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20 February 2019, Volume 41 Issue 1
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    2019, 41(1):  1-9.  doi:10.6052/1000-0879-18-154
    Abstract ( 713 )   HTML( 244 )   PDF (2778KB) ( 244 )  

    This paper discusses a basic problem: Is the coordinate transformation coefficient the component of a tensor? The conventional viewpoint is that the coordinate transformation coefficient is not the component of a tensor. To reveal the essence of the coordinate transformation coefficient, the basic concept of the tensor is revisited. A new concept, i.e. the hybrid tensor, is defined. On the basis of the new concept, the conventional viewpoint is negated: the coordinate transformation coefficient is indeed the component of a tensor. That is to say, it is the hybrid component of a metric tensor. Thus, the concept of tensors is extented.

    2019, 41(1):  10-13.  doi:10.6052/1000-0879-18-146
    Abstract ( 810 )   PDF (2227KB) ( 132 )  
    The movement of the golf ball on the green in different ways of hitting is analyzed. The influence of different hitting modes on the movement of the ball is revealed. The motion distance and the motion stability are different. This can help the golfer to control the hitting action of the putter more conveniently and accurately.
    2019, 41(1):  14-22.  doi:10.6052/1000-0879-18-222
    Abstract ( 441 )   PDF (3875KB) ( 65 )  
    According to the energy equivalent method, a semi-analytical model of the load-displacement relation for funnel-sheet specimens is proposed to correlate the Ramberg-Osgood parameters and the geometry parameters. The model is validated with the forward-predictions and the reverse-predictions in the finite element analysis. On this basis, a new method is put forward for predicting the low cycle fatigue (LCF) properties of materials by funnel sheet specimens. The LCF properties of the SS316L funnel -sheet specimens are verificated to be agree with the round bar specimens. Therefore, the LCF properties of N18 and SAPH440 at different temperatures are predicted by the method.
    2019, 41(1):  23-29.  doi:10.6052/1000-0879-18-270
    Abstract ( 247 )   PDF (18423KB) ( 61 )  
    In order to reveal the microstructure multi-phase coupling mechanism and the dynamic deformation law of the silt lightweight soil under cyclic loading, the mesoscopic multi-phase deformation mechanism and the relationship between macroscopic and mesoscopic deformation characteristics of lightweight silt soil under cyclic loading are studied by using a new indoor consolidation test and the ABAQUS finite element numerical simulation methods. The results show that the EPS content and the particle size have a significant effect on the meso-deformation characteristics of silt lightweight soil. When the EPS (expanded polystyrene) content differs by 2.0%, the maximum volumetric deformation of the silt lightweight soils differs by 4.1%. Under the same number of cycles, the relations between the deformation and the stress and strain magnitude of the EPS particles at the upper, middle and lower points in the sample are different. The deformation of the EPS particles at the upper point is the largest. The mesoscopic deformation relationship of each phase of the silt lightweight soil in different cycle periods is analyzed by a quantitative calculation. The results indicate that the deformation of the EPS particles is dominant in the whole deformation process of the silt lightweight soil, and the amount is about $60%\sim80%$ on average.
    2019, 41(1):  30-36.  doi:10.6052/1000-0879-18-216
    Abstract ( 177 )   PDF (345KB) ( 49 )  
    The semi-analytical and semi-numerical transfer function method is applied to study the high-aspect-ratio wing gust response. First, the wing gust response equations are established by combining the beam bend vibration model and the steady aerodynamic model, which are transformed by the Laplace transformation into the state-space form. Then, the analytical solution in the frequency domain is obtained by using the transfer function method. The transient response of the wing in the time domain is obtained by the numerical inversion of the Laplace transforms. By comparing with the results in the existing literature, the method is validated. Finally, the response of the wing for the One-Minus-Cosine gust and the continuous atmospheric turbulence is solved and analyzed.
    2019, 41(1):  37-42.  doi:10.6052/1000-0879-18-313
    Abstract ( 220 )   PDF (919KB) ( 72 )  
    This paper studies the bearing capacity of the frozen soil foundation of engineering constructions in permafrost areas. Based on the creep tests of the artificial frozen clay, a generalized Kelvin model is established. The large-scale artificial frozen soil freezing test platform is used to test the bearing capacity of the artificial frozen clay. It is found that the load-settlement curve could be divided into three stages, and the foundation sees a local shear failure. For the use of the ANSYS, the temperature field with consideration of the phase transition is transformed into a temperature load and a three-dimensional solid model and a generalized Kelvin model are built, with a step loading. By comparing the numerical simulation results and the model test results, it is found that the load-settlement curve is consistent, the ultimate bearing capacity is basically the same, and the basic failure mode is the local shear failure. The results show that the ANSYS could analyze the properties of the frozen soil under complex boundary and initial conditions, and the stress and displacement of the frozen soil under different loads could be obtained
    MECHANICAL ANALYSIS OF TOROFLUX
    ZHU Haidong, GAO Jian, ZHUANG Biaozhong?
    2019, 41(1):  43-44.  doi:10.6052/1000-0879-18-291
    Abstract ( 229 )   PDF (460KB) ( 66 )  
    The toroflux, as a fancy toy, involves rich mechanical behaviors. In the production process of the toroflux, the prestressed technique is used to increase some bending deformation energy internally. Due to the presence of the bending deformation energy, a folded toroflux under external disturbances can be unfolded as a Chinese lantern structure in a stable equilibrium state. And conversely, an unfolded toroflux driven by an external force moment can go into another stable equilibrium state, i.e., a folded ring. This makes a toroflux easy to be carried in the folded state and with a lightweight structure space in the unfolded state. Moreover, a toroflux around an arm or a long strip, like a silvery bubble that is flowing, moves from high to low due to the effect of the gravity. Based on the energy theory, this paper analyzes a series of mechanical behaviors of the toroflux in the folded and unfolded states.
    2019, 41(1):  45-51.  doi:10.6052/1000-0879-18-174
    Abstract ( 329 )   PDF (797KB) ( 143 )  
    The floating state of the bottomed-hollow cylinder is analyzed as compared with a solid cylinder with the consideration of the water intake at the top. The cylinder may stably float in the vertical posture when it is filled with the water or is in an inverted position in the water. As the water volume inside the cylinder is reduced, the balance position will be tilt after a fork bifurcation, and topple over finally. Calculation results of the relevant formulas and the photographs of various floating states are given for glass cups.
    2019, 41(1):  52-59.  doi:10.6052/1000-0879-18-215
    Abstract ( 314 )   PDF (3862KB) ( 58 )  
    A theoretical model and the finite element method (FEM) are used to simulate the durotaxis movement of the cell on an artificial substrate with a continuous varying stiffness for the test design. The viscoelastic properties of the cell and the dynamic reactions of the receptors and the ligands between the cell and the substrate, are all considered. The time step equal to that of producing a pair of receptor-ligand is used for discretizing the functions of the time, turning the dynamic FEM into a static one. And a condition of moving constraint for the cell structure is proposed for eliminating the singularity of the FEM matrix more easily. The simulation results show that there is a rapid fluctuation of the force in the focal adhesion during the cell durotaxis, the speed of the cell migration, as is consistent with the observation, and the migration process can efficiently last over 20 hours.
    INFLUENCE OF SHAMPOO ON THE MECHANICAL PROPERTIES OF HUMAN HAIRS1)
    YANG Pengqian, WANG Sufangy, Huan Yongy
    2019, 41(1):  60-64.  doi:10.6052/1000-0879-18-425
    Abstract ( 654 )   PDF (2316KB) ( 70 )  
    People usually pay close attention to the fragility of their hairs. Therefore some kinds of shampoo with the function of so-called “strengthening hair” come into being on the market. However the real effect is not clear. In this paper, the mechanical properties of human hairs, treated with a typical shampoo with the function of “strengthening hair”, are determined using tensile experiments. The results indicate that after being treated with shampoo, the yield stress of the hair decreases, which means that the ability to resist plastic deformation is weakened. Also, the ultimate stress and the ultimate strain are decreased, which means a reduced ability of the hair to resist the accidental breakage. In addition, Young's modulus goes down, showing a poor ability of the hair to resist the elastic deformation. To sum up, the shampoo studied in this paper is not helpful to “strengthen” or “toughen” hairs.
    2019, 41(1):  65-71.  doi:10.6052/1000-0879-18-395
    Abstract ( 207 )   HTML( 65 )   PDF (363KB) ( 65 )  
    As respond to the discussion of program and degree unit running proposed by the editorial office of Mechanics and Engineering. In this paper, six questions are proposed and participated in outlining discussion. For “throw away a brick in order to get a gem”, we hope that these questions will be exchanging of the practical experience and demonstration with related teaching and learning investigators. The six questions can be shown as following: (1) The long river of Mechanics sine about two thousand years will cut-off? (2) What is the demand of the students in our country and in the world will facing in modern times and in the future? (3) How to cognizant and understand the nature of mechanics or engineering mechanics? (4) Based on the discussion showing above, how to define the train objective with the diversity character for the program and degree unit of mechanics or engineering mechanics? (5) What are the ways for training the talents of engineering mechanics program? (6) What is the essential function of the engineering mechanics program running? These questions are not usual unreliable asking, that is important one which must be discussed and answered concerned of the colleagues in the working field of mechanics or engineering mechanics program running.
    2019, 41(1):  72-75.  doi:10.6052/1000-0879-18-116
    Abstract ( 423 )   PDF (231KB) ( 100 )  
    The high jump test of eccentric wheels in the team competition of the 11th National Zhou Peiyuan Competition on Mechanics is investigated. The dynamical model of the eccentric wheel rolling and bouncing on a slope is built. The bouncing condition is analyzed and obtained. The dynamical process from pure rolling to continuous bouncing after releasing without an initial velocity is studied. The influence of the inclined angle, the initial release angle and the friction coefficient on the bouncing behavior is revealed.
    THREE TEXTBOOKS OF THEORETICAL MECHANICS PUBLISHED IN THE 19601)
    ZHAO Xianghui, ZHUANG Biaozhong, ZHAO Yucheng, ZENG Fanlin
    2019, 41(1):  76-81.  doi:10.6052/1000-0879-18-208
    Abstract ( 473 )   PDF (191KB) ( 103 )  

    This paper reviews three excellent theoretical mechanics textbooks, published in the 1960's in China, with respect to the textbooks'general situation, the main contents, the characteristics, the scope of applications and the authors. They have been widely adopted by Chinese universities and colleges through several revisions. They are: theoretical mechanics I, II, by the Department of Theoretical Mechanics of Harbin University of Technology; theoretical mechanics, by Hao Tongsheng; theoretical mechanics, by the Department of Theoretical Mechanics of Zhejiang University.

    2019, 41(1):  82-85.  doi:10.6052/1000-0879-18-255
    Abstract ( 221 )   PDF (1145KB) ( 43 )  
    Combining the concept of mechanics with practices, introducing engineering cases to explain relevant knowledge points can enhance students' interest in learning and improve the ability of students utilizing theory in practices. Bridge, bridge supports and foundations is described. The mechanical models of the pier that suffered vertical impact and horizontal impact are simplified respectively. To the simplified pier model, with and without the rubber isolation bearing, or the anti-collision pier, comparative analysis is carried on the deformation and dynamic load coefficient of the pier. According to the conservation of energy, the related problems are analyzed and discussed, and improve the understanding ability of students to related mechanics concept.
    2019, 41(1):  86-90.  doi:10.6052/1000-0879-18-281
    Abstract ( 268 )   PDF (348KB) ( 66 )  
    The “New Engineering” is the direction of the engineering education reform based on the national strategic development, the new situation of the international competition, and the new requirements for the cultivation of innovative talents. The main goal of the “New Engineering” is to cultivate outstanding engineering and scientific talents with innovative and entrepreneur capabilities, and cross-border integration capabilities. This paper analyzes the background and the urgency of training new engineering talents, discusses the ideas and the connotation of the demonstration center for experimental mechanics in the new situation of the talent training, and puts forward some suggestions to build a new model of practical teaching.
    2019, 41(1):  91-94.  doi:10.6052/1000-0879-18-307
    Abstract ( 320 )   PDF (173KB) ( 58 )  
    The rotation-release method is for determining the number of independent linear displacement unknowns in the structural mechanics. Yet due to the incomplete consideration of the constraints in the classic method, the application of the method is limited in many aspects. To overcome the limitation of the method, a modified rotation-release method is proposed, with consideration of all kinds of constraints and the effect of the rigid bars, which reflects more directly the “rotation releasing” and the assumption for the straight bending bar from the principle level. Examples show that the modified method can be accurately applied to solve very complex problems, and if the involved mass is properly considered, the modified method can also be used to determine the number of vibration degrees of freedom under a complicated situation.
    THE DETERMINATION OF THE COMPUTATIONAL DEGREES OF FREEDOM OF BAR SYSTEMS1)
    ZHOU Jiashun, WANG Pan, OU Yanjun, HUANG Shiqing, HE Linghui, KUANG Youdi
    2019, 41(1):  95-98.  doi:10.6052/1000-0879-18-314
    Abstract ( 696 )   PDF (166KB) ( 66 )  
    This paper proposes a direct method to determine thecomputational degree of freedom $W$ of bar systems in a way of simplicityand uniformity. By taking the bar between any two adjacent joints and thejoints as the analysis objects, the direct method gives a formula$W =3 m -(3g+2h$) for the plane system with $m$ bars, $g$ single rigid joints and $h$ single hinge joints. Compared with the previous algorithms to determine $W$, this method is easy to be applied and may increase the accuracy and the efficiency. It can also be used in determining the degrees of freedom of a statically indeterminate problem.
    APPLICATION OF PROBLEM-BASED METHOD IN TEACHING STREAMLINE BERNOULLI EQUATION1)
    MENG Qingchang, DENG Hui, WANG Chong, ZHANG Zhihong, GU Jiannong, LIU Jubin
    2019, 41(1):  99-103.  doi:10.6052/1000-0879-18-321
    Abstract ( 246 )   PDF (1758KB) ( 52 )  
    In order to improve the logical reasoning ability of college students, and the teaching level of fluid mechanics, the problem-based teaching method is adopted. With the problem-oriented method in mind, step-by-step, the application of the problem-based teaching method is explained with examples in the fluid mechanics course. In the process of effective review and rigorous reasoning, scientific conclusions are drawn. The above practices achieve better teaching results, enhance the learning interest and the concentration of students, and improve students' ability of thinking and innovating independently.