Thesis. 1977. M. Arch.--Massachusetts Institute of Technology. Dept. of Architecture. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH. / Bibliography : leaf 52. / by William Roan Tibbs, Jr. / M.Arch.

Thesis (M.S.)--Massachusetts Institute of Technology, Alfred P. Sloan School of Management, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND DEWEY. / Includes bibliographies. / by Randall Richard Reyff. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Humanities, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND HUMANITIES. / Bibliography: leaves 115-118. / by Susan Kay Jackson. / B.S.

Thesis (Master of Engineering in Mechanical Engineering)--Cape Peninsula University of Technology, 2018. / South Africa’s railway system is the most highly developed in Africa. There are different kinds of transport systems in South Africa but rail transport is considered as one of an important element of the country’s transport infrastructure. In South Africa, over 2.4 million passengers make use of rail transport to get them to their destinations. However, evidence shows that train accidents have become a common occurrence across the country. Train-related accidents such as collision, derailments, platform change incidents and commuter accidents, cost South Africa over R400 million per year. The analysis of derailments indicates that the most significant single contributor to derailments is rail breaks. This contrasts considerably with prescribed relevant local and international benchmarks, which show a much lower percentage of derailments due to rail break. The frequency of derailments due to rail breaks in South Africa seems to be higher in the northern than the southern region. Furthermore, the proportion of rail breaks that result in derailment is considerably higher than the set benchmarks and therefore, if there is a rail break, then the probability of this translating into a derailment is astonishingly high. Equally, the high incidence of derailments due to rail breaks is affected by the train length and axle load and further exacerbated by the absence of track circuitry. Since derailments are a direct function of the incidence of rail breaks, focus is required to characterize the factors causing defects on rail lines. This study investigated steel rail material by characterising the piece of the damaged rail with the aim to gain a better understanding of the wear mechanism. Chemical composition analysis of steel rail sample was conducted with the use of a Scanning Electron microscopy. Hardness of steel rail was measured with a Vickers hardness tester. An Optical Microscopy was used to examine the microstructure features of the worn rail samples. This study discovered that the worn out rail, which was produced from high carbon steel with pearlite and ferrite microstructure, undergoes decarburization and a plastic deformation process. The decarburization process happens when the rail track is heated to 700 oC and above when the carbon atoms at the surface interact with the atmospheric gases and are removed from the steel as a gaseous phase. Plastic deformation is created when the iron atoms are heated above the elastic point resulting in the permanent movement of iron atoms.

Abstract not available

Insitu cementitious stabilisation is an economical, environmentally sustainable and socially advantageous means of rehabilitating pavements. With the recent availability of a wide range of binders and advanced construction equipment, the characterisation of cementitiously stabilised pavement materials has become the focus of further advancement of this technology. Australian practice has moved towards the use of Indirect Diametric Tensile (IDT) methods for the characterisation of these materials. A draft protocol for the IDT test has been prepared and specifies samples to be compacted by gyratory compactor. This procedure provides for both monotonic and repeated load testing, which aims to measure the material???s strength, modulus and fatigue life. A range of host materials, including a new crushed rock and a reclaimed existing pavement base course, were assessed when stabilised with a General Purpose cement binder as well as with a slag-lime blended binder. Materials were assess for their inherent material properties, Unconfined Compression Strength (UCS), Unconfined Compression modulus, IDT strength and modulus under both monotonic and repeated load. A number of amendments and refinements to the testing protocol were recommended. These included the use of minimum binder contents to ensure the binder was uniformly distributed and to promote heavy binding of the materials to ensure they behaved elastically. It was also recommended that samples be gyratory compacted to a pre-determined sample height to allow a constant density to be achieved. The variability of the test results was examined. UCS results were found to be comparatively as variable as other researchers had reported. IDT strength results contained a similar level of variability, which was considered to be acceptable. Modulus results, both monotonic and repeated load, were found to be five to ten times more variable than strength results, which is a generally accepted trend for modulus testing. Under repeated loading, some challenges with the test protocol were encountered. The primary challenge was obtaining reliable and repeatable diametrical displacement data for modulus calculation. This was partially overcome by the insertion of smooth spacers to prevent the Linear Voltage Displacement Transformer (LVDTs) becoming caught on the sample sides. The achievement of reliable and repeatable IDT modulus results through improved displacement measurements should be the focus of future research efforts in this area.

Flush repairs to military aircraft are expected to become more prevalent as more thick skin composites are used, particularly on the surface of the fuselage, wings and other external surfaces. The use of these repairs, whilst difficult to manufacture provide an aerodynamic, ???stealthy??? finish that is also more structurally efficient than overlap repairs. This research was undertaken to improve the design methodology of scarf repairs with reduced material removal and to investigate the damage tolerance of scarf repair to low velocity impact damage. Scarf repairs involve shallow bevel angles to ensure the shear stress in the adhesive does not exceed allowable strength. This is important when repairing structures that need to withstand hot and humid conditions, when the adhesive properties degrade. Therefore, considerable amounts of parent material must be machined away prior to repair. The tips of the repair patch and the parent laminate are very sharp, thus a scarf repair is susceptible to accidental damage. The original contributions include: ??? Developed analytic means of predicting the stresses within optimised scarf joints with dissimilar materials. New equations were developed and solved using numerical algorithms. ??? Verified using finite element modelling that a scarfed insert with dissimilar modulus subjected to uniaxial loading attracted the same amount of load as an insert without a scarf. As such, the simple analytic formula used to predict load attraction/diversion through a plate with an insert may be used to predict the load attraction/diversion into a scarf repair that contains a dissimilar adherend patch. ??? Developed a more efficient flush joint with a doubler insert placed near the mid line of the parent structure material. This joint configuration has a lower load eccentricity than external doubler joint. ??? Investigated the damage tolerance of scarf joints, with and without the external doubler. The results showed that scarf joints without external doublers exhibited a considerable strength reduction following low velocity impact. Based on the observations, the major damage mechanics in the scarf joint region following impact have been identified. These results demonstrated that it is important to incorporate damage tolerance in the design of scarf repairs.

Maintenance is constantly challenged with increasing productivity by maximizing up-time and reliability while at the same time reducing expenditure and investment. In the last few years it has become evident through the development of maintenance concepts that maintenance is more than just a non-productive support function, it is a profit- generating function. In the past decades, hundreds of models that address maintenance strategy have been presented. The vast majority of those models rely purely on mathematical modeling to describe the maintenance function. Due to the complex nature of the maintenance function, and its complex interaction with other functions, it is almost impossible to accurately model maintenance using mathematical modeling without sacrificing accuracy and validity with unfeasible simplifications and assumptions. Analysis presented as part of this thesis shows that stochastic simulation offers a viable alternative and a powerful technique for tackling maintenance problems. Stochastic simulation is a method of modeling a system or process (on a computer) based on random events generated by the software so that system performance can be evaluated without experimenting or interfering with the actual system. The methodology developed as part of this thesis addresses most of the shortcomings found in literature, specifically by allowing the modeling of most of the complexities of an advanced maintenance system, such as one that is employed in the airline industry. This technique also allows sensitivity analysis to be carried out resulting in an understanding of how critical variables may affect the maintenance and asset management decision-making process. In many heavy industries (e.g. airline maintenance) where high utilization is essential for the success of the organization, subsystems are often of a rotable nature, i.e. they rotate among different systems throughout their life-cycle. This causes a system to be composed of a number of subsystems of different ages, and therefore different reliability characteristics. This makes it difficult for analysts to estimate its reliability behavior, and therefore may result in a less-than-optimal maintenance plan. Traditional reliability models are based on detailed statistical analysis of individual component failures. For complex machinery, especially involving many rotable parts, such analyses are difficult and time consuming. In this work, a model is proposed that combines the well-established Weibull method with discrete simulation to estimate the reliability of complex machinery with rotable subsystems or modules. Each module is characterized by an empirically derived failure distribution. The simulation model consists of a number of stages including operational up-time, maintenance down-time and a user-interface allowing decisions on maintenance and replacement strategies as well as inventory levels and logistics. This enables the optimization of a maintenance plan by comparing different maintenance and removal policies using the Cost per Unit Time (CPUT) measure as the decision variable. Five different removal strategies were tested. These include: On-failure replacements, block replacements, time-based replacements, condition-based replacements and a combination of time-based and condition-based strategies. Initial analyses performed on aircraft gas-turbine data yielded an optimal combination of modules out of a pool of multiple spares, resulting in an increased machine up-time of 16%. In addition, it was shown that condition-based replacement is a cost-effective strategy; however, it was noted that the combination of time and condition-based strategy can produce slightly better results. Furthermore, a sensitivity analysis was performed to optimize decision variables (module soft-time), and to provide an insight to the level of accuracy with which it has to be estimated. It is imperative as part of the overall reliability and life-cycle cost program to focus not only on reducing levels of unplanned (i.e. breakdown) maintenance through preventive and predictive maintenance tasks, but also optimizing inventory of spare parts management, sometimes called float hardware. It is well known that the unavailability of a spare part may result in loss of revenue, which is associated with an increase in system downtime. On the other hand increasing the number of spares will lead to an increase in capital investment and holding cost. The results obtained from the simulation model were used in a discounted NPV (Net Present Value) analysis to determine the optimal number of spare engines. The benefits of this methodology are that it is capable of providing reliability trends and forecasts in a short time frame and based on available data. In addition, it takes into account the rotable nature of many components by tracking the life and service history of individual parts and allowing the user to simulate different combinations of rotables, operating scenarios, and replacement strategies. It is also capable of optimizing stock and spares levels as well as other related key parameters like the average waiting time, unavailability cost, and the number of maintenance events that result in extensive durations due to the unavailability of spare parts. Importantly, as more data becomes available or as greater accuracy is demanded, the model or database can be updated or expanded, thereby approaching the results obtainable by pure statistical reliability analysis.

Bibliography: leaves 213-234 / xviii, 234, 13 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Faculty of Engineering (Civil), 1994?

The decision sequences used for troubleshooting of complex electro-mechanical systems are often ad hoc and less than optimal. This research investigated Decision Analysis and Bayesian Networks for generating an optimal decision sequence for troubleshooting. The model that was used in this research was the bleed air control system of the Boeing 737 aircraft. The focus of this research, therefore is two-fold. First the construction of behavioral models and multistage decision-making models in Bayesian networks was proposed. Secondly, an efficient, easy-to-implement algorithm was developed to obtain a near optimal decision sequence. This algorithm can be readily adopted by the maintenance personnel for effective troubleshooting. / Graduation date: 2004