direction more than the longitudinal direction. Based on the verified model, the human body’s behavior was studied using three point restraint systems. The displacement and injury level of the 12-point restraint system was the smallest. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Young-Shin Lee received a B.S. degree in Mechanical Engi-neering from Younsei University, Korea in 1972. He received master and Ph.D. degree in Mechanical Engineering from Yonsei University, Korea in 1974 and 1980 respectively. He is currently professor and Dean of Industry Graduate School and Director of BK21 Mechatronics Group at Chungnam National University, Korea. Prof. Lee’s research interests are in area of impact mechanics, optimal design, biomechanical analysis and shell structure analysis. Jung-Hyun Lee received a B.S. degree in Mechanical Design Engineering from Chungnam Na-tional University, Korea in 2007. He received master degree in Mechanical Design Engineering from Chungnam National Uni-versity, Korea in 2009. He is currently researcher of Korea Aerospace Research Institute, Korea. Kyu-Hyun Han received a B.S. degree in Mechanical Design Engineering from Hanbat National University, Korea in 2002. He received master degree in Mechanical Design Engineering from Chungnam National University, Korea in 2004. He is currently researcher of Simuline Inc, Korea.     

Coordinating the Operation of a Robot’s Manipulator and Vision System

Russian Engineering Research - The effectiveness of autonomous service robots may be improved by coordinating the operation of the manipulators and the robot’s built-in vision system in the...     

Wear of the Counterbody at the Research Friction on Carbon Coating–Orientant in Lubricant Environments

The profile wear scars on steel balls are analyzed upon their friction in lubricant against steel coated with monocrystalline carbon doped by tungsten. Bond of ball wear with the lubricant composition and the range of test loads has been established.     

A study on the variation of the performance and the cost of power generation in a combined heat and power plant with the change of the user facility’s return temperature

Journal of Mechanical Science and Technology - A combined heat and power (CHP) system generates electricity from thermal energy and generates heat by utilizing the remaining thermal energy. The...     

Rate of the tribooxidative and diffusional wear of a tool’s contact surfaces in the machining of metals

The tribooxidative and diffusional fluxes of tool material into the blank are compared. This permits the identification of the dominant type of wear in machining, for different technological conditions.     

Surface Characterization and Erosion–Corrosion Behavior of Q235 Steel in Dynamic Flow

The study aims at investigating the surface evolution and erosion–corrosion behavior of Q235 steel during erosion–corrosion process in various dynamic flows. For the purpose, true flow fields with the average flow velocities of 0.4 and 0.8 m/s and impact angles of 0°, 30° and 90° to the sample surface were successfully measured by particle image velocimetry. The topography of erosion–corrosion surface was observed by laser scanning confocal microscopy. The evolution of localized corrosion pattern is found to be determined by impact angle, i.e., round or elliptical corrosion pit corresponds to impact angle of 90° and ribbon-like corrosion pit corresponds to 0°. The deeper corrosion pits were observed at impact angle of 30° than those at the other two impact angles owing to combined effects of shear and normal stresses. Electrochemical impedance spectroscopy of samples shows smaller radiuses of capacitive loops at velocity of 0.8 m/s than those at 0.4 m/s. Equivalent circuit analysis implies unstable surface state of sample in dynamic flow. Above results indicate that the flow velocity and impact angle play the key role in the erosion–corrosion behavior of Q235 steel.     

Overview of Rubik’s Cube and Reflections on Its Application in Mechanism

Rubik’s Cube is a widely popular mechanical puzzle that has attracted attention around the world because of its unique characteristics. As a classic brain-training toy well known to the public, Rubik’s Cube was used for scientific research and technology development by many scholars. This paper provides a basic understanding of the Rubik’s Cube and shows its mechanical art from the aspects of origin and development, characteristics, research status and especially its mechanical engineering design, as well as making a vision for the application in mechanism. First, the invention and origin of Rubik’s Cube are presented, and then the special characteristics of the cube itself are analyzed. After that, the present researches of Rubik’s Cube are reviewed in various disciplines at home and abroad, including the researches of Rubik’s Cube scientific metaphors, reduction algorithms, characteristic applications, and mechanism issues. Finally, the applications and prospects of Rubik’s Cube in the field of mechanism are discussed.     

The effect of a prosthetic crown’s design on the accuracy of mapping an abutment teeth’s shape

The objective is to carry out an in vitro assessment of tightness of Co–Cr–Mo alloy premolar and molar crowns manufactured with the use of the following technologies: casting, milling and laser melting. In order to compare the fit of crowns to abutments that served as the reference models, the Geomagic Qualify 12 software for structured-light 3D scanning and modelling was used. According to analyses of reports in the form of maps and summaries, all histograms and maps are characterized by low positive and negative values of shape deviations. All employed technologies were found to have a comparable, satisfactory accuracy of mapping the shape both in the area of the stair step and the area of side walls. The results of the studies enable to conclude that the tightness of prosthetic crowns manufactured with the use of the studied technologies is comparable and meets clinical criteria.     

Surface roughness and roundness of bearing raceway machined by floating abrasive polishing and their effects on bearing’s running noise

As the two most important indexes of bearing raceway, surface roughness and roundness have significant influence on bearing noise. Some researchers have carried out studies in this field, however, reason and extent of the influence of raceway surface geometric characteristics on bearing running noise are not perfectly clear up to now. In this paper, the raceway of 6309 type bearing＇s inner and outer ring is machined by floating abrasive polishing adopting soft abrasive pad. Surface roughness parameters, arithmetical mean deviation of the profile Ra, the point height of irregularities Rz, maximum height of the profile Rmax and roundness fof raceways, are measured before and after machining, and the change rules of the measured results are studied. The study results show that the floating abrasive polishing can reduce the surface geometric errors of bearing raceway evidently. The roundness error is reduced by 25%, Rm~x value is reduced by 35.5%, Rz value is reduced by 22% and Ra value is reduced by 5%. By analyzing the change of the geometrical parameters and the shape difference of the raceway before and after machining, it is found that the floating abrasive polishing method can affect the roundness error mainly by modifying the local deviation of the raceway＇s surface profile. Bearings with different raceway surface geometrical parameter value are assembled and the running noise is tested. The test results show that Ra has a little, Rmax and Rz have a measurable, and the roundness error has a significant influence on the running noise. From the viewpoint of controlling bearings＇ running noise, raceway roundness error should be strictly controlled, and for the surface roughness parameters, R,n~x and Rz should be mainly controlled. This paper proposes an effective method to obtain the low noise bearing by machining the raceway with floating abrasive polishing after super finishing.