The assessment of human exposure to low frequency and high frequency electromagnetic fields using the boundary element analysis

Analysis of the human body exposed to low frequency and high frequency electromagnetic fields is presented in this work. The formulation of the problem is based on a simplified thick wire model of the human body. The current distribution induced in the body is determined by solving the Pocklington integral equation for a straight thick wire via the Galerkin–Bubnov boundary element method. Once the axial current along the equivalent antenna of the body is obtained, one may calculate the induced current density, electric field, specific absorption rate, and the total absorbed power in the human body. Several realistic exposure examples are given.     

Densification behavior,mechanical properties and thermal shock resistance of tungsten alloys fabricated at low temperature

The low-temperature shrinkage of tungsten was greatly accelerated by the addition of trace Nb and Ni, and the addition of trace Nb and Ni also significantly promoted the final sintering density. The 99.1% of theory density for W–0.1 wt.%Nb–0.1 wt.%Ni material sintered at 1600 °C was obviously greater than 93.7% of theory density for W material sintered at 2000 °C. Ball milling treatment played an important role in promoting the sintering densification of W–0.1 wt.%Nb–0.1 wt.%Ni powder, and the powder milled for 10 h (W10) could be sintered to near full density (99.4% of theory density) at 1600 °C. The ball milling for 15 h has no effect in improving the sintering density, but it induced rapid growth of tungsten grains. The microhardness and tensile strength of the sintered tungsten alloys were highly dependent on its sintering density and grain size. Improving the sintering density while controlling the grain growth could effectively promote the microhardness and tensile strength. Furthermore, the improvement of thermal shock resistance of the W10 alloy was due to good microstructure and the increase in the tensile strength.     

Bayesian estimation of hourly exposure functions by crash type and time of day

The study describes an investigation of the relationship between crash occurrence and hourly volume counts for small samples of highway segments from two states: Michigan and Connecticut. We used a hierarchical Bayesian framework to fit binary regression models for predicting crash occurrence for each of four crash types: (1) single-vehicle, (2) multi-vehicle same direction, (3) multi-vehicle opposite direction, and (4) multi-vehicle intersecting direction, as a function of the hourly volume, segment length, speed limit and pavement width. The results reveal how the relationship between crashes and hourly volume varies by time of day, thus improving the accuracy of crash occurrence predictions. The results show that even accounting for time of day, the disaggregate exposure measure – hourly volume – is indeed non-linear for each of the four crash types. This implies that at any time of day, the crash occurrence is not proportional to the hourly volume. These findings help us to further understand the relationship between crash occurrence and hourly volume, segment length and other risk factors, and facilitate more meaningful comparisons of the safety record of seemingly similar highway locations.     

Influence of zirconium on mechanical properties and phase transformation in low carbon steel

The influence of zirconium on the mechanical properties and phase transformation was investigated in low carbon steel. First, the steels are subjected to a special thermomechanical regime, and the hot rolled plates were used to characterise the tensile properties and impact toughness. Second, the phase transformation behaviour of the steels with various Zr contents was evaluated by both dilatometry and metallography. Finally, to confirm the existence of Zr containing precipitates in the Zr added steels, transmission electron microscopy and energy dispersive spectroscopy were used. It was verified that plenty of fine spherical (Nb,Ti,Zr)C, which is identified to be nearly 10?nm, can be formed when the concentration of Zr is in the range of 0.015–0.030%. The effects of zirconium on the phase transformation, including proeutectoid ferrite and pearlite transformation, and mechanical properties evolution were also identified and discussed.     

The second phase particles and mechanical properties of 2124 aluminum alloy processed by accumulative back extrusion

An age-hardenable 2124 aluminum alloy was severely deformed by accumulative back extrusion (ABE) method up to three passes at 100 and 200 °C. The characteristics of the second phase particles were studied using scanning electron microscopy. The results indicated that the size of primary particles had been reduced after the first ABE pass where even much finer particles was obtained as the successive passes were applied. In addition, the secondary particles were fragmented into finer pieces after ABE at 100 °C, whereas a particle coarsening was realized as the deformation temperature rose to 200 °C. The latter was attributed to the Ostwald ripening mechanism. However, the volume fraction of secondary particles was significantly decreased after three ABE passes at 200 °C due to the occurrence of deformation induced dissolution. Additionally, the tensile properties of the processed materials were measured utilizing a miniaturized tensile testing method. The results were justified considering the evolution of the second phase particles.     

A biomechanical investigation of forces applied to the lift truck steering wheel: effects of posture,gender and hand contact on cumulative low back loading

Hand contact forces on a typical lift truck steering wheel were quantified in a laboratory to determine their effects on low back loading. A single muscle equivalent link segment model (3D Match) was used to estimate cumulative loading exposure variables at the L4/L5 intervertebral disc with and without hand contact forces. Hand contact forces significantly decreased cumulative L4/L5 compression in forward bending (FB) for males by 32% and females by 14%. Cumulative L4/L5 compression in males (37,023?±?2183?Ns) was not different from that in females (38,413?±?2224?Ns). When excluding hand contact forces, males had significantly greater cumulative L4/L5 compression (55,165?±?1593?Ns) in FB compared to females (43,255?±?1753?Ns). Hand contact forces on mobile equipment controls might result in decreased cumulative L4/L5 compression, especially in awkward trunk postures. Females may be further predisposed to injury resulting from exposure to cumulative load.     

Experimental study of friction taper plug welding for low alloy structure steel: Welding process,defects, microstructures and mechanical properties

A research investigation has been undertaken to identify the various stages and variation of welding parameters in friction taper plug welding (FTPW) process and to explore their effects on the performance and properties of the welds. According to the variation of axial force, the overall FTPW process is divided into feeding phase, pressing phase, welding phase, and forging phase. The rotating speed, welding force, and burn-off rate remain nearly constant in welding phase. However, the torque peaks in welding phase when after few seconds of welding force setting is reached. Rising the welding force would increase the peak torque, welding torque, and burn-off rate, but decrease the welding time. When improper welding parameter is used lack of bonding and incomplete filling defects would form within the weld. The microstructure of the weld metal is consist of retained austenite, pearlite, and various Widmanstätten ferrite. In heat affect zone, it is mainly of lathy upper bainite. Defect free welds exhibit favorable tensile properties of which 548.3 MPa tensile strength and 27.5% elongation that equal to the base metal could be found.     

Measurement of planar refractive index profiles with rapid variations in glass using interferometry and total variation regularized differentiation

Planar refractive index profiles with rapid variations, formed in glass, are measured with interferometry. This involves forming a bevel in the glass and orientating the fringe pattern to be normal to the bevel edge. The index profile is determined by differentiation of the phase function of the fringe pattern. The differentiation has been performed using the total variation regularization method in order to preserve rapid changes in the derivative. This new approach avoids the necessity of filtering, in order to reduce noise, in the direction perpendicular to the bevel, which would otherwise smooth out the rapid index changes. The method is assessed using a model refractive index profile that contains an index gradient of 0.24 μm^?1 and is then applied practically to measure the refractive index profile of electrically poled BK7 glass. The new approach allows the sharp transition in the index between poled and unpoled glass to be observed as well as the accumulation of potassium ions beyond the poled glass region.     

宽带噪声目标声场干涉结构图的时空变换

水听器接收的运动目标宽带噪声的频率-时间I(ω,t)声场干涉结构图随着目标的运动会发生相应的变化。这个变化将引起I(ω,t)中干涉条纹的弯曲,使得I(ω,t)和频率-距离干涉结构图不再有简单的线性映射关系。在深入分析宽带噪声运动目标频率-时间I(ω,t)和相应频率-距离I(ω,r)声场干涉结构间的非线性映射关系的基础上,提出了一种从I(ω,t)到线性I(ω,r)的时空变换方法(Time-Space Linear Transformation,TSLT)。数值仿真实验结果表明,TSLT可以有效地消除目标运动的影响,从I(ω,t)中恢复出能真实反映频率-距离声场干涉结构规律的I(ω,r)。最后给出利用运动目标宽带噪声声场干涉结构估计波导不变量的应用例。     

Effect of nanoscale boron carbide particle addition on the microstructural evolution and mechanical response of pure magnesium

In this study, the effect of nano-B₄C addition on the microstructural and the mechanical behavior of pure Mg are investigated. Pure Mg-metal reinforced with different amounts of nano-size B₄C particulates were synthesized using the disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of the developed Mg/x-B₄C composites revealed uniform distribution of nano-B₄C particulates and significant grain refinement. Electron back scattered diffraction (EBSD) analyses showed presence of relatively more recrystallized grains and absence of fiber texture in Mg/B₄C nanocomposites when compared to pure Mg. The evaluation of mechanical properties indicated a significant improvement in tensile properties of the composites. The significant improvement in tensile ductility (∼180% increase with respect to pure Mg) is among the highest observed when compared to the pure Mg based nanocomposites existing in the current literature. The superior mechanical properties of the Mg/B₄C nanocomposites are attributed to the uniform distribution of the nanoparticles and the tendency for texture randomization (absence of fiber texture) achieved due to the nano-B₄C addition.     

The effect of thermal exposure on the electrical conductivity and static mechanical behavior of several age hardenable aluminum alloys

Aluminum alloys 2014-T6, 2024-T3, 6061-T6, 7050-T7451, and 7075-T6 were thermally exposed at different times (1 min to 20 days) and temperatures 177–482 °C (350–900 F). This study was conducted to simulate the effects of heat damage on aluminum alloys and to determine the correlations existing between the static mechanical and electrical conductivity properties. Results indicate that at the temperatures below 260 °C (500 F) all five alloys showed clear correlations between the mechanical and physical properties.     

The influences of soft and stiff inclusions on the mechanical properties of cementitious composites

The embedment of microencapsulated phase change materials (PCMs) is a promising means for improving the thermal inertia of concrete. However the addition of such soft microcapsules degrades the mechanical properties, i.e., the elastic moduli and compressive strength, of cement-based composites. This study experimentally quantifies the effects of stiff quartz inclusions and soft PCM microcapsules, individually, and when added together, on the mechanical properties of cementitious composites. In addition, a variety of effective medium approximations (EMAs) were evaluated for their ability to predict the experimentally measured composite effective moduli. The EMAs proposed by Hobbs and Garboczi and Berryman (G-B) reliably estimate experimental data. The experimental data and the EMAs were applied to develop a design rule for performance equivalence, such that the composite modulus of elasticity can be maintained equivalent to that of the cementitious paste matrix, in spite of the addition of soft PCM microcapsules.     

The influence of the stitching pattern on the internal geometry,quasi-static and fatigue mechanical properties of glass fibre non-crimp fabric composites

This paper discusses the experimental results of a study comparing several aspects of the mechanical behaviour of two quasi-unidirectional non-crimp fabric composites based on non-crimp fabrics that differ only in stitching pattern. A NEW stitching pattern was compared to an industry common type (ICT). The properties studied include fabric and laminate thickness, fibre volume fraction, static tensile modulus and strength in longitudinal and transverse direction, high-speed tensile strength and tension–tension fatigue life. Statistically significant differences were observed for fabric and composite thickness, which was found to be higher for the ICT type composite. A higher fibre volume fraction was observed for the NEW stitching pattern material, as well as a higher longitudinal tensile strength at high and low speeds and a slightly higher fatigue life.     

Long term water uptake of a low density polyvinyl chloride foam and its effect on the foam microstructure and mechanical properties

The water uptake, evolution of the cell morphology and basic mechanical properties of a 48 kg/m³ commercial polyvinyl chloride (PVC) foam immersed in distilled water and seawater for up to 12 months is investigated. The samples of PVC foam immersed in distilled water showed a faster water absorption rate and water uptake than the samples immersed in seawater. For both conditions, the tensile and compressive properties of the foam evidence a plasticization effect with a small reduction in the elastic modulus (∼10%) and an increase in the ultimate tensile strain (∼19%) for 12 months of immersion. The detailed micrographic analysis conducted provides conspicuous evidence that for both conditions the cells at the surface of the foam are severely damaged after a few days of immersion, but such cell damage is superficial and does not cause severe irreversible damage to the internal cellular microstructure of the foam.     

Effect of B and B + Nb on the bainitic transformation in low carbon steels

Development of new, advanced high and ultra-high strength bainitic steels requires the selection of the optimum balance of bainite promoting elements allowing the production of the desired bainitic microstructure over a wide range of cooling rates. The addition of boron or a combined addition of boron and niobium is well known to retard strongly the polygonal ferrite formation but very little knowledge has been acquired on the bainitic transformation. Therefore, the purpose of this study is to investigate the influence of boron and boron plus niobium on the bainite transformation kinetics, microstructural evolution and mechanical properties in a low carbon steel (Fe-0.05C-1.49Mn-0.30Si). Isothermal and continuous cooling transformation diagrams were determined and followed by a detailed quantitative characterisation of the bainite microstructure and morphology using complementary advanced metallographic techniques (FEG-SEM-EBSD, SIMS and TEM). The relationship between microstructure and hardness has been evaluated. Finally, results of SIMS and TEM analyses coupled with microstructural investigations enable to propose a mechanism to explain the effect of the synergy between boron and niobium on the bainitic transformation and the resultant microstructure.     

Effect of pre‐processing annealing and ram speed on mechanical properties for low carbon steel processed by constrained groove pressing

Constrained groove pressing (CGP) has emerged for producing ultra‐fine‐grained materials with distinguished properties. Low carbon steel sheets were subjected to severe plastic deformation by constrained groove pressing process. The effect of pre‐processing annealing temperature, ram speed and number of passes on microstructure, mechanical properties and wear behaviour of the sheets were investigated. The 3 mm thick sheets were deformed by a constrained groove pressing die at ram speeds: 5 mm/min, 10 mm min^?1 and 20 mm min^?1. Furthermore, the as received sheets were annealed at 600 °C and 900 °C, then deformed at ram speed 20 mm min^?1. The annealing temperature 900 °C led to slightly coarser grains, lower strength and larger ductility compared to those obtained after annealing at 600 °C. With lowering the ram speed to 5 mm min^?1, the number of passes could be increased to 10 passes while increasing ram speed from 5 mm min^?1 to 20 mm min^?1 improved the mechanical properties; after 3 constrained groove pressing passes, the ultimate tensile strength increased from 420 MPa to 490 MPa, the hardness from 174 HV 1 to 190 HV 1 and the elongation from 7.6 % to 9.5 %. Finer grains were also obtained by increasing ram speed. Wear resistance was greatly enhanced by constrained groove pressing and by the increase in ram speed.     

Influence of retrogression temperature and time on the mechanical properties and exfoliation corrosion behavior of aluminium alloy AA7150

The tensile properties, exfoliation corrosion behavior and microstructures of the retrogression and re-aging (RRA) treated aluminum (Al) alloy AA7150 were studied. AA7150 was retrogressed at different temperatures (175 °C, 185 °C and 195 °C) for various times. It is found that as the hardness of the retrogressed AA7150 approaches the near-peak condition, the corresponding RRA treated AA7150 possesses good exfoliation corrosion resistance without strength loss. By retrogressing at 175 °C, the retrogression time can be extended to 3 h, the RRA treated AA7150 possesses a strength as high as that of conventional AA7150-T6, and its exfoliation corrosion resistance is in the vicinity to that of AA7150-T73. This enhanced exfoliation corrosion resistance was associated with the more separated η precipitates at the grain boundary. AA7150-T6 is mainly strengthened by fine GP zones with high number density, while the intra-grain micro-structure of AA7150-RRA retrogressed at 175 °C for 3 h is characterized by relatively coarse η′ precipitates.     

The effect of recycling on the mechanical response of carbon fibres and their composites

The development of processes for recycling carbon–fibre composite waste rises a question yet to be answered: how good can the performance of recycled composites be? This paper analyses fibres reclaimed in commercial facilities, and compares the performance of subsequently manufactured recycled woven composites to that of the virgin precursor (with the same fibre architecture). Different pyrolysis cycles resulted into different compromises between complete resin removal and full fibre strength retention. At the composite level, this paper shows how strength varies with the reclamation cycle, re-impregnation process and loading direction, while stiffness remains virtually unaffected. It is shown that composite tensile strength is favoured by gentle pyrolysis cycles generating little fibre damage, while compressive strength is fully retained after more aggressive cycles which completely remove the matrix. This work proves that the mechanical response of recycled composites can rival that of virgin precursors, while highlighting the benefits of application-driven optimisation of reclamation processes.     

Parabolic and cubic acceleration time integration schemes for nonlinear structural dynamics problems using the method of weighted residuals

Two algorithms are proposed for direct time integration of an equation of motion of structural dynamics problems. The performance of the proposed methods is examined by evaluating stability, order of accuracy, numerical dissipation, and algorithmic damping. The results show that critical time for instability of the proposed algorithms is larger than those of conditionally stable methods. The numerical dissipation is shown to be explicitly less than other methods. Furthermore, the proposed algorithms are non-dissipative in the low-frequency range and have favorable damping in mid- and high-frequency regimes. Three examples are carried out to evaluate the feasibility and effectiveness of the proposed algorithms.     

The effect of carbon nanotube orientation and content on the mechanical properties of polypropylene based composites

Finite element method (FEM) is used to predict the tensile and compressive stress–strain curves of single wall carbon nanotube (SWCNT) reinforced polypropylene (PP) composites. The numerical simulations, using shell and tetrahedron elements, are first carried out to investigate the effect of SWCNT orientation on the mechanical properties of the nano-composites. Second, the Grunfest–Young constitutive equation is selected to determine the effect of strain rate and solve the finite element program to analyze the mechanical behavior of the nano-composites. Third, the effect of SWCNT volume fraction is studied. In all cases, the shear and normal stresses distribution along the nanotube axis are investigated and compared with the macroscopic tensile or compressive stresses on the composites. At the same time, the stresses of the interface between SWCNT and the matrix along the loading direction are analyzed. Finally, the effects of SWCNT orientation, content and strain rate on the strength of the nano-composites are studied. From the results obtained, it was shown that strain rate can substantially affect the tensile and shear stresses of the composites, but do not significantly influence the initial tensile or compressive elastic moduli. This is especially the case for SWCNT orientation angles less than 30° and volume fractions higher than 0.74%.