bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain distributions around fasteners in laminated plates under biaxial in-plane loading
Authors: Webber J P H , Graham U , Wisnom M R
Published: October 2002

A finite element model is employed to investigate the effect of variations in biaxial in-plane applied loading on the strain distributions around a bolt-filled quasi-isotropic laminated plate. The theoretical model includes the effect of friction between a washer and the plate surface which is generated by a torque loaded bolt. It is this aspect of the investigation that is a novel feature of the work. Contour plots around the hole/washer region for all three in-plane strain components are presented and discussed. The results show that the strain distribution is very much affected by the biaxial loads and that the highest strains occur when biaxial tension and compression stresses of equal magnitude are applied. Washer friction is found to have a beneficial effect, and in some load cases strains are fairly evenly distributed over the hole/washer region.
Localized metal forming simulation by r-s-adapted arbitrary Lagrangian-Eulerian finite element method
Authors: Ghosh S , Raju S
Published: October 2002

In this paper, an adaptive arbitrary Lagrangian—Eulerian (ALE) large deformation finite element method (FEM) is developed for solving metal forming problems with strain localization. The ALE mesh movement is coupled with r-adaptation of automatic node relocation to minimize mesh distortion during the process of deformation. A strain localization phenomenon is incorporated through constitutive relations for porous ductile materials. Prediction of localized deformation is achieved through a multilevel mesh superimposition method, called s-adaptation. A few metal forming problems are simulated to test the effectiveness of this model.
Static lateral compression of aluminium tubes: Strain gauge measurements and discussion of theoretical models
Authors: Avalle M , Goglio L
Published: October 2002

This paper illustrates experimental results obtained by means of strain gauges applied on circular tubes during static lateral crushing. The aim of the work is to obtain an experimental insight regarding the strain field during lateral compression and to verify the known theoretical models.

The experimental activity involved aluminium tubes of 80 and 100 mm diameter and 2 mm wall thickness. Up to thirty strain gauges were applied on the internal and external surfaces of each tube. Additional theoretical results were obtained by means of numerical simulation performed using a non-linear finite element code. The measurements are well fitted, both qualitatively and quantitatively, by the Reid-Reddy theoretical model.
Residual stresses in alumino-thermic welded rails
Authors: Webster P J , Mills G , Wang X D , Kang W P , Holden T M
Published: October 2002

Neutron strain scanning has been used to map the residual stress field that is generated in a railway rail by a standard gap alumino-thermic weld made using routinely specified procedures. The longitudinal and vertical residual stress fields in the sections well away from the weld are characteristic of many unwelded rails, being generally tensile in the head and foot with balancing compression in the web. In the vicinity of the weld the residual stress patterns are very different. At the top and bottom surfaces of the rail the longitudinal residual stress field is strongly compressive, which is generally beneficial in that it would tend to inhibit the initiation and propagation of fatigue cracks from surface defects. Just at the surface the vertical residual stress attenuates to zero but internally, in the web region, both longitudinal and vertical components of the residual stress field are strongly tensile, which increases the susceptibility of that region to crack initiation and propagation from internal material defects. This pattern is consistent with practical operating experience, which is that most of the small proportion of alumino-thermic welds that do fail do so as a result of porosity or inclusions in the weld. It is found that the ‘boundaries’ of the ‘weld type’ residual stress fields do not coincide with the boundary of the weld, nor of the heat-affected zone, but correlate reasonably well with the positions of the extremities of the mould assembly and with the location of the steepest longitudinal temperature gradients.
A path-independent integral for stress intensity factors in three dimensions
Authors: Bainbridge C M , Aliabadi M H , Rooke D P
Published: October 2002

A path-independent surface integral is derived for the calculation of the stress intensity factor in three dimensions. The integral is based upon a type of Green's function, which is used in conjunction with Betti's reciprocal theorem. Various benchmark problems have been solved using this technique. The results were found to be in good agreement with the values obtained in previous analyses, and the method appears to offer some efficiency advantages. For example, the method presented here does not require calculations of derivatives of the stress tensor, as does the J-integral for the three-dimensional case. Such calculations of derivatives of stress are inherently numerically difficult if good accuracy is required. It can also be used for mixed-mode problems without the need for decoupling as required by other techniques. This technique is complementary to the widely used weight function technique.
A photoelastic study of the effect on subsurface stresses of the contact geometry and friction
Authors: Burguete R L , Patterson E A
Published: October 2002

Three-dimensional photoelasticity has been used to investigate the effects of contact geometry and interfacial friction on the distribution of stress in a punch acting on a semi-infinite plate and a cup-cone contact. The analysis of the data was performed using an automated polariscope based on the method of phase stepping. The results show that the included half-angle of the punch has a significant effect on the magnitude of the stress which decreases with the angle. The effect of increasing the fillet radius is to lower the maximum subsurface shear stress. Reducing the inclination of the contact interface to the applied stress in the cup-cone model had the effect of raising the peak shear stress. By varying the interfacial friction no significant change in the subsurface stress was observed. It is demonstrated that the stress field around a crack is similar to that at the edge of contact and that the use of a normalized stress intensity factor is relevant to the stress field generated at the boundary of a contact. This parametric study has demonstrated that certain design parameters can reduce the local peak stresses around contact and therefore this would lead to a lower probability of crack initiation and propagation.
Stress calculation in welds taking into account the bearing force between the welded parts
Authors: Chicurel E
Published: October 2002

Direct normal stresses in welds are usually calculated assuming that, in addition to resisting the tension and the shear loads, they alone resist all of the compression load even when the welded parts make contact in a large area. A method is proposed here assuming that, as far as direct normal stresses are concerned, the welds resist the tension stresses while the welded parts themselves resist a portion (quite often a very substantial one) of the compression stresses.
Approximate method for the analysis of components undergoing ratchetting and failure
Authors: Lin J , Dunne F P E , Hayhurst D R
Published: October 2002

An approximate method has been presented for the design analysis of engineering components subjected to combined cyclic thermal and mechanical loading. The method is based on the discretization of components using multibar modelling which enables the effects of stress redistribution to be included as creep and cyclic plasticity damage evolves.

Cycle jumping methods have also been presented which extend previous methods to handle problems in which incremental plastic straining (ratchetting) occurs. Cycle jumping leads to considerable reductions in computer CPU (central processing unit) resources, and this has been shown for a range of loading conditions.

The cycle jumping technique has been utilized to analyse the ratchetting behaviour of a multibar structure selected to model geometrical and thermomechanical effects typically encountered in practical design situations. The method has been used to predict the behaviour of a component when subjected to cyclic thermal loading, and the results compared with those obtained from detailed finite element analysis. The method is also used to analyse the same component when subjected to constant mechanical loading, in addition to cyclic thermal loading leading to ratchetting. The important features of the two analyses are then compared. In this way, the multibar modelling is shown to enable the computationally efficient analysis of engineering components.
On the post-processing of data obtained from cracked components
Authors: Ciavarella M , Demelio G , Pappalettere C
Published: October 2002

The use of a simple singular value decomposition (SVD) technique to post-process far-field data from cracked components is discussed. The technique employs the series expansion for stress or displacements ahead of the crack tip, which is available for a wide range of configurations. The use of higher-order terms, necessary for the post-processing, is beneficial for two reasons: (a) it permits the abstraction of the maximum usable amount of information; (b) it gives a better understanding of the fracture mechanics, especially regarding crack tip plasticity and dynamic propagation. Several numerical cases are examined and a comparison is made with analytical results, permitting an evaluation to be made of the pure numerical error in the post-processing.
Polymer coating as a strain witness in thermoelasticity
Authors: Barone S , Patterson E A
Published: October 2002

The work described in this paper offers the possibility of using a polymer coating as a strain witness in thermoelasticity. In particular, the efficacy of a polymer coating for making thermoelastic measurements is investigated by experiment and the supporting theory is presented. It was found that the thermoelastic response is greatest with thick coatings at high frequencies. However, thicknesses of more than 0.5 mm and frequencies greater than 5 Hz provide adequate results.
An assessment of the Sachs method for measuring residual stresses in cold worked fastener holes
Authors: Smith D J , Poussard C G C , Pavier M J
Published: October 2002

Measurements of residual stresses in 6 mm thick aluminium alloy 2024 plates containing 4 per cent cold worked fastener are made using the Sachs method. The measurements are made on discs extracted from the plates. The measured tangential residual stress distribution adjacent to the hole edge are found to be affected by the disc diameter. The measured residual stresses are also in good agreement with averaged through-thickness predictions of residual stresses from an axisymmetric finite element (FE) model of the cold working process. A finite element analysis is also conducted to simulate disc extraction and then the Sachs method. The measured FE residual stresses from the Sachs simulation are found to be in good agreement with the averaged through-thickness predicted residual stresses. The Sachs simulation was not able to reproduce the detailed near-surface residual stresses found from the finite element model of the cold working process.
Modelling plasticity in finite bodies containing stress concentrations by a distributed dislocation method
Authors: Blomerus P M , Hills D A
Published: October 2002

An efficient method for the analysis of limited plasticity at stress raising features such as notches and holes in finite bodies has been developed. A network of stationary dislocations is used to simulate the plasticity and simple constant displacement boundary elements form the borders of the geometries. The notch or hole itself is implicitly included in the formulation by using specialized kernels for these features in an infinite plane, thereby improving the numerical efficiency. The cyclic plastic behaviour of an edge-notch in an infinite plane and a finite rectangular plate are analysed under elastic-perfectly plastic, plane strain conditions. Examples of the resulting stress state after stress redistribution and plastic shakedown are displayed which aid in the reliable prediction of component life.
The finite element analysis of a strain hardening layered medium under normal loading by (a) a rigid and (b) a deformable indenter
Authors: Tang K C , Faulkner A , Sen S , Arnell R D
Published: October 2002

The finite element method (FEM) is used to investigate the normal indentation problem of a deformable indenter in contact with a strain hardening substrate coated with an elastic—perfectly plastic layer. In order to assess the influence of the deformable indenter, the solution is compared with results of a rigid sphere indenting the same system. The comparison shows that, when the indenter is assumed to be rigid, the contact pressures are significantly higher than those for the deformable indenter during elastic deformation. When plasticity is more pronounced, the peak pressures at just inside the contact edge are also higher for the rigid indenter. Similarly, the results assuming a rigid indenter give a lower value of maximum radial tensile stress along the coating surface when compared with those using a deformable indenter, which is responsible for the cracking of the film. In order to examine the effects of strain hardening, the above solutions are compared with a system having an elastic—perfectly plastic substrate. Comparison between the two sets of results shows that the strain hardening medium develops a smaller contact area and higher central and peak contact pressures inside the contact edge during plastic deformation. It also shows that the use of a strain hardening substrate alleviates the maximum radial tensile stress just outside the contact edge.
Cyclic plasticity, creep and fracture in a Nimonic alloy
Authors: Rees D W A
Published: October 2002

Deformation and fracture are examined for a cyclic loading condition in which a 24 h period of forward creep in IN 597 at 850°C is reversed (a) by a similar period of creep and (b) by fast monotonic strain-limited plasticity with and without a subsequent 1 h period of relaxation. When ratchetting is evident, it is shown that a life fraction rule based upon the Monkman—Grant law describes the observed behaviour and that, for a given creep stress, the accumulated creep strain—time plot correlates with a simple creep curve. At lower-magnitude creep dwell stresses a cyclic equilibrium state is achieved. The absence of ratchetting during equilibrium results in a net increase in rupture life and fracture strain when compared with those for simple creep under the same stress. Time-limited cyclic behaviour is compared with further cyclic tests in which the reversal occurs at fixed limits of total strain. These did not show an equilibrium condition but a progressive cyclic softening in which the creep time and strain successively diminished.

Predictions to individual creep curves are made from the mechanical equation of state and the time hardening law. However, empiricism is preferred to describe the softening behaviour observed for the alloy more precisely. A theoretical assessment is made of the effect of imposing a period of relaxation at peak reversed strain upon cyclic creep deformation and life.
An alternative finite difference method for post-processing thermoelastic data using compatibility
Authors: Barone S , Patterson E A
Published: October 2002

A finite difference technique for processing thermoelastic data for biaxial problems is presented. The method enables thermoelastic data to be smoothed at interior points and boundary information to be calculated from measured non-boundary values by an iterative procedure based on the compatibility equation. The technique has been successfully applied to quantify stress concentrations and to perform stress separation.
Disc upsetting between spherical dies and its application to the determination of forming limit curves
Authors: Vilotic D , Chikanova N , Alexandrov S
Published: October 2002

The plastic upsetting of a disc with spherical dies is investigated experimentally and theoretically to determine points on a forming limit curve. For steel specimens of various dimensions, it is found from experimental study that fracture occurs at the free surface of the specimens. Simple theoretical calculations based on the obtained experimental results are performed to determine the state of stress and strain leading to fracture initiation. An advantage of the theoretical approach proposed is that considerations of friction on the die-workpiece interface are excluded. The fracture conditions obtained are used to predict the shape of the forming limit curve at large values of the triaxiality factor.
Axial stiffness and torsional effects in a 76 mm wire rope: Experimental data and theoretical predictions
Authors: Kraincanic I , Hobbs R E
Published: October 2002

Some recent tests on a 6 × 41 wire rope of 76 mm diameter are reported. A specimen 7 m long whose ends were prevented from rotating was used with axial loads ranging up to 1.4 MN. Axial stiffnesses were measured, both for large load ranges and for small load perturbations superimposed on larger mean loads. The torque generated in the rope by axial load was measured, as was the response of the axially preloaded rope to external torque applied at the mid-point of the rope. These experimental data are reported and compared with new theoretical predictions, and with other theoretical results and a range of manufacturers' rules. Some encouraging correlations have been found.
Integration of spectral and phase-stepping methods in photoelasticity
Authors: Patterson E A , Wang Z F
Published: October 2002

The theoretical description of spectral contents analysis is extended to red-green-blue (RGB) photoelasticity. The integration of the resultant methodology for spectral analysis with phase stepping is used to achieve automatic analysis of photoelastic fringe patterns containing a minimum fringe order of no greater than four, and without the requirement for a zero-order fringe order to be present in the pattern.
Non-uniform and dynamic torsion of elastic beams Part 1: Governing equations and particular solutions
Authors: Ritchie S J K , Leevers P S
Published: October 2002

The double torsion fracture test has been widely used in the past for measuring resistance to crack growth under static loading and, more recently, under high-loading-rate conditions. Specimen deformation in this test is conventionally analysed on the basis of a one-dimensional torsion equation. Under dynamic conditions, it is imperative to establish an accurate torsion equation which can be used to model the double torsion test. The present paper describes the development, in this context, of a dynamic fourth-order partial differential equation for one-dimensional torsion, based on Barr's equation. The equation obtained in this paper accounts for the axial inertia associated with cross-sectional warping and the axial stresses which arise when warping is constrained. The equation can also accommodate non-linear elasticity. The equation is validated, using Barr's own data, for the torsional resonance problem which he studied and, using finite-element analysis, for a problem of constrained static torsion analysed by Timoshenko.
Non-uniform and dynamic torsion of elastic beams Part 2: The double torsion test
Authors: Ritchie S J K , Leevers P S
Published: October 2002

Part 1 of this paper developed a one-dimensional fourth-order partial differential equation for dynamical torsion of rectangular beams. It was then validated against static and dynamic test cases. This concluding part applies the equation to the double torsion fracture test, in which a crack propagates along the plane joining two adjacent torsion beams as they are twisted in opposite senses. The resulting model is extensively validated against experimental and finite element results. It is then used to explain the shape of the curved crack front which is characteristic of this test.
A gradientless finite element procedure for shape optimization
Authors: Heller M , Kaye R , Rose L R F
Published: October 2002

This paper presents an iterative gradientless method for the shape optimization of stress concentrators, from the context of structural fatigue life extension. The method has been implemented to interface with the finite element code PAFEC, which does not normally have an optimization capability. The key feature of the approach is to achieve constant boundary stresses, in regions of interest, by moving nodes on the stress concentrator boundary by an amount dependent on the sign and magnitude of the local hoop stress obtained from a previous iteration of a standard finite element analysis. The results of example problems are presented which include the optimization of hole shapes in flat plates and the optimization of the design of bonded reinforcements with a focus on minimizing adhesive stress while maintaining the effectiveness of the reinforcement. In all cases, it was found that significant stress reductions were achieved by way of the local shape changes due to the optimization. The method presented is considered an effective and robust alternative to the use of more expensive and complex gradient-based finite element optimization software, which is currently available commercially.
Stress intensity factors for a semi-elliptical surface crack in a T-shaped geometry Part 1: Tension and bending results
Authors: Righiniotis T D , Lancaster E R , Hobbs R E
Published: October 2002

This paper considers mode I stress intensity factors for a T-shaped geometry, representative of one flange and part of the web of a steel 1-section, which contains a flat semi-elliptical surface crack in the flange. Several crack and T-section geometries are analysed, for both tension and bending, using the finite element method. The very good agreement between the J integral and displacement methods increases confidence in the finite element solutions. The presence of the web and the flange-web intersection have a significant influence on the stress intensity factors of the plate. Based on a least-squares approximation, the stress intensity factors for the T-shaped geometry are given in the form of equations which may prove to be useful in fatigue and fracture evaluation.
Stress intensity factors for a semi-elliptical surface crack in a T-shaped geometry Part 2: Approximate solutions at the deepest point for arbitrary crack-face loading
Authors: Righiniotis T D , Hobbs R E
Published: October 2002

The Petroski-Achenbach displacement formulation is applied in conjunction with the weight function method in order to determine the mode I stress intensity factor at the deepest point of a semi-elliptical surface crack in a T-shaped geometry subjected to arbitrary crack-face loadings. The T-geometry is taken to be representative of the web and flange of an I-section and was previously investigated for tensile and bending loading. Comparison between the model developed here and the finite element solutions for two different stress distributions reveals very good agreement for shallow cracks, although the differences between the results of the weight function formulation and the finite element results increase as the crack becomes deeper and more rounded. The normalized stress intensity factors, for up to fifth-degree polynomial crack-face loading, are given in tabular form.
A quadratic boundary element formulation for three-dimensional contact problems with friction
Authors: Leahy J G , Becker A A
Published: October 2002

This paper is concerned with the development of advanced algorithms for three-dimensional frictional contact problems using a quadratic boundary element formulation. The contact variables are defined with respect to each of the surfaces using local coordinate systems. Equilibrium conditions, displacement continuity requirements and Coulomb's law of friction applied to three-dimensional contact are used to derive the contact equations. These equations are directly coupled at the contact interface to form a reduced set of determinate simultaneous equations. Four three-dimensional frictional contact applications covering stationary and advancing contact surfaces are presented in which boundary element solutions are compared with the corresponding finite element solutions. The results are presented in the form of normal contact stresses, shear stresses, relative tangential displacements and the stick-slip partitioning of the contact interface.
Crack growth in pin-loaded tubes Part 2: Comparison of experimental data with numerical results
Authors: Grant R J , Smart J
Published: October 2002

This paper details results obtained from an experimental examination of the fatigue crack growth in pin-loaded tubes. Initially, various methods of acquiring crack growth data, which can present particular difficulties for this geometry and type of connection, are briefly reviewed. The nature of crack growth in this particular pin-loaded joint is classified in terms of its trajectory, tilt and twist; crack geometric data are analysed within these categories. The work is then correlated with numerical results provided by the finite element method given in the companion paper, Part 1. The crack growth rate is also compared with published data and a satisfactory correlation found. This will enable an analyst to have more confidence in predicting the remaining life of a pin-loaded cracked tube.
Methodology to analyse aerospace structures repaired with a bonded composite patch
Authors: Naboulsi S , Mall S
Published: October 2002

Adhesively bonded composite repair of metallic structures is one of the candidate technologies that has enormous potential in the ageing aircraft. A computational tool to analyse the repaired aerospace structure using an adhesively bonded composite patch is presented. This involves the three-layer technique based on the two-dimensional finite element method for adhesively bonded composite patch repair of cracked structures. This technique is capable of characterizing the crack growth and debond growth behaviour, as well as predicting the fatigue life extension of the repaired structure with a perfectly or imperfectly bonded patch. Also, the thermal effects which may develop during bonding or during service and the non-linear material behaviour of the adhesive are incorporated in this technique. The results from the three-layer technique show good agreement with experimental results as well as a previous investigator's published numerical results. Besides the accuracy of the technique, the advantage of the two-dimensional three-layer technique is cost-effectiveness when compared with the three-dimensional finite element or performing expensive experiments on various patch configurations for design purposes. An overview of the three-layer technique to investigate a cracked metallic plate repaired with bonded composite patch is presented in this paper.
Material properties from small specimens using the punch and bulge test
Authors: Brookfield D J , Li W , Rodgers B , Mottershead J E , Hellen T K , Jarvis J , Lohr R , Howard-Hildige R , Carlton A , Whelan M
Published: October 2002

The punch and bulge test provides a technique for the determination of material properties from small specimens. Although the test has been in use for a number of years, the behaviour of the specimen is not fully understood. A finite element analysis of the test has thus been undertaken and validated by comparison with results from experiments, giving good agreement for the punch force for two differing specimen materials. The finite element analysis has enabled punch force-displacement curves, von Mises stresses, equivalent plastic strains and vertical deflections for the upper and lower surfaces of the disc to be obtained.

The finite element model has also been used to determine the relationship between the specimen yield stress and the punch force for elastic-perfectly plastic specimens. It is shown that a linear law applies over a 6:1 range of yield stresses and thus the punch and bulge test represents an effective method of yield stress measurement from small specimens.

The effect of experimental artefacts on the punch force has been investigated through finite element analysis and physical experiment. The punch force is shown to be effectively insensitive to small uncertainties in the test fixture and experimental conditions. Yield stress results are thus not significantly influenced by experimental uncertainties.
Bimaterial interface hybrid element for piezoelectric laminated analysis
Authors: Huang Y-Q , Liu M , Wu C-C
Published: October 2002

A mixed variational principle is suggested for electromechanical analysis, in which the displacements, the transverse stresses and the electric potential are taken as the primary variables, and a three-dimensional hybrid element approach is built on the principle. Two kinds of specific element, namely the bimaterial interface element and the surface element, are developed so that the interlayer traction-continuity and surface traction-free conditions of transverse stresses can be imposed exactly. Two numerical examples of intelligent laminates with piezoelectric layers bonded to the upper and lower surfaces are presented to demonstrate the efficiency of the present approach.
Theoretical analysis of composite shell intersections
Authors: Skopinsky V N
Published: October 2002

In this study, a systematic approach is presented for the stress analysis of shell intersections made of composite materials. The finite element method used is based on a modified mixed formulation and two-dimensional laminated shell theory. The calculation algorithm and capabilities of the special-purpose computer program SAIS are discussed. The numerical and the experimental results are compared. A parametric study of intersecting composite laminated cylindrical shells was performed. The numerical results presented show the effects of specific properties of composite materials on stresses in shell intersections under internal pressure loading.
Metal rapid prototyping via a laser generating/selective sintering process
Authors: Kathuria Y P
Published: October 2002

During the last decade, developments in rapid prototyping and rapid manufacturing techniques have undertaken a new dynamic turn in production technology. Besides the use of new and better performance materials, process development techniques are increasing further so as to reduce the iteration cycle of the product and production process. In this paper, based upon the selective laser sintering/generating process, certain new features of the fabrication of metal or metal matrix composite parts using CO2/Nd-YAG lasers are discussed. The basic process of beam interaction with the metallic powder is investigated, and results concerning the microstructure and shape factor are interpreted.
Adding expert support to assembly-oriented computer aided design tools
Authors: Mei H , Robison P A
Published: October 2002

This paper reports progress in the development of assembly-oriented computer aided design (CAD) software, focusing particularly on those elements which employ rule-based and other expert system technology to assist with design for assembly (DFA) analysis. The areas addressed within the CAD environment include proactive design for assembly, assistance with assembly sequence definition and improvement in design effciency by reduction of the part count.
Dynamic stabilization of the turn-milling process by parameter optimization
Authors: Pogacnik M , Kopac J
Published: October 2002

The process of turn-milling was a subject of intensive research in the late 1980s, which was followed by a number of practical applications. However, this process has not been investigated as extensively as other conventional cutting processes (turning). The main limitations preventing wider use have been the kinematics (smaller shape elements) and the dynamic instability. This paper presents guidelines showing how to avoid dynamic instability by using optimum entry—exit conditions which can be achieved through a proper set-up of the process parameters. As a result, a decision diagram is proposed.

The paper also presents the results of comparison with turning, showing that, at the same productivity, turn-milling enables better surface roughness and is much more suitable for high-speed cutting (HSC) machining than turning, where the centrifugal force restrains the process.
Voiding and printing characteristics of solder paste at different degrees of exposure
Authors: Hui I K , Ralph B
Published: October 2002

Solder paste in surface mount technology (SMT), because of operation requirements, is exposed to the atmosphere for different times. The effects of the exposure on the printing and voiding characteristics of the solder paste are presented in this paper. The evaporation of the solvents in the solder paste during exposure was substantiated by weight loss tests and optical examination, and the results show that the weight loss and exposure time relationship can be expressed by an exponential formula. The voids in the joints produced by solder paste with different degrees of exposure were quantified and recorded. It was found that an increase in the exposure was accompanied with a decrease in the void size and content. The printing characteristics of selected solder pastes after exposure to the atmosphere for various times were investigated by studying the scooping and bridging conditions of the prints. The results show that scooping is not only related to the degree of exposure of the solder paste but also to the printing direction and the stencil aperture width. The investigation results further show that the printed division increases in direct proportion to the stencil aperture division, and the exposure time of the solder paste has insignificant effects on the bridging conditions.
The iterative calculation of the Cartesian geometry of general non-Cartesian structures
Authors: Freeman J M , Ford D G
Published: October 2002

This paper describes an iterative scheme for the calculation of the Cartesian coordinates of the nodes of any rigid structure from a knowledge of internodal distances and angles. Since internodal distances can be determined accurately by laser interferometry, it is possible to derive coordinates to very high precision. The techniques constitute analytical vector and matrix methods which have been programmed in a general way to provide generic software capable of finding iteratively the Cartesian geometry of complex structures such as non-Cartesian machines. It has proved possible to include certain constraints such that specified nodes should not move in certain Cartesian directions and specified connecting lines should remain horizontal or vertical, etc. The method requires an initial estimate of the Cartesian coordinates of the nodes and then adjusts the coordinates until calculated internodal distances and angles are within tolerance. No reprogramming is necessary to analyse a new structure. Full details of the mathematical derivations are included, as are details and results of the application of the method to the Stewart platform.
Manufacturing cell scheduling using genetic algorithms
Authors: Onwubolu G C
Published: October 2002

This paper presents a new approach to the scheduling of manufacturing cells which have flow-shop configuration. The approach is based on the genetic algorithm, which is a meta-heuristic for solving combinatorial optimization problems. The performance measure demonstrated in this paper is the optimization of the mean flow time. The procedure developed automatically computes the make-span. A flexible manufacturing cell schedule is used as a case study. The genetic algorithm procedure was used to solve a published data set for simple scheduling problems. The genetic algorithm procedure was further used to solve large flow-shop scheduling problems having machine sizes of up to 30 and job sizes of up to 100 in very reasonable computation time. The results show that the genetic-algorithm-based heuristic is promising for scheduling manufacturing cells.
Virtual concurrent product development of plastic injection moulds
Authors: Britton G , Beng T S , Wang Y
Published: October 2002

This paper describes three approaches for virtual product development of plastic injection moulds. The first is characterized by the use of three-dimensional computer aided design (CAD) for product design, two-dimensional drafting for mould design and three-dimensional computer aided design/manufacture (CAD/CAM) for mould manufacture. The second is characterized by the use of three-dimensional CAD models by all three participants, but between any two participants some form of file conversion is normally required because different CAD systems are used. The first two approaches share one common feature: the models are passed serially from the product designer to the mould designer and on to the toolmaker. They represent current practice in industry. The third approach is a proposed collaborative design process. Participants can work concurrently on the same model, sharing their knowledge and experience. The process is currently being refined and will be validated later this year with a prototype system based on Unigraphics iMAN software.
Cellular manufacturing systems design using Tabu search
Authors: Songore G V , Songore V
Published: October 2002

Several techniques have appeared in the literature for the cell formation problem. However, most of these heuristics have the disadvantages that they cannot solve real-life problems typical of manufacturing firms in reasonable computational time, and deal with the part family formation and cell grouping problems separately. The Tabu search meta-heuristic is presented for resolving these problems. The minimization of intercellular movements as an objective function is demonstrated, although minimization of cell load variation and the multiobjective function option exist in the procedure developed. The results discussed for some problems taken from the literature show that the Tabu search is a promising technique for solving the cellular manufacturing systems design problem for both medium and large problem instances.
Automatic tool selection for milling operations Part 1: Cutting data generation
Authors: Carpenter I D , Maropoulos P G
Published: October 2002

The selection of tools and cutting data is a central activity in process planning and is often liable to an element of subjectivity. It is further complicated by the wide range of choice presented by the various operation types and the huge portfolio of cutters and inserts available from many different tool manufacturers. This paper describes a procedure to select consistently and efficiently tools for rough and finish milling operations performed on a computer numerical controlled (CNC) machining centre. A wide range of milling operations is considered, including faces, square shoulders, slots, T-slots, pockets, holes and profiles. An initial set of feasible tools is generated that satisfy the constraints of the tool type, the operation geometry, the insert geometry and carbide grade, the workpiece material and the machine tool capacity. Each tool consists of a holder and one or more indexable carbide inserts. Aggressive cutting data are generated for each feasible tool using a rapid search procedure in the permissible depth/width/feed space for good chip control. The cutting data are further refined by a set of technological constraints, which include tool life, surface finish, machine power and available spindle speeds and feeds. The overall cutting data optimization criterion is selected by the user from minimum cost, maximum production rate or predefined tool life. A new optimization criterion, called ‘harshness’, allows the user to influence the chip thickness that is achieved for any given cutter. Any feasible tools that fail to satisfy all the constraints and optimization criteria are discarded.
An effective genetic algorithm for job shop scheduling
Authors: Wang W , Brunn P
Published: October 2002

This paper presents an effective genetic algorithm (GA) for job shop sequencing and scheduling. A simple and universal gene encoding scheme for both single machine and multiple machine models and their corresponding genetic operators, selection, sequence-extracting crossover and neighbour-swap mutation are described in detail. A simple heuristic rule is adapted and embedded into the GA to avoid the production of unfeasible solutions. The results of computing experiments for a number of scheduling problems have demonstrated that the GA described in the paper is effective and efficient in terms of the quality of solution and the computing cost.
Prediction and reduction of build times for the selective laser sintering process
Authors: Pham D T , Wang X
Published: October 2002

This paper presents an approximate method for predicting build times for the selective laser sintering (SLS) process. The paper discusses factors that influence the build time, such as roller travel speed, build height, laser scan speed, scan area and part volume. The proposed prediction method is very simple as it depends only on the settings of the build package, rather than on details of individual scan surfaces. The paper also suggests ways to arrange parts to reduce build times.
Detection of interference elements and release directions in die-cast and injection-moulded components
Authors: Lu H Y , Lee W B
Published: October 2002

Many interference elements may exist in a die-cast or injection-moulded component which prevent the removal of the component from a die or mould cavity. Each interference element corresponds to a direction or a set of directions along which the interference element can be released. In computer aided determination of parting direction for a diecasting die or an injection mould, the two basic problems, the detection of the interference elements and the definition of corresponding release directions, should be involved. In this paper, a three-dimensional ray-detection method is introduced to detect the interference elements. The method includes sweeping a solid model, recognizing the geometric feature and extracting the shell of the interference element. A vector plane approach is proposed to solve release directions of the interference shell. The approach uses vector planes to collect the normal vectors of the shell surface, and then the release direction of a vector plane is determined by two extreme vectors on the plane. The release directions of an interference element are obtained by intersecting the release directions of all vector planes.
Finite element analysis of temperature distribution using ABAQUS for a laser-based tile grout sealing process
Authors: Lawrence J , Li L
Published: October 2002

A finite element (FE) model has been developed utilizing the commercial ABAQUS package to determine the temperature distribution generated during the high-power diode laser (HPDL) processing of a novel ceramic tile grout seal, known as an amalgamated oxide compound grout (AOCG). The model was developed specifically to find the temperatures reached at the base of the ceramic tile grout seal, since temperatures in excess of 100°C must be attained so as to ensure certain chemical changes (the complete irreversibility of the water-glass reaction required by the process). Fourier's law and Laplace's equation were employed to build the temperature field equations under appropriate boundary conditions in two-dimensional coordinates, while the ABAQUS FE model was used to calculate the temperature field and model the thermal profile in the ceramic tile grout seal. Both the FE-generated thermal profiles and the resultant operating maps predicted temperatures and vitrification depths which were consistently higher than those obtained experimentally. Notwithstanding this, a comparison of the results revealed that the predicted depths of vitrification were in very close agreement with those observed on AOCG samples treated with the HPDL.
Leakage characteristics of non-contact seal types for high-speed spindles
Authors: Chun K J , Na B C , Han D-C
Published: October 2002

Sealing is one of the most important characteristics of carrying out enhanced lubrication in high-performance machining work. High-speed spindles require non-contact sealing mechanism types. To minimize leakage, the flow control mechanism should incorporate an optimum seal design. This paper categorizes the geometry of commonly used non-contact seal types and analyses the leakage charcteristics of each type in minimizing leakage on the sealing area. The non-leaking property is estimated by the amount of pressure drop in the leakage path. Gas or liquid had previously been considered as the working fluid for most non-contact seal types including the labyrinth seal. However, it is more reasonable to apply a two-phase flow because high-speed spindles use oil mist or oil jet lubrication. Thus, a working fluid is regarded as comprising two phases: mixed flow of oil and air. Both turbulence and compressible flow models are introduced in the computational fluid dynamics (CFD) analysis. As the results of the CFD analysis in various geometric cases reveal, a protective collar type and an air jet type seal exhibit excellent sealing effects for oil mist lubrication. The minimum clearance should be located between the wall on the flow inlet and the collar, while seal size should be minimized by taking into account the thermal expansions and deflections of spindles. Based on the analytical results, an adapted model is introduced to improve the sealing capability of conventional non-contact seal types. The model entails the combined geometry of a protective collar type and an air jet type. Experimental measurements are carried out to verify improvements in sealing efficiency with the use of the adapted model. The sealing effects of employing the leakage clearance and air jet magnitude are studied using various parameters. The effected sealing improvement is attributed to the decrease in leakage clearance caused by air jetting. Thus, the seal effect is improved by the amount of air jetting but the clearance level becomes higher at the same time.
A hybrid approach for selection of optimal process parameters in abrasive water jet cutting
Authors: Chakravarthy Sitarama P , Babu Ramesh N
Published: October 2002

This paper presents a hybrid approach combining fuzzy logic principles and a genetic approach for selecting optimal parameters in abrasive water jet cutting of any material with predetermined thickness. A fuzzy model is built with the knowledge base formed by means of experimental data that is generated by varying the process parameters such as water jet pressure, jet traverse rate and abrasive flowrate at five levels each. This particular model predicts the depth of cut achievable with any given set of process parameters. A genetic algorithm employed in combination with a fuzzy model automatically determines the best combination of process parameters in abrasive water jet cutting of any material. The effectiveness of the proposed approach is demonstrated by a case study dealing with abrasive water jet cutting of black granite.
Optical sensor for detection of errors in Nd:YAG laser overlap welding of zinc-coated steel
Authors: Hand D P , Peters C , Fox M D T , Jones J D C
Published: October 2002

Laser overlap welding of zinc-coated steel is an attractive process for the automotive industry, but specific problems can occur where apparently good welds may be produced but with no join between the two sheets of material. This paper describes a simple and reliable technique for detecting these errors by analysing the light generated by the welding process, using an optical sensor which is non-intrusive to the process.