直角切口柔性平行四杆机构的输出位移分析

柔性铰链是目前被广泛用于微动机器人的主要部件之一.为了深入分析精密传动用柔性平行四杆机构的位移性能,利用材料力学弯曲变形理论的挠曲线近似微分方程,建立了计算直角切口柔性平行四杆机构输出位移的数学模型.设计了一个简单的柔性平行四杆机构模型,采用MATLAB 7.0软件对其进行理论计算,并利用商用软件ANSYS 10.0进行有限元分析.采用线切割的方法加工了一个样件,并进行了相关实验.最终结果表明：数学模型的理论值与有限元仿真值很接近,但与实际样件的实验值有一定的误差.通过误差分析,证实了存在这种误差的合理性,从而验证了所建数学模型具有较高的参考价值,可以作为柔性铰链平行四杆机构行程优化设计的指导理论.     

Failure analysis and performance comparison of Triple-LET and LET flexure hinges

A new type of flexure hinge named the Triple Lamina Emergent Torsional (Triple-LET) was proposed in this paper. Its 3D structure was designed, and its equivalent bending stiffness was also derived. Based on the equivalent formula and the finite element simulation analysis, the equivalent bending stiffness of the Triple-LET and the LET flexure hinge with the same overall dimensions were analyzed and compared. It was concluded that under the same torque, the Triple-LET flexure hinge can realize larger deformation than the LET flexure hinge. Thus, the proposed new flexure hinge is presented as a compliant joint suitable for applications where large angular rotation is desired. Failure analyses of the Triple-LET and the LET flexure hinges were also carried out, respectively. The analysis results show that the Triple-LET flexure hinge made of polypropylene can reach 180° with no plastic deformation, while the LET flexure hinge with the same overall dimensions will plastically deform once the bending angle is greater than 161.4°. The results also indicate that the range of bending angles of the Triple-LET flexure hinge made of beryllium bronze is from 0° to 128.2°, which is two times larger than that of the LET flexure hinge.     

Web-bonded FRPs for relocation of plastic hinges away from the column face in exterior RC joints

In an RC building subjected to lateral loads, the beam–column joints constitute one of the critical regions. In existing frames, which were not adequately designed, a practical way of controlling plastic hinging and implement the strong-column weak-beam concept is through the use of a web-bonded FRP retrofitting system. This paper presents the results of an experimental and numerical study carried out in order to evaluate the ability of CFRP sheets in preventing the plastic hinge formation at the face of the column in exterior RC joints. Seven scaled-down RC exterior joints of a typical Ordinary Moment Resisting Frame are tested under moderately monotonic/cyclic loads. Two specimens are used as control while the other five are CFRP-strengthened/repaired of different lengths and thicknesses. The results show that carbon fibre sheets can effectively relocate the plastic hinge away from the face of the column. Non-linear numerical results using ANSYS are also presented and discussed.     

Key features of wave energy

For a weak point source or dipole, or a small body operating as either, we show that the power from a wave energy converter (WEC) is the product of the particle velocity in the waves, and the wave force (suitably defined). There is a thus a strong analogy with a wind or tidal turbine, where the power is the product of the fluid velocity through the turbine, and the force on it. As a first approximation, the cost of a structure is controlled by the force it has to carry, which governs its strength, and the distance it has to be carried, which governs its size. Thus, WECs are at a disadvantage compared with wind and tidal turbines because the fluid velocities are lower, and hence the forces are higher. On the other hand, the distances involved are lower. As with turbines, the implication is also that a WEC must make the most of its force-carrying ability-ideally, to carry its maximum force all the time, the '100% sweating WEC'. It must be able to limit the wave force on it in larger waves, ultimately becoming near-transparent to them in the survival condition-just like a turbine in extreme conditions, which can stop and feather its blades. A turbine of any force rating can achieve its maximum force in low wind speeds, if its diameter is sufficiently large. This is not possible with a simple monopole or dipole WEC, however, because of the 'nλ/2π' capture width limits. To achieve reasonable 'sweating' in typical wave climates, the force is limited to about 1?MN for a monopole device, or 2?MN for a dipole. The conclusion is that the future of wave energy is in devices that are not simple monopoles or dipoles, but multi-body devices or other shapes equivalent to arrays.     

Investigation of the mechanical properties of friction-welded joints between AISI 304L and AISI 4340 steel as a function rotational speed

In this study, standard AISI 304L austenitic stainless steel and AISI 4340 steel couple were welded by friction welding process using five different rotational speeds. The joining performances of AISI 304L/AISI 4340 friction-welded joints were studied and the influences of rotational speed on the microstructure and mechanical properties of the welded joints were also estimated. The microstructural properties of heat affected zone (HAZ) were examined by scanning electron microscopy (SEM). The microhardness across the interface perpendicular to the interface was measured and the strength of the joints was determined with tensile tests. The experimental results indicate that the tensile strength of friction-welded 304L/4340 components were markedly affected by joining rotational speed selected.     

The flexure and torsion of bones viewed as anisotropic poroelastic bodies

Two-phase poroelastic material is taken as a model of the bone, in the sense that the osseous tissue is considered as a perfectly elastic solid and the fluid substances filling the cavities as a viscous compressible fluid. Biot's theory of consolidation is adopted, assuming interconnections between the cavities. For a transversely isotropic body the theory leads to seven linear constitutive equations, connecting seven stress components with seven deformation components, by means of eight material coefficients. The theory is applied to beam-like structural elements by using the procedure of Michell, consisting of representation of stress and deformation components as rational integral functions of the axial coordinate z.

General equations are derived for two particular cases; (a) when the stress and strain components do not depend on z, (b) when the latter are linear functions of z. The first case corresponds to the action of terminal couples (both flexural and torsional); the second case is associated with the action of terminal forces.

Illustrative examples are solved, involving (a) cylindrical bending of poroelastic plates by terminal couples, (b) pure bending of poroelastic beams of arbitrary cross section having one axis of symmetry, (c) pure torsion of poroelastic beams of arbitrary cross section.

The explicit solution of the case (b) shows that the behavior of the poroelastic material is analogous to that of a three-element visco-elastic model. This agrees qualitatively with the experimental findings of Sedlin for bones.     

Distinctive features of sulfide cracking of welded joints of pipe steel

We present the results of investigations aimed at the determination of susceptibility of welded joints in low-alloy 14GB pipe steel to sulfide cracking in the presence of technological defects. We established that these joints exhibit no susceptibility to cracking at stresses below −0.5σ_0.2 for the base metal, and thatK _Iscc in the NACE solution is equal to 28MPa√m. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6, pp. 104–106, November–December, 1996.     

Thermal effect on DWCNTs as rotational bearings

We have investigated the rotational motion and dynamic friction in a molecular bearing composed of double-walled carbon nanotubes (DWCNTs) using molecular dynamics simulations. The main study was on thermal effects due to the rotational friction. The diameters of the bearings varied between 6?and 16???for the inner shafts, and between 12?and 20???for the outer sleeves. The rotation velocity varied from 0.05?rotations?ps(-1) to 0.25?rotations?ps(-1). The simulations show that the energy dissipation, and hence the temperature of the system, increases linearly with rotation time. The value of energy dissipation is around 0.59?meV/atom per rotation at ω = 0.05?rotations?ps(-1) for a (15, 0)@(23, 0) bearing. Correspondingly, the average friction force is around 1.75 × 10(-5)?nN/atom. The dependence of the energy dissipation on the rotation velocity, the interwall distance, and the contact area of the DWCNT is also discussed. It was observed that the energy dissipation becomes lowest when the interwall distance of the DWCNT bearing reaches about 0.34?nm, the equilibrium distance of the Lennard-Jones (L-J) potential. This low energy dissipation suggests that the DWCNT can be a good candidate for a wearless rotational bearing, which supports the previous studies.     

Key features of the KSTAR helium refrigeration system

KSTAR is a fully superconducting (SC) tokamak consisting of 30 magnet coils made of Nb₃Sn and NbTi. To keep the SC magnets at proper operating conditions, all cold components of KSTAR such as the SC bus-lines, current leads, and thermal shields must be maintained at the respective cryogenic temperatures by using a helium refrigeration system (HRS). The main components of the HRS can be classified into the warm compression system (WCS) and the cryogenic systems according to their operating temperature levels. The HRS had been manufactured, installed and commissioned until March 2008 and has been operated for KSTAR campaign since then. In this paper, the result of the commissioning, operation and reliability record of the KSTAR HRS will be presented.     

Recognition of interacting rotational and prismatic machining features from 3-D mill-turn parts

Current feature recognition methods generally recognize and classify machining features into two classes: rotational features and prismatic features. Based on the different characteristics of geometric shapes and machining methods, rotational features and prismatic features are recognized using different methods. Typically, rotational features are recognized using two-dimensional (2-D) edge and profile patterns. Prismatic features are recognized using 3-D geometric characteristics, for example, patterns in solid models such as 3-D face adjacency relationships. However, the current existing feature recognition methods cannot be applied directly to a class of so-called mill-turn parts where interactions between rotational and prismatic features exist. This paper extends the feature recognition domain to include this class of parts with interacting rotational and prismatic features. A new approach, called the machining volume generation method, is developed. The feature volumes are generated by sweeping boundary faces along a direction determined by the type of machining operation. Different types of machining features can be recognized by generating different forms of machining volumes using various machining operations. The generated machining volumes are then classified using face adjacency relationships of the bounding faces. The algorithms are executed in four steps, classification of faces, determining machining zones, generation of rotational machining volumes and prismatic machining volumes, and classification of features. The algorithms are implemented using the 3-D boundary representation data modelled on the ACIS solid modeller. Example parts are used to demonstrate the developed feature recognition method.     

Microstructural features of dissimilar MMC/AISI 304 stainless steel friction joints

The microstructure and mechanical properties of dissimilar friction joints between aluminium-based MMC and AISI 304 stainless steel base materials were investigated. The microstructural features which occur in the stainless steel substrate comprise deformation twinning, formation of a fine-grained dislocation substructure in austenite, and plastic deformation. The stainless steel substrate was plastically deformed in the region close to the mid-radius of the dissimilar joint. In a similar manner, 5–10 m thick transition layers, comprising regions of locally plasticized MMC-base material, were formed close to the mid-radius location in dissimilar joints. The interlayer formed at the dissimilar joint interface comprised a mixture of oxide (Fe(Al,Cr)₂O₄ or FeO(Al,Cr)₂O₃) and FeAl₃ intermetallic phases. The notch tensile strength of dissimilar MMC/AISI 304 stainless steel joints increased when the rotational speed increased from 500 r.p.m. to 1000 r.p.m., and at higher rotation speeds, there was no effect on notch tensile strength properties.     

计及金属铰链的环形可展天线热-结构分析

空间热环境对环形可展天线在轨服役稳定性的影响很大，时刻变化着的热环境会造成天线温度的剧烈波动，从而导致天线结构的热变形，使得天线的形面精度恶化，影响天线电信号的传输甚至导致天线失效，因此有必要对天线进行热-结构分析。以环形可展天线为研究对象，考虑天线在轨服务环境中的各类因素（包括空间真空、空间低温、微重力和空间热源等），基于斯忒藩-玻尔兹曼定律和傅里叶热传导理论，利用有限元软件建立计及金属铰链的环形可展天线的热辐射-热传导分析模型，研究了环形可展天线的非均匀温度场；基于弹性热力学理论及有限元理论，建立计及与不计及金属铰链的环形可展天线的热变形分析模型，研究了非均匀温度场对环形可展天线形面精度和张力比的影响规律。研究结果表明：相较于不计及金属铰链的环形可展天线，计及金属铰链的环形可展天线的形面精度和张力比均发生恶化，其中形面精度变化值已达到毫米级。研究结果对同类型环形可展天线的热-结构分析有重要的借鉴意义，可为天线的结构设计提供参考。     

Predicting failure in non-continuous weld seams when used in joints under torsion loading

This paper compares different techniques for determining the safe strength of fillet welded lap joints under eccentric shear loading and assesses the benefit of having a torsionally closed, continuous fillet weld seam in preference to a torsionally open joint. The validity of generally using analysis based on simple torsion theory, as widely proposed in numerous design texts, is questioned and the alternative of using tubular, thin walled section and thin rectangular member torsion theory is investigated. The accuracies of the various torsional analytical techniques as applied to analysing torsionally open and closed section weld seams are compared with those given by a finite element analysis.     

An efficient design method for multi-material bolted joints used in the railway industry

A methodology to design and analyze multi-material bolted joints in hybrid train structures is presented. This methodology enables the prediction of the response of a multi-material bolted joint in a short amount of time and it is suitable to be used for large structures, where the number of bolts can be very high. The method developed is applied to a real industrial case which consists on the connection between the roof and the side of a carbody shell train structure. Experimental tests are performed on a full-size sub-component. The comparison between the experimental data and the numerical results confirms the accuracy of the method.     

Special features of the formation of the diffusion bonded joints between copper and aluminium

A metallographic study of diffusion bonds between aluminium and copper has been made in order to further understanding of the mechanism of bond formation for joints between dissimilar metals that form intermediate phases or intermetallic compounds. A three-stage mechanistic model based upon sintering principles has been proposed to explain this kind of diffusion joint.     

Plastic analysis of HSC beams in flexure

This article presents an experimental study on the plastic behaviour of HSC beams in bending. Nineteen isostatic beams were tested up to failure. The loading consisted of two symmetrical concentrated forces applied approximately at thirds of the span of the beams. The main purpose of the analysis is to characterize the plastic rotation capacity in the beams’ failure section with an experimental parameter. Bearing this in mind, a global plastic analysis of the tested beams is presented. The main variables of this study are the longitudinal tensile reinforcement ratio and the compressive strength of the concrete. The results obtained here are completed with others presented before and the whole set of results is analysed and discussed. The plastic rotation capacity of the tested beams are analysed with the rules of some codes of practice. Finally, a summary of the main conclusions is presented.

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Résumé  Ce travail décrit une etude expérimentale sur la capacité de rotation plastique de poutres en béton à haute résistance soumises à la flexion. Dix-neuf poutres isostatiques ont été testées jusqu′à la rupture avec une charge constituée par deux forces concentrées et symétriques situées environ au tiers et aux deux tiers de la portée. L′objectif principal de l′analyse est de caractériser la capacité de rotation plastique de la section de rupture avec un paramètre de la tendance plastique. Pour ceci, une analyse plastique globale des poutres testées est présentée. La résistance du béton et le taux d′armatures longitudinales de traction constituent les variables principals de cette étude. Les résultats sont complétés avec ceux d′études précédentes et sont analysés et comparés. La capacité de rotation plastique des poutres est analysée faces aux règles de quelques codes importants aussi bien faces à certaines recommendations publiées. Finallement, un sommaire des principales conclusions est présenté.