力学进展

A review on mechanisms and models for very-high-cycle fatigue of metallic materials

HONG Youshi, SUN Chengqi, LIU Xiaolong

2018, 48(1) doi: 10.6052/1000-0992-17-002

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Abstract:
The process of fatigue failure beyond 10⁷ cycles for a metallic material subjected to cyclic load is called very-high-cycle fatigue (VHCF). This review will summarize the research progress of VHCF starting with its origination in early 1980s, until the cutting-edge development in recent years. After Introduction, this review contains following parts: Origination of VHCF research, Main characteristics of VHCF, Characteristic region of crack initiation and related parameters for VHCF, Formation mechanisms and models for characteristic region of crack initiation, and Prediction models of VHCF properties. The relevant descriptions attempt to answer the following questions: What is VHCF? Why VHCF should be investigated? What are the essential scientific issues for VHCF? Why the tendency of S-N curve for VHCF is changed? Why crack initiates from the interior of material (specimen) for VHCF? What are the process and the mechanism of interior crack initiation? Some of the questions will be clearly answered, but some of them be just addressed by newly results, which require further exploration.

Study on cyclic deformation and fatigue of thermal and magnetic shape memory alloys

KANG Guozheng, KAN Qianhua, YU Chao, SONG Di

2018, 48(1) doi: 10.6052/1000-0992-17-008

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Shape memory alloys (SMAs), including the thermal and magnetic ones, have attracted wide attention from scholars and engineers, and have been successfully employed in many engineering applications due to their unique super-elasticity and shape memory effects. To further prompt the application fields of SMAs, the progresses in the microscopic and macroscopic experimental observations and theoretical studies on their thermo-mechanical and magneto-mechanical coupled cyclic deformation and fatigue failure are reviewed herein. The latest achievements on the thermo-mechanical coupled cyclic deformation and fatigue failure of the thermal (i.e., temperature-induced) SMAs including NiTi and high-temperature NiTiX ones are summarized. In addition, the research status on the magneto-mechanical coupled cyclic deformation and fatigue failure of the magnetic SMAs including NiMnGa ones are reviewed. Last, a brief summary and a prospect of future topics are provided.

Aerothermal dynamic failure of infrared window in high-speed aircraft

E Yujia, WANG Tianyu, GAO Ge, GENG Fangjuan, AI Junqiang, HAN Jiecai, ZHU Jiaqi

2018, 48(1) doi: 10.6052/1000-0992-16-047

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As one of the key components of a high-speed aircraft, the infrared window which is composed by matrix materials and functional films is widely applied. In the harsh environment, however, the infrared window works under complex aerothermal conditions, which may lead to its structural failure or dysfunction. Thus, the investigation on the aerothermal dynamic failure of infrared window in high-speed aircraft is of scientific importance and practical significance. This article reviews the studies on the aerodynamic thermal failure mechanisms of infrared windows in high-speed conditions, concerning typical materials, the aero-thermo-dynamics and structural failure or dysfunction. Finally, the prospects of further investigations on infrared windows are discussed.

Indentation tests investigation of mechanical behavior of two-dimensional materials

ZHOU Lixin, CAO Guoxin

2018, 48(1) doi: 10.6052/1000-0992-16-043

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Fully understanding the mechanical properties of two-dimensional (2D) materials is highly important for developing applications based on 2D-materials. Free-standing indentation (FSI) is currently the most common method to measure the mechanical properties of 2D-materials. The present work reviewed the state-of-the-art FSI investigations of 2D-mateirals, the issues to be considered, and some future works in this area. In FSI tests, 2D-materials are firstly transferred on the top of the substrate with cylindrical holes to create beam/drum-type samples, and atomic force microscopy (AFM) is then used to measure the indentation load-displacement relationship of these samples. Finally, the mechanical properties, including the elastic modulus and intrinsic strength, can be determined by fitting the experimental results as the indentation analysis model is developed on the basis of the continuum thin film. However, since the thickness of 2D-materials is far less than that of the continuum thin film, the van der Waals (vdW) adhesion interactions from the AFM-tip and the side-wall of substrate hole have a strong influence on the indentation response, which leads to measurement inaccuracy of the elastic modulus of 2D-materials from FSI tests. In addition, the nonlinear response of 2D-materials under large deformation as well as the stress concentration created by defects cannot be effectively described by the conventional indentation analysis model, and thus, the intrinsic stress of 2D-materials cannot be accurately determined, especially for the poly-crystalline 2D-materials. Therefore, we should correctly understand the present experimental results from FSI tests, and in the meantime, it is very necessary to further improve the FSI technique for measuring the mechanical properties of 2D-materials.

Research progress on hydrodynamics of high speed vehicles in the underwater launching process

WANG Yiwei, HUANG Chenguang

2018, 48(1) doi: 10.6052/1000-0992-16-020

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Research on hydrodynamics of high speed vehicles in underwater launch process has a prominent engineering background, and contains typical frontier scientific issues. Relevant unsteady cavitating flow issues including instability and collapse of cavities, are of~crucial importance to the analysis of dynamic load and underwater launching vehicles' safety. In this paper, we first introduce the main scientific problems and the control parameters. Then we review the physical mechanisms on the development instability, collapse and control methods of unsteady fluid cavitation. Finally, remaining challenges and development~tendency for future research are given.

Applications and developments of aeroelasticity of flexible structure in flow controls

ZHANG Jiazhong, LIU Yan, SUN Xu, CHEN Jiahui, WANG Le

2018, 48(1) doi: 10.6052/1000-0992-16-034

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There exists a very rich variety of distinctive properties which are relevant to unsteady, nonlinear flows and structural dynamics, as the flexible structures and fluids are coupled dynamically. If the aeroelastic effects are controlled and utilized properly, the aerodynamic performances and self-adaptability of aircraft wings and wind turbine blades could be improved significantly. In this paper, the progress and major challenges in aeroelasticity and its applications in flow control are reviewed, and three main directions, including the aerodynamic characteristics of the membrane wing, the drag reduction technique using flexible wall and the Sinha disturbers, are discussed in detail. In particular, the relevant studies including the experimental techniques, the numerical methods for fluid-structure interactions and theoretical methods such as nonlinear dynamics, Lagrangian coherent structure are summarized, and the great potential of the aeroelasticity in flow control and its academic values are emphasized, in order to pave the way for the researchers who are engaged in this field.

Engineering mechanical-electrical cell microenvironment in myocardium using advanced biomaterials

XU Feng, ZHANG Xiaohui, BAO Xuejiao, ZHAO Guoxu, LIU Fusheng, HUANG Guoyou, LI Yuhui, LU Tianjian

2018, 48(1) doi: 10.6052/1000-0992-17-014

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Cardiovascular diseases remain the leading cause of human death worldwide. The development of cardiac tissue engineering has provided a most potential strategy for the treatment of cardiovascular disease through regenerating functional cardiac tissues and restoring dysfunctional myocardium. The occurrence and progress of cardiovascular diseases are closely related to the changes of mechanical and electrical cell microenvironment in native myocardium. In the last decades, with the advances in biomaterials and micro- and nano-fabrication techniques, increasing evidence has demonstrated that the biomimicking of mechanical-electrical cell microenvironment is important for the maturation and functionalization of engineered cardiac tissues for the purpose of myocardium restoration. In this review, we firstly elucidated the biological basis of mechanical properties and electrical signal transmission in native myocardium, including the mechanical and electrical microenvironment in physiological and pathological conditions. Then, we reviewed the current research progress of advanced biomaterials for cardiac tissue engineering applications. Finally, we summarized the development and manipulation of mechanical and electrical microenvironment using advanced biomaterials, and the biological responses of cardiomyocytes and cardiac tissues to the biomimicking mechanical-electrical microenvironment.

The mechanical problems in tumor and tumor microenvironment

SHI Xinghua, ZHANG Luyao, LI Bo, FENG Xiqiao

2018, 48(1) doi: 10.6052/1000-0992-16-039

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Tumor microenvironment contains tumor cells, stromal cells and extracellular matrix, which plays an important role in tumor growth and development. The tumor microenvironment has its unique structural features. Physical forces in tumors can change the tumor microenvironment, disable the blood and lymphatic vessels, result in the abnormal metabolism, compress the interstitial structure, hinder the delivery of drugs, and induce stromal cells to change their behavior and promote tumor metastasis. So the forces in tumor have attracted increasing attention. In this review, we summarize the advances of mechanics problems in tumor and its microenvironments. We discuss the causes of solid stress, drug delivery and tumor metastasis. Also we introduce several strategies to restore the tumor microenvironments and their effects on tumor therapy.

Biomechanics in cartilage tissue engineering

ZHANG Chunqiu, LI Ke, GAO Lilan, ZHANG Xizheng

2018, 48(1) doi: 10.6052/1000-0992-17-007

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Articular cartilage is one kind of elastic loaded tissues. Its complex structure contains solid and liquid phases. The solid phase consists of collagens and proteoglycans, and the liquid phase consists of water and electrolyte. The microstructure of the solid phase is a type of fiber reinforced composites. Articular cartilage provides a smooth interface with low wear and friction, and plays an important role in buffering shocks, transferring loading and etc. The knee joint is subjected to a large amount of exercise and high stress, which make the articular cartilage injury common in clinic. Since there is no blood supply in cartilage tissues, they are difficult to heal once injury. Tissue engineering provides an ideal method for the treatment of defects in cartilages. Although cartilage tissue engineering has started to be applied in clinic, but the method is not widely employed. How to get the engineered cartilage, and which structure and function are suitable for the clinical use are still remaining problems to be solved. The key to the construction of functional engineered cartilage in vitro is to apply appropriate mechanical conditions in bioreactors. First, the loads ensure the effective transportation of the internal signals, nutrients and wastes; second, it is necessary to apply specific mechanical stimulations on seed cells in scaffolds; third, it needs to promote the development of the structure and function of extracellular matrix. This paper reviews the latest research in cartilage tissue engineering. This review categorizes the mechanical stimuli into three types according to different medias during the process of load transfer: namely, liquid-mediated forces, solid-mediated forces and other forces. This paper analyzes the major biomechanical problems in cartilage tissue engineering and predicts the trend of future developments. At last, this paper suggests that the synergy of mechanical and biochemical stimuli should be taken into account in cartilage tissue construction. In this way, rolling-sliding-compression load accompanied by appropriate biochemical conditions may be beneficial to realize the functional development of engineered cartilage in vitro.

Undulation force between membranes

LI Long, SONG Fan

2018, 48(1) doi: 10.6052/1000-0992-16-038

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Undulation force, originating from the thermally excited membrane fluctuations, plays a key role in regulating an astounding array of the biological functions of cells, such as cell adhesion, membrane fusion, binding-unbinding transition and membrane self-assembly. Therefore, the study on the undulation force and its laws forms a significant foundation for life science research. In view of the important role of undulation force in the regulation of cellular processes, it has been highly concerned since the concept of the undulation force was put forward in the 1970s. However, the distance dependence of the undulation force, which constitutes the most fundamental characteristics of the force, currently causes great controversy and has not been understood very well yet up to now. Here, we first overview the development of the concept of undulation force and its related research. On this basis, two controversial theories on the distance dependence of undulation force and the latest research advances are introduced in details. Furthermore, we deeply discuss the difference between the two theories, which provides a reference for further studies. Finally, we give a brief summary and prospect on current and future research focus and development trend of the undulation force.

AFM force spectroscopy and its applications on micro biomechanics

GE Lin

2018, 48(1) doi: 10.6052/1000-0992-17-011

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Atomic force microscopy (AFM) based force spectroscopy is a high-sensitive mechanical detection method. With unprecedented accuracy, this method enables the characterization of a wide range of biological and synthetic bio-interfaces, ranging from tissues, cells, membranes, proteins, nucleic acids to functional materials. Besides the possibility of high resolution imaging of biological samples from the cellular level to the molecular level, AFM-based force spectroscopy allows their mechanical, chemical, conductive or electrostatic, and biological properties to be probed, and helps addressing fundamental challenges that cannot be addressed with other techniques. In this review, we summarize basic and advanced force spectroscopy approaches in micro biomechanics and evaluate their unique advantages and limitations.

Measurement techniques of grain motion and inter-grain structures in dense granular materials

YANG Hui, ZHANG Guohua, WANG Yujie, SUN Qicheng

2018, 48(1) doi: 10.6052/1000-0992-17-010

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A dense granular material is composed of a large number of densely packed coarse grains, which is widely encountered in nature, engineering and industries, such as granular debris flows, rock-filled dams, and pebble beds in nuclear reactors. It is a typical many-body system with intrinsic characteristics of structural and dynamic heterogeneities which leads to the complicated macroscopic behavior. By developing the statistic mechanics of structure and dynamics of grains, continuum theories of granular materials can be established and such macroscopic behaviors are then expected to be described. However, it is very difficult to fulfil these objectives because of the limitations of present measurement techniques and theoretical basis. The present measurement techniques are only applicable to study ideal and simple structure problems, and do not work well for granular structures. The shortage of granular structures properties makes the connections between structure and macroscopic properties impossible. Therefore, measurements of heterogeneity in structural and dynamics are the foundation for understanding the complex bulk properties of granular materials. The authors of this paper, from different research institutions, have conducted thorough experimental studies in the past decade, which can be classified into two categories: (1) non-invasive methods, mainly including digital image velocimetry, speckle visibility spectroscopy and Xray-CT, are developed to measure the moment of single grains; (2)response spectrum methods, mainly including volume response spectrum, mechanic response spectrum and acoustic measurements, are developed to directly or indirectly detect the inter-particle contact force. In this paper, we review the fundamental principles of these methods and their limitations, and state-of-the-art studies. Finally, we conclude the paper with our experience sand lessons learned, and provide suggestions for the future work.

2018 Vol. 48, No. 1

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