Applied Mechanics and Materials Vols. 423-426

Abstract: In order to describe the mechanical characteristics of CBM wellbore surrounding rock more accurately, the article establishes the CBM wellbore surrounding rock mechanics model based on the fractal theory. According to the pores of CBM surrounding rock and the characteristics of mass fractal, people find the macro fracture and micro fracture damage characteristics and build the relationship of any scale coal strength, damage variable and fractal dimension. According to the numerical calculation method of the surrounding rock stress, people find the surrounding rock stress calculation method and the damage distribution model of the pore fractal model and fracture fractal model.

Abstract: The derivation and calculation of crack problems by using boundary element method (BEM) are presented. When calculating the node displacement, the displacement boundary integral equations are superseded by stress boundary integral equation, then a simplifier computational process is generated. Stress field and displacement field around the straight crack are calculated by using both BEM and Abaqus methods. Furthermore, the stress intensity factor (SIF) was achieved from the solution. A good agreement is found between the BEM and Abaqus results, proved that BEM is a reliable method to calculate crack problems.

Abstract: The expression for the elastic field of an expanding spherical inclusion in an infinite isotropic elastic medium is presented. The influence area of a supersonically expanding spherical inclusion is given in the form of expressions and graphs. And the difference of the influence area between supersonic expansion and subsonic expansion of a spherical inclusion is discussed.

Abstract: For the performance function with high nonlinearity around the most probable failure region, stress-strength interference model and advanced first-order second-moment method (AFOSM) can cause huge errors in the computation results. The multi-plane combination method is presented to calculate reliability of the mechanical component, in which the component reliability calculation is first transformed into a relatively simple system reliability problem, and then the equivalent calculation method is applied to estimate system reliability. The example application shows the accuracy and efficiency of the multi-plane combination method.

Abstract: The scattering waves by two elastic spheres in solid are studied. The incident wave, the scattering waves in the host and the transmitted waves in the elastic spheres are all expanded in the series form of spherical wave functions. The total waves are obtained by addition of all scattered waves from individual elastic sphere. The addition theorem of spherical wave function is used to perform the coordinates transform for the scattering waves from different spheres. The expansion coefficients of scattering waves are determined by the interface condition between the elastic spheres and the solid host. The scattering cross section is computed as numerical examples.

Abstract: The net shear strain energy density strength theory was systematically explained. Firstly, the composition of elastic strain energy and the roles of their own were analyzed, and it is pointed out that the distortion strain energy is the energy driving failure and the volumetric strain energy can help improve the material strength. Therefore, ultimate energy driving material damage should be the shear strain energy after deducting the friction effect, namely the net shear strain energy, which indicates rationality of the assumption adopted by the net shear strain energy strength theory. Secondly, the empirical laws of geomaterial strength were summarized and explained by using the net shear strain energy theory, which verifies the new theory is appropriate.

Abstract: In this paper, the dynamic compression-shear experiments on the closed-cell aluminum foam with porosity of 72%-92% are carried out by using improved split Hopkinson pressure bar. A high speed camera is used to observe the dynamic deformation behavior of the samples on the compression-shear loading. A finite element software ABAQUS is employed to simulate the dynamic compression-shear process of closed-cell aluminum foam. The results demonstrate that there is a compression-shear band on the samples during the compression-shear loading. The most severely damaged area of the material is on the compression-shear band; Low-porosity closed-cell aluminum foam has significant strain rate effect, however high-porosity closed-cell aluminum foam can ignore the strain rate effect. The yield stress of samples decreases with increasing samples angle, whereas shear stress increase with increasing samples angle, and also the corresponding time when the samples just begin to yield decreases with increasing samples angle.

Abstract: The transfer matrix method in analysis of cylindrical shell with partially covered ring-shape constrained layer damping is improved. In this new method, state vector and boundary condition vectors are independent, so the computation of state vectors first derivative is simplified. An association matrix is introduced to connect state vectors and boundary condition vectors. In the uncovered section, the parameters of damping layer and constrained layer are considered as constant and leaded into state vectors and boundary condition vectors, so the transfer matrixs dimension of uncovered and covered section are same and the total transfer matrix can be obtained easily. The validity of this method is proved by an example.

Abstract: A finite element formulation is presented for the prediction of nonlinear response of thin plates under a steady-state non-uniform temperature change over the thin plate and band limited Gaussian white noise. Thermal buckling temperatures and thermal deflections are obtained to explain the stability of panels, and modal frequencies of thermally buckled plate are obtained to explain the stiffness characteristics of panels. The stress responses of panels under thermo-acoustic loadings exhibit complex nonlinear characteristics. Miner linear accumulation damage theory and improved Rainflow counting cycle method are used for estimation of fatigue life of panels under combined thermo-acoustic loadings. Results show that the fatigue life decreases till the end of snap-through and then gives a rise trend. Afterward, the fatigue life reaches a steady state at low peak temperature area. As the peak temperature goes up sequentially, the fatigue life rises suddenly, and then reaches a steady state at high peak temperature area.

Abstract: Paper considers the problem of nonlinear theory of elasticity for inhomogeneous thick-walled sphere. The problem is solved in centrally symmetric statement. In general, all the parameters of the nonlinear dependence between the intensities of the stresses and strains are functions of the radius. As an example, solve the problem of stress distribution in the soil mass with a spherical cavity.