An analytical method for determining the crack spacing and crack width in reinforced concrete beams and one-way slabs is presented in this thesis. The locations and the distribution of cracks developed in a loaded member are predicted using the calculated concrete stress distributions near flexural cracks. To determine the stresses, a concrete block bounded by top and bottom faces and two transverse sections of the beam is isolated and analysed by the finite element method. Two types of blocks are analysed. They are: (i) block adjacent to the first flexural crack, and (ii) block in between successive cracks. The calculated concrete stress distribution adjacent to the first flexural crack is used to predict the locations of primary cracks (cracks formed at sections where the stresses have not been influenced by nearby cracks). The concrete stress distributions in between successive cracks, calculated for various crack spacings and load levels, are used to predict the formation of secondary cracks in between existing cracks. The maximum, minimum and the average crack spacing at a given load level are determined using the particular crack spacing that would produce a concrete tensile stress equal to the flexural strength of concrete. The resulting crack width at reinforcement level is determined as the relative difference in elastic extensions of steel and surrounding concrete. The accuracy of the present method is verified by comparing the predicted spacing and width of cracks with those measured by others. The analytical method presented in this thesis is subsequently used to investigate the effects of various variables on the spacing and width of cracks, and the results are presented. These results are used to select the set of parameters that has the most significant effect. A parametric study is then carried out by re-calculating the spacing and width of cracks for the selected parameters. Based on the results of this parametric study, new formulas are developed for the prediction of spacing and width of cracks. The accuracy of these formulas is ascertained by comparing the predicted values and those measured by other investigators on various types of beams under different load levels. The calculated stress distributions between successive cracks are also used to develop a new method of incorporating the tension stiffening effect in deflection calculation. First, curvature values at sections between adjacent cracks are determined under different load levels, using the concrete and steel stresses. These results are used to develop an empirical formula to determine the curvature at any section between adjacent cracks. To verify the accuracy of the new method, short-term deflections are calculated using the curvature values evaluated by the proposed formula for a number of beams, and the results are compared with those measured by others.

With increasing number of structures reaching their designed life or capacities everyday, retrofitting has become an important area in civil engineering. A popular method of strengthening and stiffening reinforced concrete ( RC ) beams is by adhesively bonding steel or FRP plates to the external surfaces. This technique has been proven to be efficient, inexpensive, unobtrusive and can be applied while the structure is in use. However, it has been found that adhesively bonded plates are prone to premature debonding prior to reaching their designed capacities, which restricts the use of existing design rules and guidelines for retrofitting RC beams using this relatively new form of structure. There are various forms of debonding including : plate end ( PE ) debonding ; critical diagonal crack ( CDC ) debonding ; and intermediate crack ( IC ) debonding. IC debonding is an especially important mechanism as it will occur at plated hinges of continuous members, and unlike other premature debonding mechanisms, IC debonding is very difficult to prevent. This debonding mechanism is associated with the formation of flexural or flexural - shear cracks in the vicinity of the plates, which causes slip to occur at the plate / concrete as well as the bar / concrete interfaces. Most research to date has been focusing on the bond - slip relationship at the plate / concrete interface, while little attention has been given to the IC debonding behaviour of flexural members. To allow safe and effective use of plated structures, it is necessary to model the debonding behaviours at the plate / concrete interface as premature debonding will affect both the strength and ductility of the members, and hence the ability of continuous structures to redistribute moment. Despite the importance of moment redistribution, very limited research has been carried out on the moment redistribution of continuous plated members. Since IC debonding is likely to occur at plated hinges of continuous members hence affecting the ductility of the hinges, the existing approaches for determining moment redistribution of reinforced concrete beams cannot be applied to plated members. In this research a numerical model based on discrete cracking and partial interaction theory has been developed which models the IC debonding of plated beams, taking into account the slips at all interfaces. This model will allow a better understanding of the IC debonding behaviour of plated members, and also from the model, the rotation capacity of both plated and unplated hinges in continuous reinforced concrete beams can be determined. Mathematical models and design rules have been developed for analysing critical diagonal crack debonding, which is dependent on the IC debonding behaviour of the plated members. Moment redistribution of beams with externally bonded and near surface mounted plates is studied through a series of tests and a mathematical model based on variation in flexural rigidity is proposed. Through the tests carried out on continuous plated beams, much moment redistribution is evident as oppose to that suggested by the existing design guidelines for plated members, where no moment redistribution is allowed for members plated with FRP. From the models proposed for IC and CDC debonding in this research, together with the existing PE debonding models available, all debonding mechanisms can now be modelled. Furthermore from the research on continuous plated beams, moment redistribution of plated beams can be analysed, allowing safe, effective and economic use of this retrofitting technique. This thesis is presented in the form of a collection of journal papers published or submitted for publication as a result of the research performed by the author. A selection of ten publications have been included in the following context, together with literature reviews performed on the related areas of studies, as well as further discussions on the papers, which consist of any additional information or work that was carried out in this research but not presented in the papers. / Thesis (Ph.D.)--School of Civil and Environmental Engineering, 2006.

Agglomerate formation is a common phenomenon that can cause operating problems in the fluid coking reactor. When agglomerates form they provide longer diffusion paths of the reaction products through the liquid layers and liquid bridges within the agglomerate, which leads to higher mass transfer resistance, trapping of the reaction products and increasing the undesired coke formation reactions. Surviving agglomerates in the reactor can also cause fouling of the reactor interior and defluidization of the bed. The ultimate coke yield was determined for agglomerates of Athabasca vacuum residue and solid particles by heating on Curie-point alloy strips in an induction furnace at 503 oC and 530 oC and in a fluidized bed reactor at 500 oC until all toluene-soluble material was converted. Coke yields from agglomerates were compared to the results from reacting thin films of vacuum residue. The average coke yield from the agglomerates was 23%, while the coke yield from thin films of 20 m thickness was 11%, which supports the role of mass transfer in coke formation reactions. The ultimate coke yield was insensitive to vacuum residue concentration, agglomerate size, reaction temperature and agglomerate disintegration. The temperature profile within agglomerates was measured by implanting a thermocouple at the agglomerate center, and a heat transfer model was used to describe the temperature variation with time. The effective thermal diffusivity of the agglomerates was 0.20 x 10-6 m2/s. Control experiments on reactions in thin liquid films confirmed that heating rates in the range of 14.8 to 148 K/s had no effect on the ultimate yield of coke

The mechanical behaviour of coated papers during folding has been investigated. This problem has been studied with experimental techniques and numerical analyses in order to give a better understanding of the folding properties of coated papers pertinent to the mechanical behaviour in general, and particularly cracking along the fold. A microscopy investigation has been performed. The surface of the folded paper has been carefully examined to study the event of fracture and related issues. The influence of the grammage on the cracking event has been studied and it was shown that the coating material would not fail if the paper sample was sufficiently thin. It was found that a stress or strain based criterion is sufficient to describe the cracking of the coating layers and that the anisotropy of paper should be taken into account when studying the folding process. The finite element method has been used for the numerical analyses remembering that the geometry of the problem is rather complicated, excluding a solution in analytical form. Using different constitutive models for the base stock, it has been shown that the deformation of the coated paper during folding is much governed by the paper substrate. The numerical results also suggested that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. Furthermore, it has also been shown that delamination buckling, in the present circumstances, has a very small influence on the strain levels in the coating layer subjected to high tensile loading. Dynamic effects have also been studied and it has been shown that a quasi-static analysis of the problem is sufficient in order to describe many of the important features related to cracking. An attempt to model strong anisotropy of paper has been presented and the results indicate that the large anisotropy in the thickness direction of coated papers needs to be taken into account in order to fully understand the mechanics of folding. Finally, an experimental investigation has been presented in order to study if important mechanical properties of the coating material could be determined by microindentation techniques. The results presented indicate that microindentation can be a powerful tool for characterization of these materials, but only if careful efforts are made in order to account for the influence from plasticity as well as from boundary effects. KEYWORDS: folding, coated papers, finite element method, cracking, indentation, anisotropy, plasticity.

No description available.

No description available.

Environmentally Assisted cracking (EAC) is a very critical materials science problem that concerns many technological areas such as petrochemical engineering, aerospace operations and nuclear power generation, in which cracking or sudden failure of materials may happen at stress far below the tensile strength. This type of corrosion is initiated at the microscopic level and is complicated due to the combination of chemistry (reaction caused by corrosive agents) and mechanics (varying load). As EAC is generally related to the segregation of impurity elements to defects (mainly grain boundaries), the symptoms of risk may not be apparent from the exterior of the metal components: hence EAC remains latent and gives no sign of warning until the failure occurs. Due to its intricate nature, conducting experiments on this phenomenon involves difficulties and requires much effort. In this work, we employed advanced molecular simulation techniques to study EAC in order to give insight into its atomistic behavior. First, Density-Functional Theory (DFT) method was used to investigate the fundamental processes and mechanism of EAC-related issues at the nanoscale level, with two case studies concerning the stress corrosion in iron and hydrogen embrittlement in palladium. When segregating to the grain boundary (GB) of iron, different impurity elements such as sulfur, phosphorus and nitrogen raise corrosion failures in a variety of ways. Hydrogen atoms, due to their mobility and small atomic size, are able to form high occupation at crystal defects, but show different interactions to vacancy and GB. Then, we used the classical Molecular Dynamics (MD) method to gain an understanding of the dynamic response of materials to mechanical load and the effects of temperature, strain and extreme conditions (high pressure shock compression) on structural properties. The MD simulations show that hydrogen maintains the highest localization at grain boundaries in the vicinity of ambient temperatures, and grain boundaries are the preferred nucleation sites for dislocations and voids. This computational work, using DFT and MD techniques, is expected to contribute to the better understanding on chemistry and mechanisms of complex environment-assisted cracking phenomenon at a fundamental level in order to beneficially complement conventional laboratory approaches.

Sulfide Stress Cracking (SSC) resistance of the newly developed API-X100 High Strength Low Alloy (HSLA) steel was investigated in the NACE TM0177 "A" solution. The NACE TM0177 "A" solution is a hydrogen sulfide (H2S) saturated solution containing 5.0 wt.% sodium chloride (NaC1) and 0.5 wt.% acetic acid (CH3COOH). The aim of this thesis was to study the effect of microstructure, non-metallic inclusions and alloying elements of the X100 on H2S corrosion and SSC susceptibility. The study was conducted by means of electrochemical polarization techniques and constant load (proof ring) testing. Microstructural analysis and electrochemical polarization results for X100were compared with those for X80, an older generation HSLA steel. Uniaxial constant load SSC testing was conducted using X100 samples and the results were compared with those reported for older generation HSLA steels. Addition of H2S to the NACE TM0177 "A" solution increased the corrosion rate of X100from 51.6 to 96.7 mpy. The effect of H2S on the corrosion rate was similar for X80. The corrosion rate for X80 increased from 45.2 to 80.2 mpy when H2S was added to the test solution. Addition of H2S enhanced the anodic kinetics by forming a catalyst (FeHSads) on the metal surface and as a result, shifted the anodic polarization curve to more current densities. Moreover, the cathodic half cell potential increased due to the decrease in pH, from 2.9 to 2.7, which shifted the cathodic polarization curve to more current densities. The increase in both the anodic and cathodic currents, after H2S addition, caused the rise in the corrosion current density. In H2S saturated NACE TM-0177 "A" solution, the X100 steel corrosion rate was higher than the X80 steel by 20%. Longer phase boundaries and larger nonmetallic inclusions in the X100 microstructure generated more areas with dissimilar corrosion potentials and therefore, a stronger driving force for corrosion. Higher density of second phase regions and larger nonmetallic inclusions acted as an increased cathode area on the X100 surface which increased the cathodic current density and consequently, increased the corrosion current density. Proof ring tests on the X100 gave a threshold stress value, C5th, of 46% YS, 343.1 MPa(49.7 ksi). The main failure was caused by SSC cracking. SSC nucleated at corrosion pits on the metal surface and microcracks in the metal body and propagated perpendicular to the applied stress. Hydrogen Induced Cracking (HIC) was observed in the X100. HIC cracks nucleated at banded martensite-ferrite interfaces and propagated along the rolling direction parallel to the applied tensile stress through the softer ferrite phase. When compared to older HSLA grades, the X100 tested in this study had a high SSC susceptibility and therefore, is not be recommended for H2S service applications. The high X100 SSC susceptibility was caused by the material high corrosion rates in H2Smedia which formed corrosion pits that acted as crack initiation sites on the metal surface and provided more hydrogen that migrated into the steel. In addition, the X100 inhomogeneous microstructure provided a high density of hydrogen traps in front of the main crack tip which promoted SSC microcrack formation inside the metal. Microcracks in the metal body connected with the main crack tip that originated from corrosion pits which assisted SSC propagation.

Many particulate processes are preferably implemented in circulating fluidized beds (CFB) over traditional low-velocity fluidization to take advantage of the many benefits of circulating systems. Fluid catalytic cracking (FCC) is one of the most successfully applied processes in CFB technology, with more than 350 FCC units in operation worldwide. Despite its extensive use, an understanding of the complex behaviour of these units is incomplete.<p> A theoretical and experimental evaluation of the fluidization behaviour was conducted in the CFB riser, standpipe, and stripper. Initially, an extension of the existing CFB in the Fluidization Laboratory of Saskatchewan was designed. The experimental program conducted in this study included an examination of the solids flow behaviour in the riser, interstitial gas velocity in the downcomer, and stripping efficiency measurements. The hydrodynamic behaviour of the stripper was modeled using Multiphase Flow with Interphase eXchanges (MFIX) CFD code.<p> The solids flow behaviour in the bottom zone of a high-density riser was investigated by measuring the local upwards and downwards solids flux. Solids circulation rates between 125 and 243 kg/(m2⋅s) were evaluated at a constant riser superficial gas velocity of 5.3 m/s. The effect of the riser superficial gas velocity of the local upflow at the riser centerline was also conducted at a solids circulation rate of 187 kg/(m2⋅s). The results show that there is little variation in the local net solids flux at radial locations between 0.00 ¡Ü r/R ¡Ü 0.87. The results indicate that a sharp regime change from a typical parabolic solids flux profile to this more radially uniform solids flux profile occurs at a gas velocity between 4.8 and 4.9 m/s.<p> To quantify stripping efficiency, the underflow of an injected tracer into the standpipe must be known. Quantification of the underflow into the standpipe requires knowledge of two main variables: the interstitial gas velocity and the tracer gas concentration profiles in the standpipe. Stripping efficiency was determined for stripper solids circulation rates of 44, 60, and 74 kg/(m2⋅s) and gas velocities of 0.1, 0.2, and 0.3 m/s. For most conditions studied, the interstitial gas velocity profile was found to be flat for both fluidized and packed bed flow. The stripping efficiency was found to be sensitive to the operating conditions. The highest efficiency is attained at low solids circulation rates and high stripping gas velocities.<p> In the numeric study, stripper hydrodynamics were examined for similar operating conditions as those used in the experimental program. Due to an improved radial distribution of gas and decreasing bubble rise velocity, mass transfer is deemed most intense as bubbles crest above the baffles into the interspace between disc and donut baffles. Stripping efficiency is thought to improve with increasing gas velocity due to an increased bubbling frequency. Stripping efficiency is thought to decrease with increasing solids circulation rates due to a lower emulsion-cloud gas interchange coefficient and a decreased residence time of the emulsion in the stripper.

Understanding the mechanical behavior of composite materials requires extensive knowledge of fracture behavior as a crack approaches an interface between the bulk material and the reinforcement structure. Overall material toughness can be greatly influenced by the propensity of an impinging crack to propagate directly through the substrate or deflect along an interface boundary. As the basis for this thesis; the assertion that an impinging crack may encounter a reinforcement structure at various incident angles is explored. This requires the ability to predict crack penetration/ deflection behavior not only normal to the reinforcement, but at various incident angles. Previous work in the area of interface fracture mechanics has used a stress or energy based approach, with recent advances in the field of a combined cohesive-zone method. Work presented here investigates the interaction between strength and toughness when using the cohesive-zone method on the problem of an impinging crack not normally incident to the interface of a composite material. Computational mechanics methods using Abaqus and user-define cohesive elements will be applied to this angled incident crack problem. A circular model based on the displacement field equations for mode-I fracture loading is introduced and verified against well-established LEFM solutions. This circular model is used to study the effects of incident crack angle on the penetration vs. deflection behavior of an impinging crack at various angles of incidence. Additionally, the effects of angle on the load applied to the model at fracture are explored. Finally, a case study investigating how the interaction between strength and toughness found using the cohesive-zone method helps to explain some of the inconsistencies seen in the interface indentation fracture test procedure. / Graduation date: 2013