Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on June 29, 2010). Bibliography: leaves 59-60.

Thesis (M.S.)--Florida State University, 2006. / Advisors: Peter N. Kalu, Namas Chandra, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed June 13, 2006). Document formatted into pages; contains ix, 60 pages. Includes bibliographical references.

A Friction Stir Welding machine is proposed and built to allow future research into the process and to provide a framework from which the application of intelligent manufacturing to industrial processes can be investigated. Initially a literature survey was conducted upon which the design of the machine could be based. The conversion of a conventional milling machine into a Friction Stir Welding machine by applying modern monitoring and control systems is then presented. Complete digital control was used to drive actuators and monitor sensors. A wireless chuck mounted monitoring system was implemented, enabling forces, torques, temperature and speed of the tool to be obtained directly from the process. Software based on a hierarchical Open Systems Architectural design, incorporating modularity, interoperability, portability and extensibility is implemented. This experimental setup is used to analyze the Friction Stir Welding process by performing data analysis using statistical methods. Three independent variables (weld speed, spindle speed and plunge depth) were varied and the independent variables (forces, torques, power, temperature, speed, etc) recorded using the implemented software. The statistical analysis includes the analysis of variants, regression analysis and the creation of surface plots. Using these results, certain linguistic rules for process control are proposed. An intelligent controller is designed and discussed, using the derived rules to improve and optimize certain aspects of the process encountered during the experimental phase of the research.

Automotive brake lining materials are complex composites consisting of numerous ingredients allowing for their optimal performance. Different types of carbons have been used in all types of brake pad formulations for more than century. The role of carbon, however, does not seem to be completely understood, since carbon materials possess a wide variety of characteristics and properties and they interact with other ingredients present in the friction process. Carbons/graphites are commonly considered to be solid lubricants but this role is only available at relatively low temperatures and at a sufficient humidity. Since regulations are increasingly limiting Cu content in brake pads and Cu exhibits extremely high thermal conductivity, graphites, being excellent heat conducting materials themselves, are often considered for use when potential Cu replacement options in the low-metallic, non-asbestos organic, hybrid, and ceramic pads are explored. This paper surveys the role of two types of graphites with high thermal conductivity but different mechanical properties and morphology: the so-called i) purified flake graphite (PFG) and the ii) resilient graphitic carbon (RGC). A successful “high-end” commercial low-metallic brake pad was re-formulated (SIU Carbondale) by removing of over 20 wt. % of Cu and replacing it with a cocktail of ingredients including 15 wt. % of these two graphite types. OEM Crown Victoria 1999 mold was used to prepare the pads and they were subjected to the SAE J2430 test and BEEP evaluation using the full-scale automotive brake dynamometer (Link Engineering) and original hardware (rotor and caliper). After friction tests, the surfaces of pads were explored using scanning electron microscopy equipped with the energy dispersive X-ray microanalysis (FEG450 and Inca System) and X-ray diffraction (Rigaku Max-Flash-B). Although the brake pad formulations were otherwise identical and were prepared at the same conditions, the performance of two different low-metallic pads was different. The effectiveness of PFG sample reached value 0.5 and wear of pad was 5.3 g, while the effectiveness was 0.4 and wear detected was 5.9 g in the case of RGC containing sample. Both formulations exhibited extremely good stability of friction during fade section and only low sensitivity to speed variations between 50 and 160 km/h. Surfaces of both pads were covered by a discontinuous (patchy) friction layer which was formed as a consequence of a gentle abrasive mechanisms involved. The different friction levels and different wear of samples were related to the specific character/differences in detected different friction layers. Importantly, the capacity of the PFG to reduce surface oxides is considerably higher when compared to the RGC. It was concluded that the proper understanding of role of individual graphitic forms in particular formulations can be very beneficial when optimizing the performance of brake pads.

The development of a CNC-based technology FSW machine to accurately produce friction stir weld samples that can be analyzed for research purposes is implemented and discussed. A process diagnosis and control scheme to improve the process monitoring and weld evaluation capabilities of an FSW machine are proposed and implemented. Basic CNC-based hardware implementation such as optical encoders and inverters for process control are explained and verified. The control scheme and framework of interfaces to the digital I/O cards for PC user interface are explained. An advanced monitoring system which senses process performance parameters such as tool temperature, 3-axis tool forces, torque and spindle speed are explained. Mechanical designs and manufacturing techniques such as tool, clamp and backing plate designs are explained and verified. The process parameters for quality optimization are investigated and optimized by making use of Correlation and Regression Analysis. The statistical data and analytical relationships between welding parameters (independent) and each of the performance parameters (dependent) are obtained and used to simulate the machining process. The weld research samples are tested for strength and integrity making use of various scientific testing techniques. The reliability of the samples are also evaluated and compared to that of other institutions. Process variables and the optimum operating range of the Friction Stir Welding machine is determined and a framework for further research into weld quality optimization is set.

This study develops and presents a friction stir weld (FSW) quality assurance tool based on control of weld zone temperature. Apart from correct tool geometry, tool tilt angle, traverse speed and forge force during welding, one important requirement is that the weld material be sufficiently plasticised (softened). The level of plasticisation is related to weld zone temperature which is primarily dependent on spindle speed, traverse speed and forge force. When all other conditions are correct, sufficiently plasticised material flows around and consolidates behind the tool without the production of voids in the weld. Typically, weld temperature varies along the weld length which may result in variations in weld quality. Weld zone temperature control makes constant weld zone temperature possible. In this study, thermocouple sensors were embedded in the FSW tool and a weld zone temperature control algorithm was developed. Spindle speed was the actuating mechanism for controlling weld temperature. The system was modelled and controllers were designed using Matlab tools. The system was simulated and the performance was compared to the system performance during welding. The control system ensures that the weld zone temperature can be maintained irrespective of the presence of thermal disturbances. Tensile testing was conducted which confirmed a range of temperature in which the welds resulted in consistent strength.

The remnant life monitoring of creep loaded high temperature and pressure components in power stations is critical to ensuring their safe and cost effective operation as failures can have severe consequences. Effective creep life condition monitoring allows for optimising component life predictions and subsequent plant maintenance decisions. In South Africa many power generation stations have been in operation well beyond their 30 year design service life, as such knowledge of the remnant creep life of high temperature and pressure components, such as steam pipelines, becomes of utmost importance. Techniques for the remnant creep life assessments of critical high temperature and pressure components must therefore be as effective as possible. The common and well accepted in-situ inspection technique for assessing creep damage in steam pipes is by the metallographic replication technique. The technique is however limited to the outer surface of the pipe, without information on damage within the wall. This research will illustrate a means of obtaining a sample for creep life analysis with depth through the wall of a pipe, as wells as an alternative technique for the repair of the sample retrieval site. A sample retrieval technique was developed that would retrieve a small diameter cylindrical sample from a cored blind hole for creep analysis by visual creep void assessment or by the small punch creep test. The small punch creep test requires only a small diameter thin disc of material for testing for which its results are comparable with conventional uniaxial creep testing which requires a much larger sample of material. The smaller sample requirement of the small punch creep test therefore allows for a vastly reduced invasive sample retrieval operation and consequently smaller repair size area. Also the fact that the sample is retrieved from a blind hole is advantageous since the pipe wall is not penetrated which would require full plant shutdown. A friction welding technique was identified as an alternative to traditional arc fusion welding for the repair of the sample retrieval site, this technique being the Friction Hydro Pillar Processing technique. Friction Hydro Pillar Processing is a solid-state welding technique and as such has a number of inherent benefits over arc fusion welding as the weld is performed below the melting temperature of the material. From a process point of view Friction Hydro Pillar Processing is ideally suited for automation, has virtually no fumes generated, minimal distortion is experienced and no spatter has to be removed afterwards. The technique has yet to see industrial application and as such development of suitable process parameters was undertaken. Finally, to apply the sample retrieval and repair operations in-situ to a steam pipe in a power plant suitable equipment was developed. Existing friction welding equipment is generally bulky workshop based equipment and is unsuitable for on-site work due to its size and weight. Therefore development of dedicated equipment was required to enable Friction Hydro Pillar Processing to be applied to steam pipes within a power plant environment.

Sliding shoulder friction stir welding (SSFSW) is an alternative joining technique to the conventional friction stir welding process. The welding mechanism comprises of a rotating probe and a non-rotating shoulder. The shoulder therefore does not contribute to any heat generation or plastic deformation. When welding thicker section material, the contribution of heat generation from the shoulder becomes less significant and most of the heat and plastic deformation must be generated by the tool probe. For this reason it was decided to develop the process for thick section AA6082-T6. Due to the stationary (non-rotating) shoulder the weld track is smooth and there is no reduction in cross-sectional area. This research is based on the development of a sliding shoulder friction stir welding tool with the ability to create joints of up to 25mm thick on aluminium alloy 6082-T6 plate as well as the associated process development. The sliding shoulder friction stir welding tool was designed, manufactured and tested by initially performing partial penetration welds with various size tool probes and then finally by performing a sliding shoulder friction stir butt weld on 25mm thick plate. As welds were performed and more knowledge gained about the process, design modifications were made. These included varying the clearance between the tool probe and stationary shoulder; the profile of the shoulder which contributes to material flow during the process; and supporting the tool probe to prevent deflection when welding thicker sections at high forge forces. From the sliding shoulder friction stir welds performed, an understanding of material flow during the process was gained when analysing the macro-sections and exit holes of the welds. Typical process forces and torques associated with the process were measured to assist with future head unit and tool designs with regard to sliding shoulder friction stir welding.

The behaviour of the quasi-harmonic type frictional oscillation for steel sliding surfaces was investigated both experimentally and theoretically. The kinetic coefficient of friction, which was expressed as a function of sliding velocity, was represented by a polynomial. The slowly varying amplitude and phase method of Kryloff and Bogoliuboff was used to solve the non-linear differential equation of motion. The calculations were carried out on the computer. The theoretical analysis suggests that the amplitude of the quasi-harmonic oscillation increases almost linearly as the driven surface velocity increases until a critical velocity is reached where the friction-velocity curve begins to flatten out. Beyond this point the oscillation diminishes to zero. Experiments were carried out mainly on unlubricated surfaces at driven surface velocities ranging from 0.5 in/sec to 25 in/sec. The results revealed that for short running distances frictional oscillation of the stick-slip type could occur. Frictional oscillation of the quasi-harmonic type existed in the system when negative slope appeared in the low velocity region of the friction-velocity curve after a run-in period. The growth and decay of the vibration amplitude with variation in driven surface velocity has been observed and this substantiates the findings of the theoretical analysis. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A study has been made of the behaviour of a hydraulic-ally driven system subject to friction induced oscillations. An experimental apparatus consisting of a heavy mass driven by a hydraulic ram was constructed. A mathematical model for the system was derived, and its validity was shown by comparison with experimental results. Studies were subsequently carried out with the mathematical model to determine the effects of varying system parameters and to verify the validity of simplifications in the governing equations. It was found that in general the effect of leakage at the piston should be negligible, and that the variation in behaviour with piston location can be predicted by a simple system stiffness correction. The effect of changing most parameters is to change the rate of tangential load application for a given average velocity of traverse, and the resulting behaviour can be predicted from the static friction relationship that has been proposed. A detailed study was made of the nature of the friction forces in effect during a stick-slip process. A relation, for the variation of the static coefficient of friction which appears more accurate than previous time of contact dependent formulations has been found. In the case of the kinetic coefficient of friction, a gradual decrease from the static value was found at the inception of slip. This has been observed before but generally it has not been recognized by investigators of stick-slip. Simple models have been given for both the static and kinetic friction behaviour. These may be useful as guide in further research into the fundamental nature of friction. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate