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08 August 2014, Volume 36 Issue 4
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    2014, 36(4):  491-492.  doi:10.6052/1000-0879-13-227
    Abstract ( 830 )   PDF (391KB) ( 878 )  
    The moment of the resultant, equivalent force about a given point of a force system, is equal to the sum of the moment of all acting forces about the same point. This theorem is usually used to determine the center of a parallel force system. In a conventional way the acting point of the resultant is set to be the center, which is difficult to be understood. In this work, an arbitrary point on the acting line of the resultant is assumed in using the theorem. The physical meaning of the center is clear and the line of action of the resultant must always pass through a fixed point.
    2014, 36(4):  420-421,402.  doi:10.6052/1000-0879-13-332
    Abstract ( 576 )   PDF (706KB) ( 960 )  
    The stability of equilibrium of an egg in liquid is an interesting example of the Lagrange's theorem in determining the stability of conservative system. It is shown that a stable straight equilibrium of an egg in liquid is possible when the specific weight of liquid exceeds a critical value. The static bifurcation problem is discussed that the number and stability of equilibrium attitudes of the egg is variable with the specific weight of liquid.
    ADVANCES IN TRUE TRIAXIAL TEST OF UNSATURATED SOILS
    ZHANG Changguang, ZHAO Junhai, CHEN Xindong, ZHU Donghui
    2014, 36(4):  413-419.  doi:10.6052/1000-0879-13-110
    Abstract ( 411 )   PDF (3204KB) ( 755 )  
    The unsaturated soil strength is the most important issue in the unsaturated soil theory and its engineering applications. But advances in the true triaxial tests of the unsaturated soils have been very slow due to the control-measurement technique and the balance time of the matric suction under complex stress states. This paper briefly reviews the rigid and flexible and compound true triaxial apparatuses and the existing true triaxial tests for the unsaturated soils. It is shown that both Mohr-Coulomb and circumscribed Drucker-Prager strength criteria are not valid for the true triaxial tests of the unsaturated soils. Different types of true triaxial tests should be conducted, particularly, for non-saturated clays. In order to improve the theoretical basis for the study of the unsaturated soils, a true triaxial strength criterion of the unsaturated soils in accordance with the actual stress conditions in the field should be established, based on the stress state variables and the strength characteristics of the unsaturated soils.
    2014, 36(4):  470-473.  doi:10.6052/1000-0879-13-228
    Abstract ( 401 )   PDF (354KB) ( 527 )  
    With consideration of shear effect and damping, the dynamic load impact of bimodulous beam is calculated based on the linear vibration theory. The vibration differential equation for the dynamic load problem of the bimodulous beam is established. The expressions of the dynamic displacement, the dynamic load factor and the impact time in the dynamic load problem of the bimodulous beam are derived. And the influence of the shear effect and the damping on the dynamic load impact of the bimodulous beam is analyzed. The computational results indicate that the influence of the shear effect and the damping on the dynamic load impact of the bimodulous beam can not be ignored in some cases.
    2014, 36(4):  466-469.  doi:10.6052/1000-0879-13-362
    Abstract ( 391 )   PDF (296KB) ( 658 )  
    A trial function method is proposed to study the longitudinal vibration of rods with variable cross-sections. A trial solution of the governing equation in a form of special functions is suggested, satisfying the governing equation, various possible coefficient functions (namely cross-section functions of rods) are determined and the exact analytical solutions of the governing equation is obtained. As an example, the frequency equations and the natural frequencies of a kind of variable cross-section rod are given, under three boundary conditions. It is shown that the trial function method is simple and convenient, and suitable for the study of the longitudinal vibration of rods with variable cross-sections. The method can also be applied to the study of the torsional vibration of rods, the vibration of membranes as well as the wave propagation in ducts.
    SHOCK WAVE LOADING OF CONTACT SURFACE DETONATION MODE
    JIN Yanjuan, ZHANG Zhu, LIU Jianyue
    2014, 36(4):  429-432.  doi:10.6052/1000-0879-13-450
    Abstract ( 356 )   PDF (814KB) ( 965 )  
    Based on the principle of superposition, an explosive contact surface detonation model is used to achieve the rectangular wave loading on a compressible solid material. Via integrating the (u, p) curve for the explosion products and the compressible fluid, the shock pressure and the shock wave loading platform width are obtained with con-sideration of the interference from the sparse wave in explosives and materials at their free edges. Theoretical analysis provides a theoretical foundation for the substantially rectangular wave loading of specimens using the contact explo-sion in the future.
    2014, 36(4):  461-465.  doi:10.6052/1000-0879-13-476
    Abstract ( 481 )   PDF (2012KB) ( 475 )  
    Seismic settlement of ground soil due to seismic loads is an issue of geotechnology. Seismic settlement tests of Aeolian soil in west of Liaoning province were conducted under the earthquake loads exceeding that would happen with 2 and 10 percent of propability in the future 50 years and in constant amplitude loads. The effects of vibration cycles, dynamic stress amplitude and moisture contents on the seismic subsidence coefficient of Aeolian soil are evaluated. An empirical formula of Aeolian soil's seismic subsidence ratio is obtained. The subsidence values of Aeolian soil field under the seismic loads and constant amplitude loads are predicted according to the layerwise summation method and its seismic subsidence is assessed. The research results provide a reference for the seismic design of Aeolian soil region in west of Liaoning Province.
    LOCATING BEAM DAMAGE BASED ON INITIAL FLEXURAL STIFFNESS DETECTION
    MA Zhongjun, ZHONG Luo, ZHANG Yiny
    2014, 36(4):  437-441,446.  doi:10.6052/1000-0879-13-550
    Abstract ( 331 )   PDF (1494KB) ( 761 )  
    The strain mode variation rate used to be applied for locating the damage of in-service beam structures. However, the uncertain initial local flexural stiffness of the beam structures is not well considered in most present studies. Therefore, the actual damage and the original uncertainty of the local flexural stiffness cannot be differentiated effectively. Therefore, the application of this index to real beam structures does not give satisfactory results. A local flexural stiffness detection method is proposed in this paper. In this method, the actual local flexural stiffness value of each segment of the beam can be obtained by solving a set of linear equations. Subsequently, the strain mode variation rate can be employed to locate the damage. It is shown that the damage can be located exactly based on the actual initial flexural stiffness parameters of the beam structures.
    Review
    2014, 36(4):  383-395.  doi:10.6052/1000-0879-14-168
    Abstract ( 954 )   PDF (3014KB) ( 1262 )  

    LBM (lattice Boltzmann method) allows straightforward calculations of the local shear rate to the second-order accuracy, so it has some advantages in the simulation of the non-Newtonian behavior of flows. Although the suitability of LBM for the non-Newtonian flow has been well demonstrated, the algorithms are mainly through instantaneously regulating the local relaxation time in the BGK (Bhatnagar-Gross-Krook) approximated collision term to match its corresponding viscosity for reflecting the effect of the local rheology variation.This approach, however, might cause some numerical instabilities when the relation time is close to 1/2.In this paper, the advances of LBM applied to generalized Newtonian flows are reviewed.The methods to mitigate numerical instabilities are described and the results are compared.Several ways of extending LBM to viscoelastic flows in the literature are introduced.Finally the prospective developments of LBM for non-Newtonian flows are suggested.

    ADVANCES IN RESEARCH OF HYDRAULIC FRACTURES IN UNCONSOLIDATED SANDS
    ZHANG Weidong, YANG Zhicheng, WEI Yameng
    2014, 36(4):  396-402.  doi:10.6052/1000-0879-13-438
    Abstract ( 457 )   PDF (3092KB) ( 825 )  
    The typical features of hydraulic fracturing of unconsolidated sands are the large number of branch fractures and micro cracks,and a certain dullness of crack tips and some shear zones. This paper analyzes the influence of the tensile shear on the fracture morphology (initiation, reorientation and dilatation). Some experimental study of hydraulic fracturing of the unconsolidated sands indicates that the filtration process is mainly affected by the fracture tip area, and the filtration commonly occurs before the crack propagation. The confining stress around the fracture tip is often the leading parameters to influence the fracture initiation and the crack opening, and the crack characteristics are integrated effects of the stress, the permeability and the flow state, which explains the hydraulic fracture characteristics.
    THE MECHANISM OF EXPLOSIVE SPALLING OF HIGH STRENGTH AND HIGH PERFORMANCE CONCRETE EXPOSED TO ELEVATED TEMPERATURE
    WANG Li, LIU Hongbin, JU Yangy, LIU Jinhui, TIAN Kaipeiyy, GE Zhishun
    2014, 36(4):  403-412.  doi:10.6052/1000-0879-13-272
    Abstract ( 595 )   PDF (2106KB) ( 825 )  
    High strength and high performance concrete (HSC/HPC) enjoys a wide application. However, the performance degradation and the thermal spalling under high temperature or fire is a bottleneck problem in its applications. Especially, the spalling mechanism is an important issue demanding a thorough study. The study of the explosive spalling mechanism of high strength and high performance concrete under high temperature or fire is reviewed in this paper, with a focus on three kinds of spalling mechanism: the vapor pressure, the thermal stress and the thermal cracking and related influencing factors, the difficulties and challenges. A multi-factor coupling spalling model is established with the steam pressure as the main factor, and the thermal stress and the thermal cracking as the secondary factors, and the high temperature spalling mechanism of HSC/HPC is quantitatively analyzed.
    Applied Research
    2014, 36(4):  422-428.  doi:10.6052/1000-0879-13-441
    Abstract ( 458 )   PDF (3729KB) ( 635 )  
    When the small scale unstable flows are excited by disturbance, they absorb energy from the basic flow field, a large scale movement pattern will arise, that is, the typhoon or the soliton will form. The forces include those related with dissipation, dispersion, advection or convection,and when all these forces come to an equilibrium, the corresponding movement pattern will be stable over a long time. With respect to the helical structure, we can investigate its similar dynamics in terms of the local energy. Theoretical analyses and simulation experiments about double typhoons by means of a large-scale geophysical fluid annulus, as well as numerical experiments (which will be carried out) may solve the following problem: whether the typhoon can be seen as a three-dimensional large scale helical soliton. It is a new idea, which is, therefore, helpful for the understanding of the formation mechanism and the dynamic characteristics of typhoon and soliton, and it is also a new research approach to combine the two aspects of the methodology.
    2014, 36(4):  433-436.  doi:10.6052/1000-0879-13-488
    Abstract ( 412 )   PDF (540KB) ( 621 )  
    Using the Betti-Rayleigh reciprocity theorem, the general solutions and the singular integral equa-tions for a two dimensional impermeable crack problem in an infinite transversely isotropic piezoelectric solid under mechanical and electrical impact loads are obtained. The unknown functions are the derivatives of the discontinuities of elastic displacements and electric potentials of the crack. Then, Gauss-Chebyshev quadrature formula and Lubich convolution quadrature formula are applied to solve the integral equations numerically. Finally, numerical solutions are obtained for a typical example. It is shown that the numerical solutions are satisfactory.
    OPTIMAL SPECIMEN DESIGN FOR LAP SHEAR TEST
    LAN Tianbao, SU Fei
    2014, 36(4):  442-446.  doi:10.6052/1000-0879-13-394
    Abstract ( 507 )   PDF (5782KB) ( 1041 )  
    In the lap-shear test, the failure of specimens is usually caused by the peel stress instead of the shear stress. With the finite element method, the lap-shear test is optimized by designing some notches in the specimen holder so that the uniformity of the shear stress is improved and the peel stress at the two ends of the specimen is reduced. The optimization is verified with the photo-elasticity experiment.
    THREE-DIMENSIONAL CELLULAR AUTOMATA MODEL FOR PREDICTING LOCAL CORROSION
    GUO Dongxu, REN Keliang, WANG Yanchang, GUO Xiaoju, ZHANG Enshan
    2014, 36(4):  447-452.  doi:10.6052/1000-0879-13-495
    Abstract ( 740 )   PDF (12875KB) ( 1527 )  
    Under the service environment, because of chemical and electro-chemical reactions between the surrounding medium and the material elements, local corrosions are easy to form on the surface of metal. The corrosion damage will degrade the useful properties of materials and weaken the strength of the structures. In order to better understand the local corrosion damage degradation process, a numerical model based on the cellular automata method for the three-dimensional simulation of the metal corrosion damage is developed In a mesoscopic scale, the single-pit corrosion and the multi-pit corrosion on the surfaces of metal are simulated under different electrolyte concentrations and temperatures. The result provides a theoretical reference for studying the degradation mechanism of metal structures under the service environment.
    THERMAL STRESSES IN ELASTIC MULTILAYER SYSTEMS
    LIU Xing, ZHU Jiaqi, HAN Jiecai
    2014, 36(4):  453-456.  doi:10.6052/1000-0879-14-107
    Abstract ( 721 )   PDF (874KB) ( 1489 )  
    Multilayer systems are widely used in the infrared widow system. Thermal stresses in the thin films are very important to the functions and reliability of the system. In this paper, the strain and stress distributions in an elastic multilayered strip are calculated. The first-order approximation and the zero-order approximation solutions are proposed for the system when the thicknesses of the film layers are much less than the substrate thickness. Specific results are calculated for the elastic thermal stresses in the ZnS-Y2O3-SiO2 infrared window. The results show that the thermal stresses based on the first-order approximation and the zero-order approximation in two film layers have a relative error about 1.54% and 0.09%, respectively. The zero-order approximation solutions can meet the accuracy requirement very well.
    THE NEW CALCULATION METHOD FOR CONTACT FORCE IN DRILLSTRING MECHANICS
    ZHOU Zhihong, QIN Jiang, GONG Xiaoxia, FENG Ding, TU Yiliu
    2014, 36(4):  457-460,452.  doi:10.6052/1000-0879-13-555
    Abstract ( 450 )   PDF (1660KB) ( 1002 )  
    The calculation of the contact force on the drillstring in the hole is a complex nonlinear problem. This paper proposes a simple and direct method to tackle the problem. Firstly, a more precise model of 3D drillstring mechanics (which is called ABIS in short)is chosen. The contact force and the displacement of the drillstring on one node is computed. Then, the relationship between the contact forces on all other nodes and the displacement of this node is generalized. Then, the flexibility formulation is developed from them, describing the influence of the whole set of contact forces on the drillstring displacement, which is more explicit than that of the ABIS. Through that formulation, a new method of computing the contact force of drillstring is obtained and tested, which greatly increases the speed of iteration.
    2014, 36(4):  474-477.  doi:10.6052/1000-0879-13-197
    Abstract ( 457 )   PDF (634KB) ( 450 )  
    This paper uses the work-energy theorem to solve the small deformation problems for a liner elastic bar. According to a geometric analysis of the deformations of a simple linear elastic bar, the work-energy theorem is found to be more effective for the purpose. A force H perpendicular to the loading force P is assumed to be applied to the bars before the loading of P, and based on the work-energy theorem, we can obtain the formula to calculate the displacement caused by P. This methodology can be extended to more complex elastic bar system such as a truss and the computer programming will be easy, which can greatly simplify the calculation of the small deformation of a truss.
    2014, 36(4):  478-482.  doi:10.6052/1000-0879-13-300
    Abstract ( 652 )   PDF (9864KB) ( 928 )  
    The Conversion Method is used to determine the displacement of a beam with one end overhanging in symmetric bending. According to the relation between angles and normal lines of the beam, the displacement equation of the conversion method (DECM) is derived to obtain the deflection and the slope of this type of beams. The variables of the equation are the deflections of the free end of the corresponding Conversion Beam, the length of the beam converted, and the coordinate of the axis of the beam. The deeetailed process of computation for a specific beam is shown. The deflections of the free ends of the left, right conversion beams are computed, then they are put in a unified formula of DECM. The complete solution of the equation of deflection and slope is obtained. Only the knowledge of the deflection curve and the superposition method is required, without differentiation and integration, and without the need to consult the table of deflections. The result is accurate. Some instances of calculation with engineering background are given.
    2014, 36(4):  483-485.  doi:10.6052/1000-0879-13-206
    Abstract ( 559 )   PDF (251KB) ( 617 )  
    From the symmetry of the coefficient matrix of the constitutive law of linear elastic bodies, one may motivated to consider the corresponding inverse proposition, i.e. whether or not the symmetry of the linear constitutive law implies the perfect elasticity of the body. A positive answer of this question may be made via the construction of an elastic potential function for the body,which indicates that the symmetry of the constitutive equation and the perfect elasticity of body are equivalent.
    2014, 36(4):  486-490.  doi:10.6052/1000-0879-13-297
    Abstract ( 572 )   PDF (875KB) ( 512 )  
    A new method is proposed to analyze the internal force in a rope in the process of an object sliding along it without friction. A set of equations for the coupled motion is established on the basis of Newton's second law. Then, it is solved numerically by using the Runge-Kutta method, and the results are fitted through the Matlab software to obtain the formulas of motion. With the combination of the fitted formulas and the equations of motion, the internal force in the rope, as the object sliding along, is determined. Under different initial states of the object, the results, analyzed by the proposed new method, show that the internal force in the rope changes periodically in accordance with the simple harmonic motion of the object. The higher the object is released, the larger velocity and acceleration it achieves when passing through the same point on the rope, so does the internal force in the rope.