This thesis presents an application of a numerical formulation incorporating the effects of joints, cracks, and fractures to a soil subsidence predictions problem, and the extension of that formulation to combined discrete slip planes and jointed media continua formulations. The results obtained are compared to each other and to a physical centrifuge simulation performed previously on the same problem.

This paper reports the results of a study into V-ribbed belt noise generated as a result of tangential belt slip. The results of experimental studies to identify the belt operating conditions associated with belt noise are presented, together with the results of analytical studies to identify the mechanism of noise generation. It is concluded that tangential slip V-ribbed belt noise generation is controlled only by the amount of slip, and that the mechanism of noise generation is harmonic excitation of the fundamental vibration mode of the belt, with stick¿slip frictional behaviour providing the impetus for the vibration

No / There are several types of disc brake instabilities associated with the brake systems; however, they are usually classified into two main categories depending on the frequency range: brake groan 0–300 Hz and brake squeal 1– 16 kHz. The groan is associated with the stick-slip motion while the squeal is associated with the modal coupling. This paper presents a detailed analysis of low frequency noise (0–300 Hz) in a commercial vehicle trailer disc brake as a result of stick-slip vibration. A range of experimental techniques are used to understand the characteristic behaviour of the caliper and the brake pads during braking events on a laboratory test rig. The analysed brake system comprised a full disc brake assembly and the trailer suspension system with a beam axle. Laser-based optical displacement sensors were used to investigate the deformation of the caliper body and the brake pads during a braking application. The contact pressure distribution at the disc/pad interfaces were also measured to gain more insight into the contact profile of the pad surfaces. Results revealed that the stick-slip phenomenon, in this study, was a result of the combination of the deformation of the caliper and the friction material formulation of the brake pads. In addition, it was observed through the testing of two different sets of pads that a low compression modulus would help to reduce the stick-slip phenomenon.

Ceramic colloidal processing routes such as slip casting, gelcasting and direct ink writing provide valuable insight into the role of interaction forces between particles, solvents, and polymeric additives in the rheology, particle packing, and strength of a ceramic green body. For difficult-to-densify ceramics such as the UHTCs, which find their place in extreme environment applications, precise control of each step of the manufacturing process is key. In this work, a fundamental study on the interaction between particles in non-aqueous slip casting is performed comparing the rheological behavior and consolidation with current models for interaction potential within a suspension. The advantages and drawbacks of such a model are discussed in relation to formulating a colloidal process for advanced ceramics such as ZrB2, and a case for a cyclohexane slip casting system resulting in low viscosity, shear-thinning behavior and green density of 64%, is made. The focus on non-aqueous colloidal processing is extended to gelcasting, involving three different sets of chemically curable polymer systems: HEMA+MBAM, TMPTA, and PEGDA. Merits of the gelcasting process including homogeneity, green strength, and processing time reduction are discussed, with the HEMA+MBAM system resulting in nearly an order of magnitude increase in green density from slip casting. Gelcast samples were also sintered to a density of 88% and capable of being processed in a variety of complex shapes with fine feature size on the mm scale. The properties examined in slip casting and gelcasting, as well as others pertaining to the setup of an extrusion-based additive manufacturing system, are carefully considered to design an ink that has been used to print ZrB2. The role of each additive as well as the solvent in creating an ink that is not only within the correct viscosity range for extrusion and shape retention, but also produces a strong and densely packed green body, is discussed. Finally, adjustment of printing parameters, and the method of using a low-cost rheology match to tune the settings of a pneumatic screw-extrusion printing setup, are explained. Each of these processes points to new and practical methods of complex shaping ZrB2 that can provide insight into processing of these challenging materials and create new avenues for their use in extreme environment applications, such as thermal protection systems in atmospheric re-entry vehicles. / Doctor of Philosophy / This work examines the use of ultra-high temperature ceramics (UHTCs), which are materials with some of the highest melting points in existence. These are an intriguing option for extreme environment applications. One such application is the protection of rockets, scramjets, and other hypersonic (speed > Mach 5) vehicles from the high temperatures experienced during flight and re-entry. In this work, the UHTC Zirconium diboride (ZrB2) is used as a reference material. For many of the same reasons UHTCs such as ZrB2 have extreme melting points, they can be difficult to manufacture, particularly in complex shapes. Like many ceramics, UHTCs are not melted and cast as metals are, but rather are processed in powder form to a compact known as a green body. The green body is placed in a high-temperature furnace at 2/3 - 3/4 of the melting point, where the powder undergoes sintering, or consolidation into a dense part. The manufacture of a green body that is versatile in its capacity to be molded into any shape, and allows for close packing of the particles in the powder compact to avoid failure-inducing flaws in the final component under intense loads, remains a challenge for UHTCs. Most UHTCs are hot pressed, where the powder alone is consolidated under intense heat and pressure, but this process offers very little complex shaping capacity or control of the uniformity of the part. In this work, three methods for green body manufacture using colloid-based routes, which all have unique capabilities and challenges, are described. The first process is slip casting, which is a centuries-old process that has been used for the manufacture of pottery, whitewares, and art ceramics. When used effectively, slip casting ensures that the forces between ceramic particles in a suspension, or "slip", are well-controlled such that the ceramic particles will not form clumps, or agglomerates, which create non-uniformities that weaken the final component. With information about the powder, solvent, and additives in a slip, the extent to which this will be effective can be predicted with mathematical models. This work compares the results of these models with slip casting suspensions in different solvent environments to gain knowledge about slip casting as an option for complex shaping of ZrB2. The second colloidal process discussed is gelcasting, in which the suspension of ceramic powder can undergo chemical gelation, or a reaction that transitions the suspension from a liquid to a solid, not unlike that of a natural gel such as gelatin, agarose, or albumin (egg white). The gel, which is loaded with ceramic powder, allows for more versatile shaping than slip casting, and shorter processing time; a gelcast ceramic is generally solidified in less than an hour, while a slip cast typically dries overnight. The presence the gel also provides strength to the green body, which is advantageous in handling as well as any machining to adjust the shape that may be necessary prior to sintering. The final process detailed in this work is direct ink writing, a type of additive manufacturing (or 3D printing). Knowledge gained from slip casting and gelcasting was used to carefully design a ceramic colloid that could be deposited in a layer-by-layer fashion to create a complex shape with high uniformity and control, as well as minimal surface cracking. The printed green bodies were compared in strength and sintering behavior to the gelcasts from previous chapters, and the expansion of shaping capacity for each route as it relates to aerospace applications, is described.

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