Atomically thin layers of transition-metal dicalcogenides (TMDCs) are often known to be metastable in the ambient atmosphere. Understanding the mechanism of degradation is essential for their future applications in nanoelectronics, and thus has attracted intensive interest recently. Here, we demonstrate a systematic study of atomically thin WTe 2 in its low temperature quantum electronic transport properties. Strikingly, while the temperature dependence of few layered WTe 2 showed clear metallic tendency in the fresh state, degraded devices first exhibited a re-entrant insulating behavior, and finally entered a fully insulating state. Correspondingly, a crossover from parabolic to linear magnetoresistance, and finally to weak anti-localization was seen. Real-time Raman scattering measurement, together with transmission electron microscopy studies done before and after air degradation of atomically thin WTe 2 further confirmed that the material gradually form amorphous islands. It thus leads to localized electronic states and explains the low temperature Coulomb gap observed in transport measurements. Our study reveals for the first time the correlation between the unusual magnetotransport and disorder in few-layered WTe 2 , which is indispensable in providing guidance on its future devices application. [4,5]. Albeit a layered material, WTe 2 devices in the two-dimensional (2D) limit have been rarely reported, with its experimental investigations mostly restrained in the bulk regime. Unlike other transition-metal dichalcogenides (TMDCs), instead of 2H phase, Td-(also addressed as 1T'-) phase of bulk WTe 2 occupies the lower energy state, whose two nearly perfectly compensated electron and hole bands result in a large unsaturated classical magnetotransport, with a parabolic dependence of the applied magnetic field B [6]. Meanwhile, strong anisotropy was found in its bulk form, which gives rise to some exotic linear magnetoresistance in a specific measurement configuration [7]. Moreover, recent angle resolved photon electron spectroscopy (ARPES) studies showed subtleness of the band structure of bulk WTe 2 [8][9][10][11], intriguing possible peculiar electronic properties in the few layered scenario. In the 2D limit, electrostatic gate can, in principle, largely tune the carrier density, thus breaking down the electron-hole balance, leading to new opportunities.Despite the fact that WTe 2 can be readily exfoliated against the weak interlayer van-der-Waals bonding, atomically thin WTe 2 is proven to rapidly age in ambient atmosphere like many of the TMDCs [12]. Together with the extinction of optical contrast and Raman signal after air exposure [13], ultra thin WTe 2 flakes were reported to exhibit, rather than the so-called semi-metal state, an insulating behavior as a function of number of layers, with the lack of a systematic analysis of the aging effect on the quantum transport [14]. Such air instability therefore hampers the further possibilities for nanoelectronic devices of, for example, few-layered WTe 2 fi...

The delamination cracks and its effects on the fracture of pipeline steel are investigated experimentally by using of Drop-Weight Tear Test (DWTT). The delamination cracks are produced by the stress perpendicular to the weak interfaces before main crack beginning or accelerating, no new delamination crack is produced during the stabile propagation of fracture. The quantity, splay degree of delamination crack and the space between two delamination cracks are influenced by the stress state of the crack tip at beginning or accelerating point of main crack and the length of delamination crack is influenced by the stress state of the crack tip during the propagation of fracture. The surface of delamination crack is cleavage fracture appearance with large cleavage facet. There is no delamination crack on the brittle fracture surface below the brittle-to-ductile temperature or on the brittle fracture region of mix-mode fracture surface with ductile and brittle region. The part of fracture surfaces with delamination crack ought to be evaluated as the shear area because the delamination cracks are produced only on the ductile fracture surface or on the ductile part of fracture surface.

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Experimental of two kinds of compact tension (CT) specimens’ creep crack propagation are carried out in this paper. Traditional fracture mechanics and three-dimensional fracture theory are compared and the results show that: The K-Tz two-parameter model can eliminate the thickness-effect on the crack growth rates in the relatively low K range, however when K exceed certain values the effect of thickness for crack growth rates still exists; The Ct and Ct-Tz model can describe the thickness-effect of creep crack growth rates in regions of high Ct; When the crack tip stress intensity factor K of the two kinds of thickness (B=5 mm, B=10 mm) specimens equal to 35 and 31 respectively, this material’s creep crack growth control parameter change from K to Ct.

Based on the classic laminate theory, a progressive damage model has been incorporated into the composite structure analysis by using a commercial code, ABAQUS, via one of its user-defined subroutine, UGENS. The developed user subroutine can be applied to simulate fiber and matrix damage processes in the general composites structures. The responses of flat laminate subjected to static contact crush have been studied to verify the efficiency of the presented damage method. The predicted load-displacement relationships, damage distribution were obtained and compared with the corresponding experiments, and the results were found to be in good agreement.