With the assumption that the rock micro-unit failure obeys the Weibull random distribution, the damage softening statistical constitutive relations are established under the true triaxial confinement state. Then, according to the geometrical conditions of the stress-strain relationship, the theoretical relationship between the constitutive model parameters and the stress-strain curve characteristic parameters during the process of rock softening and deforming is established, which enhances the adaptability of the model. Finally, the rationality of the model is verified by the measured data.
The longitudinal stiffness of an aerostat envelope is related with the pneumatic membrane structure that is analyzed in this paper. First, the scaling factor n and the internal overpressure p of the envelope configuration against the longitudinal concentrated load are obtained through theoretical analysis, together with the theoretical formula of the longitudinal stiffness. The theoretical analysis is validated by the FEM (finite element method) simulations and the test of a one-eighth scale model. The theoretical calculation method of the pneumatic membrane configuration stiffness in this paper could be used for the calculation of the mooring load of the aerostat.
An optimization method is proposed to study the flap track location of the large civil aircraft,in order to meet the design requirements of the stiffness and the deformation. First, with the proper engineering simplification of the flap based on the characteristics of the flap structure and the load, the form of support is determined. Then, according to the basic theory of structural mechanics, the flap stiffness is calculated. Based on the deformation coordination under the load, a optimization model is established. The paper offers a method also for other control surfaces.
In consideration of the shear lag effects and the shear deformation, a new warping displacement mode of curved T-beams is chosen to satisfy the axial self-equilibrium condition for the shear lag warping stress, and an accurate approach is proposed to analyze the static characteristics of curved T-beams widely used in engineering. The energy-variational principle is applied to establish the governing differential equations and the corresponding natural boundary conditions, and thus the closed-form solutions of the generalized displacements are obtained. The variations of the shear lag coefficients and the stress in the curved T-beams against the span-width ratio and the type of loading are discussed, and the role played by the self-equilibrium condition is analyzed.
The high-porosity cellular metals and the related sandwich structures are a new type of light-weight structural and functional material/structure. They are attractive for their high specific strength, high specific stiffness and excellent energy absorption capability. This paper reviews various processing techniques, the mechanical performance and the application fields of the sandwich structures with cellular metal cores. The mechanical behavior of metallic sandwich structures, including beams, plates and shells, subjected to quasistatic and dynamic loads is discussed, including theoretical predictions, numerical simulations and experimental results. The discussion also includes the deformation/failure, the dynamic response and the energy absorption of sandwich structures.
The load-unload response ratio theory has made a great progress in predicting the stability of a nonlinear system, as is reviewed in this paper, which focuses on the field of predictions of earthquakes and landslides, including its shortcomings. The development trend and applications are analyzed.
This paper reviews the latest progress in studies of the constitutive models of the FRP(fiber reinforced polymer)-confined concrete,and analyzes their theoretical basis, the characteristics and the problems of existing models, focusing on the axial compressive strength and deformation, the failure mechanism of the FRP-confined concrete, and the main factors affecting the constitutive models, such as the FRP restraint stress and the actual strain at the failure state. A basic framework for comparative analysis of constitutive models in future is suggested.
The paper reviews the studies of fatigue of concrete with a logical perspective focusing on the internal mechanism. It is shown that the existing researches can be classified into three main types: the phenomenon models based on fatigue tests, the fatigue crack propagation models based on fracture mechanics and the fatigue damage evolution models based on damage mechanics. The main features of each kind of models are summarized. Further, it is suggested that the rate process theory can explain the physical foundation of fatigue of concrete from the viewport of reductionism. In view of the considerable scatters in the results of concrete fatigue tests, the concept of the physical stochastic system is proposed.
The low-thrust trajectory optimization for the multi-asteroid exploration with time and fuel limits is studied in this paper. The optimal control problem is established based on the minimum principle and is solved by the homotopic approach. The target flyby, the rendezvous and the stay time after the rendezvous are all treated as the inner constraints. Then the global optimal control problem is solved by the homotopic approach. It is shown that the global optimal trajectory can be obtained quickly. The algorithm proposed in this paper can be employed in the mission design and the trajectory optimization for multi-asteroid explorations.
A flip-out tail fin is designed to improve the shooting quality of the fin-stabilized shell of small length-diameter ratio. Three fin-stabilized shells with fins of the same shape and different aspect radios are simulated numerically by applying the AUSM+scheme. The shear stress transport turbulence models and the lower-upper symmetric Gauss-Seidel implicit method are used to solve the 3D Reynolds-averaged Navier-Stokes equations. The differences in the aerodynamic coefficients and the aerodynamic characterstics of the projectiles when the Mach number varies from 1.5 to 3.5 are obtained and analyzed, and the applicability of fins of different aspect radios is discussed. The calculation results indicate that the lift-to-drag ratio of the C-type shell is 7% greater than that of the B-type shell in the region where the Mach number is close to 1.5; as the Mach number is above 2.5, the lift-to-drag ratio of the A-type shell is greater than that of the B-type shell and the C-type shell; the lift-to-drag ratio of the A-type shell is 5.4% greater than that of the B-type shell in the region where the Mach number is close to 3.5. The pitching moment coefficient rises in absolute value when the Mach number gradually increases, the rising trend increases with the increase of of the aspect ratio. The static stability variation ranges of the A-type shell, the B-type shell and the C-type shell are 4%~20.3%, 8.5%~23.2% and 11.4%~25.6%, respectively.
This paper focuses on solving the problem of geometrically nonlinear buckling of thin-walled cylin- drical shells under pure bending with the cross-section tending to be oval-shaped. The basic hypothesis is based on the modified Brazier simple theory that the deformation of a shell under pure bending can be simplified as a two-stage process. By the two-stage process, the longitudinal bending strain energy and the cross-sectional deformation strain energy are obtained. The relationship between the end-rotation and the applied moment is obtained through the principle of the minimum potential energy. It is shown that: the smaller the shell length parameters and the thinner the corresponding cylindrical shell wall, the greater the impact of nonlinearity will be; the smaller the shear length parameters and the smaller the effect of the boundary conditions on the deformation leading to oval section shape, the greater the impact of nonlinearity will be.
Based on the two-parameter foundation model, the buckling of orthotropic thin plates on graded elastic foundations is studied. Firstly, the buckling governing differential equation of orthotropic thin plates on graded elastic foundations and the expressions of two elastic parameters of the elastic foundation are obtained by using the energy method and the variational principle. Then, by expanding the displacement into trigonometric functions, the calculation formula of the uniaxial compression buckling load for orthotropic thin plates on graded elastic foundations with simply supported edges is obtained. In the example, the proposed solution is validated by comparing the degenerated results for an orthotropic thin plate with the classical elasticity solution. Finally, this paper studies the buckling load of the orthotropic thin plate on a graded elastic foundation, whose Young's modulus obeys a power law against the thickness. The effects of the top-bottom surfaces' Young's modulus ratio and the volume fraction exponent are also discussed.
For a beam of annular cross-section made of functionally graded materials (FGM), we assume that the physical parameters of the materials along the direction of the wall thickness varying in a simple power law. Based on the Lagrange's function and the Hamilton's principle, the Hamilton's canonical equations for the transverse free vibration of the beam are established. A symplectic eigenvalue problem of the Hamilton matrix is solved by using the symplectic method. Then, the natural frequencies and the vibration mode functions of the beam are obtained, with conditions on the two ends as the simply supported, the fixed, the cantilever and the fixed-simply supported. Numerical examples are given for the first eight order dimensionless natural frequencies against the material volume fraction, and the effect of the material volume fraction on the natural frequency is analyzed.
The automatic tensioner is widely used in the engine's front end accessory drive (FEAD) system. It plays a predominant role to reduce the dynamic tension and the transverse vibration of the belt span adjacent to the tensioner pulley. The static performances of a tensioner are characterized by three parameters including the static stiffness, the pre-torque and the damping coefficient of the tensioner. Experimental methods for measuring the tensioner force versus the displacement are presented. Also, the data processing techniques for establishing the curve of the tensioner torque versus the angular deflection, and for evaluating the parameters of the tensioner static performances are illustrated. The experiment results provide a validation for the modeling and the simulation of the static and dynamic performances of the FEAD system. The experiment techniques presented in this paper can also applied to measure the static stiffness of similar structures.
The expressions for general non-ideal systems proposed by Udwadia-Kalaba are investigated and revised with regard to the forces of ideal constraints and non-ideal constraints. The new revised expressions have a clearer physical meaning and contain the coupling between the forces of ideal constraints and non-ideal constraints, as is consistent with the original physical law. An example by using three methods validates the results of this paper.
This paper studies the inherent vibration of steel structures with the flexural member supported by a compression member by the method of Laplace transformation and singular functions. The modal functions of the compression member and the flexural member are derived, and the characteristic equation for inherent vibration frequencies of a steel structure with the flexural member supported by a compression member is obtained by the continuous conditions of supporting. It is shown that its inherent vibration frequency increases with the axial pressure.