Mechanics in Engineeringfirst published in 1979. It is administrated by the Chinese Academy of Sciences, with the Chinese Society of Theoretical and Applied Mechanics and the Institute of Mechanics, Chinese, Academy of Sciences jointly as the responsible institutions. It covers general fields of mechanics, with the widest circulation among journals devoted to mechanics in China. Its focuses are on progresses of mechanics and its interdisciplinary fields, applications in engineering, teaching notes on mechanics, profiles of scientists of mechanics, history of mechanics, interesting anecdotes, book reviews and others. With its unique features as distinguished from similar journals in China, keeps the following regular columns... More>>
08 October 2020, Volume 42 Issue 5
Review
RESEARCH PROGRESS OF FRACTURE TOUGHNESS TEST METHOD FOR LOW CONSTRAINT SPECIMENS 1)
WU Xu, SHUAI Jian, XU Kui
2020, 42(5):  535-542.  DOI: 10.6052/0459-1879-20-105
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The fracture toughness test of low constraint specimens is of great significance for the safe operation of oil and gas pipelines. In this paper, the existing fracture toughness testing methods and the development process of low constraint specimens are reviewed, and the common fracture toughness characterization parameters such as crack tip opening displacement (CTOD) and J-integral are introduced. The key problems such as the stress intensity factor, the J-integral plasticity factor, the J-integral and CTOD conversion factor, the crack size measurement method, and the digital image correlation method, in the fracture toughness test, are analyzed, and the problems that need to be further studied are summarized, to provide a necessary basis for the development of fracture toughness test of low constraint specimens.

Applied Research
EXPERIMENTAL ANALYSIS OF ACTIVE STEERING HARDWARE-IN-LOOP BASED ON SLIDING MODE CONTROL 1)
FAN Haoyang, LI Shaohua, WANG Guiyang
2020, 42(5):  543-550.  DOI: 10.6052/0459-1879-19-478
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In order to improve the safety of heavy-duty vehicles in the steering process, this paper proposes an active front wheel steering control strategy based on the sliding mode variable structure control. With this strategy in mind, an active steering controller is designed. A simplified vehicle dynamics model with two degrees of freedom and a model for a three-axle commercial vehicle are established. The co-simulation platform is built with TruckSim and Simulink, and the hardware-in-loop experiment is carried out. Under different working conditions and at different speeds, the steering stability analysis of the vehicle with or without the active steering controller is carried out. Based on this, the sensitivity analysis of the active steering influencing factors of the sliding mode variable structure control is carried out. The experimental results show that this controller strategy has a good adaptability under different working conditions.

HUMAN-LIKE CONTROL FOR SEMI-PASSIVE BIPEDAL ROBOT WALKING WITH VARIABLE LEG STIFFNESS1)
ZHANG Rui, ZHANG Qizhi, ZHOU Yali
2020, 42(5):  551-557.  DOI: 10.6052/0459-1879-20-139
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For the walking control of the semi-passive bipedal robot with variable stiffness, the human-like walking control strategy is adopted. By using the self-stabilizing characteristics of the bipedal spring loaded inverted pendulum model with variable stiffness, the rear leg stiffness is adjusted in the double support phase to keep the robot energy near the desired energy, and the position of the swinging leg touching down on the ground is adjusted in the single support phase to control the altitude and the forward velocity of the desired point. The simulation results show that the human-like control strategy can ensure a stable walking of the bipedal robot in the horizontal plane. The robot can achieve the passive periodic walking with zero-input when there is no disturbance. With the variable stiffness control of the leg, the total energy of the robot can be restored to a balance state, the robot can re-enter the steady-state walking, and the control system is robust to the external disturbance.
COMBINATION RESONANCES OF AN AXIALLY MOVING UNIDIRECTIONAL PLATE PARTIALLY IMMERSED IN FLUID WITH TIME-DEPENDENT AXIAL SPEED1)
LI Hongying, LI Xin, WANG Xueqi
2020, 42(5):  558-564.  DOI: 10.6052/0459-1879-20-037
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This paper studies the dynamic characteristics of combination resonances of a plate partially immersed in fluid with a time-dependent axial speed. Based on the theory of von Kármán large deflection plate and taking into account of the effects of the fluid-structure interaction, the tension force and the time-dependent speed, the nonlinear dynamic equations of the plate partially immersed in fluid are established. By applying the Galerkin method to discretize the equations, the nonlinear dynamic equation set in modal coordinates is then obtained. The effects of parameters such as the average speed, the pulsating speed and the tension force on the nonlinear dynamic characteristics of the system are analyzed through the multiple scale method and the numerical method. It is revealed that when a combination resonance occurs, the system shows a complex dynamic behavior, the amplitude of the first order modal response is far larger than that of the second order, and the influence of the average speed and the pulsating speed on the frequency-response curve is quite remarkable.
DYNAMIC RESPONSE OF THE CATENARY RISER IN DEEP-SEA MINING SYSTEMS 1)
KUAI Yanrong, WEI Mingzhu, WANG Xu, ZHOU Jifu
2020, 42(5):  565-570.  DOI: 10.6052/0459-1879-20-085
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With a finite element model, the dynamic response of the catenary riser of deep-sea mining systems under the action of the ocean current and the motion of the surface vessel is simulated. The results show that the maximum equivalent stress and the maximum displacement of the catenary riser change periodically with a phase difference of half a period between them. When the surface vessel moves to the highest position, the displacement of the catenary riser reaches the maximum. The maximum equivalent stress and the maximum displacement of the catenary riser increase with the increase of the displacement amplitude of the surface vessel and decrease with the increase of the period. In addition, the effect of the displacement and the period of the motion of the surface vessel on the equivalent stress of the catenary riser is greater than that on the displacement.

AEROELASTIC OPTIMIZATION DESIGN OF COMPOSITE WING WITH CONSIDERATION OF STRUCTURAL INSTABILITY
LIU Xiaochen
2020, 42(5):  571-575.  DOI: 10.6052/0459-1879-20-026
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Based on engineering mathematical solution and finite element analysis, the aeroelastic optimization technology is developed with consideration of both the wall stability constraints and the aeroelastic constraints. The aeroelastic comprehensive optimization design is carried out for a large aspect ratio composite wing. It is shown that if the stability constraints are not considered in the aeroelastic optimization of the wing, although a smaller structural weight can be achieved, the stability requirements are often not satisfied. Compared with the aeroelastic comprehensive optimization design method with consideration of the structural instability characteristics by the finite element, the optimization with the partition instability analysis of the wing structure by engineering mathematical solutions can control the variables more accurately, further reduce the structural weight and improve the structural instability factor while satisfying various performance requirements, especially, the stability constraints.
NUMERICAL STUDY OF THE PHENOMENON THAT A FERRY BOAT DRIFTS ATHWART AT THE DESERTED CROSSING
YU Yongfei, CHEN Chen, SI Tiedong, HU Ting, WEI Jiawang
2020, 42(5):  576-579.  DOI: 10.6052/0459-1879-20-108
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In order to study the phenomenon that a ferry boat drifts athwart at the deserted crossing, a numerical simulation is carried out for the motion of a boat under the water flow action. Conclusions are as follows: The boat can keep a balance both along and across the water. But it is an unstable balance along the water, it will be lost because of an external disturbance, and the boat can not restore to its homing position again. While the boat is in a stable balance across the water, it can restore to the homing position again even if the boat loses the balance under an external disturbance.
RESEARCH OF STEPPING PRESSURE AND CONTROL OF NEAR FIELD ROOF OF TASHAN COAL MINE BASED ON NUMERICAL SIMULATION1)
LI Jinbo, WANG Suling, DONG Kangxing, ZHAO Xinyu, XIE Wenqi, ZHANG Ziheng
2020, 42(5):  580-587.  DOI: 10.6052/0459-1879-20-075
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The hard roof of coal seam is directionally weakened by hydraulic fracturing technology, which can effectively control the stepping pressure distance and reduce the risk of accidents. Based on the cohesion model and the secondary development technology of the finite element platform, a numerical calculation model of coal seam mining before and after fracturing is established, the roof collapse law and its influencing factors are analyzed, and the fracture spacing design is optimized. The results show that the stepping pressure span has a positive correlation with the roof thickness and strength, and a negative correlation with the buried depth. Prefabricated fractures in tensile stress concentration areas can promote the crack initiation and propagation. Geological parameters of each rock layer should be carefully determined, as well as the location of stress concentration areas, to design the fracture spacing for controlling the stepping distance economically and effectively.
AN IMPROVED IRS METHOD FOR STRUCTURE MODEL CONDENSATION1)
YANG Qiuwei, ZHANG Jinxin, LI Cuihong
2020, 42(5):  588-593.  DOI: 10.6052/0459-1879-20-163}
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The model condensation method is widely used in the static and dynamic analysis of structures. With the model reduction, the calculation scale of structural static and dynamic equations can be effectively reduced, with the calculation time and cost saved, and to obtain a reduced finite element model matching the experimental measurement freedoms. A new IRS (improved reduced system) method is proposed in this paper by considering the second-order inertia, to effectively improve the calculation accuracy. Compared with the IIRS (iterated IRS), the proposed second-order IRS method can be used to build a more accurate reduced model with smaller calculation amount. Taking a truss structure and a frame structure as examples, the proposed second-order IRS method is verified, and the calculation results are compared with the exact solution, the Guyan condensation solution, the IRS solution and the IIRS solution. It is shown that the proposed method enjoys the best calculation accuracy, with a good engineering application prospect.
DEFLECTION OF FOUR TYPES OF CANTILEVER BEAMS WITH VARIABLE CROSS SECTION UNDER LATERAL TRIANGULAR DISTRIBUTED LOADS1)
LIAO Han, JIANG Lüfeng, LI Hengda, YANG Xingchang, LI Yinghui
2020, 42(5):  594-597.  DOI: 10.6052/0459-1879-20-015
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The deflection of cylindrical, conical, parabolic and hyperbolic cantilever beams with reversed sections under laterally triangular distributed loads is studied. Firstly, from the distribution of moment of inertia along the length direction of four types of rotating cantilever beams, the deflection curve equation under any lateral triangular distributed load is obtained. Based on the deflection curve equation under the linear load, the deflection at the lower end of the lateral triangular distributed load is obtained. Under the assumption of equal length and equal volume, the minimum deflection among the four types of cantilever beams is found by comparing the end deflection values. It is shown that among the four types of cantilever beams under lateral triangular distributed load, the characteristic parameters are within a specific range, and the deflection of the cantilever beam with hyperbolic bus is the smallest.
Research on Education
SOME PROBLEMS AND THEIR SOLUTIONS IN MECHANICS EDUCATION
HU Haiyan
2020, 42(5):  598-602.  DOI: 10.6052/0459-1879-20-356
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In the mechanics education, it is urgently needed to enhance the qualities of students in solid foundation and creative ability. Even though the enhancement has been widely recognized in the Chinese circle of mechanics education, some problems remain open in practice. Based on the talent development law, the cognitive learning law and the practice innovation law, three problems are analyzed, including the curriculum optimization, the design and development of teaching materials, and the innovation in practice, and the corresponding suggestions are made. Among them, some have been validated to be possible solutions in practice.

CONSTRUCTION OF CLASSICAL ELASTICITY SOLUTION DATABASE WITH INDEPENDENCE AND TIMELINESS MANAGEMENT1)
WANG Hongwei, TANG Jianwei, QIN Shu, ZHOU Hongwei
2020, 42(5):  603-608.  DOI: 10.6052/0459-1879-20-046
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Based on our practice of the interactive operation and visual teaching methods, the Visual C++ and the MATLAB are used to construct a classical elasticity solution database, with the independence and timeliness characteristics. In order to achieve the independence call of the data and the dynamic adjustment of the visualization module, the method of the modular design and the subprogram parallel calculation is used to build the problem description module, the parameter input module, the visualization and output module and the result call module. To ensure the timeliness of the interactive operation, the multithread parallel computing and the fast and accurate result output in the display module are used in calculation subroutines of the database. Through the application of this database, the visualized, vivid and colorful teaching purpose is achieved.
EXPERIMENTAL MEASUREMENT OF A MONKEY TOY THAT CAN STAND STEADILY AFTER A 360° SOMERSAULT1)
LI Kai, XUE Yongjiang
2020, 42(5):  609-616.  DOI: 10.6052/0459-1879-20-073
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A monkey toy that can stand steadily after a 360° somersault is analyzed in this paper by experimental methods. Firstly, the location of the center of mass of the monkey toy is determined by a suspension experiment. Then the compound pendulum method is used to measure the moment of inertia of the monkey toy. Finally, the stiffness of the spring used in the monkey toy is determined by a tension test. The motion of the monkey toy during its 360° somersault is measured by the digital image correlation method. The results show that the experimental results agree well with the theoretical analysis, and the mechanism of the motion of the monkey toy is well explained. This experimental project can enhance students' interest in experiment and scientific research.
THE RELATION BETWEEN STRENGTH AND RIGIDITY OF BEAM1)
MA Hang, MA Yongqi, DING Weidong, DING Chao
2020, 42(5):  617-621.  DOI: 10.6052/0459-1879-20-020
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In order to make a full use of the potential of materials as well as to promote the classroom teaching for the course of mechanics of materials, the strength-stiffness ratio of beams is introduced in the paper. The ratio provides a quantitative relation between the strength and the stiffness of beams in the non-dimensional form. It is independent of the magnitude of load, its value can be obtained through the finite element method or through the load test of beams. Combined with the engineering practice, the strength-stiffness ratio of beams are analyzed with its influence factors from the aspects of design and test.
THE REFORM OF TEACHING CONTENT FOR THE COURSE OF FOUNDATION SETTLEMENT
GUAN Linbo
2020, 42(5):  622-626.  DOI: 10.6052/0459-1879-20-003
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This paper puts forward the idea of reform of the course contents of the soil settlement, from the angle of the degree of consolidation of soil, to the calculation of the final settlement, and finally to different test methods and compressibility indexes. The new teaching idea makes a reasonable distinction between the basic theory of the soil mechanics and the practical application of the soil mechanics, which can not only guarantee the purity and the rationality of the basic theory, but also meet the challenge of the further development and enrichment of the theory due to the complexity of soil in practice.
COURSE EXPANSION FOR FATIGUE PROBLEM IN THE COURSE OF MECHANICS OF MATERIALS BASED ON ONLINE COURSE
FANG Mingxia, CHEN Jie
2020, 42(5):  627-632.  DOI: 10.6052/0459-1879-20-028
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With the development of network and information technology, online course platforms are playing an important role. In view of the reduction of the course hours, the book knowledge is expanded in the form of the extended reading of the online course. Based on the online course platform, this paper extends the fatigue problem of metal materials under the stable alternating load to the fatigue problem of metal materials under the unstable load and the fatigue problem of non-metal materials, and the fatigue life estimation formula is introduced through examples. Using the online platform to integrate resources and expand knowledge plays an important role in cultivating students' ability to analyze and solve problems.
TEACHING OF MACHANICS OF MATERIALS WITH ENGINEERING CASES FOR UNDERGRADUATES MAJORED IN RAILWAY AND BRIDGE1)
FENG Wenjie, LIU Lingling
2020, 42(5):  633-638.  DOI: 10.6052/0459-1879-20-036
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In the teaching of mechanics of materials, in order to enhance students' interest in learning and the ability to solve practical problems in engineering, some engineering cases are analyzed in the context of the characteristics of railway and bridge for undergraduates. On one hand, the teaching mode can further deepen students' understanding of the basic knowledge and the concepts of mechanics of materials. On the other hand, it can improve the students' ability to solve specific problems in the professional field by using the knowledge that they have learned, and can stimulate the students' enthusiasm and initiative in learning. Many years of teaching practice have proved the effectiveness of this teaching mode.
TO PROMOTE STUDENTS' INNOVATIVE ABILITY BY USING CLASSROOM DEMONSTRATION EXPERIMENTS1)
WANG Ying, ZHU Zhihui, LUO Jianyang, XIE Xiaoqing, LI Haiying, CAI Ruya
2020, 42(5):  639-641.  DOI: 10.6052/0459-1879-19-414
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One of the essential tasks of teaching is to stimulate students' innovative consciousness and to develop their innovative capabilities. Various simple and flexible experiments are proposed for demonstrations in teaching fluid mechanics, for arousing students'interest and inspiring their creativity thinking. Based on this teaching practice, this paper highlights several teaching experiences.
The Field of Mechanics
A BRIEF HISTORY OF THE WING LIFT THEORY
DING Zurong
2020, 42(5):  645-649.  DOI: 10.6052/0459-1879-19-407
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This paper reviews the process of exploration of the wing lift theory in the late 19th and early 20th centuries. It includes Newton's sine-square law, the understanding and application of the Magnus effect, Lanchester, Kutta, and Joukowsky's establishment of the wing lift circulation theory and Prandtl's establishment of the lift line theory. The historical facts are traced with stories about related scholars.

THE HISTORY OF DEPARTMENT OF WATER CONSERVANCY OF PEIYANG UNIVERSITY 1)
WU Pan, YANG Shaoqiong, JIANG Nan
2020, 42(5):  650-660.  DOI: 10.6052/0459-1879-19-405
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Based on some historical documents, this paper briefly reviews the development of the Department of Water Conservancy of Peiyang University (Tianjin University), with related events and persons. This paper focuses on the historical continuity of the water conservancy discipline and the Department of Water Conservancy from Peiyang University to Tianjin University and its position in the Chinese higher education of water conservancy; the role of Peiyang University in Chinese First Institute of Hydraulic Engineering and its development process; and the related stories of the Centre of Hydraulic Engineering, famous professors and the outstanding alumni, and shows the historical inheritance and the modernisation achievements of the Department of Water Conservancy of Peiyang University-Tianjin University in the past one hundred and twenty-five years, which inspire a new generation of Tianjin University in water conservancies. Rejuvenate the spirit of Peiyang, and deeply remember the late, outstanding alumni Yu Yuanjun and others.

ON THE CHANGES OF MEANING OF “LI” AND “LIXUE” (“FORCE” AND “MECHANICS” IN CHINESE)1)
ZHAO Huiming, ZHAO Yucheng, CHENG Hongmei
2020, 42(5):  661-664.  DOI: 10.6052/0459-1879-19-417
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The words “Li” and “Lixue” exist for a long time in Chinese. The meaning of “Li” is initially a direct and intuitive description of “human force”. Later, it developed for the description of the gravity of general objects, and then to the description of the causes of motion state change. This paper analyzes the changes of the meaning of “Li”. Chinese “Lixue (mechanics)” comes as the result of the introduction of Western learning to the East, and there are many twists and turns in the process of determining the subject name. This paper analyzes the process of determining “Lixue” as the subject name, and reveals the change of ancient Chinese understanding of “Mechanics”.
DESIGN AND PRACTICE OF SCIENCE AND TECHNOLOGY INNOVATION EXPERIMENT PROJECT IN STRUCTURE DESIGN COMPETITION1)
HE Chunbao, ZHANG Zhaojing, FENG Jinyao
2020, 42(5):  665-670.  DOI: 10.6052/0459-1879-19-418
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In view of the characteristics of the structural design competition for the civil engineering students and the training requirements for the students' practical ability, the mechanical properties of bamboo components are considered in the structural design competition,and with bamboo and glue as the raw materials,the project of the science and technology innovation experiment is designed. The compression, tension, bending and composite strength experiments of glue and bamboo are carried out on bamboo components of different lengths and thicknesses, the bearing capacity of the components are tested by loading. It is shown that the load ratio of the thick bamboo is better in tension, compression and bending,the load ratio of bamboo can be increased by glue dripping,and the nonlinear characteristics of compressed bamboo components are significant. The innovative experimental project is closely combined with the structural design competition, with a strong practicality and is conducive to the cultivation of students' ability of teamwork and innovation.
STRUCTURE DESIGN AND ANALYSIS OF A COMPETITION MODEL FOR THE 10th INTER-UNIVERSITY INVITATION CIVIL ENGINEERING COMPETITION1)
ZHANG Xun, XIAO Lin, HE Wei, ZHAN Yulin
2020, 42(5):  671-677.  DOI: 10.6052/0459-1879-19-437
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The theme of the 10th Inter-University Invitational Civil Engineering Competition is to design a curved bridge, capable of withstanding static and dynamic loadings. A model is required to have a sufficient load-carrying capacity and a reasonable stiffness. Moreover, its mass should be as small as possible. According to the model made by Southwest Jiaotong University, the steps and the methods of the structural optimization are described in terms of the material mechanical properties, the bridge conceptual design and the numerical optimization. The results of the static and dynamic numerical simulations are compared with those of prototype testing. The advantages and disadvantages of the model design are summarized.
Featured ArticleMore>>   
  • Title: RESEARCH PROGRESS OF FRACTURE TOUGHNESS TEST METHOD FOR LOW CONSTRAINT SPECIMENS 1) PDF
  • Author:WU Xu, SHUAI Jian, XU Kui
  • Abstract: The fracture toughness test of low constraint specimens is of great significance for the safe operation of oil and gas pipelines. In this paper, the existing fracture toughness testing methods and the development process of low co. . . More>>