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The need to simultaneously reduce vehicle emissions and increase the safety of passengers is encouraging the automotive industry to incorporate new technologies and materials into today's vehicles. To remain competitive, the steel industry has developed steel grades with increased energy absorbing properties allowing down gauging of body in white components to address the competition from alternative materials such as aluminium alloys and composites. Two of the more important developments are the introduction of dual phase (DP) and transformation induced plasticity (TRIP) grades for the automotive industry. These grades offer superior strength/formability and work hardening properties compared to conventional high strength grades of similar tensile strength. Utilising thinner gauge components with increased energy absorbing properties would permit addressing the mass/safety issues by the automotive industry. This paper relates the crash performance of a range of both commercial and experimental DP...

The use of high strength steels (HSS) in automotive components is steadily increasing as automotive designers use modern steel grades to improve structural performance, reduce vehicle weight and enhance crash performance. Weight reduction can be achieved by substituting mild steel with a thinner gauge HSS, however, it must be ensured that no deterioration in performance including fatigue capability occurs. In this study, tests have been carried out to determine the effects that gauge and material strength have on the fatigue performance of a fusion welded automotive suspension arm. Current finite element (FE) modelling and fatigue prediction techniques have been evaluated to determine their reliability when used for thin strip steels. Results have shown the fatigue performance of welded components to be independent of the strength of the parent material for the steel grades studied, with material thickness and joining process the key features determining the fatigue performance. The correlation between the fatigue performance of simple welded samples under uniaxial, constant amplitude loading and complex components under biaxial in service road load data, has been shown to be unreliable. This study also indicates that with the application of modern technologies, such as tailor-welded blanks (TWB), significant weight savings can be achieved. This is demonstrated by a 19% weight reduction with no detrimental effect on the fatigue performance.

The combined need for weight reduction and increased safety in modern vehicles has led automobile manufacturers to utilise the unique properties of high strength steels in their vehicles. Standard quasi-static tensile tests allow the static mechanical properties to be evaluated for any given steel grade. However, automobile designers require more advanced data, including high strain rate tensile data to fully understand the performance of a steel grade during deformation. Knowledge of the role of strain rate on a given strip steel grades deformation characteristics is essential to fully predict the behaviour of the steel during a crash event to help ensure the safety of the vehicle passengers. In the present study, three commercial strip steel grades were subjected to room temperature deformation at variable strain rates, ranging from quasi-static to dynamic loading conditions, where their obtained mechanical properties were measured. The steel grades studied were a HSLA grade (XF450), a carbon ma...

The drive to reduce vehicle mass by substituting mild steel with thinner high strength steel means that design engineers are now working closer to the design limits with respect to the fatigue performance of spot welded structures. Consequently, the present study was initiated to evaluate the factors that influence the fatigue performance of spot welded H sections so as to optimise the performance of spot welded high strength steel structures. The results obtained indicated that steel strength had little effect on fatigue performance while, in contrast, the loading mode, weld size and sheet thickness had a significant influence on it. The results of shear loading were up to 10 times greater compared with that under peel loading conditions. Under shear loading conditions full plug failures were noted, whereas with peel loaded variants partial plug failures predominated. With respect to enhancing the fatigue properties the use of larger weld sizes was shown to be beneficial.

As a result of their unique combination of strength and ductility dual phase steels play an important role in reducing weight in automobile components and improving crashworthiness. The purpose of this paper is to quantify the crash performance of dual phase steels, as defined by the influence of low and high strain deformation rates (0·001 s-1 and 100 s-1 respectively), on the tensile and work hardening properties of a range of commercial dual phase products. The objective is to establish whether dual phase steels maintain their desirable mechanical property characteristics of low yield strength, high tensile strength and high work hardening rates during plastic deformation under the application of a high strain rate loading. The results confirmed that the yield/proof strength and tensile strength increased with increasing volume fraction of second phase constituents and increasing strain rate. In particular, a dual phase steel with a microstructure consisting of a significant volume fraction (>1...

The correlation between low and high strain rate deformation characteristics and the microstructure of novel strip steel products employed by the automotive industry has been assessed. Research has been carried out to establish whether microstructural changes during high speed deformation could explain the relative attributes of mild steel, carbon manganese steel and novel dual phase steel grades of increasing yield and tensile strength, in relation to their crash behaviour. The results obtained indicate that the dual phase steel grades having similar microstructures, although with varying strength levels, displayed the same response to high strain rate loading conditions. They both exhibited a reduction in the level of hardness at high strain rate compared with low strain rate deformation. The strain rate softening effect observed with the dual phase steel was accompanied by an increase in plastic deformation of the ferrite areas around the martensitic constituent regions.

The drive to downgauge steel components by substituting mild steel with thinner high strength steel means that design engineers are now working closer to the design limits with respect to fatigue performance of spot welded structures. This study was carried out on an interstitial free mild steel and two high strength interstitial free steels, in sheet thicknesses 0.8 and 1.2 mm, representative of sheet thicknesses and grades in typical body-in-white automotive structures. The results obtained indicate that steel strength had little effect on fatigue performance for the range of steels studied. In contrast, both the loading mode and the sheet thickness had a significant influence. The results for shear loading were up to ten times greater when compared to peel loading conditions. Under shear loading conditions full plug failures were widely observed, whereas with peel loaded variants partial plug failures predominated. With respect to enhancing the fatigue properties the use of larger weld sizes wa...

In previous attempts to detect eclipse-induced AGW, it has always been difficult to establish a direct link between individual waves and a specific source. This study reports observations of travelling ionospheric disturbances made in the UK at the time of the total solar eclipse of 11 August 1999. The speed and direction of the waves were estimated by a four-station array using the HF Doppler technique. In addition, the wave observations were supported by two other propagation paths, one in the north of England close to the main array and the other further afield, between the UK and Sweden. The AGW activity following the eclipse totality was different to the background waves detected before this time in amplitude, speed and direction. The velocity vectors are consistent with a generating mechanism for the waves based on the supersonic passage of the cooled region of the atmosphere during the eclipse.

The authors thank the director and staff of EISCAT for the operation of the Tromso heater facility. EISCAT is an international facility funded collaboratively by the research councils of Finland (SA), France (CNRS), the Federal Republic of Germany (MPG), Japan (NIPR), Norway (NFR), Sweden (NFR), and the United Kingdom (PPARC). The SuperDARN Hankasalmi and Pykkvib•er HF radars are deployed and operated by the University of Leicester and funded by the PPARC (grant PPA/R/R/1997/00256), the Finnish Meteorological Institute, and the Swedish Institute for Space Physics. D.M.W. is supported on PPARC grant PPA/G/O/1997/000254.

Single box sections and T-joints (two box sections joined together at right angles) are commonly used to represent automotive components, such as pillars and sills, in laboratory testing. In the work presented herein, the torsional properties of T-joints were determined both experimentally and numerically. A factorial-design test programme comparing adhesive-bonded and spot-welded T-joints was carried out. Numerical models, generated using a general-purpose finite element program and validated against the test results, were used to investigate further the behaviour of the connection between the two box sections in a T-joint. The joining technique and the joint eccentricity at the connection (the distance of the join from the vertical box section) were found to influence the torsional properties of T-joints. Finally, an automotive T-component was analysed to examine the applicability of the T-joint results to more complex components.

A well-calibrated and validated finite element procedure, described in companion paper 1, was used in producing data on the stiffnesses, elastic limits and strengths of automotive box sections under torsion. The modelling procedure was first used in analysing all the experimental geometries, and these preliminary analyses helped to define the scope of further numerical work. This work, which consisted of 76 analyses, investigated the main effects identified—section thickness, cross-sectional area, model length and section design—and their interactions. Particular emphasis was given to quantifying the implications of the various effects on weight reduction by replacing spot welding with adhesive bonding as the fabrication technique. Further tests and analyses were also conducted to investigate the effects of weld pitch on torsional stiffness and to compare the properties of adhesively bonded, laser-welded and spot-welded sections.

Behaviour under torsion is an important performance-related property of automotive box sections. A previous experimental study has identified joining technique, section thickness and section area as the major influencing factors on the torsional behaviour of box hat sections. Using these test results as the basis, a finite element modelling strategy that can simulate the behaviour of adhesively bonded and spot-welded automotive box sections subjected to torsion is presented. The numerical study investigated the effects of material representation, mesh density and layout, and joining technique representation on the stiffness, elastic limit and ultimate strength of the box sections. The final model, calibrated and validated against test results obtained from previous work, was used in an extensive study, presented in the companion paper (Part 2), to further the understanding of the behaviour of torsionally loaded box sections and its implications on weight reduction of automotive structures.

A community-based natural resource management project in the arid Kunene Region of Namibia has evolved over time from a focus on halting poaching to ensuring community benefit from wildlife and ultimately to communities as proprietors of the wildlife resource. A Namibian NGO has used consistent and persistent ‘light-touch facilitation’ to assist communities to overcome problems in forming common property resource management institutions to manage the wildlife and conform with new government legislation. Pragmatic approaches to resolving conflicts over land and resources and to disputes between competing interest groups have enabled communities to make progress. Success has depended upon the intrinsic value communities place upon wildlife as much as instrumental incentives. Relations with the private sector have been governed by the degree of proprietorship enjoyed by communities. Copyright © 1999 John Wiley & Sons, Ltd.

Torsional rigidity is an important performance related property of an automotive body-in-white (BIW) structure, which consists of many box hat structures or box sections. An experimental study has been carried out to determine mainly the torsional stiffness but also the elastic limit and the strength of spot-welded and adhesively bonded (and weld-bonded) box sections. The relative contribution of a variety of factors, including joining system used, steel strength, sheet thickness, section area and section design, to the properties of box sections was analysed using factorial design experimentation techniques. It was found that a significant increase in torsional stiffness could be achieved by changing the joining technique, increasing the sheet thickness, increasing the section area and, to a lesser extent, changing the section design. The results are examined and discussed in the context of weight reduction in automotive structures.

When glass particles adsorb water from humid environments their low frequency dielectric properties change drastically. To investigate the polarization mechanism, variable frequency measurements upon individual glass particles (∼ 50 μm diameter) suspended in silicone oil were performed with a computer-controlled dielectrophoretic levitator. The electrical properties of individual particles have been measured in the frequency range between 10 Hz and 100 kHz. A relaxation in the induced dipole moment of moistened glass particles suspended in silicone oil is clearly evident in measured spectra. Surface moisture causes the characteristic relaxation times of soda-lime glass particles to change by up to 5 orders of magnitude. The relaxation spectra are satisfactorily modeled by the Debye equation and a model based on ohmic surface conduction appears to explain the phenomenon. This research has potential implications with respect to the controversy surrounding the influence of moisture on the performanc...

The response of the dayside ionospheric flow to a sharp change in the direction of the interplanetary magnetic field (IMF) measured by the WIND spacecraft from negative Bz and positive By, to positive Bz and small By, has been studied using SuperDARN radar, DMSP satellite, and ground magnetometer data. In response to the IMF change, the flow underwent a transition from a distorted twin-cell flow involving antisunward flow over the polar cap, to a multi-cell flow involving a region of sunward flow at high latitudes near noon. The radar data have been studied at the highest time resolution available (~2 min) to determine how this transition took place. It is found that the dayside flow responded promptly to the change in the IMF, with changes in radar and magnetic data starting within a few minutes of the estimated time at which the effects could first have reached the dayside ionosphere. The data also indicate that sunward flows appeared promptly at the start of the flow change (within ~2 min), localised initially in a small region near noon at the equatorward edge of the radar backscatter band. Subsequently the region occupied by these flows expanded rapidly east-west and poleward, over intervals of ~7 and ~14 min respectively, to cover a region at least 2 h wide in local time and 5° in latitude, before rapid evolution ceased in the noon sector. In the lower latitude dusk sector the evolution extended for a further ~6 min before quasi-steady conditions again prevailed within the field-of-view. Overall, these observations are shown to be in close conformity with expectations based on prior theoretical discussion, except for the very prompt appearance of sunward flows after the onset of the flow change.Key words. Ionosphere (Auroral ionosphere) · Magnetospheric physics (Magnetopause · cusp · and boundary layers; Magnetosphere · ionosphere interaction)

Experimental results concerning European incoherent scatter observations of heater-induced electron temperature enhancements, anomalous absorption of low-power HF probe waves, and the spectrum of stimulated electromagnetic emission (SEE) in the sidebands of a high-power HF electromagnetic wave are presented. For the experiments reported in this paper, an O mode pump wave was transmitted vertically into the F region above Tromsø, Norway, while the injected frequency was varied in small steps around the third harmonic of the electron gyrofrequency. Systematic variations with pump frequency were observed in the data obtained from all three diagnostics. Measurements of anomalous absorption, the downshifted maximum (DM) spectral feature, and heater-induced electron temperature enhancements all exhibited broad minima as the heater frequency approached the third harmonic of the electron gyrofrequency. In addition, the signal strength of the HF probe wave measured during heater off periods is also reduced at these and higher heater frequencies. The experimental findings suggest that at heater frequencies in the vicinity of the third gyroharmonic, small-scale field-aligned irregularities are not excited, whereas very small scale irregularities, of the order of a few electron cyclotron radii, which are responsible for the production of fast electrons, may be generated. The observed reduction in the diagnostic signal strength is then attributed to the ionized patches produced by these energetic electrons.

Observations of the anomalous absorption of low-power HF probe waves caused by the action of a high-power HF ordinary mode radio wave are presented. At pump frequencies in the vicinity of harmonics of the electron gyrofrequency the anomalous absorption measured on the low-power probe waves exhibit local minima. Also at these frequencies, large-scale changes deduced from phase measurements of the low-power probe waves and heater self-absorption are reduced, whereas the growth time of the anomalous absorption is increased. The electron gyrofrequency estimated from the frequency of the absorption minimum compares favorably with that derived from the International Geomagnetic Reference Field (IGRF) magnetic field model.

Interparticle force measurements have been performed upon various configurations of linear chains and planar layers of chrome steel balls immersed in a steady uniform applied magnetic field. These force measurements, made for particles in contact and at various separations, reveal that the attractive forces are enhanced in the case of particle chains parallel to the applied magnetic field and slightly decreased in the case of perpendicular layers. The magnetic saturation exhibited by the steel balls has only a modest effect on the force. Experimental data obtained for two‐particle chains correlate reasonably well to force calculations based upon a linear multipolar expansion using a relative particle permeability value of μr=100. It is also found that data obtained with longer linear chains as well as with planar particle arrays do not deviate drastically from the predictions of the two‐sphere problem.

In this article we describe a computer‐controlled active feedback dielectrophoretic (DEP) levitator and its measurement capabilities for characterizing single particles and particle chains (20–500 μm in length). Edge detection using a linear array of photodiodes is employed and an adaptive controller updates the voltage required for stable levitation at a rate of 4.7 kHz. Rms voltage fluctuations are typically less than 0.2% of the levitation voltage. The most precise data to date for the effective dipole moment of conducting particle chains up to four in length are presented along with experimental measurements of the effective dipole moment of two particle chains of unequal size as tests of accuracy and precision of the apparatus.

Measurements of the effective electric dipole moments of conducting particle chains suspended in insulating dielectric liquid reveal the influence of dielectric breakdown between particles. This breakdown can lead to reversal of the sign of the interparticle force from attractive to repulsive. Other measurements with a vibrating sample magnetometer of the effective magnetic dipole moments of ferromagnetic particle chains provide clear evidence that chaining enhances nonlinear magnetization at a field intensity about a factor of 10 below the value at which saturation is observed for single particles. Both of these physical situations are examples of how nonlinear effects can influence the electromechanical interactions of closely spaced particles. The nonlinearity is caused by the very strong field intensification that occurs in the gaps between particles for chains parallel to an applied electric or magnetic field. A correspondingly strong nonlinear effect is predicted for the forces between particles in chains.

To determine whether hemoglobin quantitations using the Hemocue system, a rapid and portable hemoglobin photometer, on fetal blood obtained via funipuncture were accurate compared to the Coulter S-Plus IV. We also examined whether gestational age or extremes in hemoglobin levels significantly affected the accuracy of the Hemocue system.We performed fetal hemoglobin quantitations using both systems on 58 specimens obtained between 18-38 weeks' gestation. Correlation between values by both systems was determined by linear regression analysis. The effects of gestational age and hemoglobin extremes on the accuracy of the Hemocue system were evaluated by stepwise regression.The mean Hemocue value was 12.0 +/- 2.4 g/dL (range 3.3-16.4); the mean Coulter value was 11.7 +/- 2.3 g/dL (range 3.6-16.2). The regression equation for Hemocue (y) versus Coulter (x) values was y = 0.72 + 0.97x; r = 0.94 (P.0001). Neither gestational age nor hemoglobin extremes significantly affected the accuracy of the Hemocue system.The Hemocue system is rapid and accurate for fetal hemoglobin quantitation between 18-38 weeks' gestation regardless of extremes in gestational age or hemoglobin levels.

Oblique ionograms received over northerly paths are often difficult to interpret, with many features not being of the form observed on the more familiar mid-latitude soundings. In particular, the ionograms contain unusual traces at frequencies close to and above the conventional or basic maximum usable frequency, i.e. above the junction frequency of the high and low angle modes. A series of experiments have been undertaken over a period of several years to investigate off-great-circle propagation mechanisms over high latitude and sub-auroral oval paths. In addition to measurements of the signal direction of arrival, oblique ionograms were also recorded over several of the paths. By these means, the characteristic ionogram signatures associated with off-great-circle propagation effects arising due to the presence of convecting patches of enhanced ionisation or sun-aligned arcs within the polar cap ionosphere, or to the presence of steep gradients to the side of the path within the mid-latitude trough region, have been identified.

Large electron density gradients in the ionosphere associated with the walls of the midlatitude trough produce tilted reflecting surfaces which lead to HF signals propagating over paths well displaced from the great circle. Measurements are presented of signals propagating over two paths along the midlatitude trough for which bearings deviations of up to 100° from the great-circle path, i.e. the expected direction of arrival, were frequently recorded. The times of occurrence and magnitude of these large deviations are consistent with the known features of the midlatitude ionospheric trough. Such large deviations of the measured bearing from the great-circle path, which far exceed the instrumental errors, have serious implications for the operation of position location systems operating within the HF band.

HF radiowave propagation over paths tangential to the auroral oval has been observed at times appreciably different from those indicated by conventional computer prediction codes. During these periods, large deviations of the ray path from the great circle direction occur, suggesting a mode of propagation not currently included in the prediction methods.

Copyright © 1991 IEE. This paper was published as: Microwaves, Antennas and Propagation, IEE Proceedings H, 1991, 138 (2), pp. 121-130. It is available from http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=68343

Copyright © 1990 IEE. This paper was published as: Microwaves, Antennas and Propagation, IEE Proceedings H, 1990, 137 (1), pp. 25-30. It is available from http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=52817

Observations of a Pc 5 micropulsation event, using the Wick half of the new SABRE auroral radar, are presented. During a 3-hour period in the early morning of September 18, 1981, a train of pulsations were recorded. Analysis revealed that there were three main events, rather than one continuous disturbance. The first event appeared as a perturbation of only one or two cycles, extending throughout the latitude of the viewing area. It was also visible in the STARE region, but the perturbation drift velocity was in the north-south direction as opposed to the east-west perturbation drift of a more conventional, toroidal mode field line resonance. The second disturbance was an isolated, one-cycle perturbation, also visible throughout both SABRE and STARE viewing areas and also having a dominant north-south velocity component. Finally, a very localized monochromatic event, lasting five cycles or more, with a period of about 5 min, was recorded. The characteristics of the third event were found to be consistent with those predicted by field line resonance theory. 18 references.

In this paper the effective dipole moment of two intersecting, electrically conducting spheres is calculated by using the method of electrical inversion. By invoking the constraint that the volume of the body formed by the two intersecting spheres must be fixed and equal to the original volume of the two spheres, a simple model for fusing biological cells, coalescing liquid droplets, etc., is developed. With this volume‐constrained effective dipole moment, the net dielectrophoretic force on merging particles may be calculated as a function of their center‐to‐center spacing.

The anomalous self-absorption of a high-power radio wave measured during recent ionospheric modification experiments exhibits a hysteresis effect. These results are consistent with the assumption that the growth of field-aligned irregularities due to the interaction of a high-power pump wave and the ionospheric plasma occurs in two stages. During the first stage, striation growth is due to an instability which has a threshold independent of striation amplitude. When the striation level is sufficiently high, the threshold of the second stage is reached. The second-stage threshold is dependent on the striation amplitude. The state of background ionosphere is also found to be an important factor influencing the observed effects.

Some results of recent high-latitude ionospheric heating experiments are presented. Phase changes were induced in a diagnostic radio wave reflected from the lower F region of the ionosphere as it passed through a region of the ionosphere which was being illuminated by a high-power electromagnetic wave. From the results obtained there are indications that anomalous absorption contributes much more than deviative absorption to ionospheric heating at high latitudes.

When a time−periodic magnetic field with a strong gradient is imposed tangentially at the interface of a ferromagnetic liquid, parametric surface instability may result. Under typical conditions this instability grows to a certain amplitude, where nonlinear dynamic effects become dominant, resulting in a standing−wave pattern. In the linearized small−amplitude limit, the surface dynamics are described by Hill’s equation. The nonlinear magnetization characteristic of the ferrofluid is successfully modeled by the Langevin superparamagnetic theory, using a single−sized particle approximation. The wavelength observed in the nonlinear amplitude limited state is successfully correlated with theory by determining the ’’most unstable wavelength’’, that is, the wavelength with the maximum growth rate for given conditions of applied magnetic field strength and frequency.