薄带连铸镁合金的研究与思考

综述了单辊铸造和双辊铸造镁合金薄带的研究进展与产业化现状,提出了存在的问题,分析了影响镁合金薄带浇铸速度的因素,指出,改善浇铸系统的传热能力是提高镁合金薄带浇铸速度的关键;立式双辊连铸系统具有更高的传热能力,镁合金薄带连铸应借鉴立式双辊连铸钢带技术.     

Computer-aided strengthening of masonry walls using fibre-reinforced polymer strips

Studies on the use of fibre-reinforced polymers (FRP) as strengthening materials of masonry walls have been numerous. FRP materials, particularly in the form of unidirectional strips, provide a highly effective method of structural intervention in masonry walls. However, the selection of the reinforcing pattern (positioning of the strips) and the calculation of respective cross sectional FRP areas still remains a problem, which is solved in this study through the development of a methodology that relies on strut-and-tie modelling. This methodology has been implemented in a computer programme that enables the definition of the locations where FRP strips should be placed in masonry walls subjected to in-plane loading. Moreover, the tensile forces in the ties can be used to calculate the required FRP cross section areas, hence the number of strips in each location. Hence, a valuable tool for the dimensioning of interventions in masonry walls using FRP materials in the form of strips has been developed. Applications of the tool in simple case studies (masonry walls with openings subjected to both vertical and horizontal loads) are also provided. Finally, a comparison between results predicted by this strut-and-tie model and those from an experimental study found in the literature adds some confidence to the model.     

Electrostatics of interdigital transducers

Interdigital transducers are systems of conducting strips on a piezoelectric halfspace; in some systems, the groups of strips repeat periodically over a transducer counting hundreds of strips that can be considered infinite. An infinite planar periodic system of groups of strips with adequate period, sufficiently large if necessary, is considered to model an electric field in the plane of strips. There are electric charge distributions on strips either resulting from an external voltage source applied to the strips or induced by a propagating surface acoustic wave in the piezoelectric substrate. The latter case is equivalent, in the electrostatic approximation applied in this paper, to strips embedded in an already existing, spatially variable electric field. A method is presented for evaluation of the spatial spectrum of charge distribution that is responsible for either the surface wave generation or the scattering by strips in weak piezoelectrics. It overcomes certain numerical difficulties arising when Fourier transform is computed from the already evaluated numerical representation of the square-root singular charge distribution at the strip edges.     

Influence of FRP wrapping techniques on the compressive behavior of concrete prisms

Results of an experimental investigation on the compressive behavior of concrete prisms with square cross-section, externally wrapped with carbon fiber reinforced plastic (CFRP) sheets are presented. The effects of the following parameters were analyzed: local reinforcement at the corners and continuous layers; horizontal and vertical discontinuous strips; number of continuous layers—length of specimens.An analytical model is proposed to determine the maximum bearing capacity of compressed concrete members with square cross-section and externally wrapped with FRP for the different configurations examined, and also able to consider the strength reduction with the length increase of concrete members. Analytical results are then compared with the experimental data available in the literature, showing good agreement.     

Eddy currents in a transverse MRI gradient coil

A transverse gradient coil (x- or y-coil) of an MRI-scanner is modeled as a network of curved circular strips placed at the surface of a cylinder. The current in this network is driven by a time-harmonic source current. The low frequency applied allows for an electro-quasi-static approach. The strips are thin and the current is assumed to be uniformly distributed in the thickness direction. For the current distribution in the width direction of the strips, an integral equation is derived. Its logarithmically singular kernel represents inductive effects related to the occurrence of eddy currents. For curved circular strips of width much smaller than the radius of the cylinder one may locally replace the curved circular strip by a tangent plane circular strip. This plane geometry preserves the main characteristics of the transverse current distribution through the strips. The current distribution depends strongly on the in-plane curvature of the strips. The Petrov–Galerkin method, using Legendre polynomials, is applied to solve the integral equation and shows fast convergence. Explicit results are presented for two examples: a set of 1 strip and one of 10 strips. The results show that the current distributions are concentrated near the inner edges and that resulting edge-effects, both local and global, are non-symmetric. This behavior is more apparent for higher frequencies and larger in-plane curvatures. Results have been verified by comparison with finite-element results.     

Experimental analysis of historic masonry walls reinforced by CFRP under in-plane cyclic loading

External bonding of Fiber Reinforced Polymers (FRPs) has become a popular technique for strengthening historic masonry wall buildings in seismic area. Although FRPs seem to improve response of historic masonry walls under in-plane shear loading, further investigations must specify a number of aspects for both researchers and practitioners. This paper presents an experimental analysis pertaining to the response of unreinforced and reinforced historic masonry walls built using full clay bricks in scale 1/3rd. On the basis of previous experimental research carried out by shear tests on triplets and unreinforced walls, a shear criterion for historic unreinforced masonry (HURM) has been assumed. In this experimental analysis two HURM walls, characterized by double T shape, were subjected to in-plane cyclic loading to shear cracking. The damaged walls were reinforced using horizontal–vertical and diagonal Carbon FRP strips. An anchorage system was also put into place to improve the adhesion of the strips used; the historic reinforced masonry (HRM) walls were tested by cyclic loading until failure. The experimental results are illustrated and discussed taking into account the delamination failure of the CFRP strips. Finally, the increase obtained in walls’ shear capacity is analysed considering theoretical bilinear diagrams and the coefficient of ductility.     

The impact of perceptual treatments on driver's behavior: From driving simulator studies to field tests—First results

Our study focused on the lateral position of drivers in relation to risk on rural crest vertical curves, using a field site proposed by a local operator of the French road network (Conseil Général de Maine-et-Loire, 49). The final goal was to test one road treatment on this field site. The study consisted of three stages. The first, using driving simulators, selected two perceptual treatments (i.e., rumble strips on both sides of the centerline and sealed shoulders) from five that were tested in order to help drivers maintain lateral control when driving on crest vertical curves. The rumble strips were installed first on the field site.     

Experimental analysis of historic masonry walls reinforced by CFRP under in-plane cyclic loading

External bonding of Fiber Reinforced Polymers (FRPs) has become a popular technique for strengthening historic masonry wall buildings in seismic area. Although FRPs seem to improve response of historic masonry walls under in-plane shear loading, further investigations must specify a number of aspects for both researchers and practitioners. This paper presents an experimental analysis pertaining to the response of unreinforced and reinforced historic masonry walls built using full clay bricks in scale 1/3rd. On the basis of previous experimental research carried out by shear tests on triplets and unreinforced walls, a shear criterion for historic unreinforced masonry (HURM) has been assumed. In this experimental analysis two HURM walls, characterized by double T shape, were subjected to in-plane cyclic loading to shear cracking. The damaged walls were reinforced using horizontal–vertical and diagonal Carbon FRP strips. An anchorage system was also put into place to improve the adhesion of the strips used; the historic reinforced masonry (HRM) walls were tested by cyclic loading until failure. The experimental results are illustrated and discussed taking into account the delamination failure of the CFRP strips. Finally, the increase obtained in walls’ shear capacity is analysed considering theoretical bilinear diagrams and the coefficient of ductility.     

Anisotropic stress in window-plated Permalloy thin films

Measurements of stress have been made in window-plated strips of Permalloy with different aspect ratios and the results have been related to finite-element simulations. It is found that the in-plane stresses in the window-plated strips are similar to those expected in strips fabricated from a sheet film with an initial biaxial stress state. The effect of annealing the strips is to increase the difference between the two principle in-plane stresses. The implications of this stress state for the magnetic anisotropy of the strips is discussed     

The extensible uplifted strip

Summary The frictional contact behaviour of extensible and flexible strips on rigid ground and loaded by transversal pressure is considered analytically. Complete and asymptotic solutions are presented. For specific cases diagrams are derived which can be used for engineering applications. One practical relevance of these problems is discussed with regard to the uplift of the bottom plate of vertical unanchored liquid storage tanks. The complicated behaviour of the uplift of a strip adhered to the ground is briefly investigated. Analytically obtained results of these nonlinear problems are compared with finite element solutions.With 8 Figures     

An experimental investigation on flexural behavior of RC beams strengthened with prestressed CFRP strips using a durable anchorage system

This paper investigates the effectiveness and feasibility of a prestressed carbon fiber-reinforced polymer (CFRP) system for strengthening reinforced concrete (RC) beams. The proposed prestressing system with a novel anchorage allows the utilization of full capacity of the CFRP strips. Eight small-scale and two large-scale concrete beams strengthened different configuration of prestressed CFRP strips are tested under static loading conditions up to failure. The main parameters considered include the level of prestressing applied, ranging from 20% to 70% of the tensile strength of the CFRP strips, and the use of mechanical anchorages at both ends of the CFRP strips. Thanks to the durable anchorage, the full range of flexural behavior was investigated including post-debonding. The results indicate that the beams strengthened using prestressed CFRP strips exhibited a higher first-cracking, steel-yielding, and experimental nominal moments as the level of prestressing force increased up to a certain point. After analyzing prestress effects in small scale tests, an optimum prestress level for strengthening concrete beams using CFRP strips is proposed and verified in large scale tests.     

Branching of Plastic Strips near the Tip of a Notch under Longitudinal Shear

We solve the problem of a crack of longitudinal shear with a plastic zone, formed by an arbitrary number of strips that go out from the crack tip. Tangential stresses along the strips are equal to the yield limit of the material. The obtained solution shows that stresses exceed the yield limit outside the strips, and this excess decreases with an increase in the number of strips and tends to zero as their number tends to infinity. The lengths of the strips of the zone under study asymptotically approach the lengths of similar strips on which the conditions of plasticity are satisfied. We show that, for localization of deformations in a single strip near the tip of a V-shaped notch, it is sufficient that the yield limit of the material along the bisecting plane of the notch be smaller than the yield limit in other directions.     

制冷系统立式水冷冷凝器管内污垢的自动清洗技术

对管内水垢使立式水冷冷凝器的运行效率影响的严重性进行了实测分析 ,从提高年平均运行效率的角度对现在常用的污垢清洗方法作了简单评述 ,介绍了新研究的纽带自动清洗技术原理和管内的膜状旋流色水试验以及初次应用试验 ,结果表明综合效益颇高     

Effects of rolling and sintering temperature on peel strength of bonding interfaces for Ag/Cu bimetallic strips

Abstract

Cu/Ag bimetallic strips were prepared by roll bonding in the temperature range 293-873 K and sinter treating in the temperature range 523-1073 K. The interface peel strength was determined and the peeled surface morphology observed. High peel strength is obtained from the excellent metallurgical joint given by solute interdiffusion and matrix recrystallisation under sintering conditions 523-673 K for bimetallic strips rolled at ambient temperature. Sintering in the temperature range 873-1073 K results in reduced peel strength due to increased void formation at the interface, although some local contacts on the mated surface could melt and merge at 1073 K. Low peel strength due to poor metallurgical bonding is obtained if the bimetallic strips are roll bonded at temperatures lower than 623 K. The peel strength dramatically decreases due to the thick oxide layer present between the two strip surfaces when the bimetallic strips are roll bonded at excessively high temperatures.     

Electromagnetic field and ac power loss enhancements at the edges of adjacent strips in a superconducting cable

In most flexible superconducting cables the current is carried by a series of strips laid along the length of the cable with small gaps between their edges to accommodate bending. One consequence of dividing the conductor into strips is an enhancement of the electromagnetic fields in the vicinity of the gaps. The ac losses in the superconductor are thereby also enhanced. Data are presented which enable the effects of these field and loss enhancements on cable performance to be assessed. In particular it is found that there is an optimum corner radius for the strips to achieve a minimum increase in loss compared to a smooth tube and that this increase need not be large for a suitably rounded corner. A non-uniform distribution of the strips around the cross-section of the cable can be deleterious while any radial displacements are likely to increase the losses considerably.     

Interaction of free-surface waves with floating flexible strips

The method developed by the author to derive a set of algebaic equations to solve the interaction of free-surface waves with a single floating rigid or flexible two-dimensional platform with small draft is extended to the case that the platform consists of strips with different constant flexural rigidity and mass. The method is based on the application of Green's theorem, with a specific choice of the Green function to arrive at a differential-integral equation along the platform. This equation can be solved exactly by means of superposition of exponential functions, a standard method to solve a set of linear differential equations. After integration with respect to the space coordinate the residue theorem leads to both the dispersion relation along each individual strip and an algebraic equation for the coefficients. Due to very fast convergence with respect to the number of coefficients taken into account the series are truncated. Depending on the water-depth, in each series three to ten terms are taken into account. Results are shown for a structure consisting of several strips that are tightly connected and for disjoint strips. In the latter case the computation of the water level between the strips is also computed. The water level and the reflection and transmission coefficients are not unknowns in the algebraic equation, but are computed afterwards by means of Green's theorem.     

Effects of transverse rumble strips on safety of pedestrian crosswalks on rural roads in China

The primary objective of this study is to evaluate the impacts of transverse rumble strips in reducing crashes and vehicle speeds at pedestrian crosswalks on rural roads in China. Using crash data reported at 366 sites, the research team conducted an observational before-after study using a comparison group and the Empirical Bayesian (EB) method to evaluate the effectiveness of transverse rumble strips in reducing crashes at pedestrian crosswalks. It was found that transverse rumble strips may reduce expected crash frequency at pedestrian crosswalks by 25%. The research team collected more than 15,000 speed observations at 12 sites. The speed data analysis results show that transverse rumble strips significantly reduce vehicle speeds in vicinity of pedestrian crosswalks on rural roads with posted speed limits of 60 km/h and 80 km/h. On average, the mean speed at pedestrian crosswalks declined 9.2 km/h on roads with a speed limit of 60 km/h; and 11.9 km/h on roads with a speed limit of 80 km/h. The 85th percentile speed declined 9.1 km/h on roads with a speed limit of 60 km/h; and 12.0 km/h on roads with a speed limit of 80 km/h. However, the speed reduction impacts were not found to be statistically significant for the pedestrian crosswalk on the road with a speed limit of 40 km/h. The study also looked extensively at the influence area of transverse rumble strips on rural roads. Speed profiles developed in this study show that the influence area of transverse rumble strips is generally less than 0.3 km.     

The impact of perceptual treatments on lateral control: A study using fixed-base and motion-base driving simulators

This research was carried out as part of the French national multidisciplinary research project, PREDIT-SARI. Using a driving simulator, it aimed to test the effectiveness of road treatments intended to inform drivers about the risk of losing control on rural roads with “crest vertical curves” (Landis et al., 2004). [Rosey, F., Auberlet, J.M., Bertrand, J., Plainchault, P., 2008. Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study. Accid. Anal. Prev. 40, 1515-1523, Scopus.] used a fixed-base driving simulator to test four perceptual treatments intended to help drivers maintain lateral control when driving on crest vertical curves and found that two of them, rumble strips on both sides of the centerline and sealed shoulders, were more effective than the others. This first study prompted us to ask if non-visual sensory cues (e.g., vestibular or proprioceptive perceptions) could influence driver perception and consequently lateral control. We therefore conducted a second study on a motion-base driving simulator, using the same virtual 3D database. The results showed that: (1) drivers drive closer to the center of their lane when there are rumble strips on both sides of the centerline, or when there are sealed shoulders, than they do with the current marking system (i.e., continuous lines), and (2) the impact of the two tested perceptual treatments was replicated on both types of driving simulator.     

Effects of temperature and B4C content on the bonding properties of roll-bonded aluminum strips

The presence of ceramic particles between metal strips in metal matrix composite processing by roll bonding affects their bonding properties. In this study, roll bonding of commercial pure aluminum (AA1100) strips in the presence of various B₄C contents at different thickness reductions was focused. Furthermore, the effect of rolling temperature (at ambient temperature and 473 K) on the bonding properties of the strips was investigated via peeling tests. The results showed that the presence of the B₄C particles between the aluminum strips reduces the bond strength and weld efficiency; in contrast, they are increased by increasing temperature. Therefore, by increasing temperature it is possible to use the higher amounts of the B₄C particles between the aluminum strips.     

Impact of perceptual treatments on lateral control during driving on crest vertical curves: a driving simulator study

Approximately 48% of all fatal collisions in Europe are classified as single-vehicle run-off-road or head-on collisions. These crashes relate to trajectory control (road departure) and represent a safety challenge. In France, single-vehicle run-off-road crashes represent 21% of all crashes and head-on collisions represent 11%. This study evaluated the effectiveness of four perceptual treatments (i.e., a painted center line, post-delineators, rumble strips on both sides of the center line and sealed shoulders) in supporting the driver to maintain lateral control; that is, to support the driver to keep in the center of his/her lane. Forty-three participants drove a fixed-base driving simulator, on a simulated straight 3 km rural road with two crest vertical curves (CVC). Four sections were chosen for analysis: a reference section (i.e., the first CVC), a test section (i.e., the second CVC), a pre-test section (i.e., immediately before the second CVC) and a post-test section (i.e., immediately after the second CVC). The results showed that drivers drive more at the center of their lane with the rumble strips on both sides of the center line and with the sealed shoulders than with the actual marking (here center line) or other treatments.