Analytical solution for functionally graded anisotropic cantilever beam under thermal and uniformly distributed load

The bending problem of a functionally graded anisotropic cantilever beam subjected to thermal and uniformly dis-tributed load is investigated,with material parameters being arbitrary functions of the thickness coordinate. The heat conduction problem is treated as a 1D problem through the thickness. Based on the elementary formulations for plane stress problem,the stress function is assumed to be in the form of polynomial of the longitudinal coordinate variable,from which the stresses can be derived. The stress function is then determined completely with the compatibility equation and boundary conditions. A practical example is presented to show the application of the method.

Measurement of length-scale and solution of cantilever beam in couple stress elasto-plasticity

Owing to the absence of proper analytical solution of cantilever beams for couple stress/strain gradient elasto-plastic theory, experimental studies of the cantilever beam in the micro-scale are not suitable for the determination of material length-scale. Based on the couple stress elasto-plasticity, an analytical solution of thin cantilever beams is firstly presented, and the solution can be regarded as an extension of the elastic and rigid-plastic solutions of pure bending beam. A comparison with numerical results shows that the current analytical solution is reliable for the case of σ0 〈〈 H 〈〈 E, where σ0 is the initial yield strength, H is the hardening modulus and E is the elastic modulus. Fortunately, the above mentioned condition can be satisfied for many metal materials, and thus the solution can be used to determine the material length-scale of micro-structures in conjunction with the experiment of cantilever beams in the micro-scale.

ACTIVE VIBRATION CONTROL OF A CANTILEVER BEAM USING PIEZOELECTRIC SENSORS AND ACTUATORS

The topic of vibration control with distributed actuators has been the subject of many researches. This paper is concerned with the vibration control of a cantilever beam equipped with piezoelectric ceramics as sensors and actuators. One piezoelectric ceramic is bonded to the structure and provides control input for the structure, while the other piezoelectric ceramic provides the feedback signal. An approach to identification and control is presented. Observation spillover is eliminated by prefiltering the sensor data. A procedure used to determine actuator and sensor location, is discussed based on the modes to be controlled. Finally, the experimental results are presented to verify the proposed method.

Analytical solutions for plane problem of functionally graded magnetoelectric cantilever beam

In this paper, an exact analytical solution is presented for a transversely isotropic functionally graded magnetomelectro-elastic （FGMEE） cantilever beam, which is subjected to a uniform load on its upper surface, as well as the concentrated force and moment at the free end. This solution can be applied for any form of gradient distribution. For the basic equations of plane problem, all the partial differential equations governing the stress field, electric, and magnetic potentials are derived. Then, the expressions of Airy stress, electric, and magnetic potential functions are assumed as quadratic polynomials of the longitudinal coordinate. Based on all the boundary conditions, the exact expressions of the three functions can be determined. As numerical examples, the material parameters are set as exponential and linear distributions in the thickness direction. The effects of the material parameters on the mechanical, electric, and magnetic fields of the cantilever beam are analyzed in detail.

Effects of Adhesive Characteristic on the Test Results of Damping Material's DMP

In the measurement of damping material's dynamic mechanical performance(DMP) using flexural resonating cantilever beam method,the specimen's adhesive characteristic influences the test precision and accuracy. Taking its effect into account,the improved measurement equations based on the resonance method are presented. The simulated results show that,for the sake of weakening the adhesive's influence on the measured results,the adhesive should be spreaded as thin as possible when specimen is prepared,the adhesive's density and loss factor should be selected as small as possible also,and its Young's modulus should be selected according to the damping material being measured;the same adhesion condition effects differently on the test results of different damping materials,i.e. the error due to the adhesive is more inconspicuous if the damping layer has bigger thickness,modulus,loss factor and a certain density according to the damping material being measured. These conclusions provide theoretical basis for selecting adhesive,improving adhesion technology,and designing specimen.

VIBRATION SUPPRESSION OF CANTILEVER LAMINATED COMPOSITE PLATE WITH NONLINEAR GIANT MAGNETOSTRICTIVE MATERIAL LAYERS

In this paper, a nonlinear and coupled constitutive model for giant magnetostrictive materials （GMM） is employed to predict the active vibration suppression process of cantilever laminated composite plate with GMM layers. The nonlinear and coupled constitutive model has great advantages in demonstrating the inherent and complicated nonlinearities of GMM in re- sponse to applied magnetic field under variable bias conditions （pre-stress and bias magnetic field）. The Hamilton principle is used to derive the nonlinear and coupled governing differential equation for a cantilever laminated composite plate with GMM layers. The derived equation is handled by the finite element method （FEM） in space domain, and solved with Newmark method and an iteration process in time domain. The numerical simulation results indicate that the proposed active control system by embedding GMM layers in cantilever laminated composite plate can efficiently suppress vibrations under variable bias conditions. The effects of embedded placement of GMM layers and control gain on vibration suppression are discussed respectively in detail.

表面效应对热-机多孔悬臂纳米梁力学性能的影响

表面效应对纳米结构的力学性能有重要影响。飞机上很多微纳尺度的结构可简化为悬臂梁。本工作分析表面效应对随从载荷作用下梯度多孔材料纳米悬臂梁在高温环境下非线性力学响应的影响。基于GurtinMurdoch表面弹性理论和非线性梁理论,建立梯度多孔材料梁在随从载荷以及温度场中的非线性控制微分方程。假定梯度多孔材料的性能在整个厚度范围内连续变化,且沿厚度呈两种余弦形式的非均匀孔隙率分布模式。采用打靶法求解梯度多孔材料悬臂纳米梁在热-随从载荷下的非线性力学响应。获得各种孔隙率系数和不同非均匀升温下悬臂纳米梁非线性力学响应的数值解,详细讨论材料表面弹性常数和表面应力对纳米悬臂梁力学响应的影响。结果表明:不同孔隙率系数和不同非均匀升温下梁的力学行为是不同的;纳米梁表现出十分显著的表面效应。

薄膜材料弯曲测试方法的验证研究

在国家标准《微机电系统(MEMS)技术薄膜材料的弯曲试验方法》制定阶段,为验证该标准中测试方法的准确性和实用性,设计并制备了4种尺寸的悬臂梁结构,并利用纳米力学测试系统记录其弯曲形变过程,获取了待测结构的形变-应力曲线。通过该标准可实现薄膜材料弯曲力学性能的有效表征。对弯曲试验的测量数据进行分析,实验结果表明,基于该测试方法10次的重复性达到0.32%,同类型的测试结构具有较强的规律性,靠近悬臂梁根部的测试点表现出更高的机械刚度,与理论预测完全一致。因此,该标准中所采用的弯曲测试方法可重复性好,可用于薄膜材料的弯曲力学性能测试。

三维有限元方法分析“All-on-4”技术的生物力学特征

背景:随着无牙颌修复需求增加,“All-on-4”技术被广泛应用。种植体与天然牙的载荷传递方式不同,三维有限元分析可研究功能载荷作用下种植体及周围骨组织的应力分布,并在此基础上为寻找适合的种植体材料、优化种植体的几何结构、设计临床手术方案提供了研究方法。目的:对三维有限元分析法在“All-on-4”技术方面的相关研究作一综述。方法:检索中国知网和PubMed数据库2003-2023年相关文献,英文检索词为“Finite Element Method,All-on-4,edentulous,Biomechanics”,中文检索词为“有限元,All-on-4,无牙颌,生物力学”,根据纳入排除标准筛选符合标准的文献,最终纳入65篇文献进行综述。结果与结论:①对水平骨量不足的情况,研究者们可以选择应用窄直径种植体,但需要注意悬臂的存在对应力分布的影响,降低失败的风险。②“All-on-4”概念通过倾斜远中种植体的方法,减少骨的应力分布,但在不同的颌骨类型中,远中种植体倾斜的理想角度还需要进一步的研究。③悬臂的存在会增加种植失败的风险,将悬臂长度/AP距(CL/AP)的比值控制在0.9时,有助于减少机械并发症的发生。④用弹性模量较低的材料制作支架时,支架自身的应力较小,但会增加种植体、中央螺丝、基台及种植体周围骨组织的应力,相反使用弹性模量较大的材料,会降低修复体组件和种植体周围骨组织的应力,但支架本身的应力较高。⑤“All-on-4”概念可以实现较好的力学平衡,但需结合患者自身的具体情况制定一个长期有效的治疗方案。⑥合理的咬合设计是影响种植治疗成功的关键,尖牙引导牙合和组牙功能牙合在修复体的寿命方面无差异。然而,影响咬合设计的原因有很多,未来还需要进一步的体外实验以及大量临床研究来探索“All-on-4”理想的咬合设计。

非金属复合材料接触网腕臂应用性能研究

接触网腕臂装置简化结构,提升绝缘等级,降低重量是发展的趋势。非金属复合材料具有重量轻、强度高、绝缘性能好的特点,通过与传统金属材料进行机械、电气方面的性能对比,探究非金属增强复合材料应用于接触网腕臂装置的显著效果。研究非金属增强复合材料腕臂装置结构型式和复杂成型工艺,并利用有限元仿真进行模拟分析优化提升;深入对比分析不同结构和材质的腕臂装置,系统总结应用特点,提出非金属增强复合材料用于接触网腕臂的适用性。

煤矿悬臂式掘进机可靠性技术研究设计

悬臂式掘进机是煤矿掘进工作面使用工况最恶劣、负载情况最复杂的设备,其可靠性制约着高截割性和高智能性的发挥,对煤矿快速掘进、使用成本以及安全生产有着重要的影响,在分析掘进机可靠性影响因素、可靠性故障规律及可靠性设计难点的基础上,从可靠性设计、可靠性材料、可靠性运维3个方面提高掘进机产品的可靠性。可靠性设计、可靠性材料、可靠性运维等方面的改进优化有助于快速提升掘进机产品的可靠性,为煤矿快速掘进向自动化、智能化及无人化方向发展提供可靠的技术保障。

复合材料圆柱壳体的层间断裂韧性分析

针对复合材料圆筒的层间性能分析,通过双悬臂梁试验(Double Cantilever Beam,DCB),得到了复合材料I型层间开裂与载荷对应关系,并根据GIC计算公式得到了材料I型断裂韧性。通过三点弯试验(EndNotched Flexure,ENF),计算了材料II型断裂韧性。建立了有限元模型,将I型断裂韧性、II型断裂韧性代入材料本构模型参数,对该结构层间性能设计与评估提出理论指导。

基于铝合金腕臂自动预配的腕臂管废料减省方法研究

铝合金以其机械强度高、防腐性能强的特点成为我国高速铁路接触网腕臂的优选材质。传统的腕臂管分选主要由人工完成,工作效率低,劳动强度高,科学的腕臂管分选有利于资源合理分配,降低废料率,提高经济效益。本文结合我国高速铁路发展现状,总结接触网铝合金腕臂预配的特点,分析现阶段铝合金腕臂预配中腕臂管的废料率,研究腕臂自动化预配过程中原料管减省方法,并通过实践验证腕臂管优选算法的优势,为接触网腕臂预配材料减省提供一种解决方案,助力降低轨道交通建设成本。

接触网绝缘腕臂电气性能研究及优化

为提高接触网腕臂的绝缘性能,简化结构设计,减少检修维护工作量,开展绝缘材料在接触网腕臂上的应用尤为重要。通过分析绝缘材料腕臂的试验结果,论证了绝缘材料应用于接触网腕臂的可行性及优势;结合腕臂电场分布特性的仿真研究,并考虑实际服役环境,优化了腕臂的结构设计,降低了绝缘失效风险。研究结果为绝缘材料在特殊环境下电气化铁路接触网腕臂的应用奠定了基础。

压电智能柔性梁振动主动控制研究

利用压电陶瓷作为作动器 ,对柔性悬臂梁进行了振动主动控制研究 .分析了压电结构振动主动控制的原理和方法 .采用独立模态控制法对柔性悬臂梁的前两阶模态实施主动控制 .实验结果表明 ,通过振动主动控制明显增加了柔性悬臂梁的结构阻尼 ,取得了十分有效的振动抑制效果 .

材料阻尼测试方法研究

采用基础激励下的共振驻留法,研究了用双悬臂梁试件测试材料阻尼的原理方法和实施途径,通过数值仿真计算分析了双悬臂梁试件两臂的不平衡程度对阻尼测试精度的影响,提出了用双悬臂梁试件测试材料阻尼时提高测试精度的方法。

基于TMS320F2812的悬臂梁振动半主动控制

基于压电元件的主动振动控制不仅需要复杂的信号处理系统,而且需要庞大的能量供给系统;被动控制中电感和电阻参数对环境变化适应能力差,而且低频控制时需要很大的电感,不容易实现。为了克服主被动控制存在的缺点,提出了一种基于同步开关阻尼技术的半主动振动控制的新方法。利用TMS320F2812处理器,通过合理的开关控制算法,使埋入复合材料悬臂梁约束端的压电元件上的电压极性在适当的时候进行翻转,使其电压始终与应变反相,从而达到振动控制的效果。实验结果表明,该方法可以使悬臂梁一阶振动模态减小3.164 1 dB。

原子力显微镜用于微尺度材料力学性能表征的研究进展

原子力显微镜(AFM)是纳米科学研究的有力工具。从AFM的原理出发,分析了探针与样品之间作用力的计算过程,介绍了确定悬臂弹性常数的几种方法,并综述了AFM在生物材料、薄膜材料、纳米结构、单分子操作和纳米力学实验中的研究进展。

功能梯度悬臂梁弯曲问题的解析解

将功能梯度悬臂梁作为平面应力问题处理.根据正交各向异性弹性体的基本方程,引入应力函数,假设所有材料常数沿厚度方向按同一函数规律变化,采用弹性力学半逆解法,求得功能梯度悬臂梁在端部集中力和力矩作用下的解析解.所得到的解,对任意梯度函数均成立,且退化到各向同性均匀弹性情况下的结果,与已有的理论解相一致.对弹性模量分别按指数函数和幂函数梯度变化的算例进行了分析,结果显示功能梯度梁的轴向位移仍近似直线变化.

梯度功能压电悬臂梁的几个解析解

研究了密度梯度功能压电悬臂梁在轴向和横向均布荷载以及外加直流电压分别作用下的解析解。首先求得了悬臂梁在体积力呈非线性变化时相应问题的应力函数 φ和电位移函数 Ψ,进而求得梁中弹性场和电场的解析解。作为特例 ,同时还得到了常体力和无体力情况下悬臂梁的解答 ,并进行了讨论。