Investigation on nonlinear multi-scale effects of unsteady flow in hydraulic fractured horizontal shale gas wells

A unified mathematical model is established to simulate the nonlinear unsteady percolation of shale gas with the consideration of the nonlinear multi-scale effects such as slippage, diffusion, and desorption. The continuous inhomogeneous models of equivalent porosity and permeability are proposed for the whole shale gas reservoir including the hydraulic fracture, the micro-fracture, and the matrix regions. The corresponding semi-analytical method is developed by transforming the nonlinear partial differential governing equation into the integral equation and the numerical discretization. The non-linear multi-scale effects of slippage and diffusion and the pressure dependent effect of desorption on the shale gas production are investigated.     

弹塑性复合材料力学性能的细观研究

应用细观力学的Eshelby等效夹杂理论研究了复合材料的弹塑性问题。以铝基复合材料为例,建立了多轴载荷下复合材料弹塑性应力-应变关系,并且理论预报与实验结果符合较好,分析了夹杂形状、体积分数及加载路径对材料宏观性能的影响。同时,还研究了热塑性复合材料热膨胀系数与工艺温度之间的变化规律,分析了热残余应变对材料设计的影响。     

A constitutive model and elastoplastic analysis of structures under cyclic loading

A constitutive model for cyclic plasticity is briefly outlined. Then the model is implemented in a finite element code to predict the response of cyclic loaded structural components such as a double-edge-notched plate, a grove bar and a nozzle in spherical shell. Comparision with results from other theories and experiments shows that the results obtained by using the present model are very satisfactory.The Project Supported by National Natural Science Foundation of China.     

A meso elastoplastic constitutive model for polycrystalline metals based on equivalent slip systems with latent hardening

A meso material model for polycrystalline metals is proposed, in which the tiny slip systems distributing randomly between crystal slices in micro-grains or on grain boundaries are replaced by macro equivalent slip systems determined by the work-conjugate principle. The elastoplastic constitutive equation of this model is formulated for the active hardening, latent hardening and Bauschinger effect to predict macro elastoplastic stress-strain responses of polycrystalline metals under complex loading conditions. The influence of the material property parameters on size and shape of the subsequent yield surfaces is numerically investigated to demonstrate the fundamental features of the proposed material model. The derived constitutive equation is proved accurate and efficient in numerical analysis. Compared with the self-consistent theories with crystal grains as their basic components, the present theory is much simpler in mathematical treatment. Project supported by the National Natural Science Foundation of China (Grant No. 19732006).     

Initial Development of the Prefracture Zone Near the Tip of a Crack Reaching the Interface Between Dissimilar Media

The Wiener–Hopf method is used to analyze, within the framework of a plane static problem, the prefracture zone near the tip of a mode I crack reaching the interface separating two isotropic media and containing a corner point     

Nonlinear Dynamic Bending Analysis of Plates Using a Higher-Order Shear Deformation Theory

The transient dynamic elastoplastic bending analysis of plates is investigated. Higher-order shear deformation theory is employed for the purpose, so as to have more realistic transverse shear representation. The formulation requires C⁰ continuity for nodal variables. Isoparametric parabolic finite element discretization is adopted. The yield criteria incorporated are von Mises and Tresca along with associated flow rules. The isotropic hardening is also included. Equations of motion are satisfied at discrete time intervals using direct integration method and central difference scheme. A special mass lumping scheme is adopted. As critical time step is very important in explicit integration scheme, precaution has been taken so as to have the time step smaller than the critical one. Numerical examples are solved and compared with solutions from literature. The formulation is shown to be superior in comparison to previous formulations, being more generic in all respects.     

Unified analysis of liquefaction and the ground flow phenomenon

Loose saturated sand behaves as a solid before liquefaction but as a fluid when the excess pore water pressure equals the initial confining stress, after which it recovers its strength. A simple constitutive equation for loose saturated sand was developed to express the phase transformation between a solid and fluid during liquefaction and the ground flow phenomenon. This constitutive equation was used for a shaking table test, and its applicability was investigated by comparing numerical and experimental results Published in Prikladnaya Mekhanika, Vol. 43, No. 8, pp. 129–144, August 2007. An erratum to this article is available at .     

Shock adiabat features,phase transition macrokinetics,and spall fracture of iron in different phase states

Abstract

Results are presented of systematic experimental investigations of shock adiabat and evolution of multiwave configurations for a number of steels in the range up to 100GPa; of stress relaxation kinetics in the front of the elastic and phase precursor from different initial states: uσ_x = 15, 25, 49, and 59GPa; and of data on spa11 fracture of iron in α —, ε —, γ —, and liquid phases under conditions of uniaxial deformation as well as under volumetric omnidirectional tension. Changes in material microstructure and microhardness of samples subjected to shock wave loads of 15, 25, 200, and 1000 GPa are analyzed.

Investigations of steels with the initial state in α and γ phases of iron and with different original heat treatment show that, in stress waves of low intensity (σ_x? 10–25 GPa), as well as under quasi-static tension-compression tests and impact tests, differences in their behavior and properties are clearly displayed. As the amplitude of longitudinal stresses increases up to 200–250 GPa, differences in their compressibility and in the character of spal1 fracture begin to smooth down.     

CLOSED-FORM SOLUTIONS FOR ELASTOPLASTIC PURE BENDING OF A CURVED BEAM WITH MATERIAL INHOMOGENEITY

The elastoplastic pure bending problem of a curved beam with material inhomo- geneity is investigated based on Tresca＇s yield criterion and its associated flow rule. Suppose that the material is elastically isotropic, ideally elastic-plastic and its elastic modulus and yield limit vary radially according to exponential functions. Closed-form solutions to the stresses and radial displacement in both purely elastic stress state and partially plastic stress state are presented. Numerical examples reveal the distinct characteristics of elastoplastic bending of a curved beam composed of inhomogeneous materials. Due to the inhomogeneity of materials, the bearing capac- ity of the curved beam can be improved greatly and the initial yield mode can also be dominated. Closed-form solutions presented here can serve as benchmark results for evaluating numerical solutions.