Direct-shear mode

Virtually all devices that use controllable MR fluids operate in a valvemode, direct-shear mode, or a combination of these two modes. Diagrams of the basic valve and direct-shear modes are shown in Fig. 6.76. Examples of valve-mode devices include dampers, and shock absorbers. Examples of direct shear-mode devices include clutches, brakes, chucking and locking devices, and some dampers. 

Fig. 6.76. Two modes of MR fluid operation a valve-mode, b direct-shear mode...

Fig. 6.78. Controllable force range possible with MR fluid damper Direct-Shear Mode...

A crack in a body may grow as a result of loads appHed in any of the three coordinate directions, lea ding to different possible modes of failure. The most common is an in-plane opening mode (Mode I). The other two are shear loading in the crack plane (Mode II) and antiplane shear (Mode III), as defined in Figure I. Only Mode I loading is considered herein. 

Slip is not always a purely dissipative process, and some energy can be stored at the solid-liquid interface. In the case that storage and dissipation at the interface are independent processes, a two-parameter slip model can be used. This can occur for a surface oscillating in the shear direction. Such a situation involves bulk-mode acoustic wave devices operating in liquid, which is where our interest in hydrodynamic couphng effects stems from. This type of sensor, an example of which is the transverse-shear mode acoustic wave device, the oft-quoted quartz crystal microbalance (QCM), measures changes in acoustic properties, such as resonant frequency and dissipation, in response to perturbations at the surface-liquid interface of the device. 

The shear-mode acoustic wave sensor, when operated in liquids, measures mass accumulation in the form of a resonant frequency shift, and it measures viscous perturbations as shifts in both frequency and dissipation. The limits of device operation are purely rigid (elastic) or purely viscous interfaces. The addition of a purely rigid layer at the solid-liquid interface will result a frequency shift with no dissipation. The addition of a purely viscous layer will result in frequency and dissipation shifts, in opposite directions, where both of these shifts will be proportional to the square root of the liquid density-viscosity product v Pifti-... 

In symmetry directions, notably when 0 = 45°or 90°, these expressions simplify considerably. Along all symmetry axes the shear modes are degenerate (i.e. the shear velocity is independent of the polarization) and all the modes are pure (Auld 1973). 

Analyzing the expressions (44)-(46) one can easily see that non-zero contribution of the Jahn-Teller system to the elastic moduli takes place only to the Cs modulus (or to the velocity of the slow shear mode of the (110) direction) and this contribution is... 

The deposition of noble metals onto oscillating quartz crystals of the thickness shear type, for fine adjustment of their frequency, has already been carried out for many years by frequency standard manufacturers. The idea of using the frequency decrease by mass deposition to determine the weight of the coating is comparatively new. Sauerbrey [35] and Lostis [36] were the first to propose the quartz-crystal microbalance. The AT-cut crystal oscillating in a thickness shear mode was found to be best suited for this purpose. The thickness xq of an infinite quartz plate is directly related to the wavelength A. of the continuous elastic transverse wave, the phase velocity vq of that wave and the frequency vq (i.e. the period xq) of the oscillating crystal, as shown in Fig. 4 ... 

QCM can be described as a thickness-shear mode resonator, since weight change is measured on the base of the resonance frequency change. The acoustic wave propagates in a direction perpendicular to the crystal surface. The quartz crystal plate has to be cut to a specific orientation with respect to the ciystal axis to attain this acoustic propagation properties. AT-cut crystals are typically used for piezoelectric crystal resonators[7]. The use of quartz crystal microbalances as chemical sensors has its origins in the work of Sauerbrey[8] and King [9] who... 

Two alternative modes of fracture have been defined, both involving shear on the crack plane. In mode II, shear is parallel to rhe crack propagation direction. In mode III, shear is normal to the propagation direction. These types of fracture are important in long-fibre composites and in adhesives, because of anisotropy. They are of minor importance in thermoplastics. Cracks in isotropic materials tend to turn in a direction normal to the tensile stress, giving mode I fracture, whatever the initial orientation of the crack plane. 

Fig. 3.4 DMA results of the pristine Nation film, the Ni-doped MFR IPMC with applied magnetic field in parallel and perpendicular directions. The resulting storage modulus (a) loss modulus (b) and tan 5) (c) in a frequency range from 0.01 to 100 Hz in shear mode. Reprinted from [Park and Kim (2007)] with permission from Elsevier, Copyright 2007.

Figure 1 Wave propagation modes of piezoeiectric resonators. Ciosed arrows indicate particie dispiacement, open arrows direction of wave propagation. TSM, thickness shear mode FPW, fiexurai piate wave SAW, surface acousfic wave SH-APM, shear horizonfai acousfic piafe mode. (Reprinted with permission from Angewandfe Chemie infernafionai Edition (2000) 39 4004-4032 2003 Wiiey-VCH.)...

FIGURE 4.1.21 3D positioning multilayer actuator. Notice that the x- andy-stacks are using shear mode with the spontaneous polarization perpendicular to the applied electric field direction. 

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