Xie Heping

Thermal-mechanical coupled effect on fracture mechanism and plastic characteristics of sandstone

Scanning electronic microscopy (SEM) was employed to investigate fractographs of sandstone in mine roof strata under thermal-mechanical coupled effect. Based on the evolution of sandstone surface morphology in the failure process and fractography, the fracture mechanism was studied and classified under meso and micro scales, respectively. The differences between fractographs under different temperatures were examined in detail. Under high temperature, fatigue fracture and plastic deformation occurred in the fracture surface. Therefore, the temperature was manifested by these phenomena to influence strongly on micro failure mechanism of sandstone. In addition, the failure mechanism would transit from brittle failure mechanism at low temperature to coupled brittle-ductile failure mechanism at high temperature. The variation of sandstone strength under different temperature can be attributed to the occurrence of plastic deformation, fatigue fracture, and microcracking. The fatigue striations in the fracture surfaces under high temperature may be interpreted as micro fold. And the coupled effect of temperature and tensile stress may be another formation mechanism of micro fold in geology.

FRACTAL GEOMETRY AND FRACTURE OF ROCK

The irregular and rough profile of fracture surfaces of rock can be regarded as having self-similarity statistically. The authors apply a new geometry—fractal geometry to describe this irregularity. Fractal models of the transgranular fracture and the combined intergranular and transgranular fracture are established. The fractal character of fracture surface of rock is examined by electron scanning and optical fractographic analyses. Finally, the relation between fractal dimension and macromechanics quantities of rock fracture is obtained.

An improved method of collocation for the problem of crack surface subjected to uniform load

Abstract An improved method of boundary collocation for the problem in which the crack surface is subjected to uniform load is developed. A new stress function which is based on the stress boundary condition of crack surface is proposed. The conditions on the external boundaries are satisfied approximately by the collocation method. This improved method is applied to calculating the stress intensity factor (SIF) values of different angle cracks of square and circular internally cracked plates in which the crack surface is subjected to uniform normal compressive stress q σ or uniform shear stress q τ . The new stress function and the calculation procedure are more convenient and simpler than other collocation techniques investigated [1, 2].

A fractal model and energy dissipation for en echelon fractures

Abstract Observations from the field and the laboratory show that en echelon fractures within fracture zones have a Riedel within Riedel structure. The tensile failure mechanism of formation of en echelon fractures can be described by the pile-ups of shear crack-dislocations. A fractal model can be used to simulate the Riedel within Riedel geometry, allowing the direct measurement of the fractal dimensions of en echelon fracture systems. The energy dissipation of the en echelon fracture system can be deduced using a fractal damage evolution model which explains the evolution process of the system. The fractal nature of the fractures can be used to derive an accurate estimate of total energy dissipation.

On star product fractal surfaces and their dimensions

In this paper, by using fractal curves, a family of fractal surfaces are defined. Each fractal surface of this family is called Star Product Fractal Surface (SPFS). A theorem of the dimensions of the SPFS is strictly proved. The relationship between the dimensions of the SPFS and the dimensions of the fractal curves constructing the SPFS is obtained.

The theory of fractal interpolated surface and its applications

In this paper, the principle of construction of a fractal surface is introduced, interpolation functions for a fractal interpolated surface are discussed, the theorem of the uniqueness of an iterated function system of fractal interpolated surface is proved, the theorem of fractal dimension of fractal interpolated surface is derived, and the case that practical data are used to interpolate fractal surface is studied.

Fractal geometry derived from geometric inversion

In this paper, the conception of fractal geometry derived from geometric inversion is introduced. A ramified self-inverse fractal with symmetry and a self-inverse fractal dust set are constructed. The authors extend the conception of the fractal osculation and propose a new notion—fractal envelope. Finally, two examples of self-inverse fractal (soap and egg) are given.

ANALYSIS OF NONLINEAR LARGE DEFORMATION PROBLEMS BY BOUNDARY ELEMENT METHOD

In this paper, the author deduces an approximate solution of nonlinear influence function in rate form for two-dimensional elastic problems on current configuration by the method of co-moving coordinate system. Here BEM formulation of large deformation based on Chens theory[I] is given. The computational processes of nonlinear boundary integral equation is discussed. The author also compiles a nonlinear computing program NBEM. Numerical examples show that the results presented here is available to the solution of engineering problems.