bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Studies of a Head/Disk Interface Subjected to Impulsive Excitation During Nonoperation
Authors: Ishimaru Naohiko
Published: February 2008

Experimental studies on a head/disk interface (HDI) subjected to half-sine shock acceleration during nonoperation have been carried out using a dummy drive. Permanent damage to the disk surface due to the collision between head and disk (slap movement), which is an index showing the shock-proof performance, has been investigated by measuring the degradation of recorded signals. Physical quantities of HDI movement under shock acceleration have been measured comprehensively using various sensors housed in the dummy drive. The results are as follows. The slap movement of the head suspension assembly (HSA) is the dominant phenomenon governing the shock-proof performance of a HDI. This movement does not occur until the inertia force acting on the HSA exceeds the loading force. It is more violent as the magnitude of acceleration increases. Higher loading force, smaller equivalent mass of HSA, lower rigidity, and higher hardness of the disk contribute to better shock-proof performance. The duration of shock acceleration is not related to resonance frequency of the disk but to that of the HSA. It is possible to estimate the slap movement quantatively from the loading force, the equivalent mass of HSA, and the duration of acceleration.
Dynamic Friction Measurements of MoS2 Coated Ball Bearing Surfaces
Authors: Lovell M. R. , Khonsari M. M. , Marangoni R. D.
Published: February 2008

The friction behavior of MoS2 coated bearing surfaces operating under ultra-low-speeds with velocity reversal is investigated. Forty-two sets of exclusively ultra-low-speed operating conditions were examined that include rotational speeds in the range of .01–1 deg/s, normal loads varying from 81.6 to 185.4 N per ball, silicon nitride (Si3N4) and steel ball bearing elements and MoS2 coating thicknesses of 4000 Å and 10000 Å. The friction torque of coated bearing surfaces was found to exhibit Dahl hysteresis behavior. General trends for the two unknown parameters of Dahl’s model, the rest slope, σ, and the steady torque. Ts, were established for MoS2 solid lubricant films. The results of the coated friction measurements were compared to that of oil-lubricated bearings operating under similar conditions. In addition, a series of experiments were conducted to examine the film behavior at operating speeds from .01–50 deg/sec. Under the conditions tested, the coated friction torque was found to be relatively invariant with velocity. Implications to the field of controls, as applied to precision positioning and tracking instruments are discussed.
Experimental and Theoretical Rotordynamic Characteristics of a Hybrid Journal Bearing
Authors: Sawicki J. T. , Capaldi R. J. , Adams M. L.
Published: February 2008

This paper describes an experimental and theoretical investigation of a four-pocket, oil-fed, orifice-compensated hydrostatic bearing including the hybrid effects of journal rotation. The test apparatus incorporates a double-spool-shaft spindle which permits independent control over the journal spin speed and the frequency of an adjustable-magnitude circular orbit, for both forward and backward whirling. This configuration yields data that enables determination of the full linear anisotropic rotordynamic model. The dynamic force measurements were made simultaneously with two independent systems, one with piezoelectric load cells and the other with strain gage load cells. Theoretical predictions are made for the same configuration and operating conditions as the test matrix using a finite-difference solver of Reynolds lubrication equation. The computational results agree well with test results, theoretical predictions of stiffness and damping coefficients are typically within thirty percent of the experimental results.
Inward Flow of Surface Materials at Back-Ends of Billets During Al-Extrusion, Part 1: A Finite Element Model
Authors: Hou Jin
Published: February 2008

In hot extrusion of Al-profiles, the billet-container boundary is characterized by the sticking condition. The outer surface layer of the billet is stuck to the container wall. At the back-end of the billet, the metal flow is complicated. The surface material, which is initially stuck to the wall, will be scraped away by the pad and flow inward into the billet. This kind of inward flow of surface material is usually undesirable and it is important to control such flow so that no surface material should be found in extruded profiles. In order to study this phenomenon, a model is proposed for the metal flow at the back-end, in which the rigid-plastic FEM is used. A computer program FEMBA has been developed based on the model. The simulation results are in qualitatively good agreement with experiments.
Inward Flow of Surface Materials at Back-Ends of Billets During Al-Extrusion, Part 2: Influence of Process Parameters
Authors: Hou Jin , Sta˚hlberg Ulf , Bengtsson Bo
Published: February 2008

In order to study the inward flow of surface materials at back-ends of billets during Al-extrusion, a FEM model has been proposed and a computer program, named FEMBA, have been developed for PCs. The model and the program FEMBA have been described in part one. In this work, the program FEMBA has been used as a tool to study the flow of surface materials at the back-end under different conditions. The influence of process parameters on the inward flow has been studied. It is found that thickness of surface layer, temperatures and friction at the pad/billet contact surface have significant influence on the inward flow of surface materials. Ram speed can have some influence. The influence of temperatures of the billet, container and pad has been studied separately.
Automated Deburring with a Filamentary Brush: Prescribed Burr Geometry
Authors: Stango Robert J. , Chen Lienjing , Cariapa Vikram
Published: February 2008

In this paper, a dynamic model for removal of edge burrs with a compliant brushing tool is reported. Description of the burr geometry is assumed to be known through on-line measurement methods such as a computer vision system in the flexible manufacturing cell. Dynamic response of the brush/workpiece system is evaluated on the basis of experimentally obtained data. Master Curves are introduced as machining descriptors which characterize the incremental burr removal performance of the brush/workpiece system, leading to the development of an analytical dynamic model for orthogonal burr removal using a finite-width brushing tool. Based upon the dynamic model for material removal, a control strategy for automatic deburring is presented for burr configurations having constant height as well as variable height. A closed-form solution for transverse brush feed rate is obtained which is applicable for removal of burrs having variable height, as described by suitable geometry functions. For illustrative purposes, simulations are carried out for a straight-edge burr profile and sinusoidal burr geometry. Results are reported which identify important relationships among brush feed rate, brush penetration depth, and brush rotational speed. In order to help assess the validity of the proposed analytical model and control strategy, experimental results are reported for a combination ramp/straight-edge burr configuration. The results demonstrate generally good correlation between the predicted and actual profile for the edge burr that has been machined. In addition, some important observations include; (1) burr removal is most rapidly carried out by using the highest brush speed and deepest brush/workpiece penetration depth, subject to the condition that the brush fiber is not damaged, (2) Currently available polymer abrasive brushing tools exhibit very slow machining characteristics and must be improved in order to be used in a production environment where burr size is appreciable, (3) Material removal characteristics of the leading and trailing edge of brushes may be a source of error which merits further investigation.
An Experimental Investigation into the Effect of Cutting Fluid Conditions on the Boring of Aluminum Alloys
Authors: Cozzens D. A. , Rao P. D. , Olson W. W. , Sutherland J. W. , Panetta J. Mark
Published: February 2008

Boring tests were conducted on aluminum alloys to investigate the effects of cutting fluid on machining performance. Statistically designed experiments were used to examine the role of such process variables as tool geometry, cutting conditions, work material, cutting fluid presence, cutting fluid concentration, and hydraulic oil contamination of cutting fluid. Responses for the boring tests were surface texture, forces, and observed built-up edge (BUE). The results indicate that the cutting fluid presence, oil concentration, and hydraulic oil contamination do not play a significant role in process performance under the conditions tested.
Material Constitutive Modeling Under High Strain Rates and Temperatures Through Orthogonal Machining Tests
Authors: Lei S. , Shin Y. C. , Incropera F. P.
Published: February 2008

This paper presents a procedure to characterize deformation behavior applicable to various engineering materials in machining processes. Orthogonal machining tests are used to obtain the relationship between shear stress, strain, strain rate and temperature. Shear plane temperature is measured by an infrared thermal imaging system and compared with the Loewen and Shaw model. A new procedure to determine strain rate in the shear zone is proposed based on a triangular shear zone model and grain boundary determined by optical microscopy. Finally, a constitutive model for a low carbon steel, determined by the procedure, is presented and compared with existing results.
Finite Element Simulation of Twin-Roll Casting Process with an Implementation of Slip/Friction Boundary Condition
Authors: Chang Jee-Gong , Weng Cheng-I
Published: February 2008

The twin-roll casting process is simulated by a general thermomechanical model by using a versatile finite element method. The multidomain method is employed to deal with the solid and liquid phases separately. This includes treating the liquid phase as an Newtonian fluid and the solid phase as a viscoplastic metal. Furthermore, a friction model is proposed to analyze the rolling effect of the completely solidified metal. From the results of this study, the implementation of the friction model can produce a reasonable flow field of the solidified metal. In addition, the non-slip condition severely restricts the motion of the solidified metal and introduces inaccuracy on the temperature, velocity and stress fields as compared to the current approach.
Journal Asymmetric Heating—Part I: Nonstationary Bow
Authors: Larsson Bjo¨rn
Published: February 2008

A relation between journal vibration and asymmetric temperature in the lubricant-journal interface is derived. The bearing consists of five equally distributed tilting-pads. An arbitrary synchronous harmonic journal vibration is allowed. Heat conduction in the rotor shaft for nonstationary bearing temperature is solved. The result is presented as a frequency response of the shaft bow. Influence of air-convection and different bearing widths is investigated.
Thermal Elastohydrodynamic Lubrication of Non-Newtonian Fluids With Rough Surfaces
Authors: Wang J. M. , Aronov V.
Published: February 2008

The characteristics of thermal elastohydrodynamic lubrication by non-Newtonian fluids for rough surfaces is investigated theoretically. The general Reynolds equation for two-sided striated roughness lubricated by power law fluids is established using a perturbation approach. New correction factors for the pressure flow and the shear flow are derived; these factors integrate both lubricant rheology and surface roughness characteristics. A more effective numerical algorithm is adopted to obtain the solutions for wide ranges of operating conditions. Observations and discussion lead to further understanding of the various interactions among different factors in a elastohydrodynamic lubrication process.
Bouncing Vibration and Complete Tracking Conditions of a Contact Recording Slider Model on a Harmonic Wavy Disk Surface
Authors: Ono Kyosuke , Takahashi Kan
Published: February 2008

An extended study of the general characteristics of the bouncing vibrations of a contact recording head slider was done for a single-degree-of-freedom slider model bouncing on a harmonic wavy disk surface with linear contact stiffness and damping. The relationship between bounce height and waviness frequency and the role of a top contact point necessary for stable bouncing vibrations are discussed. Since the dynamic contact force increases to ten times the static slider load even when the bounce height is only one nanometer, the importance of complete tracking without separation is discussed. Then the complete tracking conditions of disk surface waviness under disturbances of ten nanometer bounce height are calculated for various design parameter values, including the waviness phase. It is also shown that a collision model can predict almost the same complete tracking zones as an elastic contact model.
Inadequacy of a Conventional Keulegan-Carpenter Number for Wave and
Current Combination
Authors: Zdravkovich M. M.
Published: February 2008

The physical consideration, taken as a starting point, has been based on the change of duration of each wave half-cycle by the superposition of a current. The Keulegan-Carpenter number could reflect that feature if the wave plus current velocity replaces the wave velocity as the reference velocity. It is also argued that the ratio of current to wave velocity is a more appropriate parameter than the reduced velocity. The modified Keulegan-Carpenter numbers separate different observed flow regimes in a coherent manner in drag coefficient and current-to-wave velocity plane.
Static Rolling Bearing Models in a C.A.D. Environment for the Study of Complex Mechanisms: Part II—Complete Assembly Model
Authors: Bourdon A. , Rigal J. F. , Play D.
Published: February 2008

This is the second part of two companion papers, the first of which is “Static Rolling Bearing Models in a C.A.D. Environment for the Study of Complex Mechanism: Part I—Rolling Bearing Model.” A general methodology for the accurate modeling of the nonlinear behavior of ball and roller bearings is proposed. A stiffness matrix is defined both for each rolling element and for the complete rolling bearing. Thus, it can be introduced into standard finite element models of complex mechanical systems, with the aim of predicting mechanical behavior and load and strain distributions. This method is applied to two cases of helicopter and automobile gearboxes. Deformable bearing rings considerably modify contact angle and load distribution, thus the coefficient values of the stiffness matrix are different from the classical values. The paper highlights how important it is to consider an overall model of the mechanical system rather than a local one in the vicinity of the bearings.
Analysis of Lubricating Characteristics of Rotary Compressors for Domestic Refrigerators
Authors: Yoshimura Takao , Ono Kyosuke , Inagaki Koˆ , Kotsuka Hideki , Korenaga Atsushi
Published: February 2008

We investigated the lubricating characteristics between a vane and piston lubricated with an oil-refrigerant mixture. Theoretical analyses were performed using mixed elastohydrodynamic lubrication analysis theory, taking metallic contacts into account. Lubricating conditions were evaluated by comparing the theoretical results of piston dynamics based on actual surface roughness distributions measured by SEM, with the experimental results measured under practical operation. We conclude that (1) lubricating conditions between the vane and piston can be assumed to be within the mixed lubricating zone, in which the coefficient of friction changes from 0.04 to 0.08, and the contact force is almost equally supported by oil film and metallic contact; (2) the coefficient of friction decreases as the contact force increases because the ratio of pressure rise of the oil film to the decrease in clearance is much greater than that for metallic contact pressure; and (3) in mixed EHL analysis, it is important not only to measure the actual surface roughness but also to select the appropriate contact model.
Experimental Study on the Mechanism of Lubrication in Hydrodynamic Porous Thrust Bearings With a Wavy Surface
Authors: Ohtsuka Shigeru , Hayakawa Motozo
Published: February 2008

Hydrodynamic fluid lubrication theory is applied to thrust bearings with three-dimensional, wave-shaped axial end surfaces. Optimizations of the wave height and surface porosity are experimentally determined using lubrication characteristics such as the friction coefficient and worn-out surface conditions. Lubrication characteristics such as the friction coefficient, temperature rise, thrust flotation, and oil consumption rate are evaluated for an estimation of life expectancy. In this research, the results of this theoretical application on thrust bearings clearly showed considerable improvement over conventional thrust bearings. Furthermore, this experimental research has clarified the lubrication conditions of various thrust-loaded axial end surfaces.
Elastohydrodynamic Film Thickness in Elliptical Contacts With Spinning and Rolling
Authors: Zou Qian , Huang Changhua , Wen Shizhu
Published: February 2008

In this paper, a theoretical model for the film thickness prediction of elastohydrodynamic lubrication of elliptical contacts with spinning and rolling/sliding motions is presented, in which 1) an effective ellipticity ratio ke is introduced to present the ellipse feature instead of the normal ellipticity ratio k in case of that the entraining velocity at the center of contact ellipse is at an angle with minor axis, 2) Roelands and Dowson-Higginson’s equations are adopted to express the influence of pressure upon lubricant viscosity and density, 3) multilevel/multigrid techniques, with low complexity and good stability, are used for the purpose of reducing computing time in the complex numerical analysis. With this model the characteristics of film shape and pressure distribution of elastohydrodynamic lubrication of elliptical concentrated contacts with spinning and rolling/sliding were discussed. The results showed that the spinning motion has significant influence on the film shape and pressure distribution. Based on a large number of numerical results of elastohydrodynamic lubrication analysis of elliptical concentrated contacts with spinning and rolling/sliding, new expressions for the minimum and central film thickness prediction were regressed. Their accuracy was analyzed by comparisons with numerical results of an evaluation set and others’ expressions under pure rolling and/or sliding condition. The comparisons showed that the two new expressions have satisfactory accuracy and potential application to engineering analysis and design.
Transition Process From Contact to Floating State in a Squeeze Air Film
Authors: Kajiwara K. , Harayama Y. , Ueda R. , Sonoda T.
Published: February 2008

This paper presents a series of trials of direct detection of the transition process of a squeeze film, from the contacting state into the floating one. The material was initially placed on the surface of a vibrator constituting a squeeze air film. Three electrical trials were performed to certify whether the material could be elevated after the vibrator was excited. When this is done, clearance is expected between the surfaces of the test material and the vibrator. This may be regarded as the equivalent of a change in electrical resistance from almost zero to infinity, with a kind of parallel-plate capacitor being formed. First, detection through DC current was carried out. The experimental result, however, reveals that the resistance never does become infinite, although the equivalent contacting area calculated from this value is very small. Second, detection through DC voltage was performed by terminating the clearance with parallel resistance. The experimental results verify the appearance of the floating state. Third, the average clearance could be detected by regarding it as a parallel-plate type capacitor. Here a Langevin type piezoelectric transducer was used as the vibrator. Through these experimental results an important fact was observed: the waveform of the voltage applied to the transducer is closely related to the movement of the clearance in the time domain.
Effects of Laser Textured Disk Surfaces on a Slider’s Flying Characteristics
Authors: Hu Yong , Bogy David B.
Published: February 2008

Recently, laser texturing has captured the attention of head/media interface engineers in the hard disk drive industry because it provides precision in the landing zone placement while eliminating the transition zone of a mechanically textured landing zone. It also offers excellent tribological performance in terms of low CSS stiction and good durability. These advantages make it the solution of choice for high-end magnetic hard disk drives. This paper models the effects of laser bumps and laser textured disk surfaces on the Headway AAB slider’s flying characteristics. Two commonly used laser bump profiles (“Sombrero” and “Volcano” types) and various texture patterns are numerically generated in the simulator. The slider’s dynamic responses to these moving laser bumps and textures under two outer rail flying conditions are simulated, and the effects of various bump/texture parameters on the slider’s fly height, pitch, roll and their modulations are discussed. The laser texture mechanism is explained by examining the air bearing pressure profiles induced by the moving laser textures.
Constitutive Equations and the Correspondence Principle for the Dynamics of Gas Lubricated Triboelements
Authors: Miller B. , Green I.
Published: February 2008

A new method for characterizing the dynamic behavior of gas films in triboelements is developed. The new method is based on an expansion of the step jump method. In this method, the dynamic character of the gas film is preserved in the form of its force response to a step jump stimulus. Transforming this step response into the frequency domain yields the frequency dependent stiffness and damping properties of the gas film. By approximating the step response with analytic constitutive models and using the elastic-gas film correspondence principle, it is possible to determine the system characteristic equation in analytic form and to find closed-form solutions for stability, transient and forced responses. Requirements are given for choosing constitutive models that comply with the second law of thermodynamics. The new analytical solution method offers a significant time savings compared to direct numerical methods, and it is much more conducive to parametric studies.
Molecular Orientation of Polymer Lubricant Films: Its Tribological Consequence
Authors: Gao Chao , Vo Tam , Weiss Joel
Published: February 2008

The objective of this paper is to demonstrate, from experiments and modeling, how and why molecular orientation of functional end groups of perfluoro-polyether (PFPE) lubricants play an important role in the tribological performance of thin film magnetic disks. These disks typically have an amorphous carbon overcoat upon which a thin lubricant layer is deposited using dip-coating technique. Glancing-angle FTIR (Fourier Transform Infra-Red Spectrometry) is used for measuring molecular orientation of planer functional end groups. A molecular orientation index (MOI) was defined as 1 for randomly oriented functional end groups. The MOI is mathematically derived as 3 (maximum) for lubricant molecules oriented with their functional end groups perpendicular to the surface, and as 0 (minimum) if lubricant molecules oriented with their functional end groups parallel to the surface. The MOI is shown to depend on processing conditions and lubricant film thickness. The tribological performance of the lubricant films was evaluated using drag-mode contact start-stop testing. It was found that wear durability of the lubricant films (~2 nm) with MOI ~ 1.5 is a few times better than those with MOI ~ 0.5 to 1.0. No significant difference in the amount of bonded lubricant film was detected over the range of MOI studied. Nor was there a detectable relationship with hydrophobicity. It was inferred from decreased MOI values due to thermal effects and storage time that a smaller MOI value corresponds to a lower free energy state of the lubricant film. Interestingly, MOI values for bonded lubricant films for Process A are found to be close to 3.0, suggesting that almost all functional end groups in the bonded films are oriented perpendicular to the carbon surface, close to 2.0 for process B, and close to 0 for process C, meaning that almost all functional end groups in the bonded films from process C are oriented parallel to the carbon surface. Relationship between physical/chemical bonding configurations and MOI values are graphically presented in detail. Based on this relation, a simple model on lubricant film structures for the three processes studied is presented. The model MOI values agree very well with measured MOI values as a function of lubricant thickness for all three processes, and the model also appears to account for the observed tribology performance for the MOI values studied (0.5 ~ 1.5).
Elastic-Plastic Analysis of Stresses and Initiation of Cracks in a Ceramic Coating Under Indentation by an Elastic Sphere
Authors: Hayashi K. , Yuan F.
Published: February 2008

The elastic-plastic contact problem of a ceramic coating on a half-space indented by an elastic sphere is solved by the use of the finite element method under a variety of conditions. An elastic-plastic material behavior with isotropic strain hardening was employed. Results for stresses, during loading and after unloading, on the surface and along the axis of symmetry are presented and formation of cracks is discussed in detail, emphasizing the influence of the thickness of coating. It is shown that the circumferential stress on the surface of the coating is highly tensile so that radial cracks are induced for a sharp indenter. But, for a blunt indenter, the radial stress is tensile and is always larger than the circumferential stress, leading to the formation of circumferential cracks. It is also shown that, in the case of a sharp indenter, radial cracks can be induced during unloading.
The Profile Development of a Twin-Land Oil-Control Ring During Running-In
Authors: Visscher M. , Dowson D. , Taylor C. M.
Published: February 2008

This paper presents experimental results of motored engine tests on the wear and profile development of a twin-land oil-control ring. It is shown that the roughness height of the plateau honed liner decreases during running-in, indicating that the deeper grooves remain unaffected. The piston lands are much smoother, and do not show a significant overall change in surface roughness. The profile development results are compared with computer predictions in order to verify the theoretical modeling. It is indicated that the worn land profiles remain tapered, with an inclination resembling the twist angle of the ring. However, there remains a difference in the experimental and the numerically predicted land inclinations. This is probably due to the piston tilt, which was not included in the theoretical model.
The Development of Nanocrystalline CBN for Enhanced Superalloy Grinding Performance
Authors: Ichida Y. , Kishi K.
Published: February 2008

CBN grinding wheels are increasingly used on a wide range of engineering materials. This paper compares the grinding performance of monocrystalline (M-CBN) and polycrystalline (P-CBN) abrasives with a newly developed nanocrystalline (N-CBN) abrasive, when grinding nickel-based superalloys. The N-CBN grits possess average crystal grain diameters less than 1 μm compared to average primary grain diameters of 2.3 μm for P-CBN. It was found that the nanocrystalline CBN grits possess higher fracture strength which give reduced wear rates and yield an order of magnitude increase in grinding wheel life. Analysis of the cutting edge distribution shows that the reduced wear rate of N-CBN is due to the predominance of a micro-fracturing mode of abrasive wear. The size of this micro-fracturing is considerably smaller in N-CBN than in P-CBN.
Improvement of EDM Performance With Advanced Monitoring and Control Systems
Authors: Rajurkar K. P. , Wang W. M.
Published: February 2008

The electrical discharge machining (EDM) process performance depends on maintaining an appropriate machining gap with a servo system and discharge pulse parameters with a pulse power generator. The integration of the state-of-the-art monitoring and control technologies can substantially improve the performance of the EDM process. This paper reviews the research and development of advanced monitoring and control systems for die-sinking EDM and wire EDM during the last two decades. Important research activities include different EDM gap monitoring systems, servo and pulse adaptive control systems, and knowledge base control systems.
Comparison of the Low-Speed Frictional Characteristics of Silicon
Nitride and Steel Balls Using Conventional Lubricants
Authors: Lovell M. R. , Khonsari M. M. , Marangoni R. D.
Published: February 2008

The friction behavior of Si3 N4 ceramic balls operating under ultra-low-speeds with velocity reversal is investigated. Twenty-one sets of exclusively ultra-low-speed operating conditions were examined that include rotational speeds in the range of .01–1 deg/s, normal loads varying from 81.6 to 185.4 N per ball, and two conventional lubricants: DTE 24 and SAE 20 oil. General trends for the friction torque behavior of ceramic balls were established. Theoretical expressions and empirical correlations are presented for evaluation of the steady torque, Ts, and the rest slope, σ. These relationships can be used in Dahl’s model to completely characterize the hysteresis friction behavior of ceramic balls. The results of the ceramic ball friction measurements were compared to that of steel balls operating under identical conditions. In addition, a series of experiments was conducted to extend the operating speeds from .01–500 deg/s. Under the conditions tested, the lubrication regimes from boundary to fluid-film were identified.
Structural Health Monitoring Using Vibration Measurements and Engineering Insight
Authors: Zimmerman D. C. , Kaouk M. , Simmermacher T.
Published: February 2008

Several system identification algorithms have been proposed that make use of analytical models and measured modal data to determine the location and/or extent of structural damage. In particular, the authors have proposed a computationally attractive Minimum Rank Perturbation Theory (MRPT) which determines perturbation matrices to the mass, damping, and/or stiffness matrices. Inspection of these perturbation matrices provides insight to both the location and extent of structural damage. This paper documents our practical experience in applying MRPT theory to a variety of structures. The ability to incorporate engineering insight and judgment into the algorithm is shown to enhance the performance of the MRPT technique when faced with real-world issues.
Life-Cycle Engineering Design
Authors: Ishii K.
Published: February 2008

Life-cycle engineering seeks to incorporate various product life-cycle values into the early stages of design. These values include functional performance, manufacturability, serviceability, and environmental impact. We start with a survey of life-cycle engineering research focusing on methodologies and tools. Further, the paper addresses critical research issues in life-cycle design tools: design representation and measures for life-cycle evaluation. The paper describes our design representation scheme based on a semantic network that is effective for evaluating the structural layout. Evaluation measures for serviceability and recyclability illustrate the practical use of these representation schemes.
Inelastic Analysis of Components Using a Modulus Adjustment Scheme
Authors: Babu S. , Iyer P. K.
Published: February 2008

Mechanical components and structures loaded into inelastic region can fail by low cycle fatigue (LCF). Evaluation of inelastic strain is an important stage in the LCF life prediction methodology. Different techniques, viz., experimental methods, elastic-plastic finite element analysis (FEA), and robust methods, can be used to predict inelastic strains. The state predicted by available robust methods does not correspond to equilibrium state of the component. A method called MARS (modulus adjustment and redistribution of stress) based on linear elastic FEA has been developed to obtain equilibrium and kinematic distributions close to the actual one. The proposed method uses an iterative strategy combined with a modulus reduction technique.
Fatigue Life Estimation for Internal Threads in Class 1 Components
Authors: Kumar R.
Published: February 2008

Heat exchangers, steam generators, and other pressure vessels in nuclear power plants are equipped with bolted closures for the purpose of in-service inspection and maintenance. The ASME Boiler and Pressure Vessel Code specifies that all Class 1 components meet the fatigue life requirements for level A and B service conditions. In the case of bolted closures, it is often found that the bolt/stud is the most critical part. In many situations, the bolts fail to meet the fatigue requirements for the design life of the equipment. In such cases, the bolts can be replaced after certain duration based upon their fatigue life. However, the mating threads in the flange (which is an integral part of the vessel) are still a concern. While the replacement of the bolts is relatively easy and inexpensive, the corrective action (e.g., replacement or repair) for the flange is usually difficult and expensive, or impossible. Hence, it is important to have a reasonable estimate of the fatigue life of internal threads to alleviate or minimize the concern. In this paper, a simplified approach is presented for this purpose. Considering various bolt sizes, commonly used thread series, and typical Class 1 component materials, it is shown that the fatigue life of the internal threads is about three times the fatigue life of the bolt threads. This conclusion greatly reduces or eliminates the concern for in-service replacement or repair of the components with internal threads.
A Reliability Assessment Method in Strain-Based Fatigue Life Analysis
Authors: Zhao J. , Tang J. , Wu H. C.
Published: February 2008

For the purpose of fatigue reliability assessment based on strain-life analysis, a family of reliability-defined ε-Nf curves, called R-ε-Nf curves, is constructed by considering the interference model of fatigue strain capacity and applied strain history. The main effort of this work is to define reliability factors which are used to modify the conventional ε-Nf curve into a family of R-ε-Nf curves. A major contribution of this paper is to define two “unique” reliability factors, one for elastic-strain-life relation and the other for plastic-strain-life relation, for a certain reliability by using an empirical ε-Nf curve.
Sizing Design Sensitivity Analysis and Optimization of a Hemispherical Shell With a Nonradial Penetrated Nozzle
Authors: Rusu-Casandra A. L. , Grindeanu I. R. , Chang K.-H.
Published: February 2008

This paper presents a sizing optimization of a hemispherical shell with a nonradial penetrated nozzle, under internal pressure loading. The objective of the optimization is to decrease the stress concentration in the intersection area, through the variation of the thicknesses of the shells, on condition the volume have a minimum value. This is accomplished by performing a stress analysis and by developing a sizing optimization. The variational equations of elasticity and an adjoint variable method are employed to calculate sizing design sensitivities of stresses. This continuum approach combined with a gradient method could be applied to broad classes of elastic structural sizing optimization problems.
Creep Behavior of a Large Full-Size Welded Austenitic Steel Plate
Authors: Koundy V. , Allais L. , Delhaye M.
Published: February 2008

The high-temperature design codes are presently considering the use of stress reduction factors for designing welded structures submitted to creep. These reduction factors are derived from creep tests which are generally made on small specimens and are not necessarily representative of large-size geometries. These codes are very likely overconservative, consequently uneconomical and need to be improved; an investigation to assess and quantify the supposed size effect is required. This paper presents an experimental and numerical study on creep behavior at 600°C of full-size welded joints taking into account real full-thickness of weldings. The material investigated is the austenitic stainless steel 316L(N) with manual metal arc welds using the 19 Cr 12 Ni 2 Mo electrode grade. The creep laws used in calculations are those obtained from tests using small specimens, but some coefficients of their theoretical formulation have been modified to obtain a better coherence with fullsize specimen data. Between small and large full-size specimens, experimental results show no significant difference in time to rupture, and the same location of fracture, at the center of the weldment, is observed. Finite element simulations performed for full-size welded joints provide rupture times that are consistent with measured values. The calculated percentage of the damaged volume in the weld metal as a function of load levels and of creep-time duration is studied; it shows that the creep-rupture times for high stress loading are determined with higher accuracy than for low stress loading.
A Creep Damage Estimation Method for In-Service Fossil Fuel Boiler
Superheater Tubes
Authors: Nogata F. , Takahashi H.
Published: February 2008

Because mechanical properties of structural materials for high-temperature use, such as boiler tubing, degrade during long-term service, it is essential to detect toughness degradation by means of a nondestructive and simple field test technique. A grain boundary etching technique is developed to detect material degradation, and assess creep strength and notch toughness. An etching test using a picric acid solution with a wetting agent or using 20 percent HNO3 with alcoholic solution was found to have great potential for the nondestructive estimation of grain boundary embrittlement caused by carbide and sigma precipitation in SUS stainless steel. The feasibility of this estimation procedure was determined showing the relationships between Charpy impact energy (CVN) and grooving width (WGS), and creep damage ratio (Φ) and WGS. Superheater tubes of fossil fuel boiler were tested on site to demonstrate the validity of this technique.
Numerical Simulation of Cross-Flow-Induced Fluidelastic Vibration of Tube Arrays and Comparison With Experimental Results
Authors: Eisinger F. L. , Rao M. S. M. , Steininger D. A. , Haslinger K. H.
Published: February 2008

Tube arrays exposed to air, gas or liquid cross-flow can vibrate due to vortex-shedding, turbulence, or fluidelastic instability. The major emphasis of this paper is on the phenomenon of fluidelastic instability (or fluidelastic vibration). A numerical model is applied to the simulation of fluidelastic vibration of representative tubes in a tube bundle, based on S. S. Chen’s unsteady flow theory. The results are validated against published data based on linear cases. The model is then applied to a nonlinear structure of a U-bend tube bundle with clearances at supports, and the computed results compared to those obtained by experimental testing. The numerical studies were performed using the ABAQUS-EPGEN finite element code using a special subroutine incorporating fluidelastic forces. It is shown that the results of both the linear and nonlinear modeling are in good agreement with experimental data.
The Effect of Gasket Creep-Relaxation on the Leakage Tightness of Bolted Flanged Joints
Authors: Bouzid A. , Chaaban A. , Bazergui A.
Published: February 2008

The loss of tightness of bolted flanged joints is primarily due to the relaxation of the joint; in particular, the clamping load is affected by the amount of relaxation that a gasket exhibits over time. Test methods are available for evaluating the ability of a gasket to maintain a given compressive stress. It is necessary, however, to evaluate the response of the joint members to a small change in gasket thickness produced by the effect of creep-relaxation. This paper presents an analytical evaluation of the effect of gasket creep-relaxation on the remaining gasket stress taking into account the flexibility of all joint members, thus allowing the evaluation of the required tightening load on the gasket. The results obtained by this approach are shown to agree with those determined finite on an experimental rig made up of 4-in. class-600-lb pair of flanges. Axisymmetric finite element models of larger flange assemblies are also used for comparison. The results show that creep-relaxation of gaskets has a major influence on the remaining compression load on the gasket.
Plastic Deformation and Burst of Pressurized Multilayered
Cylinders
Authors: Tadmor E. B. , Durban D.
Published: February 2008

A large strain analysis is presented for internally pressurized multilayered tubes, in generalized plane strain. Material behavior is modeled by an elastoplastic deformation theory with an orthotropic yield function, introduced by Hill, and arbitrary hardening. Elastic compressibility is neglected. An exact solution is given, in terms of quadratures, along with a general condition for burst. Simple yet useful relations are derived for thin-walled cylinders with the neglect of elastic strains. For rigid/nonlinear-hardening response, we obtain an expression for the onset of burst in terms of overall effective moduli. A few numerical examples are given and the possibility of locating an optimal two-layer configuration is discussed. It appears that optimization with respect to weight is attainable provided that appropriate materials are selected.
Advances in Dynamic Relaxation Techniques for Nonlinear Finite
Element Analysis
Authors: Sauvé R. G. , Metzger D. R.
Published: February 2008

Traditionally, the finite element technique has been applied to static and steady-state problems using implicit methods. When nonlinearities exist, equilibrium iterations must be performed using Newton-Raphson or quasi-Newton techniques at each load level. In the presence of complex geometry, nonlinear material behavior, and large relative sliding of material interfaces, solutions using implicit methods often become intractable. A dynamic relaxation algorithm is developed for inclusion in finite element codes. The explicit nature of the method avoids large computer memory requirements and makes possible the solution of large-scale problems. The method described approaches the steady-state solution with no overshoot, a problem which has plagued researchers in the past. The method is included in a general nonlinear finite element code. A description of the method along with a number of new applications involving geometric and material nonlinearities are presented.
Experimental Study on Seismic Responses of Piping Systems With
Friction—Part 2: Simplified Analysis Method on the Effect of
Friction
Authors: Kobayashi H. , Yokoi R. , Chiba T. , Suzuki K. , Shimizu N. , Minowa C.
Published: February 2008

Friction between pipe and support structure is generally known to reduce seismic response of the piping systems. Vibration tests using large-scale piping model with friction support were carried out to evaluate the reduction effect. The piping response was mainly governed by the first modal deformation. The simplified analysis method based on linear response spectrum analysis was developed and confirmed to be applicable. In this method, the reduction effect by friction is treated as equivalent viscous damping ratio. This paper deals with the analysis method, and the comparison between the experimental results and analytical ones.
Stress Analysis on Rectangular Cross-Sectional Ring
Headers
Authors: Murata M. , Utzinger M. B. , Chen D.-H. , Nisitani H.
Published: February 2008

For rectangular cross-sectional ring headers, the authors’ theoretical stress analysis is presented to agree with actual stresses by measurement with strain gages. Therefore, this analytical method is applicable for similar rectangular cross-sectional ring headers. When the aspect ratio (length of two cylinders/radius difference between two cylinders) is more than three, moments originating at the end of finite long cylinders and tangential stresses on the half-length of both cylinders are almost the same as values from infinitely long cylinders. Regarding the welds between flat cover plates and cylinders, cover plate designs can be remarkably thinner by changing the weld shape, that is, by using T-joint weld with a single-bevel groove, than compared to Type (i) in PG-31 of ASME Code.
An Analysis of Pipe Flange Connections Using Epoxy
Adhesives/Anaerobic Sealant Instead of Gaskets
Authors: Sawa T. , Sasaki R. , Yoneno M.
Published: February 2008

This paper deals with the strength and the sealing performance of pipe flange connections combining the bonding force of adhesives with the clamping force of bolts. The epoxy adhesives or anaerobic sealants are bonded at the interface partially instead of gaskets in pipe flange connections. The stress distribution in the epoxy adhesives (anaerobic sealant), which governs the sealing performance, and the variations in axial bolt force are analyzed, using an axisymmetrical theory of elasticity, when an internal pressure is applied to a connection in which two pipe flanges are clamped together by bolts and nuts with an initial clamping force after being joined by epoxy adhesives or anaerobic sealant. In addition, a method for estimating the strength of the combination connection is demonstrated. Experiments are performed and the analytical results are consistent with the experimental results concerning the variation in axial bolt force and the strength of combination connections. It can be seen that the strength of connections increases with a decrease in the bolt pitch circle diameter. Furthermore, it is seen that the sealing performance of such combination connections in which the interface is bonded partially is improved over that of pipe flange connections with metallic gaskets.
Nonlinear Fatigue Damage Accumulation Under Random Loading
Authors: Zhu W. Q. , Jiang M. X.
Published: February 2008

The analytical expressions for the probability densities of the cumulative fatigue damage and fatigue life and for the reliability function are obtained for a mechanical or structural component subject to stationary random stress process on the basis of a stochastic theory of fatigue damage accumulation proposed by the first author and his co-worker and the Morrow’s nonlinear damage rule. The comparison between the results from Morrow’s and Palmgren-Miner’s damage rules for the case when the stress is a narrow-band stationary Gaussian process with zero mean is made and some important conclusions are drawn.
On Analysis of Fluidelastic Instability in Air-Water Mixture
Authors: Marn J. , Catton I.
Published: February 2008

Cross-flow-induced vibrations are important phenomena in the power generation industry as they may severely damage the heat exchanger tubes due to violent oscillations and clashing. The fluidelastic instability was identified as the main driving force behind the vibrations and is highly dependent on the flow regime (single-phase versus two-phase flow). The vorticity formulation has been shown in the past to sufficiently describe the phenomena of cross-flow-induced vibrations in cylindrical arrays. This paper attempts to use the existing, well-established equations (see Bottoni and Sengpiel, 1992) and compares the results of a fluidelastic instability of an air-water mixture to available experimental data. The proposed problem is solved using finite differences by discretizing the computational domain and assuming the initial positions of the tubes.