考虑导线偏心覆冰对四分裂导线舞动的影响

采用风洞试验获得典型新月形覆冰四分裂导线的升力、阻力和扭矩系数随风攻角的变化规律。基于ABAQUS有限元软件提出一种考虑偏心覆冰作用的导线数值模拟方法,并利用算例验证了该方法的正确性。在此基础上,利用ABAQUS用户自定义子程序UEL编写气动载荷单元,实现考虑偏心覆冰作用的导线舞动数值模拟方法。采用该方法与传统数值模拟方法对典型新月形覆冰四分裂导线的舞动特征进行对比分析。结果表明,该方法能准确反映覆冰导线运动过程的扭转特性。考虑偏心覆冰作用后,覆冰四分裂导线的位移和扭转角幅值明显增大,振动形态更为复杂。因此,在研究覆冰导线舞动时,有必要考虑偏心覆冰作用的影响。     

Effect of material nonlinearity on crack propagation

A common test specimen for studying the dynamic characteristics of a crack is that of the so-called double cantilever beam. A starter crack is usually introduced at one end by a wedge action splitting the beam at the mid-section and producing an initial crack of certain length. Depending on the loading condition the crack first picks up speed and then slows down as it increases in length. This work is concerned with the effect of material nonlinearity on the motion of a running crack. An extensive amount of theoretical results are presented, with details of velocity and acceleration related to time and crack length parameters. The results are useful to the experimentalists for collecting data on the dynamic fracture of engineering materials.     

Y对耐热铝导体材料铸态组织和性能的影响

随着特高压输电技术在我国的大力发展,铝合金导体材料作为特高压输电线路的主要组成部分,受到业内的广泛关注.本文采用电导率测试、硬度测试、金相显微镜和扫描电镜观察等手段,研究添加不同含量稀土Y对铸态Al-Zr耐热铝导体材料的影响.研究结果表明:Y元素和Fe、Si等杂质元素形成金属间化合物,可净化基体,改变杂质相的形态和分布,使其粒子化、球化和细化.Y元素在枝晶网络和晶界分布,从而细化晶粒和枝晶组织,但添加量达到0.5%时晶粒细化不均匀.当Y含量为0.2%时,电导率达到60%IACS;当Y含量为0.3%时,硬度达到最高值20.9HBS,且电导率并无明显下降.加入0.3%Y可使耐热铝导体材料获得较好的综合性能.     

Effect of angle of incidence during deposition on Ti-Pd-Au conductor film adhesion

The influence of a number of the preparation conditions on the adhesive properties of the Ti-Pd-Au metallization on Ta₂N film resistors was investigated. Test samples consisted of a filament-evaporated conductor film on an unpatterned Ta₂N film on glass, sapphire and Al₂O₃ ceramic substrates. The adhesive properties of the Ti-Pd-Au films were examined as a function of the angle of incidence at which the Ti and Pd atoms were deposited. In addition the adhesive properties were examined after heat treatment in air and after electroplating gold. Transmission electron microscopy and density measurements established that at higher angles of incidence (>60°) Ti and Pd films became increasingly porous and that adhesion at the Ti-Pd interface degraded rapidly upon exposure to air. Both evaporated and plated Au layers appear to offer little protection for films evaporated under these conditions. Good adhesion was found to be independent of the substrate material and of the method used for gold deposition when the Ti-Pd films were evaporated at angles of incidence of 48° or less.     

Effect of exposure to aggressive stimuli on aggressive driving behavior at pedestrian crossings at unmarked roadways

BackgroundAggressive driving, influenced by the proneness of driving aggression, angry state and provoking situation, is adversely affecting traffic safety especially in developing countries where pedestrians frequently cross an unmarked crosswalk. Exposure to aggressive stimuli causes driving anger and aggressive driving behaviors, but the exposure effect on higher and lower aggression drivers and their cumulative changes under successive exposures need more investigation.ObjectivesAn experiment was conducted to examine (1) driving behaviors of individuals with higher and lower aggressive driving traits when approaching pedestrian crossings at unmarked roadways with and without aggressive provocation; and (2) cumulative changes of driving performance under repeated provocations.MethodWe conducted a driving simulator study with 50 participants. Trait of aggressive driving served as a between-subjects variable: participants with an Aggressive Driving Scale (ADS) total score of 30 or more (for men) or 23 or more (for women) were regarded as higher aggressive drivers; lower aggressive drivers were those individuals whose ADS total scores were 21 or less (for men) or 13 or less (for women). Exposure to aggressive stimuli (provoked vs. non-provoked condition) served as a within-subjects variable. Several aspects of the participants’ minimum driving speed, lateral distance from a simulated pedestrian, lateral deviation, and subjective measures were collected.ResultsWe found that drivers with higher aggressive driving traits were more likely to feel irritated and fail to give way for pedestrians and drove closer to pedestrians when exposed to sustained honking and improper passing compared to the non-provoked condition. This trait × state interaction only occurred when pedestrians crossed the street from the right roadway edge line. In addition, we observed an accumulation effect of exposure to aggressive stimuli on driver's aggressive behaviors at pedestrian crossings.ConclusionsEnvironmental design, law enforcement, and educational campaign may have practical value for reducing pedestrian and driver conflicts at unmarked roadways.     

Effect of material nonhomogeneity on crack propagation characteristics

The influence of material nonhomogeneity on the behavior of a moving crack is investigated. The model assumes a running crack in a material whose elastic properties may differ from those of the surrounding material. Theoretical calculations showed that the energy stored in elements ahead of the crack can be raised or lowered depending on the crack velocity, the crack length and the degree of material nonhomogeneity which is associated with the ratio of the shear moduli and the distance between the crack and the neighboring material with different elastic properties. Based on the strain energy density theory, predictions are made on how material nonhomogeneity can influence the initiation and/or arrest characteristics of cracks.     

Effect of annular secondary conductor in a linear electromagnetic stirrer

This paper presents the variation of average axial force density in the annular secondary conductor of a linear electromagnetic stirrer. Different geometries of secondaries are considered for numerical and experimental validation namely, 1. hollow annular ring, 2. annular ring with a solid cylinder and 3. solid cylinder. Experimental and numerical simulations are performed for a 2-pole in house built 15 kW linear electromagnetic stirrer (EMS). It is observed for a supply current of 200 A at 30 Hz the force densities in the hollow annular ring is 67% higher than the equivalent solid cylinder. The same values are 33% for annular ring with a solid cylinder. Force density variation with supply frequency and current are also reported. Numerical simulations using finite element model are validated with experimental results.     

Effect of polymer additives on propagation of turbulence front

A study is made of the propagation of a turbulent region formed by vibrations of plates with holes in solutions of polyoxyethylene and guar resin. Polymer additives are found to appreciably affect the motion of a turbulence front.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 43, No. 2, pp. 220–224, August, 1982.     

Effect of joule heat on the distribution of electric current in a cylindrical conductor

Analyzed are the thermal conditions in a cylindrical conductor whose electrical conductivity is temperature-dependent. It is shown that a sufficiently large current is crowded toward the conductor surface with a change in the heat balance at the surface. The behavior of cylindrical semiconductors under analogous conditions is also examined.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 2, pp. 345–350, August, 1972.     

Effect of electromagnetic force on the pressure drop and coupling loss of a cable-in-conduit conductor

In the central solenoid (CS) insert experiment performed with the International Thermonuclear Experimental Reactor CS model coil, significant changes in the pressure drop and coupling losses were observed during coil energization. This phenomenon was quantitatively analyzed from the viewpoint of the deformation of the cable shape in the CS insert conductor due to an electromagnetic force acting on the cable. A new calculation model was proposed to provide the relation between the electromagnetic force and hydraulic characteristics of the conductor. Calculation results indicated that there seemed to be a gap of 1.3 mm between the cable and jacket created by the electromagnetic force when the CS insert was operated at 40 kA and 10 T, which can cause the decrease of the pressure drop by 12% and also the decrease of the local void fraction of the cable from 36.3% to approximately 34%. The latter well explained the increase of coupling losses. A local void fraction of 34.5% is suggested from the calculation in order both to reduce the amount of deformation and to maintain the coupling losses at acceptable level for this type of large current-carrying conductor.     

Effect of acid corrosion on crack propagation of concrete beams

The effect of acid corrosion on crack propagation of concrete beams was theoretically studied by the method of crack extension resistance curve. Based on this method, a calculation approach was proposed to determine fracture stress intensity factors in crack propagation of concrete beams. Loop iteration analysis was carried out to calculate maximum bearing capacity load, unstable crack toughness, resistance toughness curve, cohesive toughness curve and load–crack mouth opening displacement. Both bilinear and nonlinear softening traction–separation curves were adopted for each of these calculation parameters. The analysis results of each showed the effect of acid corrosion degrees. The influence of acid corrosion on fracture properties was discussed through the calculated results of cohesive toughness curves. These five kinds of simulated results were basically consistent, before the load attained the maximum value. However, with further crack propagation, cohesive toughness of nonlinear softening model was significantly larger than that of bilinear softening model, and the descending branch of P–CMOD curve by nonlinear law is higher than that by bilinear law. To validate the approach, tests of specimens under six different corrosion periods were experimentally studied, using three-point bending notched concrete beams soaked in sulphuric acid solution. The Double-K fracture parameters were investigated based on the test results, and load–crack mouth opening displacement curves for different acid conditions were obtained using synchronous sampling of a load sensor and clip-gauge. Numerical results by bilinear softening model showed a good correlation with the experimental ones.     

Effect of crazes on the propagation of cracks in polystyrene

A study of the fracture surfaces of polystyrene has revealed a direct connection between the fracture path and the shape and distribution of crazes. The effect is demonstrated by two examples; firstly, the propagation of a crack through initially uncrazed material and, secondly, the propagation of a crack through material containing an array of planar crazes parallel to the plane of propagation. It is shown that cracks propagate preferentially along crazes and that the formation of crazes in the stress field of a propagating crack results in the “hackle” surface normally associated with the propagation of cracks at high velocities.     

Effect of the corrosive medium on propagation of short cracks

Conclusions The results show that the crack depth in the range 0.2–1.3 mm affects the chemically determined crack growth rate in 50SiMn7 high-strength steel under the effect of the alkaline sulfate-saturated solution of Ca(OH)₂ (pH 12.1). In free corrosion conditions and a load constant with time, the upper boundary of the depth of the chemically small crack for the given system is 1.3 mm. In the saturated solution of CaSO₄ this boundary is below 0.2 mm. This experimentally confirmed effect of the chemically small cracks makes it possible to increase the crack depth from 0.12 to 0.25 mm at a given load of 900 MPa.The article was sent to the editorial board in the German language. Authorized translation by S. Ya. Yarema.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 13–20, March–April, 1990.     

Effect of temperature and environment on crack propagation in graphite

Crack propagation studies were carried out on POCO AXF-5Q and ATJ-S graphite as a function of temperature and environment (for example H₂ O, and CO and He). Crack growth rates in both graphites was essentially insensitive to the external environments at all temperatures. A transition from stable to catastrophic crack growth occurred at a particular temperature for each material. A definite effect of crack plane orientation with respect to the ATJ-S graphite billet was observed.     

Effect of thickness on ductile fatigue crack propagation in polycarbonate

Resistance to slow fatigue crack propagation in polycarbonate is investigated with respect to specimen thickness. In the thickness range considered (0.33–3.22 mm), microscopic analysis reveals that a zone of yielded material constitutes the resistance to crack propagation. As the sheet thickness is increased, the amount of yielded material per unit crack surface is reduced. Consequently, faster crack growth rates are observed with increasing specimen thickness. Crack layer theory is applied to analyse crack propagation kinetics and stability. Accordingly, a specific enthalpy of damage (yielding) is found constant for the thickness range considered and is equal to 60 J g^–1 . It is further noticed that as the thickness increases, resistance to crack initiation increases.     

Effect of residual stress on crack propagation in MDPE pipes

Crack propagation behaviour in single edge notched specimens prepared from medium-density polyethylene (MDPE) pipe is examined under creep condition. The crack grown from an exterior notch (inbound) initiated faster than that grown from an interior notch (outbound). Subsequently, the outbound crack propagated monotonically to ultimate failure. The inbound crack showed anomalous behaviour involving two arrest stages prior to ultimate failure. The pipe is found to possess substantial residual stresses. The energy release rate for each case was calculated taking into account the respective residual stream distribution. The fact that the rates of crack propagation are not a unique function of the energy release rate indicates that the fracture is also influenced by morphological gradients imposed by processing conditions.     

Effect of crystalline morphology on fatigue crack propagation in polyethylene

An investigation of the influence of crystalline morphology on fatigue crack propagation (FCP) resistance in a slightly branched polyethylene is presented. Various thermal histories have been utilized to generate samples with different crystalline microstructures and the samples were characterized thoroughly using standard methods. Estimation of tie molecule densities was obtained from measurements of brittle fracture stress. Differences in FCP behaviour for the quenched and annealed samples were shown to be dictated by a competing effect between the degree of crystallinity and tie molecule density. Further, larger spherulite size and distribution appeared to have a deleterious effect on fatigue properties. In general, crystalline microstructure is shown to have a significant influence on fatigue crack propagation behaviour.