Tubular structures such as circular tubes and square tubes under axial compression, are widely used as structural components in engineering applications. Considering the difference of tube geometries, boundary conditions and material properties, we classify the failure of tubes under axial compression into 5 different mechanisms: progressive buckling, global buckling, inversion, expansion and splitting. In this paper, the theoretical, experimental and numerical studies about the different failure modes of tubes under axial compression are reviewed, and the mechanical responses and energy absorption properties are compared and discussed.
Defects may lead to wood fracture under low stress state. In this paper we summarize the state-ofthe-art of wood fracture toughness along the grain, which is an important mechanical parameter of wood. We introduce main fracture toughness test methods, and analyze the advantages and disadvantages of different test methods and data processing methods. We focus on the related influence factors of the fracture toughness, such as wood species, density, moisture content, wood fiber bridging effect, specimen span/depth ratio, and so on. Moreover, we summarize the research results of the fracture toughness's size effect. Considering the wide usage of engineered wood products in practice, the research sate of wood adhesive bonds fracture is also introduced.
propose a novel method for low-energy low-thrust transfer orbit between parking orbits around Jovian moons. Using a "halo-like section", the manifold is simply parameterized and patched by the multibody Lambert algorithm based on collocation method. Then by using the global optimization algorithm, a preliminary optimization result is obtained with minimal fuel consumption. The transfer orbits with lowthrust propulsion are optimized and designed by the homotopic method with multi-body environment and the multi-circle transfer orbit design method with fixed perigee height. The proposed method may be applied to transferring orbit design between other celestial bodies. In summary, we have proposed new design ideas and methods for low-energy low-thrust transfer orbit with multi-body environment.
Subway has become a big city's main traffic tool.A subway station may easily become terrorist attack object.This directly affects the subway operation safety. It is important to enhance the subway station structure protection and antiknock ability. In this paper, the rock breaking and protection of subway station are explored by combined study of theoretical analysis, numerical simulations and experiments. Using the calculation method with discontinuous elements, three-dimensional calculation model is set up. Explosion wave propagation and dissipation regularity and damage to structures are studied, based on the discrete model of block element. The antiknock seismic performance of the station management layer of concrete pillar concrete,steel, bandages concrete and foam sandwich steel armor layer concrete is analyzed under low-energy explosions. According to different protective structure, attenuation of stress wave, and energy absorption performance, the optimization of subway station structure and structure protection type have important practical application value.
In this paper, we define the residual force vector as a structure damage index,and give the detailed theoretical derivation for residual force vector according to the structure eigenvalue equation.Takinga simple supported truss as a research target, we carry the local damage identification of truss by use of residual force vector,and identify the single and multiple local damage of truss structure.We further explore the impact of noise on the accuracy of damage identification by introducing damage localization index and considering the existence of noise in actual measurements. Theoretical analysis and numerical results show that the residual force vector can identify local small damage of the truss structure beam effectively and have good noise immunity.
There has been a continuous growth for applying large diameter horizontal thin-walled circular cylindrical shell (HTCCS) for air and flue gas ducts, raw coal or pulverized coal piping. HTCCS under nonaxisymmetric loading is usually designed according to the membrane theory or global beam theory, which is inadequate to capture the bending and shear stresses in the shell located near the load edges. In this paper, the total internal forces in a thin HTCCS under ashes, snow, wind, gravity or seismic loads are determined from the combined membrane and moment theories. The exact solutions obtained complies with the results of finite element analysis. These study results can be extended to the design of HTCCS subjected to similar non-axisymmetric loading.
It is very important to accurately calculate a riser's natural frequency for ensuring a safe use of the riser and preventing the occurrence of resonance. Considering the influence of the uniform distribution of axial force and the top tense, a transverse vibration mechanics model of the riser is established.Based on Newton's law and the vertical and horizontal bending beam theory and the stress analysis of micro unit,transverse free vibration of fourth order linear partial differential equation of the riser is achieved. Using the method of separation of variables, we simplify it to a fourth order ordinary differential equation with variable coefficients. To get the analytic solution for transverse free vibration natural frequency, the integral method is used. With examples, we show the following results. First, the uniform distribution of axial force has great effect on natural frequency and vibration mode. Secondly, when the top tension is unchanged and the distribution of axial force is reduced, riser's natural frequency increases; meanwhile when distribution of axial force is constant and the top tension increases, riser natural frequency increases. Thirdly, with high calculation accuracy and speed, the integral method is capable to solve the fourth order ordinary differential equation with variable coefficients, and provides reliable theoretical basis for optimal design of the riser.
Based on the Goodman contact element, we improve the Bingham model on the basis of the Clough-Duncan hyperbolic equation to establish an elastic-visco-plastic constitutive model for soil-structure interface. This soil-structure interface model is developed by the FRIC subroutine of ABAQUS. A series of long-term interface shear tests are performed to verify the above model by using the stress controlled soilstructure interface shearing test apparatus. The results show that the established model is able to effectively simulate the mechanical behavior and time effect of soil-structure interface; the normal stress has greater effect on the mechanical behavior of the soil-structure interface, and the larger the normal stress, the more obvious time effect of the interface is.
In order to accurately describe casing collapse under lateral load, we assume that the shape of the stress deformation zone of the casing is two arcs in plastic deformation. We establish casing damage mechanics balance relationship based on theprinciple of virtual work under lateral loads, then derive the casing damage mechanics model by the Fresnel integral. With the engineering practice of Daqing oilfield,weconduct casing collapse test. The new formula leads to a far smaller average relative error than that obtained from the API formula. From the viewpoint of energy, the paper provides a new research method for the study of casing collapse deformation under external load.
Cable failure often occurs when the production string runs into an inclined wellbore. A finite element model for the string stress is proposed. A clearance unit is introduced to resolve the contact force and contact position between string and wellbore.By the cable wear risk assessment,combined with the drilling rigs heading, a reasonable riding position of cable when running into the well is calculated, which reduces wearrisk. According to our analysis, the upper part of the string contacts with the higher edgeor side edge of wellbore, while the lower part contacts with the lower edgeor the side edge of the wellbore. The reliability of the evaluation method is testified,and the analysis result can be used for reference when riding the cable in field operations.
In order to study the dynamical characteristics and structure damage of Ceshi Pagoda in Xingjiao Temple, which is one of the world heritage of culture buildings, we conducted in-situ dynamical test by super low frequency dynamical test system. Stimulated by a random vibration, the velocity response data in the top of each floor is gathered after wave filtering. By self spectral and inter spectral analysis with integral transform, the first and second stage of frequencies and vibration modes are acquired along the horizontal direction. A finite element model of Ceshi Pagoda is constructed, based on the measured data. The vibration characteristics are calculated for decreasing elastic modulus. Then they are contrasted with the test results.The structure damage analysis is performed, based on Improvement Shape Method for damage parameter identification. The results show that the first and the second stage vibration frequencies are close to each other along NS and EW direction. The first stage vibration mode is bending type, and the second is bending and shearing type. The effective elastic modulus of Ceshi pagoda is much smaller than that of a masonry structure in good conditions. Therefore, the damage of masonry pagodas can be recognized from the results of dynamical test and numerical calculation, after the elastic modulus of complete masonry structures is defined.