考虑材料参数变化的高强钛管数控弯曲回弹行为研究

目的研究钛管数控弯曲回弹角、回弹半径的变化规律,揭示回弹角和回弹半径变化特征的形成机制。方法基于有限元软件平台,建立考虑收缩应变比-弹性模量变化的Ti-3Al-2.5V钛管数控弯曲成形及回弹全过程的有限元模型。结果回弹角随弯曲角和相对弯曲半径的增加而增加;回弹半径在弯曲角小于30°时,随弯曲角的增加而先变化很小,后显著增加;弯曲角大于30°时,回弹半径随弯曲角的增加而逐渐减小。回弹半径随相对弯曲半径的增加而增加。弯曲角越大,应力分布区域越大,回弹变形越大;相对弯曲半径越大,弯管中处于弹性变形的区域占总变形区域的比例较大,回弹变形越大。结论考虑两参数变化时对回弹角和回弹半径的变化趋势无显著影响,但获得的回弹角和回弹半径均大于忽略两参数变化时的值;考虑收缩应变比-弹性模量变化时,弯曲变形区沿外脊线的拉应力大于忽略两参数变化时的拉应力,卸载回弹时,管材发生大的弹性恢复,表现为回弹角和回弹半径的增加。     

A study on thermomechanical deformation of elastic beam with embedded shape memory alloy wires

The bending deformation of an elastic beam with eccentrically embedded shape memory alloy (SMA) wires under the activation of electrical current has been investigated. A procedure, which accounts for the effect of transient heat transfer and gives rise to the beam bending responding to prescribed input electrical current profile is used for analysis. It is found that influences of ambient temperature, electric current intensity and prestrain of SMA on the bending deformation of beam are significant.     

形状记忆合金(SMA)弹簧驱动器的变形研究

建立了可作为软体机器人中的形状记忆合金(SMA)弹簧驱动器的变形模型,获得了模型的待定参数A1、A2、A3、B1、B2、B3,并对该模型进行了实验验证。首先基于Clausius-Clapeyron方程和泰勒展开式,使用待定参数法建立了SMA弹簧的变形模型,描述了SMA弹簧的变形量、负载和温度之间的非线性关系;然后根据热平衡方程建立了电加热情况下的SMA弹簧温度变化模型,并获得了加热时间与弹簧温度的关系曲线;继而进行了零负载状态下的变形实验,根据实验结果计算出变形模型中的待定参数;最后通过定长通电驱动和定载荷通电驱动实验,验证了模型的正确性。所建模型能够为软体机器人中的SMA弹簧驱动器的控制方案建立提供参考。     

形状记忆合金混杂复合材料弯曲变形的设计

为了预报形状记忆合金混杂复合材料的物理性能与弯曲变形能力,提出了兼顾常规力学性能和主动变形能力的系统的设计方法.以形状记忆合金体积含量为主要设计变量,分析了丝状、带状及板状形状记忆合金埋入复合材料层合板后,这种混杂复合材料力学性能的变化.经过某种特殊加工的板状NiTi合金,不但增大了NiTi合金的体积含量,还增大了形状记忆合金电阻值,以此来提高NiTi合金的响应速度.采用有限元方法进行设计计算及分析,验证了该设计方法的正确性.     

SMA-based smart soft composite structure capable of multiple modes of actuation

This paper introduces the design of a smart soft composite (SSC) actuator capable of multiple modes of actuation. This actuator combines four shape memory alloy (SMA) wires embedded in a soft matrix where one or two SMA wires can be activated to induce the actuator into either the bending mode, the twisting mode or the combined bending and twisting mode of actuation. Experimental results for actuators of different lengths were obtained for all modes of actuation and the actuator is capable of large deformations in all modes and directions of actuation. Then a simple FEA model was used to predict the range of deformation for different lengths in the different modes of actuation. This model is able to predict accurately the bending and twisting angles of the actuator for the different modes of actuation. The 120 mm actuator is capable of deformations up to approximately 160° in both the pure bending and pure twisting modes and of approximately 80° for both twisting and bending in the combined twisting and bending mode of actuation.     

An analytical method for free vibration analysis of Timoshenko beam theory applied to cracked nanobeams using a nonlocal elasticity model

This paper is concerned with the free transverse vibration of cracked nanobeams modeled after Eringen's nonlocal elasticity theory and Timoshenko beam theory. The cracked beam is modeled as two segments connected by a rotational spring located at the cracked section. This model promotes discontinuities in rotational displacement due to bending which is proportional to bending moment transmitted by the cracked section. The governing equations of cracked nanobeams with two symmetric and asymmetric boundary conditions are derived; then these equations are solved analytically based on concerning basic standard trigonometric and hyperbolic functions. Besides, the frequency parameters and the vibration modes of cracked nanobeams for variant crack positions, crack ratio, and small scale effect parameters are calculated. The vibration solutions obtained provide a better representation of the vibration behavior of short, stubby, micro/nanobeams where the effects of small scale, transverse shear deformation and rotary inertia are significant.     

Large bending actuator made with SMA contractile wires: theory,numerical simulation and experiments

In this paper, the modeling, numerical simulation and experimental validation of the deformation of a composite cantilever beam actuated by shape memory alloy (SMA) wires are presented and discussed. The structural model incorporates a number of non-classical features such as laminated construction and anisotropy of constituent material layers, transverse shear deformability, distortion of the normals, and fulfillment of interfacial shear traction continuity requirement. Suitable for use in standard finite element codes, a numerical procedure is developed for solving the geometric non-linearity of the host structure and the hysteretic non-linearity of SMA wires, which is based upon the updated Lagrangian formulation. The application concerns an elastomeric beam with embedded and pre-stressed SMA wires at an offset from the neutral axis, which act as large bending actuators resulting from the thermally induced reversible transformation strains. The experiments and numerical simulation demonstrate the good predictive capability of the model proposed and the powerful role played by SMAs as large bending actuators.     

形状记忆合金丝加固古建筑木结构直榫节点抗震性能研究EI北大核心CSCD

古建筑木结构中的半刚性榫卯节点在地震中往往先于梁柱等构件发生破坏,是加固保护的关键部位。设计了一种新型形状记忆合金(SMA)丝预防性加固装置,对采用该装置的5个直榫节点及1个未加固节点进行了低周反复荷载试验,研究了采用不同根数和不同预拉应变的SMA丝加固节点的破坏形态、弯矩-转角关系、强度退化、刚度退化、耗能性能、自复位能力以及变形能力,并提出了SMA丝加固直榫节点的抗弯承载力计算方法。结果表明:SMA丝加固节点的抗弯承载力均有不同程度的提升,加固节点的最大抗弯承载力为未加固节点的1.49倍;与未加固节点相比,加固节点的强度退化不严重,表明SMA丝可以在节点转角较大时,仍能持续为节点提供抗弯承载力;加固节点最大转动刚度是未加固节点的2.24倍;随着节点转角的增大,未加固节点的耗能能力逐渐减小,而加固节点的耗能能力先增大后减小;在相同的转角下,随着SMA丝根数和预拉应变的增加,节点相对残余变形均减小,自复位能力增强。研究成果可为古建筑木结构榫卯节点的预防性加固保护提供参考。     

基于形状记忆合金的新型消能减震装置抗震性能研究

本文首先通过形状记忆合金的材性试验研究了形状记忆合金的超弹性变形性能,并将其等效拟合为多线性模型,得到其设计参数,并详细介绍了分析计算时所采用的形状记忆合金的本构模型。然后,针对框架结构的变形特点,提出了一种基于形状记忆合金的消能减震装置,即在底层框架柱的反弯点附近设置锚固装置,形状记忆合金索的上端固定在锚固装置上,将其下端锚固在地下,在震时通过其来回反复变形耗散地震能量。然后通过有限元程序对设置形状记忆合金索的新型框架与普通框架进行静力推覆分析和低周反复分析,研究表明新型框架不仅屈服承载力和极限承载力高于普通框架,而且其滞回环更加饱满,累积塑性滞回耗能能力提高了41.4%,形状记忆合金索的滞回环也很饱满,具有优良的耗能能力,最后,还比较了对角设置形状记忆合金索的框架的耗能能力与本消能减震装置的耗能能力。因此该消能减震装置在减轻框架柱震害方面具有一定的工程应用价值和前景。     

平板颤振导数的参数弹性研究

提出了颤振导数的“参数弹性”概念;基于复模态理论,计算了平板颤振导数的平板宽度、质量、质量惯矩、竖弯频率、扭转频率和空气密度6种参数弹性;绘制了8个颤振导数的参数弹性曲线和诺模图,分析了各自特点,获得了无量纲参数对颤振导数参数弹性的影响规律。分析结果表明,新提出的参数弹性具有概念无量纲、简洁、直观、实用特点,为颤振导数参数分析提供了一种新的有效途径。     

A theoretical model for the bending of a laminated beam with SMA fiber embedded layer

A theoretical model for the bending of a laminated beam bonded with shape memory alloy (SMA) fiber reinforced layer is presented. The constitutive relations of the SMA layer are obtained by using the method of micromechanics. The bending of the laminated beam is then discussed, and the relationship between bending moment, curvature and temperature are provided. The governing relationships obtained in this paper can be used for theoretical predications of thermomechanical properties of beam-like SMA actuators.     

Adaptive finite element analysis of geometrically non-linear plates and shells,especially buckling

Based on both moderate and finite rotation bending theories of thin elastic shells including shear deformation, adaptive non-linear static finite element analysis is treated within a displacement approach and h-adaptivity. The a posteriori error indicator given by Rheinboldt, gained by linearization, is investigated in order to decide whether the deformations influence the indicator explicitely and how parameter dependent problems (like the Reissner–Mindlin model) behave in the process of adaptation. In order to achieve overall consistency, dimensional adaptivity (to 3-D elasticity) is implemented within disturbed subdomains, especially at supports. Results are that Rheinboldt's error indicator is valid under certain restrictions but not directly at bifurcation points and that robustness is not improved by adaptation. Nested quadrilateral finite elements are used for studying pre- and post-buckling states of plates and shells.     

A nonlocal higher-order curved beam finite model including thickness stretching effect for bending analysis of curved nanobeams

In the present work, a finite element approach is developed for the static analysis of curved nanobeams using nonlocal elasticity beam theory based on Eringen formulation coupled with a higher-order shear deformation accounting for through-thickness stretching. The formulation is general in the sense that it can be used to compare the influence of different structural theories, through static and dynamic analyses of curved nanobeams. The governing equations derived here are solved introducing a 3-nodes beam element. The formulation is validated considering problems for which solutions are available. A comparative study is done here by different theories obtained through the formulation. The effects of various structural parameters such as thickness ratio, beam length, rise of the curved beam, loadings, boundary conditions, and nonlocal scale parameter are brought out on the static bending behaviors of curved nanobeams.     

新型自复位黏弹性阻尼支撑力学性能研究

提出了一种新型的自复位黏弹性阻尼支撑(self-centering viscoelastic damping brace,SCVEDB),该支撑利用形状记忆合金的拉伸变形和黏弹性材料的剪切变形共同耗散能量,同时利用形状记忆合金的超弹性特性复位。设计和加工了SCVEDB最基本的模型,对该支撑试件进行了循环往复荷载作用下的力学性能试验,研究了位移幅值、加载速率、SMA丝数量、黏弹性材料的厚度对其性能的影响,同时通过割线刚度、耗散能量、等效阻尼比、自复位比4个参数量化分析了SCVEDB的力学性能。对SMA丝进行了循环拉伸试验,利用OpenSees平台建立了SMA的材料本构数值模型,然后将其与模拟黏弹性材料的Bouc-Wen模型并联,建立了该支撑的力学模型,进而模拟了支撑的力学性能,数值模拟结果与试验结果吻合较好。     

On the harmonic response of plates with the shear deformation effect using the elastodynamic solution in the boundary element method

The harmonic response of plates is studied by using the frequency domain solution in conjunction with the direct boundary integral equation (DBIE) for Mindlin's model. The shear deformation and rotatory inertia effects in that model can be switched off in the presented formulation and a DBIE for the classical bending model is then obtained, which includes an additional degree of freedom for the tangential boundary rotation. The frequency responses were obtained to map the plate behavior and they were calculated both with and without the effects of the shear deformation and the rotatory inertia. The analyses were finished when the first natural frequency was identified. The results were compared to available solutions in the literature, employing three-dimensional elasticity theory, the Mindlin and the classical bending models.     

A Size-Dependent Functionally Graded Higher Order Plate Analysis Based on Modified Couple Stress Theory and Moving Kriging Meshfree Method

A size-dependent computational approach for bending, free vibration and buckling analyses of isotropic and sandwich functionally graded (FG) microplates is in this study presented. We consider both shear deformation and small scale effects through the generalized higher order shear deformation theory and modified couple stress theory (MCST). The present model only retains a single material length scale parameter for capturing properly size effects. A rule of mixture is used to model material properties varying through the thickness of plates. The principle of virtual work is used to derive the discrete system equations which are approximated by moving Kriging interpolation (MKI) meshfree method. Numerical examples consider the inclusions of geometrical parameters, volume fraction, boundary conditions and material length scale parameter. Reliability and effectiveness of the present method are confirmed through numerical results.     

Mechanical Behavior of a Functionally Graded Rectangular Plate Under Transverse Load: A Cosserat Elasticity Analysis

In this article, a static analysis of a functionally graded (FG) rectangular plate subjected to a uniformly distributed load is investigated within the framework of Timoshenko and the higher order shear deformation beam theories. The mechanical behavior of the plate is analysed under the theory of Cosserat elasticity. In the framework of infinitesimal theory of elasticity, the bending of the plate is analyzed subjected to transverse loading. A set of governing equations of equilibrium are obtained based on the method of hypothesis. A semianalytical solution is presented for the governing equations using the approximation theory of Timoshenko. The solutions are validated by comparing the numerical results with their counterparts reported in the literature for classical Timoshenko plate theory.     

Mean‐strain eight‐node hexahedron with optimized energy‐sampling stabilization for large‐strain deformation

A method for stabilizing the mean‐strain hexahedron for applications to anisotropic elasticity was described by Krysl (2015). The technique relied on a sampling of the stabilization energy using the mean‐strain quadrature and the full Gaussian integration rule. This combination was shown to guarantee consistency and stability. The stabilization energy was expressed in terms of input parameters of the real material, and the value of the stabilization parameter was fixed in a quasi‐optimal manner by linking the stabilization to the bending behavior of the hexahedral element (Krysl, submitted). Here, the formulation is extended to large‐strain hyperelasticity (as an example, the formulation allows for inelastic behavior to be modeled). The stabilization energy is expressed through a stored‐energy function, and contact with input parameters in the small‐strain regime is made. As for small‐strain elasticity, the stabilization parameter is determined to optimize bending performance. The accuracy and convergence characteristics of the present formulations for both solid and thin‐walled structures (shells) compare favorably with the capabilities of mean‐strain and other high‐performance hexahedral elements described in the open literature and also with a number of successful shell elements. Copyright © 2015 John Wiley & Sons, Ltd.     

环境介质对形状记忆合金弹簧记忆回复效应的影响*

针对SAM电火花加工机器人加工时常用的3种工作介质水、煤油和乳化液，研究了SMA弹簧的记忆恢复变形特性和变形规律。结果表明，对应不同的环境介质，SMA弹簧的记忆回复变形量与驱动电流间存在一一对应关系，通过控制驱动电流可控制记忆回复变形量。在不同环境介质中SMA弹簧的记忆回复变形速度的变化趋势是一致的，都是先随着回复位移的增加而增加，在接近中间段时达到最大，然后随着位移的增加而减小。驱动电流是对SMA弹簧动态变形速度影响最 明显的参数，通过选择合适的驱动电流可有效地控制SMA弹簧的回复变形速度。     

Hygrothermal deformation of orthotropic nanoplates based on the state-space concept

This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied.