Lecturer, Al-Nahrain University -Physics
In the present work, a multiscale model for describing the cohesive energies for different materials is derived and then applied on Nano scale materials to interpret their behavior. The derived model is based on a new theory that is called time of events theory. The new model, which is a non-Born-Oppenheimer model has the ability to take into account the size effects of different atoms on the cohesive energies between these atoms. This offers more precise predictions for the mechanical properties and enable the interpretation of some of the weird mechanical properties near the Nano scale.
Abstract: The fatigue fracture behavior of chlor-alkali monolayer membranes is investigated under a condition similar to the membrane electrolysis cell service environment, i.e., at 86°C in brine solution. The linear elastic fracture mechanics (LEFM) approach, i.e., da/dN vs. AK, is implemented in this study. It is found that the fatigue crack propagation behavior of the chlor-alkali membranes can be successfully characterized via the LEFM technique. The fatigue fracture surfaces of the membranes are also investigated using stereo-optical microscopy and are found to show typical fatigue striation patterns. Detailed experimental procedures for preparing and testing of the membranes are presented.
Pub.: 01 Apr '94, Pinned: 31 Oct '17
Abstract: •An equivalent LEFM model for cohesive fracture interacting with a capillary fluid.•Analytical solution for LEFM threshold of the brittleness number.•Critical pressure for instantaneous pipe failure predicted by fracture mechanics approach.
Pub.: 01 Sep '17, Pinned: 31 Oct '17
Abstract: Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern–Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone effect on the ductile rock fracture.
Pub.: 07 Dec '11, Pinned: 31 Oct '17