The objective of this study is to present the mode I stress intensity factor distribution (SIF) along the crack-front for a wide array of semicircular and semi-elliptical surface cracks inside of a pressurized thick-walled cylinder. A three-dimensional finite element package ANSYS is used to evaluate the SIF for multicracked cylinder with number of cracks from n=1 to 128, the ratio of crack-depth to the wall thickness a/t=0.05 to 0.6, the ellipticity of the crack (the crack-depth to the semi-crack length) a/c=0.2 to 1.5, the ratio of the outer to the inner radius ro/ ri=2. A substructuring technique is introduced which solved a coarse model meshed with ten-node isoparametric elements and applied the resulting displacements in the boundary surface of a submodel which is built employing singular elements along the crack-front to produce the 1/√r singularity . The SIF is evaluated using nodal-displacement method. To validate the modeling and analysis procedure of the present results various configurations were solved using this method and compared to other finite element solutions. The present results were in very good agreement: less than 5 % comparing with Raju and Newman's results and within 8 % of Kirkhope's results. An empirical equation to calculate the maximum SIF, was developed in this study. The equation was obtained by nonlinear fitting of the finite element results and the error was within ± 5.7 %.

Modelling damage in composite materials has played an important role in designing composite structures. Although numerical models for the progressive damage in laminated composites (e.g. transverse cracking, delamination and fibre breakage) have been developed in the literature, there is still a need for further improvement. This thesis aimed at developing damage models suitable for predicting intra-laminar and inter-laminar damage behaviour in fibre-reinforced composite materials. Several approaches such as fracture mechanics and continuum damage mechanics have been adopted for constructing the damage model. Meso-macro-mechanics analysis was performed to gain an insight into the entire damage process up to the final failure of the composite laminate under various conditions. Cohesive elements were placed in the finite element model to simulate the initiation and propagation of matrix crack and delamination in cross-ply laminates. This helped to understand the direct interactions between damage modes, i.e. whether one damage mode would initiate the other damage mode. The formation of a single matrix crack and its propagation across the layer thickness was also revealed. A new cohesive zone/interface element model was developed to consider the effect of through-thickness compressive stress on mode II fracture resistance by introducing friction into the constitutive law of the conventional cohesive zone model. Application of the model to practical problem in composite laminates shows that this model can simulate delamination failure more accurately than the cohesive element in ABAQUS.Damage models based on continuum damage mechanics were proposed for predicting intra-laminar damage and interlaminar damage. Five intra-laminar failure modes, fibre tension, fibre compression, matrix tension, matrix compression and shear failure, were modelled. Damage initiation was predicted based on stress/strain failure criteria and damage evolution law was based on fracture energy dissipation. The nonlinear shear behaviour of the material was considered as well. These models have been implemented into ABAQUS via a user-defined material subroutine and validated against experimental/numerical results available in the literature. The issue related to numerical implementation, e.g. convergence in the softening regime, was also addressed. Numerical simulation of the indentation test on filament-wound pipe was finally conducted and damages generated in the pipe were predicted using the above developed damage models. The predictions show an excellent agreement with experimental observations including load/indentation responses and multiple delaminations shape and size. Attempt was made to detect damage-induced leakage path in the pipe after indentation.

Lifetime prediction of components in Alloy 600 is a major concern for nuclear power plants. Alloy 600 components have been shown to be susceptible to stress corrosion cracking (SCC). In the 1990’s, an engineering model was developed in order to predict the life time as a function of the main macroscopic parameters (stress, environment, material), based on laboratory results. This model has since been used to predict the ranking of various Alloy 600 components, using the knowledges of the manufacturing and service conditions for each component. It was applied successfully in the case of forged control rod drive mechanism (CRDM) nozzles. However, it was found necessary to improve this model to account for the strain history of the different components. Predictions using the model, investigated from an array of test results on Alloy 600 in laboratory primary water, have demonstrated that the time for initiation differed significantly according to the strain path applied to the specimen. The present work is dedicated to assess SCC results from samples with different strain paths and different level of cold work in order to better understand the manufacturing conditions on SCC. The samples are machined in three different directions and tested at different durations in order to model the time for transition (transition between slow and fast propagation) as a function of cold work, strain path and stress. Thermomechanical treatments are also applied on two different heats of Alloy 600: forged WF675 (very susceptible to SCC in as received conditions) and rolled 78456/337 (non susceptible to SCC in as-received conditions) in order to transform the forged microstructure into a microstructure close to the rolled microstructure and vice-versa. These microstructures are then tested in primary conditions and the results are compared to the results obtained on as-received material in order to get a better understanding of manufacturing process and microstructure parameters regarding SCC behaviour.

The construction of coastal ports requires the use of materials that meet the demands of the marine environment, to prevent underwater concrete structures from cracking and spalling easily; basalt fiber is used to delay the expansion of concrete and prevent the formation of cracks. This research studies the behavior of concrete for prefabricated piles with Portland Cement Type I and basalt fibers added in 0.1%, 0.3% and 0.6%; the results indicate that the fiber is suitable for concrete, the slump decreases, the compressive strength increases for specimens cured in tap water and sea water, the relationship between resistances does not vary, and the depth of carbonation decreases.

No description available.

M. S.

Saudi Aramco is investigating the potential use of oxidized disulfide oil (ODSO), a refinery waste, as a solvent to replace water in zeolite preparation for the implication in industrial processes such as Fluidized Catalytic Cracking (FCC) aiming to increase propylene production. Utilizing ODSO helps Saudi Aramco reduces its processing costs, creates a value for this solvent and reduces the zeolite synthesis cost. One major concern is the effect ODSO may have on the catalytic performance of the prepared zeolites. This study investigates the catalytic cracking of 1-hexene and 2-methyl-2-butene (2M2B) at various WHSV and temperatures over ZSM-5 catalysts prepared from gels with SiO$_2$/Al$_2$O$_3$ ratios (SAR) of 50 and 25 and various ODSO/water substitutions. Six ODSO-based ZSM-5 catalysts were prepared and characterized in terms of acidity, morphology, and textural properties. The impact of catalyst composition and properties on conversion and selectivity is examined and compared to commercial ZSM-5 catalysts with similar SAR (CBV2314 and CBV5524G). At 477 h$^{-1}$ WHSV, ODSO-based catalysts achieved 80% 1-hexene conversion with 53-60% propylene selectivity, outperforming commercial catalysts (52%). However, 2M2B cracking exhibits slower reaction rates and more oligomerization cracking, resulting in lower conversion (46-61%) and propylene selectivity (22-29%). Notably, MAR- 2-3 (30% ODSO, 50 SAR gel) shows the best performance among the ODSO catalysts in terms of stability and selectivity, with results comparable to the commercial catalysts. We noticed, on the other hand, that ODSO-based catalysts possess larger crystals and higher acid site density compared to the commercial catalysts leading, generally, to a decreased stability. These findings enhance understanding of waste-based zeolites in catalytic cracking processes and guide the development of improved ODSO-based catalysts for petrochemical applications.

Biodiesel is one of the most widely used biofuels in the world, due in part to its simplicity of production, compatibility with existing engines, and reduction of green house gas emissions. However, technical difficulties with biodiesel include: (1) the need of highly refined oil for ASTM compliance, (2) incompatibility with the petroleum-diesel pipeline distribution system, and (3) a relatively small inventory of expensive feedstocks. Issues (1) and (2) could be overcome by the production of biofuels using chemical processes associated with petroleum refining. Catalytic lipid cracking could result in green diesel, a fuel chemically similar to conventional diesel but derived from a clean renewable feedstock. The impact of phosphorus poisoning on catalytic cracking of lipids has been studied in this work using both homogeneous and heterogeneous catalysts. Catalytic cracking of model lipids was shown to occur in a homogeneous liquid phase with triflic acid, a superacid 100 times more acidic than sulfuric acid. Products obtained from the reaction were heavily oxygenated and generally unsuitable for fuel use, suggesting the need for heterogeneous catalytic cracking. Reaction kinetics show a high linear dependence on Brönsted system acidity, with an overall reaction order of 3. The affect of phosphorus on heterogeneous acid cracking was then studied. Since lipid feedstocks contain small amounts of phospholipids knowledge of the interactions between phospholipids and zeolites is crucial to a system-wide understanding of the lipid cracking process. Phosphorus-containing compounds were used to poison ZSM-5 (a solid zeolite catalyst) in order to simulate the cracking of phospholipids. Model compounds were then cracked over the poisoned zeolite, with differences in product distribution and kinetics based on phosphorus loading recorded. It was shown that phosphorous has a dramatic effect on both conversion and product distribution of cracking reactions. It is believed that phosphorous binds irreversibly to heterogeneous active sites, causing the majority of deactivation. To address the issue of limited feedstock availability, research was also undertaken to find new lipids sources for biofuel use. It was determined that lipids extracted from microorganisms grown in a municipal wastewater treatment system could be suitable. However, any phosphorous must be removed before catalytic cracking of the extracted lipids.

In the present study, the problem of optimization of thermal cracker (pyrolysis) operation is discussed. The main objective in thermal cracker optimization is the estimation of the optimal flow rates of different feeds (such as, Gas-oil, Propane, Ethane and Debutanized natural gasoline) to the cracking furnace under the restriction on ethylene and propylene production. Thousands of combinations of feeds are possible. Hence the optimization needs an efficient strategy in searching for the global minimum. The optimization problem consists of maximizing the economic profit subject to a number of equality and inequality constraints. Modelling, simulation and optimal operation via optimization of the thermal cracking reactor has been carried out by gPROMS (general PROcess Modelling System) software. The optimization problem is posed as a Non-Linear Programming problem and using a Successive Quadratic Programming (SQP) method for solving constrained nonlinear optimization problem with high accuracy within gPROMS software. New results have been obtained for the control variables and optimal cost of the cracker in comparison with previous studies.

M.S.