An exploration of the perceptions of the average driver''s speed compared to perceived driver safety and driving skill

This study investigates the self-enhancement bias in driver attitudes, the finding that drivers rate themselves better than the average driver on safety and skill perceptions (Svenson, 1978 and Svenson, 1981; McCormick et al., 1986). A sample of 86 New Zealand drivers were asked their perceptions of their own and others' speeds in two conditions, 50 km/h and 100 km/h. The results established the self-enhancement bias for speed and safety, but not skill. Between 85% and 90% of drivers claimed to drive slower than the ‘average driver.' A new methodological technique derived from Harré and Gillett (1994) was used to investigate the direction of the self-enhancement bias. The results support the Downward Comparison Theory (Wills, 1981) because drivers consider other drivers negatively, rather than exaggerating their self-perceptions.     

Discussions of three-dimensional models for mixed-mode fatigue crack growth

This technical note discusses several three-dimensional models for mixed-mode fatigue crack growth that were developed recently by Bian and coauthors [1], [2], [3], [4] and [5]. However, these models are found being formulated from a generally incorrect three-dimensional crack-front stress field for embedded elastic elliptical cracks. The corresponding correct crack-front stress field for the elliptical cracks is thus presented, and then the three-dimensional fatigue crack growth models are corrected and expressed in much simpler functions.     

Dynamic observation of dislocation-free deformation process in Al, Cu, and Ni thin foils

Dislocation-free plastic deformation, which occurs under extraordinarily high internal stress comparable to ideal strength of metals, was discovered in thin foil portion produced by ductile fracture of fcc Au by dynamic observation of the deformation process [1, 2, 3, 4 and 5]. In the present study, the deformation process of thin foil portion in other fcc metals (Al, Cu, Ni) was examined in the same manner. In all these fcc metals, production of vacancy-type point defect clusters was confirmed during deformation without dislocations. Also, the dislocation-free deformation was found to progress under extraordinarily high internal stress levels corresponding to 14% elastic deformation in Ni, 12% in Cu, and 4% in Al. Especially in Al, as temperature decreased, the number density of stacking fault tetrahedra produced during deformation increased, along with increasing of the detected elastic deformation. These results indicate that internal stress level is a key factor in generalizing the new theory regarding dislocation-free plastic deformation.     

Influence of anisotropy on the transient hygroscopic stresses in polymer matrix composites with cyclic environmental conditions

The transient residual stresses in polymer matrix composites induced by cyclic variations in temperature and moisture are very important and must be taken into account in the design of composite materials, particularly aerospace structures e.g. aircraft. Aiming to reduce these stresses, we have studied the influence of anisotropy on the hygrothermal behaviour of the laminated plates. The objective, here, is to contribute to the optimal design of composite structures. The anisotropy is evaluated using the degree of anisotropy introduced from polar representation of tensors [1, 2, 3, 4 and 5]. Various laminates, with controlled and random stacking sequences, were analysed under typical boundary conditions and with the same hygrothermal loading. The results show that the thermal and hygroscopic stresses vary differently with the degree of anisotropy in such a way that their superposition does not lead to a growth of the intern resulting stresses. The other obtained results show that the knowledge of the degree of anisotropy of the laminate permits us to predict the state of different stresses in the ply frame.     

Magnetoelectroelastic multi-inclusion and inhomogeneity problems and their applications in composite materials

We have studied the average magnetoelectroelastic field in a multi-inclusion or inhomogeneity embedded in an infinite matrix. The magnetoelectroelastic inclusion and inhomogeneity problems are discussed [1], and a numerical algorithm to evaluate the magnetoelectroelastic Eshelby’s tensors for the general material symmetry and ellipsoidal inclusion shape is developed. The solutions for the magnetoelectroelastic inclusion and inhomogeneity problems are applied to study the multi-inclusion and inhomogeneity problems. It is shown that the average field in an annulus surrounding an inclusion embedded in an infinite magnetoelectroelastic medium only depends on the shapes and orientations of two ellipsoids, which generalizes Tanaka and Mori's observation in elasticity [2]. The average field in a multi-inclusion is then determined exactly, from which the average field in a multi-inhomogeneity is obtained, using the equivalent-inclusion concept [3]. The solutions of multi-inclusion and inhomogeneity problems serve as basis for an averaging scheme to model the effective magnetoelectroelastic moduli of heterogeneous materials, which generalizes Nemat-Nasser and Hori's multi-inclusion model in elasticity [4]. The model is further extended to predict the effective thermal moduli of the heterogeneous magnetoelectroelastic solids, generalizing the recent work of Li on the thermal expansion coefficients of elastic composites [5]. The proposed model recovers Mori–Tanaka and self-consistent approaches as special cases. Finally, some numerical results are given to demonstrate the applicability of the model. The potential techniques to enhance the magnetoelectric effect in practical composites are also discussed.     

Production of porous carbon thin films by pulsed laser deposition

Pulsed laser deposition (PLD) has been used together with the Glancing Angle Deposition (GLAD) technique [1 and 2] for the first time to produce highly porous structured films. A laser produced carbon plasma and vapour plume was deposited at a highly oblique incident angle onto rotating Si substrates, resulting in films exhibiting high bulk porosity and controlled columnar microstructure. By varying the substrate rotation rate, the shape of the microcolumns can be tailored. These results extend the versatility of the GLAD process to materials not readily deposited by means of traditional physical vapour deposition techniques.     

An integrated database and expert system for failure mechanism identification: Part I—automated knowledge acquisition

An integrated database and expert system has been developed for identifying the failure mechanism of mechanical components. The system comprises six major modules: database and management system, case maintenance; knowledge acquisition and editing; expert system; explanation and test-recommendation facilities; and user interface. Part I of a two-part paper details the knowledge acquisition and editing module, as presented here. Part II describes the remaining modules and also gives test results [9]. The method used for automated knowledge acquisition is an inductive learning algorithm, which was modified from PRISM [2] to handle noisy and missing data. Using the algorithm, a total of 48 rules were induced from 477 training examples gathered for the identification of 15 different failure mechanisms such as brittle fracture, fatigue, and stress corrosion cracking. Fifty-nine attributes were used to distinguish one failure mechanism from the others. They include pitted, beach marks, microvoids, etc. The knowledge editing function is provided to allow the verification of induced rules by the human expert.     

On the concept of e-maintenance: Review and current research

The importance of the maintenance¹ function has increased because of its role in keeping and improving system availability and safety, as well as product quality. To support this role, the development of the communication and information technologies has allowed the emergence of the concept of e-maintenance. Within the era of e-manufacturing and e-business, e-maintenance provides the opportunity for a new maintenance generation. As we will discuss later in this paper, e-maintenance integrates existing telemaintenance principles, with Web services and modern e-collaboration principles. Collaboration allows to share and exchange not only information but also knowledge and (e)-intelligence. By means of a collaborative environment, pertinent knowledge and intelligence become available and usable at the right place and time, in order to facilitate reaching the best maintenance decisions.

This paper outlines the basic ideas within the e-maintenance concept and then provides an overview² of the current research and challenges in this emerging field. An underlying objective is to identify the industrial/academic actors involved in the technological, organizational or management issues related to the development of e-maintenance. Today, this heterogeneous community has to be federated in order to bring up e-maintenance as a new scientific discipline.     

Target system neutronics study for NXGENS

The Materials Test Station (MTS) [E. Pitcher, G. Muhrer, H. Trellue, Neutronics Assessment of the LANSCE Materials Test Station as an Irradiation Facility for the JIMO Space Reactor, LA-CP-04-0903.[1]], a spallation target station, planned for construction at the Los Alamos Neutron Science Center (LANSCE), will provide the opportunity to test the prototype of a long-pulse spallation source neutron scattering instrument (NXGENS). In this paper, we present the target-moderator neutronics optimization study that was performed in support of NXGENS.     

An integrated database and expert system for failure mechanism identification: Part II—the system and performance testing

An integrated database and expert system has been developed for assisting the human analyst in identifying the failure mechanism of mechanical components. The system comprises six major modules: database and management system; case maintenance; knowledge acquisition and editing; expert system; explanation and test-recommendation facilities, and user interface. The knowledge acquisition and editing module has been detailed in Part I of a two-part paper [6]. The overall system and the details of other modules are described here. The system has been implemented using the M4 expert system shell, Microsoft Access database software, and Visual Basic. Illustrative examples are used to show the capability of the system. Also reported are the results obtained from four different tests to determine the system performance.     

From mine to refrigeration: a life cycle inventory analysis of the production of HFC-134a

A life cycle inventory analysis has been conducted for the production of HFC-134a (1,1,1,2-tetrafluoroethane, CH₂FCF₃)¹ through from basic raw materials (crude oil, natural gas, sulphur and fluorspar) to the pure product delivered to industrial customers. The analysis was based on real industrial operations in Japan, USA and UK. It showed that production required limestone, water and transition metal catalysts, in addition to the basic raw materials, and that the energy required to provide these raw materials in a form that can be used at the plants and to process them through intermediates into HFC-134a is the equivalent of 4.52 tonnes of CO₂ per tonne of product. Environmental releases associated with HFC-134a included waste salt brine (to the sea), mine tailings (mainly “country” rock landfilled at the mine) and small quantities of calcium sulphate and spent catalyst (both sent to landfill). In addition, greenhouse gases amounting to the equivalent of 2.1 tonnes of CO₂ per tonne of product were emitted to the atmosphere from the plants studied, an effect very much smaller than that estimated in previous studies mainly because the real release rates from current processes are very much less than those assumed in prior work. The global warming potential^{, 2} of HFC-134a is 1300, meaning that, during the first 100 years following the release of one tonne, the effect on climate change is equivalent to 1300 tonnes of carbon dioxide. Consequently, the 6.6 tonnes of carbon dioxide equivalent, emitted during production in the form of energy required and other greenhouse gases, is of relatively little importance and the key requirement to reduce environmental impact is containment during use.     

Optimum design of dome contour for filament-wound composite pressure vessels based on a shape factor

Filament-wound composite pressure vessels are an important type of high-pressure container that is widely applied in the commercial and aerospace industries. This study investigates the optimum design of dome contours for filament-wound composite pressure vessels, subjected to geometrical limitations, winding condition, and the Tsai–Wu failure criterion and maximizing shape factor, the feasible direction method being employed. An actual design example, presented by Fukunaga et al. [19], is adopted to study the optimum dome contour using the present method. Results reveal that the dome contours using the present method, Fukunaga et al.’s method and the netting method can be approximated using elliptic curves, and that the depth is the major parameter for optimizing the design of dome contour, and the dome, designed using the present method has stronger structure and greater internal volume than those designed using other approaches. Results reveal that the present method is usable for the optimum design of dome contours for filament-wound composite pressure vessels.     

Interface structure in the growth of semiconductor crystals using the Bridgman–Stockbarger method

In this paper we assume, like in Balint et al. [Mater. Sci. Semiconductor Process. V3/3 (2000) 115–121], that the melt/solid interface in the case of vertically stabilized Bridgman–Stockbarger semiconductor growth system is a thin layer, masking the crystal, where a weak form of the periodical structure of the crystal exists. In these conditions, using a new diffusion coefficient in the equation of the dopant transport in the interface region, we compute the axial and radial variation of the dopant field in this region for crystal and melt with thermophysical properties similar to the gallium-doped germanium. We compare the results to those obtained in Mater. Sci. Semiconductor Process. V3/3 (2000) 115–121 [1], where we have changed the diffusion coefficient only in the boundary condition for the dopant concentration at the melt/solid interface.     

Punching behavior of biaxial hollow slabs

The invention of a new kind of hollow slab with plastic balls as hollow bodies entailed the necessity to investigate its structural behavior. Because of its main field of application as a flat slab, the punching shear capacity is one of the most interesting properties of this slab. To investigate the influence of the cavities on the punching behavior, tests were carried out at the Institute for Concrete Structures in Darmstadt. In addition to these tests nonlinear computations using the Finite Element Method were performed. The computations allowed parametric studies to get a better understanding of the structural behavior without doing further expensive tests. Finally, necessary modifications of existing design recommendations according to the German design code DIN 1045 [1] were developed.     

A novel axisymmetric variational analysis of stress transfer into fibreS through a partially debonded interface

Most existing models for the problem of fibre/matrix stress-transfer through a partially debonded interface roughly solve the stress distribution in the debonded zone, neglecting the presence of the perfectly bonded zone. However the stress interactions between two zones is what makes the problem essentially different from the stress-transfer problem for a perfectly bonded interface. This paper suggests a variational approach based on the principle of minimum complementary energy not only in a perfectly bonded zone but also in a zone with a discontinuous interface. The debonded interface is treated as an external boundary on which a presumed interfacial shear stress is specified. A new analytical model, including stress non-uniformity in the radial direction and crack interaction, is derived to describe the stress state around fibre breaks and debonding tips in a single fibre embedded in an infinite matrix. For the presumed shear stress at the debonded interface the minimisation procedure renders the most accurate closed-form solution (under used assumptions) for both interactive zones. Finally, the ‘best’ shear stress distribution at the debonded interface is found by using Coulomb’s friction law and simple numerical iterations. The stress profiles along both axial and radial directions are presented and compared with results from a numerical model[1] available in the literature and also from finite-element analysis. Good agreements are achieved. Extensive applications of this approach and the derived model are also discussed.     

Deformation and strain distribution in plasma sprayed nickel–aluminum coating loaded by a spherical indenter

The deformation underneath a spherical indent was investigated on samples prepared by the bonded-interface technique from a plasma sprayed nickel–5%aluminum coating. Prior to the spherical indentation a set of Vickers micro-indents was produced as fiduciaries on one of the cross-sections. This allowed the calculation of plastic strain components from the relative displacements of micro-indents during subsequent surface indentation. Using a modified procedure based on a method proposed by Tabor [1], stress–strain curve was evaluated by measuring the contact radii of spherical indentations produced at several different loads. The derived stress–strain relationship was used in 2D and 3D finite element models to estimate the plastic deformation field under the indenter. The comparison between the measured and calculated strain profiles revealed notable differences. The normal plastic strain in the direction along the vertical axis of indentation displayed higher values directly under the indenter compared to the finite element analysis which predicted lower values under the indenter and less rapid decrease of the plastic strain with depth. The differences were attributed to the compaction of the lamellar structure in the plasma sprayed coatings. The compaction of the lamellae was directly observed on polished coating cross-sections.     

Initial stages of growth of GaN over (0001) Al2O3 substrate using MBE: a crystallographic analysis of the defects

An AlN buffer layer grown on (0001) sapphire substrate by molecular beam epitaxy has been studied. It is found to be made of small grains having a common [0001] axis parallel to that of the substrate. Some grains are rotated around this axis and the angle rotation can reach 20° leading to a new epitaxial relationship (0001)_sap//(0001)_AlN and [11

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0]_sap//[21

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0]_AlN. A model for the atomic structure of one of these grain boundaries is proposed using high resolution electron microscopy and extensive image simulation.     

Determination of the elastic properties of a barrier film on aluminium by Brillouin spectroscopy

The surface wave dispersion for a barrier oxide film on aluminium has been determined from surface Brillouin scattering measurements carried out on films of thicknesses of 0.2, 0.35 and 0.45 μm. The measured velocities of the generalised Rayleigh mode, the pseudo interfacial mode and of several Lamb modes conform to simulations performed for stiffening layers [1]. The longitudinal velocity and the shear velocity of the layer have been calculated from the experimental dispersion curve.     

Vertical MOS-gated pin-diodes: MOS-gated tunneling transistors in Si(100) and Si(111)

Tunneling devices are an interesting alternative to conventional MOS-devices due to their high speed switching capabilities. Recently, it was shown that tunneling transistors based on vertical MOS-gated pin-diodes can be fabricated. The pin-diodes themselves were grown by means of UHV-MBE on highly n⁺-doped Si(100)-substrates with a 100 nm thick intrinsic channel region. The top contact was formed by the deposition of a highly-doped B δ-layer with a peak doping amount of approximately 10²¹ cm⁻³ for the necessary abrupt pn-junction and 300-nm p⁺-contact region. At a low supply voltage of −0.2 V, a current gain of three orders of magnitude with saturation behavior is achieved [1]. In the present contribution, we have shown the influence of the amount of B in the δ-layer and of the abruptness of the drain-channel-junction on the transistor behavior. For that, we have discussed the characteristics of MOS-gated pin-diodes on Si(111) with ultra-sharp B δ's with a peak doping amount between 10²⁰ and 10²¹ cm⁻³ and a peak width <3 nm, in comparison with MOS-gated pin-diodes on Si(100) presented in Hansch et al. [1]. In order to obtain these highly doped ultra-sharp B δ-layers, a phase-transition from an electrically inactive Si(111)- -R30° B surface phase into an electrically active one was induced by rapid thermal annealing.     

Characterisation of dislocations, nanopipes and inversion domains in GaN by transmission electron microscopy

Transmission electron microscopy is used to analyse a range of defects observed in hexagonal GaN films grown on sapphire and GaN substrates by metalorganic chemical vapour deposition. Large angle convergent beam electron diffraction is used to analyse the Burgers vectors of dislocations and to show that hollow tubes, or nanopipes, are associated with screw dislocations having Burgers vectors±c. Weak-beam electron microscopy shows that dislocations are dissociated into partials in the (0001) basal plane, but that threading segments are generally undissociated. The presence of high densities of inversion domains in GaN/sapphire films is confirmed using convergent beam electron diffraction and the atomic structure of the {

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} inversion domain boundary is determined by an analysis of displacement fringes seen in inclined domains.