bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Study on the Thermal and Residual Stress by Welding and Laser Surface Hardening Using a new Two-Dimensional Finite Element Model
Authors: Yang Y S , Na S J 
Published: February 2007

The transient thermal stress and residual stress in bead-on-plate welding and laser surface hardening was analysed by employing a new two-dimensional finite element model. In the formulation, the sliced solution domain possessing one element in the welding or hardening direction was introduced to allow the change of longitudinal total strain along the width and depth of the specimen. The longitudinal total strain, which makes the resultant force in the longitudinal direction zero, was used as the boundary condition. To determine the longitudinal total strain, the equations of the compatibility, force equilibrium and moment equilibrium were considered. Calculation of the transient temperature distribution was based on the two-dimensional finite element model of the quasi-stationary condition. By using the proposed model the thermal and residual stresses of the bead-on-plate welding and laser surface heat treatment were successively calculated. Especially in laser surface hardening, the thermal stress was induced mainly from the temperature gradient and martensitic phase transformation, which was found to have a greater influence on the residual stress than the former. The computed results were compared with those obtained by the conventional two-dimensional model of the plane strain condition. The simulation results revealed that the present model could more reasonably describe the thermal and residual stresses than the plane strain model.
Internally Pressurized Machined Domed Ends—a Comparison of the Plastic Buckling Predictions of the Deformation and Flow Theories
Authors: Galletly G D , Błachut J , Moreton D N 
Published: February 2007

The present series of tests, involving six machined steel torispherical shells subjected to internal pressure, was designed to highlight the difference in the buckling predictions of the deformation and the flow theories of plasticity. For the geometries selected, deformation theory predicted that bifurcation buckling would occur for all the domes tested, whereas flow theory predicted buckling in only two of them. In the tests, low-amplitude waves (detected by probes) appeared in all six of the domes. In four of the domes, the low-amplitude waves grew with increasing pressure and became buckles which were visible to the naked eye. Assuming that the occurrence of low-amplitude waves can be considered as buckling of a dome, then deformation theory predicted the failure mode correctly in all six cases. Flow theory was correct in only two cases. The agreement between the initial experimental buckling pressures and those predicted by deformation theory was reasonably good, the ratios varying between 0.71 and 0.94. For three of the domes, the buckling pressures were also found by the Southwell plot technique. These latter agreed best with the deformation theory predictions. The shell buckling program used for analysis purposes was BOSOR 5 and its predictions were checked using five other independent shell buckling programs. One reason for the incorrect prediction of the failure mode by flow theory may be the neglect of initial geometric imperfections in the analysis. Some preliminary calculations including them seem to confirm the hypothesis.
Measuring Vehicle Drag Forces Using an On-Board Microcomputer
Authors: Passmore M A , Jenkins E G 
Published: February 2007

The force resisting the straight-line motion of a road vehicle on a flat track consists of mechanical resistance and aerodynamic drag. It is necessary to measure these component forces over the speed range of the vehicle to obtain data for performance calculations and for the accurate calibration of modern chassis dynamometers used in fuel economy and exhaust emission tests. Continuous measurement of wheel torque, vehicle speed, airspeed and direction enables estimates to be made of the various drag forces that bring the vehicle to rest during a coastdown test. The data are analysed using a sophisticated parameter optimization routine to determine the numerical values of the coefficients in a mathematical model of the total road load. Repeatability of the results are assessed by calculating the uncertainties in the values obtained from a number of track tests. A brief description of the on-vehicle data acquisition and processing system is given, and the advantages of an advanced test and analytical process are demonstrated.
The Implications of Technical Developments on Future European Braking Regulations
Authors: Oppenheimer P 
Published: February 2007

Road vehicle braking systems provide a good example of the increasing use of electronics in vehicles (for example, anti-lock braking systems) and the trend towards the adoption of new technologies (for example, brake-by-wire, electric braking, diagnostics, multiplexing, radar/automatic braking). This paper examines the implications of these developments for future vehicle regulations, including the rule-making process and compliance testing. The present European ECE and EEC braking standards are summarized and the progress towards ‘harmonization’ with the US Federal Standards is reported. The advent of electronic anti-lock braking systems has been anticipated within Annexes to the European regulations; however, a more detailed examination of the potential electronic system opportunities for failure warning and diagnostics is currently in progress. Product liability, failure mode and effects analysis and electromagnetic compatibility are major subjects for consideration in future vehicle regulations; a radical new approach to traffic safety legislation may be opportune.
Investigations on Research Engines with Visible and Infrared Optical Access
Authors: Hands T , Collings N , Ma T 
Published: February 2007

This paper details the progress made in an experimental study of knock in spark ignition engines undertaken between the Cambridge University Engineering Department and Ford Research and Engineering Centre. A general-purpose, optically accessed cylinder head of standard configuration and capable of high-speed operation has been designed and built. This head has been used in preliminary direct emission studies of knock. The same cylinder head, together with a photographic Ricardo Hydra, has been used in an infrared study of cylinder radiative emissions. By maximizing the combustion chamber surface emissions, observations regarding surface temperature characteristics with and without knock have been made. By minimizing the emissions from combustion chamber surfaces, the strong emission from the flame from itself has been used to produce once-per-cycle images of flame propagation.
Fast Response Tip Clearance Measurements in Axial Flow Compressors—Techniques and Results
Authors: Parrish C J 
Published: February 2007

As part of an investigation of the effects of tip clearance performance of development axial flow compressors, a system for detecting rotor blade tip rubs has been developed and a tip clearance measuring system modified to detect clearance changes at a bandwidth of 500 Hz. Mean clearance changes have been measured as well as changes during surge. Rotor orbit has also been investigated and the system has become an important means of monitoring rotordynamic behaviour. Subharmonic components of rotor orbit have been discovered.
The Fatigue Performance of Notched Composite Material Systems
Authors: Kellas S , Morton J , Curtis P T 
Published: February 2007

In this work results are reported from an experimental fatigue programme. The role of the constituent materials upon the fatigue performance of a given composite material system was studied. This involved comparisons of the residual strength, damage development, and in some cases fatigue life. A new method of approach, based upon a unique characteristic fatigue parameter, termed the damage transition stress, St, was also introduced. It has been shown that the employment of the characteristic parameter can simplify the comparison of different material systems considerably. Four graphite reinforced material systems were evaluated: (a) standard epoxy system, (b) toughened epoxy system, (c) thermoplastic system and, (d) high temperature system. It was found that three of the four material systems examined (a, b, and d) were more sensitive to hygrothermal environments, so far as the development of fatigue damage is concerned. In general, the tensile residual strength, in all material systems, showed a marked improvement, whereas the effect of environment and fatigue damage combination upon the compressive strength was more complex. Presentation of the fatigue data in the form of linear S-N plots allowed the determination of St, and its dependence upon environment and material systems. A material dynamic toughness was also identified.
Objective Measurement of Knee Laxity and Stiffness with Reference to Knee Injury Diagnosis: Part 1: Design Considerations and Apparatus
Authors: Dahlkvist N J , Seedhom B B 
Published: February 2007

Apparatus capable of objectively evaluating the laxity of the knee in vivo has been developed. The equipment consisted of a microcomputer-controlled machine, into which the leg was firmly clamped. The mechanical properties of the knee were measured by slowly applying a load to the tibia, while the femur was held stationary, and monitoring the resulting displacement of the tibia. Three separate tests could be performed: anterior-posterior drawing, varus-valgus rotation and tibial rotation. The tests were carried out on both legs of each subject, making six tests in all. The forces versus displacement (or torque versus rotation) took the form of a hysteresis loop. From these a total of 24 variables describing the stiffness, laxity and visco-elastic properties of the knee were calculated.
A Comparative Study of the Shear Stress Induced in the Leakage Backflow Produced by Four Types of Heart Valve Prostheses
Authors: Haggag Y A M 
Published: February 2007

The clinical selection of a prosthetic heart valve requires the consideration of many factors. These include the pressure drop across the prosthesis, the amount of leakage backflow when the valve is closed as well as the associated shear stress within this flow for a particular valve design. Major emphasis has been placed upon the documentation of the pressure drop across prosthetic valves. Consideration of the shear stress induced in the leakage backflow associated with prosthetic valves, however, has received less attention. The purpose of this investigation, therefore, is to determine theoretically the extent of this particular shear stress for four types of currently used mechanical prosthetic cardiac valves. All valves have the same tissue annulus diameter of27 mm. The leakage backflow is relatively small compared to the main forward flow through the orifice. However, it is important from the haemolysis point of view. The effect of the shear stress on the suspected occurrence of haemolysis is analysed by two theoretical approaches: (a) the laminar flow approach, and (b) the entry flow approach, and then compared with the findings of previous investigators dealing with the critical shear stresses which may damage the red blood cells. It was found that both approaches give practically equal shear stresses under the same pressure differential for all valves investigated. Some haemolysis is expected to occur but it is generally compensated by bone marrow hyperfunction, since that type of shear stress is sustained for only a short duration of time.
A Simple Procedure for Determining Spatial and Transient Variations of Cooling Rate within a Specimen during Cryopreservation: Part 2: Graphical Solutions
Authors: Diller K R 
Published: February 2007

The ability to analyse the cooling rate history and its spatial distribution is useful in predicting the response of a biological specimen to a specific cryopreservation protocol. Although analytical and numerical methods exist for performing rigorous analyses of these thermal processes, their practical use requires considerable time and/or mathematical sophistication. In Part I of this paper a theoretical basis was presented for the development of a graphical analysis procedure for determining cooling rate that is quick and straightforward to apply. In this paper derived graphs are presented, from which the instantaneous cooling rate may be determined for specimens of a wide range of physical shapes. These dimensionless graphs have been derived for determination of cooling rate as a function of time, position, the system's physical properties and the thermal boundary conditions. Numerical examples are presented for analysing the cooling of biological specimens for specific preservation protocols, illustrating solution both by computation using the tabulated constants from tables in the first paper and by reading directly from the graphed solutions.
Effect of Tube Ovalling on Pressure Wave Propagation Speed
Authors: Anderson Eur Ing A , Johnson G R 
Published: February 2007

For physiological and other flows it is often assumed that the pressure pulse wave speed is given by the classic Moens-Korteweg expression and this may be used, for example, to assist in the determination of in vivo blood vessel wall incremental Young's modulus. A number of physical factors affecting the value of this wave speed have been reviewed in the literature, but the effect of slight ovalling of the tube cross-section is rarely mentioned. The analysis for a tube of elliptic cross-section shows that even a very small degree of ovalling can cause quite substantial reductions in Young mode wave propagation velocities compared with the classic Moens-Korteweg expression. Bending-induced changes in cross-section shape with internal pressure increase the apparent elasticity of the tube wall. Experimental confirmation is provided by waterhammer wave speed measurements in a copper tube that has been ovalled by coiling. Even though the Young mode is not dominant in this case, as it would be for a physiological case, the measured wave speed is quite clearly less than the Moens-Korteweg theory and it can be shown that the small degree of measured tube ovality explains this.
Similarity Considerations on Wall Heat Losses in Internal Combustion Engines
Authors: Eilts P 
Published: February 2007

The drop in wall heat losses with increasing engine size is shown not to be due to the decreasing surface-volume ratio, because this influence is compensated by the engine speed, which also drops. Instead, the heat-transfer coefficient decreases as the cylinder bore becomes larger. The dependence of the heat-transfer coefficient on engine size is explained using Reynolds' analogy. This dependence can be used to determine approximately changes in wall heat losses resulting from differences in engine size and the subsequent effects on indicated efficiency. It is found that only a minor part of the differences in efficiency between small and large engines is due to size-dependent changes in wall heat losses.
A Study on Prediction of Welding Current in Gas Metal arc Welding Part 2: Experimental Modelling of Relationship Between Welding Current and Tip-to-Workpiece Distance and its Application to Weld Seam Tracking System
Authors: Kim J W , Na S J 
Published: February 2007

The weld joint tracking sensor is indispensable to improve the flexibility of the arc welding robot application. Recently, some sensing methods that utilize the electric arc signal, or more correctly the welding current in gas metal arc welding (GMAW), have been developed and are prevalently in use. The welding current, however, is directly affected not only by the tip-to-workpiece distance, but also by the welding voltage and wire feed speed. Thus a model that is able to determine the welding current in response to the tip-to-workpiece distance was proposed for the gas metal arc welding process. The model was developed by using the factorial experiment and least-squares method to the variables of welding voltage and wire feed speed. The relationship between welding current and tip-to-workpiece distance determined by the proposed model was compared with the experimental ones and it was revealed that both the results show good agreement within the considerably wide range of welding conditions. The model was used for developing a weld seam tracking system which controls the moving speed of a welding torch in the height direction. It could be shown that there is a successful capability of seam tracking in flat welding of V-groove butt joins. Furthermore, the model can be used for the analysis of the weld pool formation and weld bead geometry, and also for the determination of appropriate process parameters.
A Study on Heat Flow in Circumferential Pipe Welding Using a Semi-Analytical Finite Element Method
Authors: Lee H-J , Na S-J 
Published: February 2007

The heat flow during circumferential welding of a small-diameter aluminium pipe, which cannot be assumed to be in the quasi-stationary state because of heat accumulation, was analysed by employing a semi-analytical finite element method. The circumferential distribution of arc heat flux and temperature was simulated in the form of an expanded series to calculate the three-dimensional heat flow with a two-dimensional solution domain. The arc heat distribution, assumed as a Gaussian form, was expressed in several circumferential line heat sources by using the Fourier series expansion. The solution domain was divided into two sub-domains to apply the two types of series with two different numbers of the expanding term, which results in the reduction of the calculation time. The thermal cycles and isotherms in the rz plane calculated by using the proposed semi-analytical finite element method agreed fairly well with the experimental results adopted from a reference. Due to the heat buildup the fusion zone increases in its size as the welding proceeds. The temperature near the heat source rises also as the welding proceeds, but the shape of the circumferential temperature distribution of a ring element was maintained almost unchanged during the entire welding process except the welding start. The proposed semi-analytical finite element method could be considered as very useful for analysing the heat flow in circumferential welding of small-diameter pipes because of its simple formulation and short computing time.
Statistical Theory of Machine Tool Stability
Authors: Baradie M A El 
Published: February 2007

Machine tool chatter is essentially a statistical phenomenon. The dynamic characteristics of the machine tool structure as well as the dynamic coefficients of the cutting process are statistical quantities that show scatter when determined in repeated tests. In this paper a generalized statistical theory of chatter has been developed. This takes into consideration the scatter of the dynamic data of the machine structure and/or that of the dynamic cutting coefficients. The dynamics of the cutting process has been presented by a mathematical model, based on deriving the cutting coefficients from steady state cutting data. The dynamics of the machine tool structure and the cutting process, being input to the theory, were determined experimentally. At the thresholds of stability, the statistical variations due to the dynamic cutting coefficients amount to ±17 per cent at the 99 per cent confidence level, while the statistical variations due to the structure dynamics amount to ±5.2 per cent only, at the same confidence levels. Therefore the predicted thresholds of stability can be specified only in terms of mean values with confidence limits.
A Study on Arc Sensor Algorithm for Weld Seam Tracking in Gas Metal Arc Welding of Butt Joints
Authors: Kim J-W , Na S-J 
Published: February 2007

The positional accuracy requirement of the welding torch with respect to the weld seam is the major impediment in arc welding robot applications. The weld seam tracking sensor is essential to improve the flexibility of arc welding robot applications. In this study, an arc sensor which utilizes the electrical signal obtained from the welding arc itself was developed for gas metal arc welding of butt joints. In order to overcome the fluctuation in the welding current signal, the current signal was fitted to a curve which is inversely proportional to the trace of the tip-to-workpiece distance by using the quadratic curve-fitting method. The availability of the curve-fitted welding current signal was investigated and the seam tracking results of the system that uses the curve-fitting method were compared with the ones of another system that controls the moving speed of the welding torch in the height direction.
A Study on Three-Dimensional Transient Heat Flow in Circumferential GTA Welding of Pipes Using Periodicity Conditions
Authors: Lho T-J , Na S-J 
Published: February 2007

A transient three-dimensional finite difference mode (FDM) of the heat flow in the circumferential GTA welding of pipes was developed and applied to calculate the temperature distribution in the workpiece. In order to minimize the computing time required for solving the FDM equations as much as possible, the alternating direction implicit (ADI) scheme which makes use of the tridiagonal matrix algorithm efficiently was adopted. Based on the characteristics of the pipe welding process, the periodic boundary condition was applied to calculate the temperature distribution in the 8 direction. For treating the moving heat source effectively, the grid meshes with variable spacings were regenerated at each time step. In order to decrease the interpolating error by grid remeshing, the temperature values at new meshes were interpolated from those at old meshes by using the periodic spline function. The temperature-dependent thermal properties, the latent heat and the convective and radiative boundary conditions were included in the model. The calculated sizes of the fusion and heat-affected zone were compared with the observed values after experiments.
Elastohydrodynamie Lubrication of Big-End Bearings Part 2: Ratification
Authors: Aitken M B , McCallion H 
Published: February 2007

The elastohydrodynamic analysis developed in Part 1 of this work is ratified against previous Ruston and Hornsby big-end studies. Sufficiently close correlation with published in situ film-thickness measurements allows big-end bearing performance to be determined with some confidence; significant new insight was obtained. Elasticity body forces from connecting-rod motion were found to be an integral component of the big-end representation; it is a prevalent misconception that these forces can be neglected from theoretical as well as experimental test-rig works. Film collapse mechanisms, likened to vapour cavitation, were observed in the dynamically loaded elastic bearing; these were not detected in equivalent rigid bearing simulations. Cyclic minimum film thickness was observed during inertial loading, irrespective of gas force loading. Two separate minimum-film conditions were identified: one in the connecting-rod's neck and a second, at higher load, in the rod's cap. The second condition is critical from a design standpoint; significantly thinner films are predicted than by rigid bearing theory.