Finite element methods fracture geometry

The AUGUR information on defect configuration is used to develop the three-dimensional solid model of damaged pipeline weldment by the use of geometry editor. The editor options provide by easy way creation and changing of the solid model. This model is used for fracture analysis by finite element method with appropriate cross-section stress distribution and external loads. 

Four research teams—AECB, CLAY, KIPH and LBNL—studied the task with different computational models. The computer codes applied to the task were ROCMAS, FRACON, THAMES and ABAQUS-CLAY. All of them were based on the finite-element method (FEM). Figure 6 presents an overview of the geometry and the boundary conditions of respective models, including the nearfield rock, bentonite buffer, concrete lid, and heater. The LBNL model is the largest and explicitly includes nearby drifts as well as three main fractures... 

The extended finite element method (XFEM) for treating fracture in composite materials is proposed by Huynh and Belytschko [191]. This methods work with meshes that are independent of matrix/inclusion interfaces and the discontinuities and neartip enrichments were modeled. In order to describe the geometry of the interfaces and cracks in this method, level sets were employed, so that there is no need for explicit representation of either the cracks or the material interfaces. The other researchers such as Du et al. [192] and Ying et al. [193] used XFEM to model material interfaces in particulate composites with more in detail. 

The DCB test, the blister test, and several other geometries are somewhat amenable to the analytical analyses needed for fracture mechanics. As a consequence, most early fracture mechanics analyses focused on such geometries. Modern computational methods, particularly finite element methods (FEM), have lifted this restriction. A brief outline of how FEM might be used for this purpose may be helpful. Inherent in fracture mechanies is the concept that natural cracks or other crack-like discontinuities exist in materials, and that failure of an object generally initiates at such points [13,16,17,23-25]. Assuming that a crack (or a debonded region) is situated in an adhesive bond line, modern computation techniques can be used to facilitate the computation of stresses and strains throughout a body, even where analytical solutions may not be convenient or even possible. 

Obviously, key questions which now arise are how good are these various analytical and finite element analysis methods at yielding a value of the adhesive fracture energy, Gc, (a) which is independent of the details of the peel test geometry, for example, independent of the peel angle and thickness of the peel arm and (b) which agree with results from other test methods, for example, with values of Gc from standard linear-elastic fracture-mechanics (LEFM) tests. 

---