Electric admittance analysis of quartz crystal resonator in thickness-shear mode induced by array of surface viscoelastic micro-beams

The electric admittance of a compound system composed of a thickness-shear mode （TSM） quartz crystal resonator （QCR） and an array of surface viscoelastic micro-beams （MBs） is studied. The governing equations of the MBs are derived from the Timoshenko-beam theory in consideration of shear deformation. The electrical admittance is described directly in terms of the physical properties of the surface epoxy resin （SU-8） MBs from an electrically forced vibration analysis. It is found that both the inertia effect and the constraint effect of the MBs produce competitive influence on the resonant frequency and admittance of the compound QCR system. By further comparing the numerical results calculated from the Timoshenko-beam model with those from the Euler-beam model, the shear deformation is found to lead to some deviation of an admittance spectrum. The deviations are revealed to be evident around the admittance peak（s） and reach the maximum when a natural frequency of the MBs is identical to the fundamental frequency of the QCR. Besides, a higher order vibration mode of the MBs corresponds to a larger deviation at the resonance.

Rear-Surface Deformation of a Water Drop in Aero-Breakup of Shear Mode

Deformation of water drops in shock-induced high-speed flows is investigated with a focus to the influence of primitive flow parameters on the rear-surface deformation features. Two typical deformation patterns are discovered through high-speed photography. A simple equation to evaluate the radial acceleration of the drop surface is derived. The combined use of this equation and outer flow simulation makes it possible for us to reconstruct the profiles of the early deformed drops. The results agree well with the experiments. Further analysis shows that the duration of flow establishment with respect to the overall breakup time shapes the rear side profile of the drop. Thereby the ratio of the two times, expressed as the square root of the density ratio, appears to be an effective indicator of the deformation features.

Investigations of thickness-shear mode elastic constant and damping of shunted piezoelectric materials with a coupling resonator

Shear-mode piezoelectric materials have been widely used to shunt the damping of vibrations where utilizing surface or interface shear stresses. The thick-shear mode （TSM） elastic constant and the mechanical loss factor can change correspondingly when piezoelectric materials are shunted to different electrical circuits. This phenomenon makes it possible to control the performance of a shear-mode piezoelectric damping system through designing the shunt circuit. However, due to the difficulties in directly measuring the TSM elastic constant and the mechanical loss factor of piezoelectric materials, the relationships between those parameters and the shunt circuits have rarely been investigated. In this paper, a coupling TSM electro-mechanical resonant system is proposed to indirectly measure the variations of the TSM elastic constant and the mechanical loss factor of piezoelectric materials. The main idea is to transform the variations of the TSM elastic constant and the mechanical loss factor into the changes of the easily observed resonant frequency and electrical quality factor of the coupling electro-mechanical resonator. Based on this model, the formular relationships are set up theoretically with Mason equivalent circuit method and they are validated with finite element （FE） analyses. Finally, a prototype of the coupling electro-mechanical resonator is fabricated with two shear-mode PZT5A plates to investigate the TSM elastic constants and the mechanical loss factors of different circuit-shunted cases of the piezoelectric plate. Both the resonant frequency shifts and the bandwidth changes observed in experiments are in good consistence with the theoretical and FE analyses under the same shunt conditions. The proposed coupling resonator and the obtained relationships are validated with but not limited to PZT5A.

Design and analysis of a shear mode piezoelectric energy harvester for rotational motion system

A shear mode piezoelectric energy harvester for harvesting energy from rotary motion is developed.The kinetic energy in the form of rotation is converted into electrical form of energy by piezoelectric principle with oscillation of piezoelectric patch through magnetic shear force.Efforts have been made to increase the output power using shear mode of operation.In order to estimate the induced voltage of piezoelectric patch,a mathematical model and an Finite Element(FE)model are developed.Considering various parameters,optimization of the harvester was made.Analytical and Finite Element Method(FEM)results are compared and good agreement has been found.The total average output power of 358.44 Wis generated when rotary speed of hub of about 600 RPM.

Effect of Different Shear Modes on Morphology and Mechanical Properties of Polypropylene Pipes Produced by Rotational Shear

Oriented “shish-kebab” structures could be obtained by shearing to enhance the mechanical properties of polymer samples markedly.However,the effect of shear mode on mechanical properties is still uncertain.The study of stepped hoop shear field on the isotactic polypropylene(iPP)pipe was developed through applying a self-designed rotational shear system(RSS).The effect of stepped shear field on the microstructure and comprehensive properties of iPP pipe was investigated by the comparison with continuous shear.It could be found that the loosely-assembled shish-kebabs with the larger size were formed in the continuous shear pipes,but the smaller and tightly-stacked ones existed in the pipes with stepped shear.Surprisingly,due to differential morphologies under different shear modes,better comprehensive mechanical properties were obtained in the pipes with stepped shear.

In-plane shear(ModeⅡ) crack sub-critical propagation of rock at high temperature

In-plane shear crack sub-critical propagation of rock at high temperature was studied by finite element method and shear-box(i.e.compression-shear) test with newly designed electrically conductive adhesive method.Numerical and experimental results show that the normalized shear(Mode Ⅱ) stress intensity factors,K ⅡT/KT0 is decreased as the temperature increases because high temperature can improve stress distribution at crack tip and reduce the Mode Ⅱ stress intensity factor.Microscopic features of fractured surface are of little pits and secondary micro-cracks in the vicinity(1.5-4.0 mm) of the crack tip.The chevron-shape secondary cracks gradually merge in the length of about 4-5 mm and disappear along the direction of crack propagation.Stable shear crack propagation time is increased with the increasing temperature while the stable shear crack propagation rate is decreased with the increasing temperature,since high temperature can increase the shear(Mode Ⅱ) fracture toughness and prevent the crack growth.It is necessary to ensure the ligament of specimen long enough to measure the maximum unstable crack propagation rate of rock.

Effect of holes on in-plane shear(Mode Ⅱ) crack sub-critical propagation of rock

Shear-box(i.e.compression-shear) test and newly designed electrically conductive adhesive method were used to measure shear crack sub-critical propagation time and rate of sandstone specimen.Different cubic specimens with and without holes were tested to study the effect of holes on the shear crack sub-critical propagation.Numerical and experimental results show that three independent variables of hole,the interval distance S,the distance between the center of hole and the crack tip L,and hole radius R,have different contribution to the ratio of stress intensity factor of the specimen with holes to that of the specimen without hole,KⅡ/KⅡ0.Increasing S and decreasing L and R will result in the decrease of KⅡ/KⅡ0 and help crack arrest.The weight relation of the independent variables for KⅡ/KⅡ0 is S>L>R.The specimen DH3 with the largest value of S and the smallest values of L and R has the longest sub-critical crack propagation time and the smallest sub-critical crack propagation rate.Adding two suitable holes symmetrically to the original crack plane in rock specimen is considered to be a potential method for crack arrest of rock.

Effects of Magnetic Shear on the Resistive Wall Mode Instability in a Cylindrical Model

The linear evolution of a resistive wall mode(RWM)with magnetic shears was analytically studied in a cylindrical geometry.The incompressible magnetohydrodynamic(MHD)equations were solved by the Fourier analysis method,and various equilibrium magnetic fields were considered.The shear in the magnetic field had an unstable effect on the linear evolution of the RWM.The linear growth rate increased obviously with increase of the magnetic shear rate for higher magnetic shears.Slow plasma rotation could stabilize the RWM with low magnetic shears,but the plasma rotation could not stabilize the RWM with high magnetic shears.The stabilizing effects of the wall conductivity on the RWM are more efficient for lager magnetic shear.

Energetic-ion excited internal kink modes with weak magnetic shear in q0> 1 tokamak plasmas

The energetic particle driven internal kink mode is investigated in this paper for q0〉 1 tokamak plasma with weak magnetic shear. With the effect of energetic particles, the m/n = 1/1 internal mode structure in tokamak plasma does not appear as a rigid step-function when safety factor passes through q = 1 rational surface. It is found that even when the rational surface is removed, the mode may be still unstable under the low magnetic shear condition if the energetic particle drive is strong enough; with the low shear region of safety factor profile widening, the mode becomes more unstable with its growth-rate increasing. Furthermore, we find that the existence of the q = 1 rational surface does not have a significant effect on the stability of the plasma if energetic particles are present, which is very different from the scenarios of the ideal-MHD modes.

Elastic-viscoplastic field at mixed-mode interface crack-tip under compression and shear

For a compression-shear mixed mode interface crack, it is difficult to solve the stress and strain fields considering the material viscosity, the crack-tip singularity, the frictional effect, and the mixed loading level. In this paper, a mechanical model of the dynamic propagation interface crack for the compression-shear mixed mode is proposed using an elastic-viscoplastic constitutive model. The governing equations of propagation crack interface at the crack-tip are given. The numerical analysis is performed for the interface crack of the compression-shear mixed mode by introducing a displacement function and some boundary conditions. The distributed regularities of stress field of the interface crack-tip are discussed with several special parameters. The final results show that the viscosity effect and the frictional contact effect on the crack surface and the mixed-load parameter are important factors in studying the mixed mode interface crack- tip fields. These fields are controlled by the viscosity coefficient, the Mach number, and the singularity exponent.

Effect of shear equilibrium flow in Tokamak plasma on resistive wall modes

A code named LARWM with non-ideal magnetohydrodynamic equations in cylindrical model is used to describe the instability in Tokamak plasma surrounded by a conducting wall with finite resistivity. We mainly take three factors related to the shear equilibrium plasma flow into consideration to study the stabilizing effect of the shear flow on the resistive wall modes （RWMs）. The three factors are the velocity amplitude of flow, the shear rate of flow on plasma surface, and the inertial energy of equilibrium plasma flow. In addition, a local shear plasma flow is also calculated by the LARWM code. Consequently, it is found that the inertial energy of the shear equilibrium plasma flow has an important role in the stabilization of the RWMs.

Analysis of thickness-shear and thickness-twist modes of AT-cut quartz acoustic wave resonator and filter

The thickness-shear （TS） and thickness-twist （TT） vibrations of partially electroded AT-cut quartz plates for acoustic wave resonator and filter applications are theoretically studied. The plates have structural variations in one of the two in-plane directions of the plates only. The scalar differential equations derived by Tiersten and Smythe for electroded and unelectroded AT-cut quartz plates are used, resulting in free vibration resonant frequencies and mode shapes for both fundamental and overtone fam- ilies of modes. The trapped modes with vibrations, mainly confined in the electroded areas, are found to exist in both the resonator and the filter structures. The numerical results for the trapped modes are presented for different aspect ratios of electrodes and material properties, providing a reference to the design and optimization of quartz acous- tic wave resonators and filters.

Maximum twin shear stress factor criterion for sliding mode fracture initiation

Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is the maximum twin shear stress factor criterion. The authors studied a finite width plate with central slant crack, subject to a far field uniform uniaxial tensile or compressive stress.

聚丙烯纤维增强橡胶砂固结不排水剪切试验

鉴于橡胶砂作为回填材料时承载力低和变形量大的问题,采用加入聚丙烯纤维(PPF)的方法提高橡胶砂的力学性能,提出了聚丙烯纤维增强橡胶砂的半干拌式制备方法,通过48组聚丙烯纤维增强橡胶砂、普通橡胶砂和纯砂试样的固结不排水剪切试验,探究了聚丙烯纤维掺量和橡胶掺量等参数对聚丙烯纤维增强橡胶砂主要力学变形特征参数的影响.结果表明:聚丙烯纤维对橡胶砂弹性模量的影响较小;聚丙烯纤维增强橡胶砂具有先剪缩后剪胀破坏的特征,其偏应力与轴向应变关系为应变硬化型;聚丙烯纤维可有效提高橡胶砂的内摩擦角和黏聚力;聚丙烯纤维增强橡胶砂破坏偏应力的提升效果十分显著,最高可提高3倍.

Numerical linear analysis of the effects of diamagnetic and shear flow on ballooning modes

The linear analysis of the influence of diamagnetic effect and toroidal rotation at the edge of tokamak plasmas with BOUT++ is discussed in this paper. This analysis is done by solving the dispersion relation, which is calculated through the numerical integration of the terms with different physics. This method is able to reveal the contributions of the different terms to the total growth rate. The diamagnetic effect stabilizes the ideal ballooning modes through inhibiting the contribution of curvature. The toroidal rotation effect is also able to suppress the curvaturedriving term, and the stronger shearing rate leads to a stronger stabilization effect. In addition,through linear analysis using the energy form, the curvature-driving term provides the free energy absorbed by the line-bending term, diamagnetic term and convective term.

剪法及温湿度对钙果4号试管苗增殖效应的影响

钙果4号试管苗在同一配方培养基继代多次后容易出现种苗老化现象。利用钙果4号试管苗茎切段腋芽萌发成梢的特性,剪掉苗木中上部茎段,对剩留的剪切苗进行保护处理,剪切时注意从基部往上最多预留2个腋芽,然后放置于湿度为65%~73%、温度为29±1℃的环境下继代培养。结果显示,腋芽可萌发出2.8个嫩梢,嫩梢长度约为4.69 cm,嫩梢上着生叶片的叶面积、叶绿素含量、比叶重等指标良好,无黄化、老化现象。结果表明,通过调整剪切方式、温湿度等因素,可减缓种苗老化,为下次继代培养提供合格材料。

不同倾斜方式对倾斜液化场地地震响应的影响分析

在倾斜场地地震液化后,土体的侧向流动扩展引起的场地失效以及大变形问题的研究中,不同的倾斜方式会对试验结果产生一定的影响,而目前针对不同倾斜方式对倾斜液化场地土体地震动力响应影响评价的研究成果还较为少见。根据课题组开展的水平液化自由场振动台试验,首先基于OpenSees有限元平台建立了水平液化自由场有限元计算模型,在数值模型中考虑了模型箱对场地土地震响应的影响,通过对比数值计算结果与试验结果验证了数值模型的可靠性。在此基础上建立了倾斜液化自由场有限元计算模型,分别建立了层剪箱整体倾斜模型、层剪箱场地土倾斜模型和刚性箱场地土倾斜3种不同的数值模型来模拟振动台试验中采用的不同的倾斜方式。通过对比,分析了在0.3g汶川地震卧龙波作用下3个数值模型计算得到的自由场土体动力响应结果,并讨论了3种不同的倾斜方式对计算结果的影响,最后给出了针对倾斜液化场地地震动力响应数值模拟和振动台试验研究中的一些有参考价值的结论。

不锈钢槽式预埋组件受剪性能研究

为研究不锈钢槽式预埋组件在剪力作用下的破坏模式和承载性能,完成了3组9个带混凝土基材的不锈钢槽式预埋组件试件的受剪试验。试验结果表明,平行受剪工况下破坏模式为齿牙剪切破坏,垂直受剪工况下破坏模式为混凝土边缘破坏及槽道卷边受弯破坏。在试验的基础上,通过ABAQUS软件建立了有限元分析模型,并验证了模型的准确性。通过数值分析研究了齿牙尺寸、混凝土强度、边缘距离、锚件中心线间距及预埋槽道有效埋深等参数对极限承载力的影响。结果表明,平行受剪工况下,平齿型槽道的齿牙数量、宽度及厚度的增加均可提高极限承载力,齿牙高度对极限承载力影响较小;垂直受剪工况下,平齿型和燕尾型槽道的混凝土强度及边缘距离的增加均可提高极限承载力,而锚件中心线间距的增加则使极限承载力降低,预埋槽道有效深度对极限承载力影响较小。给出了不同破坏模式下的受剪承载力计算公式,通过试验结果与有限元模拟结果的对比,验证了承载力计算公式的有效性。

基于数字图像技术的致密砂岩纯剪裂缝断裂过程实验

纯剪应力状态下致密砂岩断裂过程是理解致密砂岩破坏失效机理的关键,然而在纯剪应力状态下,初始裂缝是发育扩展为I型裂缝或II型裂缝却一直有所争议。本文基于新型光学测量技术数字图像相关法和双切边压缩实验理论方法,开展了双切边压缩实验并通过数字图像相关法得到了位移和应变场。实验结果表明:双边开槽压缩实验能在槽尖(预制裂缝尖端)产生纯剪应力状态;致密砂岩试件起裂过程包含2个阶段的I型裂缝,第一阶段裂缝从槽尖起裂,第二阶段裂缝从试件中心两槽尖相连区域起裂。本文研究成果为数字图像技术应用在岩石断裂力学领域提供了新思路,对分析水力压裂中致密砂岩纯剪裂缝的演化规律有一定参考价值。

基于性能的含可更换耗能梁段高强钢框筒结构抗震性能研究

含可更换耗能梁段的高强钢框筒结构(HSS-SFT-RSL)结合了耗能梁段耗能强、钢框筒抗侧刚度大、高强钢承载力高等优点,是一种抗震性能优良的结构体系.传统设计方法需要进行复杂的迭代和计算才能使结构达到预期性能目标,且无法较为准确地控制结构的塑性发展顺序和破坏模式,本文采用课题组提出的基于性能的塑性设计方法(PBPD)各设计一个30层HSS-SFT-RSL算例和含可更换剪切型耗能梁段的普通钢框筒结构(CS-SFT-RSL)算例,通过静力和动力弹塑性分析对比两算例的抗震性能.结果表明:采用PBPD法设计的两算例具有相似的顶点侧移角和破坏模式,HSS-SFT-RSL算例抗侧刚度略低,但极限承载力更高;在罕遇水准地震下,两算例各层耗能梁段均能参与耗能,层间侧移角沿结构高度分布均匀,避免了薄弱层,残余层间变形较小,有利于耗能梁段更换和结构震后功能的快速恢复.