bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Crack Propagation in Offshore Structures: The Sensitivity of Component Lifetime to Wave Distribution Models
Authors: Ahmad-Shariff A. , Swailes D. C. , Metcalfe A. V.
Published: February 2008

Stress variations induced by wave loading can lead to fatigue crack growth in structural components of offshore structures. This paper is concerned with the influence of the form of the statistical distributions for wave height on the damage accumulation and lifetime of a structural component. Damage accumulation is modeled by a stochastic Paris-Erdogan equation in which the increase in crack size is proportional to a power (m) of the range of the stress intensity factor. Analytic expressions for the mean and variance of damage, and approximate mean lifetime, of a component are derived for the case in which m equals 2. It is seen that these depend on both the mean and variance of the stress distribution. The results are compared with those obtained by simulation, and the adequacy of the approximation is demonstrated. Simulation results using Rayleigh and Weibull distributions for wave heights are also given for the case in which m equals 3. It is shown that the Weibull distribution gives a better fit to empirical wave height distributions than does the Rayleigh distribution. Furthermore, when m equals 3, there is a substantial difference between results obtained by fitting Rayleigh and Weibull distributions to wave height data. The former leads to considerable overestimation of lifetimes. It is argued that Weibull distributions are more appropriate in determining lifetimes since the two parameters in the distribution allow more accurate representation of the mean and variance of the stress distribution.
Uncertainty Modeling for Fatigue Strength Assessment of Welded Structures
Authors: Fricke W. , Mu¨ller-Schmerl A.
Published: February 2008

The results of fatigue tests are characterized by much scatter. Such scatter is further increased if data from different test series are combined to derive, for instance, characteristic values for individual types of welded joints used in codes. Characteristic values are normally applied to the design of fatigue-resistant ship and offshore structures in connection with the nominal stress approach using S-N curves. More advanced approaches such as the hot-spot stress approach and the notch stress approach are applied to an increasing extent. Such approaches explicitly consider certain influence factors and allow the scatter of these factors to be treated individually. This way, probably even the total uncertainty can be reduced. After reviewing the different approaches used for fatigue strength assessment, the sources of scatter are addressed and assigned to factors considered in the different approaches. Based on published data of fatigue tests and imperfections observed in real structures, an attempt is made to quantify the uncertainties of the different factors and to draw conclusions for their individual consideration in the approaches mentioned.
Extreme Value Analysis of North Sea Storm Severity
Authors: Elsinghorst C. , Groeneboom P. , Jonathan P. , Smulders L. , Taylor P. H.
Published: February 2008

In this paper we consider the estimation of North Sea storm severity, for storms with return periods in the interval 100 to 500 yr. The analysis consists of: modeling the tail-distribution for a set of data for storm severity (using, e.g., storm hindcast data); estimating extreme storm severity; estimating confidence intervals for extreme storm severity; validating the bias and variance of estimates using simulation studies, for known underlying model forms; and estimating the robustness of extreme quantile estimates with respect to misspecification of the underlying model for the tail-distribution of storm severity. Applications to NESS (Northern European Hindcast Study) hindcast data at clusters of locations in the northern, central and southern North Sea are considered. Results suggest, in particular, the existence of a physical upper limit for storm severity in the North Sea and a close to constant value for the extreme value index, γ ≈ −0.2.
Fatigue Life of Cathodically Protected Tubular Joints of Offshore Structures
Authors: Ramachandra Murthy D. S. , Gandhi P. , Raghava G.
Published: February 2008

Steel jacket platforms are widely used for production and processing of oil from offshore fields. Tubular joints of these structures are susceptible to fatigue or corrosion fatigue cracking due to cyclic wave action, stress concentration, and corrosive environment. The submerged part of the structure is cathodically protected against corrosion by fixing sacrificial anodes at various places. The effect of cathodic protection on the fatigue life of tubular joints was studied by conducting fatigue tests on 13 T and Y-joints in air, under free corrosion, and with cathodic protection. The results of the studies are discussed in this paper.
Pipeline Purging Principles and Practice
Authors: Johnson J. E. , Svedeman S. J. , Kuhl C. A. , Gregor J. G. , Lambeth A. K.
Published: February 2008

Gas purging, a process of displacing one gas by another gas, occurs on a routine basis in the natural gas industry when pipelines are purged into and out of service. In a project sponsored by the Gas Research Institute and in cooperation with the American Gas Association (A.G.A.), the purging practices as outlined in the A.G.A.’s Purging Principles and Practices manual were reviewed because many of today’s pipeline purging operations occur under conditions not addressed directly in the manual. The program focus is on the purging procedures outlined in Chapter 8 of the manual entitled “Gas Transmission and Distribution Pipes.” The technical objective of the Project was to develop an understanding of the scientific principles upon which safe, practical purging practices can be based. Direct displacement and inert gas slug purging operations are explained in terms of dispersion and mixing parameters and their relationship to the gas velocity. Field data compared to the results of an analytical mixing model. Computer software for planning safe and cost-effective pipeline purges has been developed. Finally, recommendations for revising Chapter 8 of the A.G.A. manual are presented.
An Experimental Investigation of Tubular T-Joints Under Cyclic Loads
Authors: Cheng S. M. , Swamidas A. S. J. , Wallace W. , Wu X.
Published: February 2008

This paper presents an experimental study of fatigue crack initiation and growth in tubular T-joints, simulating the extreme case of those used for offshore platforms. The crack locations and profiles were recorded and fractographic examinations were carried out to reveal the mechanisms of crack initiation, growth, and crack closure. The relationships between crack length/depth and the numbers of fatigue cycle were analyzed using the Paris equation. During testing, the static strain responses at selected gage locations were also recorded. The variations in the static strains caused by the formation and growth of cracks were correlated with fatigue cycles by a characteristic equation. These results and correlations are useful for understanding the fatigue damage process and for monitoring the development of such damage in tubular T-joints of offshore structures.
Reliable Riser Systems for Spars
Authors: Finn L.
Published: February 2008

The Spar concept as a floating vessel is now recognized as a reliable and economic option for developing deepwater offshore hydrocarbon reservoirs. Many of the advantages of the Spar concept are attributed to the variety of riser systems that can be accommodated. This paper presents a discussion of design considerations for the top tensioned and steel catenary risers deployed from a Spar offshore production vessel. Results from extreme event strength analysis, Spar motion and current-induced fatigue analysis, and a riser-to-riser wake interference analysis are presented. Steel catenary risers are presented, including a comparison of results for risers supported by a Spar and a Semi. These analyses demonstrate that simple and reliable riser systems can be designed for use with the Spar platform concept.
Probabilistic Risk Prediction of Submarine Pipelines Subjected to Underwater Explosion Shock
Authors: Zong Z. , Lam K. Y. , Liu G. R.
Published: February 2008

A simple procedure is proposed in this paper to estimate the global failure probabilities of a submarine oil pipeline subjected to underwater explosion shock wave. The deterministic response of a pipeline subjected to an underwater shock loading is first given by solving a simplified fluid-structure interaction problem. Compared with an FEM/BEM coupling model, the present method gives good results at much lower computational efforts. Then, the Monte Carlo method is used to find the global failure probabilities of the pipeline. Finally, a practical example is given.
The Bivariate Distribution of Wave Heights and Periods in Mixed Sea States
Authors: Rodri´guez G. , Guedes Soares C.
Published: February 2008

The probabilistic structure of the bivariate distribution of sea wave heights and periods in sea states with two-peaked spectra is examined by means of numerically simulated wave records. Two-peaked sea states are classified in nine representative groups, in terms of two dimensionless parameters. The asymmetric and bimodal nature of the distribution is examined for each one of these two parameters.
Rotational Speed Control of an OWC Wave Power Plant
Authors: Justino P. A. P. , de O. Falca˜o A. F.
Published: February 2008

The paper deals with the control of an oscillating water column wave energy plant, equipped with a Wells turbine driving a variable speed electric generator. The control of the plant is achieved by changing the electric torque through the power conditioning equipment. The control has to meet several requirements: rotational speed allowable range, energy quality, and allowable fluctuations in power delivered to the grid. On the other hand, the turbine is expected to perform efficiently, and so its rotational speed should approximately match the sea conditions (it should be higher in more energetic sea states). Three different control strategies are described. Results of numerical simulations are presented for two of them, and are found to satisfy the prescribed requirements.
An Investigation Into the Effect of Turret Mooring Location on the Vertical Motions of an FPSO Vessel
Authors: Thiagarajan K. P. , Finch S.
Published: February 2008

Turret-moored floating production storage and offloading (FPSO) vessels have found application in several offshore oil and gas fields in Australia’s North West Shelf (NWS). These vessels are either custom-built or converted tankers, with an internal or external turret. The position of an internal turret is decided based on a number of design considerations, primarily, available deck and interior space, and weathervaning capabilities. It is known that turret position can influence vertical motions and accelerations of a vessel, but this factor has not been given much importance, in comparison with the effects on the horizontal plane motions, primarily surge. This paper presents the results of a pilot study conducted at the Australian Maritime College, Tasmania, to study the vertical motions of a single-point moored FPSO model in waves, while systematically varying the mooring position across the length of the model. The displacement of the vessel was held constant at 50-percent-loaded condition. A single-point mooring system was designed and implemented on the model to simulate the prototype turret mooring system. Results show that the mooring location significantly affects the vertical motions and accelerations of the vessel. Astern turrets were found to produce higher heave and pitch than other locations tested. Although turrets positioned close to the longitudinal center of gravity produced the lowest overall motions, it is suggested that turret position forward of midships be preferred, as it provides a balance between lowering vertical motions and improving weathervaning characteristics.
The Effect of Prior Cutting Conditions on the Shear Mechanics of Orthogonal Machining
Authors: Stevenson R. , Stephenson D. A.
Published: February 2008

It has been proposed several times in the metal-cutting literature that the machining process is non-unique and that the instantaneous machining conditions depend on the prior machining conditions (e.g. depth of cut, rake angle etc.). To evaluate the validity of this concept, a series of experiments was conducted using a highly accurate CNC machining center. For these experiments, the machining conditions were changed during the course of an orthogonal cutting experiment in a repeatable manner and the measured forces compared as a function of prior history. Tests were conducted on several tempers of 1100 aluminum and commercial purity zinc to evaluate the effect of material properties on the machining response. It was found that the change in measured cutting forces which could be ascribed to prior machining history was less than 3 percent and that material properties, particularly work hardening response, had no discernible effect on the magnitude of the difference.
Accuracy and Time in Surface Measurement, Part 1: Mathematical Foundations
Authors: Liang R. , Woo T. C. , Hsieh C-C.
Published: February 2008

Accuracy and time are known to be conflicting factors in measurement. This paper re-evaluates the two-dimensional sampling problem for measuring the surface roughness and establishes that an optimal sampling strategy can be obtained by utilizing the point sequences developed in Number Theory. By modeling a machined surfaces as a Wiener process, the root-mean-square (RMS) error of measurement is shown to be equivalent to the L2-discrepancy of the complement of the sampling points. It is further shown that this relationship holds for more general surfaces, thus firmly linking the minimum RMS error of the measurement to the celebrated lower bound on L2-discrepancy asserted by Roth (1954), a 1958 Fields medalist.
In-Process Monitoring of Surface Roughness Utilizing Ultrasound
Authors: Coker S. A. , Oh S. J. , Shin Y. C.
Published: February 2008

This paper presents the capability of an ultrasonic system for the in-process surface roughness measurement of machined parts. The system uses a focused ultrasonic transducer to measure the reflected amplitude variation of an ultrasonic beam incident on the surface. The robustness of the system is examined by applying the technique to different machined surfaces and investigating the effect of various coupling fluids. Experimental results show that the technique is applicable to the surfaces produced by most production processes. In addition, the capability of in-process measurements is demonstrated by adapting the system to a CNC machining center. Results show in-process measurements correlate well with off-line profilometer data. Tolerance to machine vibration is also shown by comparing the measurement data with the machine spindle on and off.
Model-Based Predictive Control of Workpiece Accuracy in Bar Turning
Authors: Shawky A. M. , Elbestawi M. A.
Published: February 2008

In this paper a real-time model-based geometric control system is proposed for workpiece accuracy in bar turning. An on-line ultrasonic measurement system that operates in the presence of cutting fluid is employed for workpiece diameter measurement. A state space mechanistic model is used to overcome the delay in the feedback loop. A Kalman Filter is used in a predictor-corrector fashion to update model predictions using on-line measurements. A full state feedback controller with an integral control action is designed and used to manipulate the tool position in real-time for machining error compensation. The performance of the proposed control strategy is evaluated through cutting experiments performed on a CNC turret lathe retrofitted with an open architecture controller.
Improvement of Chip Breaking in Machining Low Carbon Steel by Cryogenically Precooling the Workpiece
Authors: Ding Y. , Hong S. Y.
Published: February 2008

Ductile materials such as AISI1008 low carbon steel characteristically exhibit poor chip breaking in conventional machining practices. This paper presents an environmentally clean cryogenic machining process which improves the breakability of AISI1008 chips by lowering the chip temperature to its embrittlement temperature. In this study, the brittle-ductile transition temperature of AISI1008 was experimentally determined to be between −60°C and −120°C. The discussion is focused on whether the chip can reach the embrittlement temperature before it hits an obstacle. A finite element simulation predicted the chip temperatures under various cutting conditions. Liquid nitrogen (LN2) was used to prechill the workpiece cryogenically. The results from the cutting tests indicate a significant improvement in chip breakability for different feeds and speeds by using this cooling technique. However, the effectiveness of cryogenetically prechilling the workpiece was found to be heavily dependent on cutting speed.
A Tool Deflection Compensation System for End Milling Accuracy Improvement
Authors: Yang M. Y. , Choi J. G.
Published: February 2008

In an effort to reduce machining surface errors due to tool deflection in the end milling process, methods regulating cutting forces have been implemented with online feed rate controls. Such schemes are able to improve the parts dimensional accuracy, but unfortunately they can exhibit undesirable aspects in which the alleviation of the cutting conditions deteriorates the productivity. In addition the frequent changes of the feed rate would spoil the surface quality. As a new approach to achieve the precision machining efficiently, this paper introduces a tool deflection compensation system. This compensation system is a computer controlled special tool adapter which is capable of measuring the cutting forces and minutely adjusting the position of the tool without interfacing with the NC controller of the milling machine. Such a system allows for on-line estimation of the tool deflections and reduction of the surface errors. Experimental investigations for typical shaped workpieces representing various end milling situations are performed to verify the ability of the system to suppress the surface errors due to tool deflections in more productive machining condition.
Simulation and Measurement of Chatter in Diamond Turning
Authors: Marsh E. R. , Yantek D. S. , Davies M. A. , Gilsinn D. E.
Published: February 2008

This paper considers chatter in diamond turning of aluminum. A nonlinear chip area model is developed for use with the classic single degree of freedom cutting model. The chip area model is formulated as a function of the change in depth of cut between consecutive passes. This function is shown to be highly dependent on the quadratic term when turning the diameter of cylindrical workpieces with round-nosed diamond tools. The cutting model is further extended to include an impact disturbance to the cutting process. The recent research in ultra-precision machining is incorporated to properly account for the rise in specific cutting energy at extremely light depths of cut. Simulations of the resulting tool displacement show close agreement with experimental measurements.
Determination of the Temperature of a Machined Surface
Authors: Chu T. H. , Wallbank J.
Published: February 2008

A technique for measuring temperature close to the primary cutting edge in turning has been developed. The cutting temperatures of a 0.16 percent carbon bright drawn mild steel, have been measured for a range of cutting speeds and feedrates at a constant depth of cut. Tool nose radius was also varied. The correlations for the workpiece temperature of cutting speed and feedrate have been developed. The results show that the temperature correlates well with cutting speed and feedrate but the nose radius has little effect. Cutting forces were measured by a dynamometer and these were used to find the non zero forces at zero feedrate. These forces have been related to the deformation of the work material near the cutting edge of the tool and a method for calculating the cutting temperatures from these has been proposed.
Mechanical Study for the Cutting and Clinching Process of Electronic Component Leads
Authors: Engel P. A. , Wu Kee Rong , Zhai Xuejun , Janisiewicz Stan
Published: February 2008

As various small electronics components are being rapidly moved along an assembly line, their leads must be cut and clinched into holes of a circuit board for the next soldering operation. This process must be achieved economically both in time, and in combating wear by preserving the cutting tools’ sharpness. The present study investigates the shearing action and subsequent fracture in cutting. Plastic analysis for both cutting and forming (clinching) is presented with the support of measured data obtained on a prototype machine employed in the research. Wear analysis of the cutting surfaces leads to a recognition of the role played by various geometric parameters such as lead shape, cutter and anvil angles, cutter and anvil distance, etc.
Chatter in the Strip Rolling Process, Part 3: Chatter Model
Authors: Yun I-S. , Ehmann K. F. , Wilson W. R. D.
Published: February 2008

The central problem of the analysis and prevention of chatter in rolling operations is in understanding the conditions which lead to dynamic instability. By analogy with metal cutting operations, it appears that a few basic mechanisms may be responsible for the occurrence of self-excited vibrations in rolling. The three most significant mechanisms are: negative damping, mode-coupling and regeneration. In this paper, negative damping and mode-coupling are considered separately in an “artificial” manner to make inroads toward a better basic understanding of rolling instability.
A Micromechanical Study of High Temperature Ti-Al Powder Compaction
Authors: Ren F. , Chandra A. , Tvergaard V.
Published: February 2008

Process induced micro-scale evolutions can greatly influence the strength and resilience of a high temperature ceramic and intermetallic component. A micromechanical study, based on a unit cell approach, is carried out in the present work to investigate these evolutions during compaction of titanium aluminide multi-phase intermetallics at elevated temperatures. The quasi-coupled unit cell analysis can provide an avenue for investigating scalability and migratability of laboratory results to full scale productions with perturbed material compositions. Effects of various macro-scale process design considerations (e.g., tooling stiffness, spatial distribution of thermal fields) on micro-scale evolutions are investigated in detail. It has been observed that a more economic (and usually more flexible) container increases the likelihood of micro-crack nucleations, while spatially non-uniform intra-particle thermal fields can be utilized to alleviate processing induced micro-cracks in the final compacted product. Possibilities for process design modifications are also discussed.
Numerical Studies of Gas Jet/Molten Layer Interaction During Laser Cutting
Authors: Lim C. K. , Molian P. A. , Brown R. C. , Prusa J. M.
Published: February 2008

The interaction of the gas jet with the molten layer during reactive-gas assisted laser cutting is investigated. The Navier-Stokes equations in each region are solved with an implicit finite-difference algorithm. The erosion front is modeled as a free surface and its profile is determined from the interaction. Equilibrium oxidation reactions are assumed and the laser is operating in TEM00 mode. Results for laser cutting of 3.175 mm and 6.35 mm thick mild steel with an oxygen jet are presented to illustrate the details of the gas jet/molten layer interaction.
High Performance Milling Torque Sensor
Authors: Smith D. A. , Smith S. , Tlusty J.
Published: February 2008

Machine tool supervision and control algorithms require reliable and effective sensor signals to operate properly. In effort to satisfy this need, a high stiffness, wide bandwidth torque sensor for use in milling has been developed which directly measures the torque applied to a milling cutter during operation. The sensor is designed to fit between the tool and holder on conventional tooling with very little effect on the cutting process. The sensor is strain gage based and provides a virtually distortionless torque measurement over a bandwidth from DC to 2000 Hz when using a 100 mm diameter face mill on a commercial machining center. High torsional stiffness was achieved to provide a wide measurement bandwidth while allowing enough material strain, in the sensing element, to provide sufficient resolution of the milling torque. The radial stiffness of the sensor was also designed to be large enough not to compromise the stability and accuracy of the machine tool. The sensor is designed to house the critical electronic components which amplify the small voltage strain gage signal and convert the measurement into digital samples. These samples are continuously transmitted from the rotating spindle, in all positions, to a stationary receiver. Because the sensor is part of a structural system which also includes the spindle, tool holder and tool, the frequency response has distortions associated with the vibrational modes of the system. In order to obtain a wide undistorted bandwidth, a compensation filter having the reciprocal response of the sensor has been designed and implemented on a digital signal processor (DSP). The combined system of the sensor cascaded with the DSP provides a flat magnitude and linear phase frequency response.
Modelling the Natural Resting Aspect of Small Regular Shaped Parts
Authors: Chua P. S. K. , Tay M. L.
Published: February 2008

This paper presents a mathematical model for predicting the natural resting aspect of parts of regular shapes but of different sizes based on stability considerations. The objective of this model is to facilitate the design of effective and efficient orientating devices for vibratory bowl feeders. The results from the mathematical modelling were compared with the theoretical models and experimental results of other investigators. Good agreement was obtained.
A Mechanistic Model to Predict the Cutting Force System for Arbitrary Drill Point Geometry
Authors: Chandrasekharan V. , Kapoor S. G. , DeVor R. E.
Published: February 2008

A mechanistic model is developed to predict the forces for arbitrary drill point geometry. The cutting lips are divided into elements and the elemental forces are determined from a fundamental oblique cutting model. A method is developed to parametrically define the cutting lip in three-dimensional space and to determine the oblique cutting parameters (cutting angles and chip thickness) at each element on the cutting lip. The model does not require calibration experiments for each point geometry. The conical drill is used to determine the model coefficients for a tool and workpiece material combination and these are used for other drill point geometry. Model simulations match experimental data very well for four commercial drill point geometry—the Racon, Helical, Bickford and Double angle drill points.
Mathematical Modeling and Experimental Verification of Stationary Waterjet Cleaning Process
Authors: Leu M. C. , Meng P. , Geskin E. S. , Tismeneskiy L.
Published: February 2008

The use of stationary waterjet for the removal of coating material from the substrate is investigated analytically and experimentally. In the analysis, the cleaning width as a function of standoff distance, water pressure, and nozzle radius is derived by considering the structure of waterjet and the cleaning mechanism. Also derived are the relations of the optimal cleaning standoff distance and maximum cleaning width to the critical cleaning standoff distance, and how the water pressure and nozzle radius affect this critical standoff distance. These derived analytical relations are verified with experimental results.
High-Speed Scanning of Piezo-Probes for Nano-fabrication
Authors: Croft D. , McAllister D. , Devasia S.
Published: February 2008

Low scanning speed of piezo-probes has been a fundamental limitation of scanning probe based nano-fabrication techniques. Typical scan-rates achieved are limited, by structural vibrations of the piezo-probe, to about 1/10th the fundamental vibrational frequency of the piezo-probe. Faster scanning of piezo-probes is achieved here (experimental results are presented) by using inversion of the piezo-dynamics—this approach uses a feedforward input voltage, applied to piezo-probe, to compensate for piezo vibrations.
Intelligent Vision-Based Part-Feeding on Dynamic Pursuit of Moving Objects
Authors: Lee Kok-Meng , Qian Yifei
Published: February 2008

The paper addresses the problem of picking up moving objects from a vibratory feeder with robotic hand-eye coordination. Since the dynamics of moving targets on the vibratory feeder are highly nonlinear and often impractical to model accurately, the problem has been formulated in the context of Prey Capture with the robot as a “pursuer” and a moving object as a passive “prey”. A vision-based intelligent controller has been developed and implemented in the Factory-of-the-Future Kitting Cell at Georgia Tech. The controller consists of two parts: The first part, based on the principle of fuzzy logic, guides the robot to search for an object of interest and then pursue it. The second part, an open-loop estimator built upon back-propagation neural network, predicts the target‘s position at which the robot executes the pickup task. The feasibility of the concept and the control strategies were verified by two experiments. The first experiment evaluated the performance of the fuzzy logic controller for following the highly nonlinear motion of a moving object. The second experiment demonstrated that the neural network provides a fairly accurate location estimation for part pick up once the target is within the vicinity of the gripper.
A Control System for Chatter Avoidance by Ramping the Spindle Speed
Authors: Soliman E. , Ismail F.
Published: February 2008

This paper presents a new control system for chatter avoidance in milling. The control system monitors the cutting process using a statistical indicator named the R-value which is computed from the cutting force signal. When chatter is detected, the control system ramps the spindle speed in search of a speed at which chatter ceases. The system does not involve time consuming computations and therefore is suitable for on-line implementation. Also, it does not interrupt the cutting process by halting the feedrate or the spindle speed. Simulations showed that the control system has a significant chatter avoidance potential in the high speed range, and also for partial and full immersion cuts. The system was implemented successfully to avoid chatter in slotting and half immersion down milling.
Mechanics and Dynamics of Ball End Milling
Authors: Altıntas¸ Y. , Lee P.
Published: February 2008

Mechanics and dynamics of cutting with helical ball end mills are presented. The helical ball end mill attached to the spindle is modelled by orthogonal structural modes in the feed and normal directions at the tool tip. For a given cutter geometry, the cutting coefficients are transformed from an orthogonal cutting data base using an oblique cutting model. The three dimensional swept surface by the cutter is digitized using the true trochoidal kinematics of ball end milling process in time domain. The dynamically regenerated chip thickness, which consists of rigid body motion of the tooth and structural displacements, is evaluated at discrete time intervals by comparing the present and previous tooth marks left on the finish surface. The process is simulated in time domain by considering the instantaneous regenerative chip load, local cutting force coefficients, structural transfer functions and the geometry of ball end milling process. The proposed model predicts cutting forces, surface finish and chatter stability lobes, and is verified experimentally under both static and dynamic cutting conditions.
Edge Fracture Characteristics of Abrasive Grain
Authors: Hagiwara S. , Obikawa T. , Usui E.
Published: February 2008

Fracture onset coefficients and edge shape transition probabilities made it possible to evaluate the edge fracture characteristics of abrasive grain rationally. By grinding tests of single grain, these probabilities were determined for five materials: regular aluminum oxide, white aluminum oxide, single crystal aluminum oxide, green silicon carbide and black silicon carbide. Using these probabilities, transitions of edge shape distributions were calculated by applying the theory of Markov process to clarify the difference of abrasive materials in edge fracture. As a result, these probabilities proved to be an appropriate index for edge fracture characteristics of grinding grain materials.
Effect of Flyash Addition on the Quality of Al-11%Si Alloy Castings Produced by V-Process
Authors: Kumar Pradeep , Gaindhar J. L. , Holi Suresh
Published: February 2008

Energy is important for modern civilization and the electrical power from thermal stations is a major source of energy on which hinges the functioning and growth of mankind. In almost all major countries of the world thermal power stations are getting bigger and are generating huge quantities of flyash as a waste from their mammoth boilers. Despite extensive research on flyash, its utilization level is still low although it is considered as a novel and useful material in various fields such as building and road construction, agriculture, refractory works, water treatment, foundry, etc. In the present work flyash has been used as an additive to the silica sand in the V-process molds and its effects on the surface finish and total solidification time of the Al-11%Si alloy castings have been studied. Results indicate that the surface finish of the castings improves by the addition of flyash. Total solidification time of the castings reduces when the flyash has been added beyond 25 percent.
Diagnosis of Multiple Fixture Faults in Panel Assembly
Authors: Apley D. W. , Shi J.
Published: February 2008

This paper presents a modeling procedure and diagnostic algorithm for fixture related faults in panel assembly. From geometric information about the panel and fixture, a fixture fault model can be constructed off-line. Combining the fault model with inline panel dimensional measurements, the algorithm is capable of detecting and classifying multiple fixture faults. The algorithm, which relies heavily on the fault model, is based on least squares estimation. Consequently, the test is of relatively simple form and is easily implemented and analyzed. Experimental results of applying the algorithm to an autobody assemble process are provided.
An On-Line Monitoring System to Recognize Stitch Defects Through Thread Motion and High Speed Image Analyses
Authors: Cox R. N. , Titus K. J. , Clapp T. G.
Published: February 2008

A sensor system that inspects a garment as it is being sewn has the potential to eliminate much of the cost associated with inspection and to improve product quality. An economically feasible on-line stitch quality monitoring system is under development that utilizes commercially-available, low-cost piezoelectric sensors and a PC-based Linux data acquisition system. The sensors respond to the vibration caused by the thread motion and output a corresponding waveform used to study and model the formation of single stitches. As a result, the presence of periodic occurrences can be identified and attributed to proper stitch formation. Conversely, the absence of such events can be utilized to signal the presence of single stitch defects and diagnose their causes. Finally, high speed image analysis of the sewing threads has verified conclusions drawn from the output signals of the piezoelectric sensors and contributed to a better understanding of the dynamics involved in high speed sewing.
Effect of In-Plane Exit Angle and Rake Angles on Burr Height and Thickness in Face Milling Operation
Authors: Hashimura M. , Hassamontr J. , Dornfeld D. A.
Published: February 2008

Burrs formed by milling are three-dimensional in nature. Therefore the three-dimensional effects on milling burr formation in 304L stainless steel were considered. An important aspect of the three-dimensional effects is the exit order of the tool edges because the burr remains near the final exit position of the tool along the workpiece edge. The geometric parameters of the workpiece and tools were varied to change exit order in the workpiece around the cutting edge. Moreover in this paper, classification of milling burrs based on burr location, shape and mechanism is also proposed to avoid confusion. The milling burrs were classified according to three locations, five shapes and four burr formation mechanisms based on fractography. The exit burr on the exit surface and the side burr on transition surface of workpiece were mainly analyzed. The effect of in-plane exit angle and radial rake angle on burr formation were shown and the burr formation mechanism for each burr was also discussed.
Residual Stresses and Workpiece Deformation Due to Polishing and Plating of Computer Hard Disk Substrates
Authors: Klamecki B. E.
Published: February 2008

Residual stress distributions due to plating and polishing were determined for nickel-phosphorus plated aluminum alloy disks. Knowledge of these stresses provides insight into the material deformation and removal processes, information as to the effects of processing conditions on residual stress magnitude and can also serve as a basis for development of models of material deformation and removal in polishing. Measured disk shape data was fitted to an analytical solution for plate displacement due to bending moments, and residual stresses were calculated. Plating and polishing residual stresses were separated. Polishing residual stress is compressive indicating differential plastic deformation between the surface and interior regions of the workpiece. Residual stresses produced in polishing operations in which process motions were constrained so that polishing was unidirectional were measured. The results show large differences between amounts of deformation in the polishing direction and the direction perpendicular to it.
Chatter Suppression via an Oscillating Cutter
Authors: Yang F. , Zhang B. , Yu J.
Published: February 2008

Chatter is one of the critical issues in a machining process since it deteriorates the surface quality of a workpiece and reduces machining efficiency. A new method is developed to suppress chatter in which an oscillating cutter is used to machine the workpiece through a stepping motor and a transmission mechanism so as to vary tool rake angle continuously and periodically in process. Theoretical analyses are performed on the stability of the cutting system, and verified by the experimental studies. Both theoretical analyses and experimental results indicate that the method can suppress chatter in a turning process effectively. With the application of an oscillating cutter, the amplitude can be reduced by 80 percent in cutting a steel workpiece.
Computer Analysis of the Dynamic Contact Behavior and Tracking Characteristics of a Single-Degree-of-Freedom Slider Model for a Contact Recording Head
Authors: Ono Kyosuke , Yamamura Hiroshi , Mizokoshi Takaaki
Published: February 2008

This paper presents a new theoretical approach to the dynamic contact behavior and tracking characteristics of a contact slider that is one of the candidates of head design for future high density magnetic recording disk storages. A slider and its suspension are modeled as a single-degree-of-freedom vibration system. The disk surface is assumed to have a harmonic wavy roughness with linear contact stiffness and damping. From the computer simulation of the time history of the slider motion after dropping from the initial height of 10 nm, it is found that the contact vibration of the slider can attenuate and finally track on the wavy disk surface in a low waviness frequency range. As the waviness frequency increases, however, the slider cannot stay on the disk surface and comes to exhibit a variety of contact vibrations, such as sub- and super-harmonic resonance responses and finally comes to exhibit non-periodic vibration. It is also found that, among design parameters, the slider load to mass ratio and contact damping can greatly increase the surface waviness frequency and amplitude for which the stable tracking of a contact slider is possible.
Improved Design With Noncylindrical Profiles of Gas-Lubricated Ringless Pistons
Authors: Etsion I. , Gommed K.
Published: February 2008

This paper describes the results of a search for an optimum profile that will maximize the dynamic stability of gas lubricated ringless pistons. Previous work indicated that the common cylindrical piston design is not the best choice for this purpose. Many noncylindrical profiles were investigated for ringless pistons used in helium gas cryocoolers. An improved design was found that considerably extends the range of stable operation of these systems.
An Experimental Investigation of the Steady-State Response of a Noncontacting Flexibly Mounted Rotor Mechanical Face Seal
Authors: Lee An Sung , Green Itzhak
Published: February 2008

Recent theoretical work on the dynamics of the noncontacting flexibly mounted rotor (FMR) seal has shown that it is superior in every aspect of dynamic behavior compared to the flexibly mounted stator (FMS) seal. The FMR seal is inherently stable regardless of the operating speed, the maximum relative misalignment response is smaller, and the critical stator misalignment is larger. All these are measures of superior performance. This work undertakes the experimental investigation of the dynamic behavior of a noncontacting FMR seal. The steady-state response of the FMR seal was measured at various operating conditions. The results are given in terms of dynamic and static transmissibilities, i.e., amplitude ratio of responses to two forcing inputs: the initial rotor and fixed stator misalignments. These are then compared to the analytical predictions. Further, operation maps are drawn for each set of operation conditions. The maps indicate how safely (away from contact) the seal operates. It is shown that the combination of the seal parameters that maximize the fluid film stiffness is optimal for safe noncontacting operation.
Fundamental Differences Between Newtonian and Non-Newtonian Micro-EHL Results
Authors: Chang L. , Zhao W.
Published: February 2008

Numerical analyses of micro-EHL problems have shown remarkably different results with Newtonian and non-Newtonian rheological models. However, no consensus has been reached whether a Newtonian model can be used in micro-EHL analysis. It is difficult to prove the point numerically as researchers use different numerical methods, grid sizes, time steps, and convergence criteria. This paper analytically studies the fundamental differences between Newtonian and non-Newtonian micro-EHL results. Algebraic governing equations are derived in terms of dimensionless parameters of the problem. Results are obtained for a range of key dimensionless parameters of practical interest. These results suggest that Newtonian and non-Newtonian micro-EHL results would be qualitatively different and the differences would be most pronounced with surface roughness of short wavelengths. Since surface roughness of machine elements contains substantial short-wavelength contents, a Newtonian rheological model is likely to generate misleading micro-EHL results under all operating conditions under which the shear-thinning effect of the lubricant is significant.
A Numerical Scheme for Static and Dynamic Simulation of Subambient Pressure Shaped Rail Sliders
Authors: Cha Ellis , Bogy D. B.
Published: February 2008

A numerical scheme based on the finite difference technique is developed to simulate the steady-state flying conditions and dynamic responses of subambient pressure sliders with shaped rails. In order to suppress numerical difficulties caused by the clearance discontinuities present in the subambient pressure sliders, the control volume formulation of the linearized generalized lubrication equation is utilized. For the shaped rail sliders, a method of averaging the mass flow across the rail boundaries is implemented. Furthermore, the power-law scheme by Patankar, is implemented in calculating the mass flows. The resulting equation is solved using the alternating direction implicit method. For the simulation of steady-state flying conditions, a variable time step algorithm is implemented for the purpose of reaching the steady-state values as quickly as possible. This numerical scheme is very efficient in that the coarse finite difference mesh is sufficient for numerical stability, and that the time step changer very much improves the convergence rate. The static flying heights of the Transverse Pressure Contour and the “Guppy” slider are calculated for different disk velocities and slider skew angles. For the Guppy slider, the dynamic responses of the slider to a cosine bump and disk runout are simulated.
Mixed Lubrication Characteristics Between the Piston and Cylinder in Hydraulic Piston Pump-Motor
Authors: Fang Yi , Shirakashi Masataka
Published: February 2008

This paper presents a method for evaluating the lubrication characteristics between the piston and cylinder in a swash-plate type axial piston pump-motor under mixed lubrication conditions. A numerical analysis is carried out in order to obtain the metal contact force between the piston and cylinder, and the contact ratio λ is shown to represent the mixed lubrication condition both for the pump and the motor strokes. The contact ratio, λ, is also obtained experimentally by detecting electric resistance between the piston and cylinder in a practical swash-plate type machine. The experimental result is expressed by a relationship between λ and SO (the ratio of dynamic pressure to supply pressure) as indicated by the numerical analysis. In conclusion, the mixed lubrication characteristics between the piston and cylinder in a swash-plate type pump-motor is expressed by λ−SO curve irrespective of the operating conditions such as the supply pressure or the rotation speed.
Asymptotic Analysis of Ultra-Thin Gas Squeeze Film Lubrication for Infinitely Large Squeeze Number (Extension of Pan’s Theory to the Molecular Gas Film Lubrication Equation)
Authors: Matsuda R. , Fukui S.
Published: February 2008

Ultra-thin gas squeeze film characteristics are analyzed by extending Pan’s asymptotic theory for infinite squeeze number to the molecular gas film lubrication equation which was derived from the linearized Boltzmann equation and is valid for arbitrary Knudsen numbers. The generalized asymptotic method is shown to solve the boundary value equation which contains the flow rate coefficient as a function of the product of pressure P and film thickness H. Numerical results are obtained for a circular squeeze film. The PH ratio and the load carrying capacity ratio to those of continuum flow both decrease when the average film thickness is less than several microns because of molecular gas effects.
Bend Allowance and Developed Length Calculation for Pressbrake Bending
Authors: Pourboghrat F. , Stelson K. A.
Published: February 2008

Developed length refers to the length of the unstretched fiber measured over both bent and straight sections of a bent sheet. Bend allowance is a term coined by Sachs as a measure of the length of the unstretched fiber in the bent section. Sachs’ empirical equation for calculating bend allowance is not physically based and is independent of material and forming conditions. A physics-based model for calculating bend allowance and developed length for a strain hardening sheet metal formed by pressbrake bending is presented. Effects of material properties and tooling geometry on the calculation of these parameters are considered. It is shown that unlike Sachs’ assumption, it is the deformed shape and not the neutral axis shift or thinning that is important for calculating the developed length in pressbrake bending. It is also shown, by comparing calculated and measured data, that better accuracy can be obtained when the proposed method is used instead of Sachs’ empirical equation.