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Research progress of elastic topological materials

CHEN Yi, ZHANG Quan, ZHANG Yafei, XIA Baizhan, LIU Xiaoning, ZHOU Xiaoming, CHEN Changqing, HU Gengkai

2021, 51(2): 189-256. doi: 10.6052/1000-0992-21-015

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Topological insulators, originated in quantum systems, are recently generalized to electromagnetic, acoustic, and elastic wave fields due to interesting wave controlling provides, such as unidirectional and dissipationless energy transportation. This new kind of materials provide unprecedented possibilities for engineering wave flows. This paper will introduce the basic theory of topological insulators and summarize the research progress of topological insulators in elastic fields. Based on one-dimensional and two-dimensional discrete models, preliminary concepts of topological insulators, such as Dirac cone, band inversion, Berry curvatures, topological invariants, are introduced. The design and progress of valley Hall insulators, Chern insulators as well as spin Hall insulators are introduced afterward, followed by discussions on high-order topological insulators. The last part of this paper covers topological phenomena in static mechanics, including topological solitons and toplogical zero energy modes.

A review of theories and methods for hypersonic nozzle design

WANG Yunpeng, JIANG Zonglin

2021, 51(2): 257-294. doi: 10.6052/1000-0992-20-002

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In the field of hypersonic flight technology, especially the study of high-enthalpy flows, the hypersonic wind tunnel test, at present, is still the most reliable and convenient research method. For the development of hypersonic wind tunnels, one of the most important performance indicators is the uniform flow quality, which depends on the theories and methods of hypersonic nozzle design, and is the core technique of wind tunnel design. For the design of a two-dimensional axisymmetric contour nozzle, this paper first reviews the main theories and traditional design methods that have played an important role in the design of hypersonic nozzles, including the theoretical methods, the approximate methods, and the correction methods for both. Then, due to the high-temperature gas effects, the difficulties and problems faced in the design of high-enthalpy nozzles are analyzed in detail. In terms of the changes in the physical properties of the test gases, the development of high-temperature boundary-layer, and the effects of non-equilibrium processes, this paper also reviews the domestic and foreign research progresses in the design of hypersonic and high-enthalpy nozzles. Finally, the development of theory and method for designing the high-enthalpy nozzle is prospected, and we expect it to promote the development of hypersonic nozzle design technology in China.

Research progress of impact-resistance strategies and biomimetic mechanism in animal evolution

XING Yun, YANG Jialing

2021, 51(2): 295-341. doi: 10.6052/1000-0992-20-027

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After a long period of natural selection, animals in nature have evolved a variety of efficient, reliable, and adaptable impact-resistance strategies and body-protective mechanisms to resist impact loads from the complex environment they live in, protecting the organisms from injury when they carry out the intense biological activities. These naturally biological defensive systems are characterized by superiorly impact-resistance tolerance, highly energy-dissipated efficiency, and reusability compared to the traditional protective structures used in engineering. In recent years, more and more researchers have paid attention to the study on biomechanical behavior and biomimetic mechanism of organisms in resisting impact loading. In this paper, combining the recent studies in this field, we reviewed the latest research progress in impact-resistance strategies and body-protective mechanisms of various animals in nature and related bio-inspired designs and engineering applications. In particular, we summarized and discussed the unique evolutionary process and extraordinary mechanical properties of biological impact-resistant structures under different loading environments and introduced the related investigations on the biomimetic applications in resisting impact loads. Finally, we analyzed the challenges and developments of the research on impact-resistance strategies and biomimetic mechanisms in animal evolution. This review provides practical data for researchers and engineers and offers a useful reference and bionic basis for the impact-resistance and protective designs of reusable energy absorption devices and aircraft structures.

Curvature-affected instabilities in membranes and surfaces: A review

XU Fan, YANG Yifan, WANG Ting

2021, 51(2): 342-363. doi: 10.6052/1000-0992-20-038

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Instability of soft materials and membrane structures usually shows similar wrinkling patterns across length scales, which has aroused considerable interest in the past twenty years. Curvature and mechanics are intimately connected in thin-film structures, and curvature plays a key role in the critical threshold, mode selection, and post-buckling evolution. Here, we review the advancement of instability mechanics of thin-film structures in the past two decades, from planar to curved geometry, focusing on the curvature-affected instability of stretched membranes and film-substrate systems under various stimuli. Development of the theoretical models and numerical methods of finite strain plate/shell advances fundamental understanding, quantitative prediction, and tracking of multiple bifurcation transitions in morphology and shape of thin-film structures. It not only promotes the in-depth insight into instability mechanism but also guides wrinkle-resistant control and the effective design of morphology-related multifunctional surfaces and membrane structures via harnessing instability.

Verification of local scattering theory as is applied to transition prediction in hypersonic boundary layers

LI Site, DONG Ming

2021, 51(2): 364-375. doi: 10.6052/1000-0992-21-016

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The e^N method is one of the most widely used transition-prediction approaches with clear physical meaning, which however fails to take into account the effects of surface abrupt changes, such as roughness elements, gaps, steps, etc., in boundary-layer flows. However, the latter appears frequently on the surface of flying vehicles. A recently developed local scattering framework provides an effective means to address this issue. Based on the physical mechanisms of transition, the theoretical framework quantitatively describes two regimes, the local receptivity and the linear-mode scattering, leading to a modification of the transition criterion by the parameterized receptivity and transmission coefficients. In order to confirm the effectiveness of the theoretical framework, a set of direct numerical simulations of hypersonic boundary-layer flows are designed, namely, introducing the same inflow modal perturbations for two cases with a smooth surface and a rough surface, respectively. The transition processes are simulated, and the roughness effect on transition is quantified. The numerical results are found to agree well with the theoretical predictions of the linear-mode scattering regime.

Full-field video-based vibration measurement of mechanical equipment

CHEN Liqun, YANG Tianzhi

2021, 51(2): 376-381. doi: 10.6052/1000-0992-21-012

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This paper summarizes the trends and application of full-field vibration measurement based on video-based methodology. It focuses on the unique advantages of the two scenarios: vibration measurement of large-size and moving equipment. We summarize the latest progress and challenges in recent years, and finally, briefly present the outlook in this field.

Soft active materials and soft robots surviving extremely high hydrostatic pressure

QU Shaoxing

2021, 51(2): 382-385. doi: 10.6052/1000-0992-21-029

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The experiment proves that the soft robot can be driven under extremely high hydrostatic pressure (110 MPa), with actuators made of soft active materials and the electromechanical system constructed via the soft-hard hybrid method.

A pioneer of aeronautics in new China — Zhang Azhou

HU Haiyan, Wang Lifeng

2021, 51(2): 386-405. doi: 10.6052/1000-0992-21-018

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Professor Zhang Azhou (Chang O’Chou) was a famous scientist and educator in aeronautical engineering and solid mechanics in China. In the second half of the 20^th century, in particular, when China had a difficult time to initiate industrialization, Prof. Zhang pursued a life-long course to solve challenging problems and cultivate young talents and made outstanding achievements to meet the major needs of the nation in aeronautical engineering. This article comprehensively surveys the academic career of Prof. Zhang, focusing on his major contributions to the fields of the structural strength of aircraft, structural dynamics, and inverse problems of engineering dynamics, with a summary of his academic features in researches. The article presents his spirit of serving the nation in the aeronautical industry, demonstrates, via numerous examples, his core role in the tests of the structural strength of the first aircraft made in the People’s Republic of China, his leading role in the researches on static/dynamic strength of aircraft structures in China, as well as his important role in supervising young talents in both mechanics and aeronautics.

Deformation and failure of amorphous, solidlike materials

Falk M L, Langer J S

2021, 51(2): 406-426. doi: 10.6052/1000-0992-21-034

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Since the 1970s, theories of deformation and failure of amorphous, solidlike materials have started with models in which stress-driven, molecular rearrangements occur at localized flow defects via shear transformations. This picture is the basis for the modern theory of shear transformation zones (STZs), which is the focus of this review. We begin by describing the structure of the theory in general terms and by showing several applications, specifically, interpretation of stress-strain measurements for a bulk metallic glass, analysis of numerical simulations of shear banding, and the use of the STZ equations of motion in free-boundary calculations. In the second half of this review, we focus for simplicity on what we call an athermal model of amorphous plasticity, and use that model to illustrate how the STZ theory emerges within a systematic formulation of nonequilibrium thermodynamics.

2021 Vol. 51, No. 2

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