Conformal elasticity of mechanism-based metamaterials

Deformations of conventional solids are described via elasticity, a classical field theory whose form is constrained by translational and rotational symmetries. However, flexible metamaterials often contain an additional approximate symmetry due to the presence of a designer soft strain pathway. Here we show that low energy deformations of designer dilational metamaterials will be governed by a scalar field theory, conformal elasticity, in which the nonuniform, nonlinear deformations observed under generic loads correspond with the well-studied—conformal—maps. We validate this approach using experiments and finite element simulations and further show that such systems obey a holographic bulk-boundary principle, which enables an analytic method to predict and control nonuniform, nonlinear deformations. This work both presents a unique method of precise deformation control and demonstrates a general principle in which mechanisms can generate special classes of soft deformations.

Tunnel Squeezing Deformation Control and the Use of Yielding Elements in Shotcrete Linings: A Review

Shotcrete lining shows high resistance but extremely low deformability. The utilization of yielding elements in shotcrete lining, which leads to the so-called ductile lining, provides a good solution to cope with tunnel squeezing deformations. Although ductile lining exhibits great advantages regarding tunnel squeezing deformation control, little information has been comprehensively and systematically available for its mechanism and design. This is a review paper for the purpose of summarizing the development history and discussing the state of the art of ductile lining. It begins by providing a brief introduction of ductile lining and an explanation of the importance of studying this issue. A following summary of supporting mechanism and benefits of ductile lining used in tunnels excavated in squeezing ground conditions is provided. Then, it summarizes the four main types of yielding elements applied in shotcrete lining and introduces their basic structures and mechanical performances. The influences of parameters of yielding elements on the supporting effect are discussed and the design methods for ductile lining are reviewed as well. Furthermore, recommendations for further research in ductile lining are proposed. Finally, a brief summary is presented.

Spatiotemporal Deformation of Existing Pipeline Due to New Shield Tunnelling Parallel Beneath Considering Construction Process

In this paper, we study the effects of the shield tunnel construction on the deformation of an existing pipeline parallel to and above the new shield tunnel. We propose an analytical solution to predict the spatiotemporal deformation of the existing pipeline and consider different force patterns of the shield tunnelling, i.e., ground volume loss, support pressure, frictional force, and torsional force. The proposed method is validated by the monitoring data of Subway Line 3 of Nanchang and provides a reasonable estimation of the pipeline’s deformation. The parametric analyses are performed to study the influences on the pipeline’s deformation. The main advantage of our paper is that the spatiotemporal characteristics of the existing pipeline’s deformation are analysed, providing longitudinal deformation curve (LDC), deformation development curve (DDC), and grouting reinforcement curve (GRC). Compared with the perpendicular undercrossing project, both LDC and DDC have the same profiles and maximum values and move forward as a whole with the shield tunnel advance. Thus, the spatiotemporal deformation of the overall pipeline can be extrapolated from the deformation of two known points on the pipeline. The spatiotemporal characteristic curves combined with LDC, DDC, and GRC can suggest feasible, effective, and economical construction and grouting schemes to control the pipeline’s deformation after the deformation control standards have been determined.

Деформация тонких пленок полуметаллов методом купольного изгиба подложки

The results of a study of the semimetal films deformation produced by dome bending of the substrate are presented. Deformation control was carried out by means of X-ray diffraction analysis. It is shown that the dome bending method can be used to study films under planar deformation in a film-substrate system with different thermal expansion coefficients. The maximum in-plane deformation for bismuth films of 1 mkm thickness order was found. It was shown that the deformation created by the dome bending of the substrate in combination with the use of substrates with different temperature expansion makes it possible to obtain a relative in-plane deformation of bismuth films up to 0.8% at 300 K.

The Construction Countermeasures of Shallow-Buried Small Spacing Tunnel Undercrossing Cultural Relic Buildings: A Case Study

Based on the background of the reconstruction project from Changqing Chenzhuang-Pingyin section of G220 east-deep line in China, a special tunnel structure and construction plan was carried out according to the construction measures of the shallow-buried small spacing tunnel passing underneath cultural relic buildings, and a comprehensive deformation control scheme of “CRD construction method single-arm excavation + surface grouting prereinforcement + advanced large pipe shed presupport” was put forward. The results of numerical simulation and on-site construction monitoring showed that the overall deformation of aqueduct foundation generally increases first, then decreases and increases again, and finally tends to be stable. The effects of surface grouting prereinforcement and advance large pipe shed presupport are obvious. The comprehensive deformation control scheme can ensure the safety of the existing construction and meet the safety prevention and control requirements.

Analysis of Deformation Characteristics of Filled Subgrade Treated by Micro-Pile

Deformation control of fill subgrade is a difficult point in the field of highway engineering. This article relies on the treatment project of micro-piles for subgrade deformation of K555 + 070～K557 + 710 section of Qingdao-Yinchuan Expressway. Settlement and stress monitoring was carried out at the toe of the roadbed, the shoulder, and the center of the roadbed. We use Midas/GTS modeling trial calculation. A new method to check the simulation results of the deviation rate is proposed. A calculation model of the stress and deformation of the subgrade in the whole life cycle is established. The results of comparative analysis, monitoring, and simulation are as follows. ① The compression and consolidation of the fill account for most of the settlement and deformation of the roadbed in the whole life cycle. ② Subgrade center settlement is the sensitive part of subgrade deformation. ③ After piles are added, the deformation extremes at the toe of the slope, the shoulder, and the center of the roadbed are all reduced by more than 96%. The research results can provide theoretical guidance for the analysis of the stress and deformation characteristics of the subgrade before and after the micro-pile treatment.

Finite Element Simulation and Deformation Control of High-Speed Milling of Al7050-T7451 Thin-walled Parts

Background: To reduce environmental pollution and improve resource utilization, lightweight equipment has become an important development trend of manufacturing. Therefore, thin-walled parts are being widely used in automobiles, aerospace, etc. due to their lightweight and high specific strength. However, they usually deform during machining due to poor stiffness. Objective: To reduce the machining deformation, the finite element method has been used to analyze the deformation law of thin-walled parts. Method: A 3D milling model of Al7050-T7451 thin-walled parts was established. Then, the influence of hole structure, rib, and auxiliary support on the deformation was investigated under the condition of optimized parameters. Moreover, some related patents on the research of machining deformation of thin-walled parts were also consulted. Results: The results showed that the established 3D model could accurately predict the machining deformation of thin-walled parts. The machining deformation on the edges is more severe due to holes that weaken the stiffness of thin-walled parts. Besides, ribbed slab and auxiliary support can shorten machining deformation by 71.9% and 65.2%, respectively.

Deformation Control Analysis of Unequal-Length Bridge Piles of Urban Rail Transit Tunnel Crossing Urban Expressway Elevated Bridge

Taking the viaduct project of the main road bridge of Fushi road between Jinding Street station and Jinanqiao Station of line 11 of Beijing subway as the background, due to geological reasons, the length of the pile of the main road bridge of Fushi road is 60m to the west of Xin’an road in the north, the pile length of the bridge east of North Xin’an road is 21.5m, and line 11 of Beijing subway passes between two piles of unequal length. This paper simulates the whole construction process with the method of numerical analysis, analyzes the causes of the deformation of the bridge piles by calculation, puts forward the measures of grouting reinforcement in the whole section, sums up the deformation rules of the unequal length bridge piles, and puts forward the deformation control values, in order to ensure the safety of Rail Transit Construction, for the follow-up similar projects to provide a basis and reference.