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•The early Carboniferous MTC was remagnetized during the Late Carboniferous–Early Permian.•The Late Permian HTC represents a primary characteristic magnetisation.•The Alashan Terrane ...migrated to the NCB during the Early–Middle Triassic and Early Cretaceous.
Rock magnetic and paleomagnetic studies have been carried out on the early Carboniferous limestones and the Late Permian purple sandstones sampled in the eastern Alashan Terrane (ALT), northwest of China. Two components were isolated from the Early Carboniferous limestone by thermal progressive demagnetisation: a low unblocking temperature component (LTC) of recent origin; a pre-folding medium temperature component (MTC) (the paleomagnetic pole is λ=13.1°N, Ф=11.0°E, A95=7.0°) that is probably the result of the hydrothermal fluids from the Qilian Orgenic Belt acquired during the Late Carboniferous–Early Permian. Also, two components were separated from the Late Permian purple sandstone by thermal progressive demagnetisation: the LTC with the recent viscous remanent magnetisation, and the higher temperature component (HTC) revealed from three sections which has passed a regional fold test at the 95% probability level and reversal test, suggesting a primary characteristic magnetisation. The corresponding paleomagnetic pole is λ=27.2° N, Ф=18.8° E, A95=12.0°. The apparent polar wander path (including early Carboniferous, late Carboniferous-Early Permian, Late Permian and Early–middle Triassic poles) of the ALT is significantly different with those of the NCB. Comparison of the APWPs between the ALT and NCB shows a strong similarity. If the APWP of Hexi Corridor–Alashan rotated counterclockwise around an Euler pole at 44°N, 84°E by 32°, then the coeval APW path of the ALT overlaps to that of the NCB. This result indicates that the ALT migrated to the NCB after the Early–Middle Triassic along a tectonic boundary located between Helanshan Mountain and Zhuozishan Mountain, and finally amalgamated to the NCB before the Early Cretaceous.
The relationship between the Alashan Terrane and North China is a contentious issue given the discovery of allochthonous detrital zircons in Middle Ordovician flysch sandstones from the southwestern ...Ordos Margin and the large differences in palaeolatitudes between the North China and Tarim cratons. We have collected a suite of Middle to Late Devonian sedimentary rocks from the Niushoushan Mountains at the southeastern margin of the Alashan Terrane, adjacent to the western margin of the Ordos Basin of the North China Craton (NCC). U–Pb dating and Lu–Hf isotopic studies were carried out on detrital zircons from these rocks. The zircon U–Pb ages define five age populations: 0.4–0.7Ga (peak at 488Ma), 1.0–1.3Ga (peaks at 1001 and 1152Ma), 1.5–1.8Ga, 2.4–2.8Ga (prominent peak at 2506Ma and secondary peaks at 2668 and 2796Ma) and >3.0Ga (peak at 3332Ma). One detrital zircon yielded a Hadean age of 4022±17Ma. Zircons with U–Pb age spectra of 2.4–2.7 and >3.0Ga and their corresponding εHf(t) values are significantly different from those in the NCC, indicating that these detrital zircons are not from the NCC, which implies that the Alashan Terrane was not part of North China until the Middle to Late Devonian. U–Pb age spectra of zircons dated at 1.0–1.3Ga, 2.4–2.7Ga, and >3.0Ga, and their corresponding Hf isotope data, have a strong similarity with zircons from East Gondwana and the South China Craton.
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•The Alashan Terrane was separated with North China until the Middle–Late Devonian.•The Alashan Terrane had strong similarity with East Gondwana in Middle–Late Devonian.•A 4.0Ga detrital zircon was first discovered in the Northern China.
Auxetic material is a metamaterial engineered to achieve negative Poisson's ratios through special design of microstructure. As a typical 3D auxetic material, 3D cross-chiral structures (CCS) ...possesses significant auxetic behavior and the mechanical properties can be tuned over a wide range. In this paper, mechanical responses of CCS are systematically investigated by experiments, numerical simulations and theoretical analysis. Three typical failure modes are observed during the compression process. As the tilt angle of struts increases, the CCS shows a transition from the compression-dominated to the bending-dominated deformation mechanism. The Young's modulus of the CCS can be enhanced 8.5 times, simply by changing the angle of the strut by 20°. The CCS can also show a higher energy absorption capacity with absorption efficiency of about 50%, which is higher than most previously reported cellular materials. Additionally, a new theoretical model based on large deformation theory is established to predict the plastic yield stress, and good agreement is obtained with the numerical simulations and experiments, which indicates that the present model can significantly improve the accuracy of the estimation. The results of this paper may be helpful for designing of energy absorbing devices and personal protection with 3D auxetic materials.
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•Three typical failure modes of the CCS observed in both experiments and simulations are controlled by the configuration.•CCS shows a transition from the compression-dominated to the bending-dominated in deformation mechanisms as q increases.•CCS shows absorption efficiency of about 50%, which is higher than most previously reported cellular materials.•Based on large deformation theory, the theoretical model could present more accurate predictions of plastic yield stress.
Based on a 2D cross chiral structure, two novel 3D cross chiral structures (structure-1 and structure-2) with negative Poisson's ratios were proposed in this paper. Structure-1 could be evolved into ...structure-2 by adding a star structure. Analytical models of the two auxetic cellular structures were established based on the Timoshenko beam theory. The Young's modulus and Poisson's ratio of the cellular structures were obtained in all principal directions, which were verified by finite element method (FEM). Structure-1 exhibits anisotropic auxetic behavior while structure-2 shows uniform auxetic behavior in all three principal directions with all on-axis Poisson's ratios closer to the limit of -1. Additionally, the extra addition of star structure can enhance the Young's modulus of structure-2 significantly in the case of same relative density, compared to structure-1. Moreover, the effect of parameter variation on elastic properties of two structures and the comparison with other classical 3D auxetic structures were also thoroughly studied and discussed in detail. These results are expected to eventually contribute to the advance of research and the application of new 3D auxetic structures in the future.
The intensive applications of polymer in many engineering composites have imposed an urgent need on the understanding of the mechanical behavior and deformation mechanism of the polymer under cyclic ...loading. This paper presents the results of a numerical study on the behavior of amorphous polyethylene (PE) subjected to cyclic tensile and compressive loads using molecular dynamics (MD) simulations, based on a united-atom approach. The effects of polymer chain length, the number of chains and strain rates are studied at first. Hysteresis loops, as well as visco-elastoplastic of PE under cyclic loading predicted by MD simulations are qualitatively in agreement with previous experiments. Three distinct hysteresis loops observed in successive loading-unloading reveal the contribution of elasticity, viscosity and plasticity under different loading strains, respectively. The rubber-like recovery behavior of PE at low temperature is attributed to that the mobility of molecular chains is constrained at low temperature. Energy analysis shows that the van der Waals energy and dihedral angle energy are considered to be the primary factors that affects the cyclic behavior of PE.
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∙The cyclic behavior of polyethylene (PE) under different loading conditions below the glass transition temperature was investigated at the nanoscale.∙PE exhibits highly recoverable behavior at extremely low temperature and can retain even after several cycles.∙The friction and torsion of molecular chains dominate the deformation of PE under cyclic loading.
Evolutionary algorithms (EAs) have been applied with success to many numerical and combinatorial optimization problems in recent years. However, they often lose their effectiveness and advantages ...when applied to large and complex problems, e.g., those with high dimensions. Although cooperative coevolution has been proposed as a promising framework for tackling high-dimensional optimization problems, only limited studies were reported by decomposing a high-dimensional problem into single variables (dimensions). Such methods of decomposition often failed to solve nonseparable problems, for which tight interactions exist among different decision variables. In this paper, we propose a new cooperative coevolution framework that is capable of optimizing large scale nonseparable problems. A random grouping scheme and adaptive weighting are introduced in problem decomposition and coevolution. Instead of conventional evolutionary algorithms, a novel differential evolution algorithm is adopted. Theoretical analysis is presented in this paper to show why and how the new framework can be effective for optimizing large nonseparable problems. Extensive computational studies are also carried out to evaluate the performance of newly proposed algorithm on a large number of benchmark functions with up to 1000 dimensions. The results show clearly that our framework and algorithm are effective as well as efficient for large scale evolutionary optimisation problems. We are unaware of any other evolutionary algorithms that can optimize 1000-dimension nonseparable problems as effectively and efficiently as we have done.
To evaluate the influence of a rigid bus on the interconnected post electrical equipment with a sliding fitting, this article conducted shaking table tests on two full-scaled ±800 kV ultra-high ...voltage post insulators. Simplifying the rigid bus with a sliding fitting serving as a linear spring and damper allowed us to create a dynamic model of the stand-alone insulators and establish advanced two-piece interconnected post electrical equipment. Later, parametric analyses were carried out on the dynamic model. The results showed that the frequencies of the interconnected system were similar to those of the stand-alone counterparts if the dynamic characteristics of the two interconnected items were similar. The seismic responses of the interconnected system generally decrease compared with those of the stand-alone insulators. Thus, the seismic performance of the rigid bus interconnected electrical equipment system could qualify as having a stand-alone status if the dynamic characteristics of the equipment items are similar. The connection stiffness greatly affects the seismic responses of UHV composite post electrical equipment.
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