Axial rotation as a cause of loss of interference in a shrink fitted split disc assembly

На примере составного диска, созданного посредством операции горячей посадки, изучается прочность такого соединения на отрыв. Отрывные усилия создаются в качестве центробежных инерционных сил при вращении диска относительное его центральной оси. Показывается, что созданный натяг в сборке имеет выраженную тенденцию к уменьшению. Однако для его обнуления необходимы достаточно значительные угловые скорости вращения. Приведен пример расчета придельной угловой скорости в зависимости от первоначального нагрева охватывающей детали сборки, термомеханических свойств материала сборки и геометрических параметров итоговой конструкции. Подобные расчеты в снижающемся натяге совершенно необходимы, когда эксплуатационные условия требуют принять вращение составного диска в качестве части его функциональных обязанностей. On the example of a composite disk, created by means of a hot-fit operation, the pulloff strength of such a disk is studied. separation forces as centrifugal forces with relative rotation of its central axis. It is shown that the created interference fit in the assembly has a pronounced tendency to decrease. However, for vanishing, sufficiently significant angular velocities of rotation are required. An example of calculating the near-limit angular velocity, depending on the original covered part of the assembly, of the thermomechanical properties of the material and the geometric characteristics of the final structure is given. Such computations in decreasing interference are essential when operating conditions require the rotation of the composite disc to be accepted as part of its functionality.

Time-History Analysis of Composite Materials with Rectangular Microstructure under Shear Actions

It has been demonstrated that materials with microstructure, such as particle composites, show a peculiar mechanical behavior when discontinuities and heterogeneities are present. The use of non-local theories to solve this challenge, while preserving memory of the microstructure, particularly of internal length, is a challenging option. In the present work, composite materials made of rectangular rigid blocks and elastic interfaces are studied using a Cosserat formulation. Such materials are subjected to dynamic shear loads. For anisotropic media, the relative rotation between the local rigid rotation and the microrotation, which corresponds to the skewsymmetric part of strain, is crucial. The benefits of micropolar modeling are demonstrated, particularly for two orthotropic textures of different sizes.

Study of the Error Caused by Camera Movement for the Stereo-Vision System

The stereo-vision system plays an increasingly important role in various fields of research and applications. However, inevitable slight movements of cameras under harsh working conditions can significantly influence the 3D measurement accuracy. This paper focuses on the effect of camera movements on the stereo-vision 3D measurement. The camera movements are divided into four categories, viz., identical translations and rotations, relative translation and rotation. The error models of 3D coordinate and distance measurement are established. Experiments were performed to validate the mathematical models. The results show that the 3D coordinate error caused by identical translations increases linearly with the change in the positions of both cameras, but the distance measurement is not affected. For identical rotations, the 3D coordinate error introduced only in the rotating plane is proportional to the rotation angle within 10° while the distance error is zero. For relative translation, both coordinate and distance errors keep linearly increasing with the change in the relative positions. For relative rotation, the relationship between 3D coordinate error and rotation angle can be described as the nonlinear trend similar to a sine-cosine curve. The impact of the relative rotation angle on distance measurement accuracy does not increase monotonically. The relative rotation is the main factor compared to other cases. Even for the occurrence of a rotation angle of 10°, the resultant maximum coordinate error is up to 2000 mm, and the distance error reaches 220%. The results presented are recommended as practice guidelines to reduce the measurement errors.

South Tarim tied to north India on the periphery of Rodinia and Gondwana and implications for the evolution of two supercontinents

Constraining the positions of, and interrelationships between, Earth’s major continental blocks has played a major role in validating the concept of the supercontinent cycle. Minor continental fragments can provide additional key constraints on modes of supercontinent assembly and dispersal. The Tarim craton has been placed both at the core of Rodinia or on its periphery, and differentiating between the two scenarios has widespread implications for the breakup of Rodinia and subsequent assembly of Gondwana. In the South Tarim terrane, detrital zircon grains from Neoproterozoic–Silurian strata display two dominant populations at 950–750 and 550–450 Ma. Similarly, two main peaks at 1000–800 and 600–490 Ma characterize Neoproterozoic–Ordovician strata in northern India. Moreover, the two dominant peaks of South Tarim and north India lag two global peaks at 1200–1000 and 650–500 Ma, which reflect Rodinia and Gondwana assembly, arguing against a position within the heart of the two supercontinents. Ages and Hf isotopes of Tarim’s detrital zircons argue for a position on the margin of both supercontinents adjacent to north India with periodic dispersal through opening and closing of small ocean basins (e.g., the Proto-Tethys). Alternating tectonic transitions between advancing and retreating subduction in North Tarim coincide with periodic drift of South Tarim from north India in Rodinia and Gondwana, emphasizing the importance of retreating subduction in supercontinent dispersal. Moreover, the Rodinia-related orogenic belts spatially overlap the Gondwana-related orogenic belts in the two blocks, indicating no significant relative rotation of India and Tarim during the evolution from Rodinia to Gondwana.

Breakdown of semiclassical description of thermoelectricity in near-magic angle twisted bilayer graphene

The planar assembly of twisted bilayer graphene (tBLG) hosts a multitude of interaction-driven phases when the relative rotation is close to the magic angle (θ = 1.1°). This includes correlation-induced ground states that reveal spontaneous symmetry breaking at low temperature, as well as the possibility of non-Fermi liquid (NFL) excitations. However, experimentally, the manifestation of NFL effects in transport properties of twisted bilayer graphene remains ambiguous. Here we report simultaneous measurements of electrical resistivity (ρ) and thermoelectric power (S) in tBLG for several twist angles between θ ≈ 1.0°-1.7°. We observe an emergent violation of the semiclassical Mott relation in the form of excess S close to half-filling for θ≈1.6° that vanishes for ≥ 2°. The excess S (≈2 μV/K at low temperatures T ≈10 K at θ≈1.6°) persists up to ≈ 40 K and is accompanied by metallic T-linear ρ with transport scattering rate (1/τ) of near-Planckian magnitude 1/τ ≈ k_BT/h_bar. Closer to θ_m, the excess S was also observed for fractional band-filling (ν≈ 0.5). The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG.

Depolarizing Chipless Tags with Polarization Insensitive Capabilities

A novel depolarizing chipless tag configuration with high angular insensitivity is presented. The basic tag comprises two dipole resonators arranged with a relative rotation of 45°. The proposed configuration improves the depolarization properties performance of a single dipole over the ground plane which provides a peak with perfect polarization conversion only if the electric field impinges at 45° with respect to the dipole resonator. The second dipole arranged at 45° compensates the cross-polar reduction which is observed when the electric field is not correctly polarized. Indeed, when the field is tilted by 90° with respect to the first dipole, it forms an angle of 45° with the second one. The proposed configuration is also analyzed for providing multiple frequency peaks. A tag with 4 angular independent frequency peaks laying between 2 GHz and 5.5 GHz is designed. Angular frequency maps are used to illustrate the peculiar frequency shifts achieved when the electric fields rotate in the plane of the dipole. Finally, a prototype of the polarization insensitive tags is fabricated and measured to confirm the simulated results.

Automatic weaving method for three-dimensional composite preforms using vision system

Three-dimensional composite preform is the main structure of fiber-reinforced composites. During the weaving process of large-sized three-dimensional composite preform, relative rotation or translation between the fiber feeder and guided array occurs before feeding. Besides, the weaving needles can be at different heights after moving out from the guided array. These problems are mostly detected and adjusted manually. To make the weaving process more precise and efficient, we propose machine vision-based methods which could realize accurate estimation and adjustment of the relative position-pose between the fiber feeder and guided array, and make the needles pressing process automatic by recognizing the position of the weaving needles. The results show that the estimation error of relative position-pose is within 5%, and the rate of unrecognized weaving needles is 2%. Our proposed methods improve the automation level of weaving, and are conducive to the development of preform forming toward digital manufacturing.