Plastic deformation of metallic alloys usually takes place through slip, but occasionally involves twinning. In particular, twinning is important in hexagonal close packed materials where the easy slip systems are insufficient to accommodate arbitrary deformations. While deformation by slip mechanisms is reasonably well understood, less remains known about deformation by twinning. Indeed, the identification of relevant twinning modes remains an art. In this paper, we develop an universal framework combining fundamental kinematic definition of twins with large scale atomistic calculations to predict twinning modes of crystalline materials. We apply this framework to magnesium where there are two accepted twin modes -tension and compression, but a number of anomalous observations. Surprisingly, our framework shows that there are a very large number of twinning modes that are important in the deformation process of magnesium consistent with the anomalous observations. Thus, in contrast to the traditional view where plastic deformation is kinematically partitioned between a few modes, our result argues that the physics of deformation in HCP materials is governed by an energetic and kinetic competition between numerous possibilities. Consequently, our findings suggest that the commonly used models of deformation physics need to be revisited in order to take into account a broader and richer variety of twin modes, and potentially points to new avenues of improving the mechanical properties. *
surface. This design deployed a bulk piezoelectric structure as an entire resonator without any other elastic structures, to increase the shock resistance, the energy conversion efficiency and decrease the fabrication complexity. However, the PZT material itself has the characteristic of low quality factor, low output signal and much mechanical noise, compared with the silica-based material. As a result, how to increase the output signal and the sensitivity is a hot topic for piezoelectric gyroscopes (Cheng et al. 2013).On the other hand, the development of the MEMS silicon vibrating gyroscopes shows that the mode matching is a valid solution to increase the output signal and sensitivity of the gyroscopes (Tanaka et al. 1995). The mode matching is to match the resonant frequency between the drive mode and the sense mode, and to eliminate the frequency split. In most of the vibrating gyroscopes, the exact calculation and design should be made to implement a good characteristic. The ring vibrating gyroscope is a kind of degenerate gyroscope (He and Najafi 2002), which has an inherent axial symmetric resonator and utilizes a degenerate vibration mode pair as the drive and sense modes to maximize the energy transfer between the two modes. The degenerate gyroscopes have an inherent mode matching, which improves the characteristic and increases the sensitivity of the devices. In recent years, more and more attentions have been attracted by the degenerate gyroscopes, including the ring vibrating gyroscopes (He and Najafi 2002; Najafi 2000, 2001) and the hemispherical resonator gyroscopes (Zotov et al. 2012;Pai et al. 2012;Cho et al. 2013).This paper proposes a novel disk-like solid piezoelectric gyroscope based on the in-plane bulk acoustic wave (BAW) resonance. This design combines the solid piezoelectric gyroscopes with a disk-like resonant structure which is inherently mode matched. The structure not only obtains the high shock resistance and energy conversion efficiency Abstract This paper introduces a MEMS piezoelectric solid disk gyroscope. The gyroscope operates in an inplane elliptic bulk acoustic wave mode with a frequency of 284 kHz. This gyroscope is an improvement of the solid piezoelectric gyroscope. A device, 6 mm in diameter, has been fabricated through the microelectromechanical systems process, and achieved a relatively high sensitivity and bias instability. In this paper, it is described that the design, fabrication, circuit system and characteristics of the piezoelectric solid disk gyroscope.
Ever since its discovery, graphene has been revolutionizing the field of materials science and engineering, showing promise towards use in a variety of applications. Examples of some of the many remarkable properties of graphene include allowance of the electric field-effect at room temperature [1], high thermal mobility and electronic conductivity [2, 3], and unprecedented high-strength and quantum effects (e.g. the quantum Hall effect and relativistic behavior of carriers) [4]. The discovery of graphene has expanded the area of quantum materials, leading to the discovery of additional 2D materials-such as dichalcogenides (TMDCs), hexagonal boron nitride (h-BN), silicene, germanene, black phosphorene [5, 6]-with similarly-intriguing properties.Despite the inherently-remarkable properties associated with these materials, engineering intervention is still sometimes necessary to achieve certain, otherwise-unattainable properties. For instance, device-driven applications necessitate modification of a candidate material's electronic structure. Probabilistic factors hinder the ability to control these properties, although contemporary engineering techniques-such as doping and strain engineering [7, 8]-have curbed the extent of these probabilistic factors, allowing for the tuning of material properties on demand.Similarly, nanodevices with multiple layers of 2D materials have been developed [9][10][11] in order to expand the envelope of attainable properties. In these devices, the layers weakly interact by van der Waals forces and the atoms form Moiré patterns when subjected to rotations. Interestingly, recent studies have shown that the
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