Browsing by Author "Dr. Ronald Scattergood, Committee Member"

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Fabrication, Distortion, and Metrology of Shrink Fit Electrical Connections
(2003-09-01) Morrissey, Patrick; Dr. Jeffrey Eischen, Committee Chair; Dr. Ronald Scattergood, Committee Member; Dr. Thomas Dow, Committee Member
The fabrication of pulsed power experiments on systems such as ATLAS at Los Alamos National Labs requires assembly of shrink fit or press fit joints. These joints are used to carry large electrical currents on the order of several megamperes for Z-pinch cylindrical implosions of thin-walled cylinders. The joints, which represent the shrink fit or press fit interfaces between cylindrical components (1100 aluminum liners and copper glide planes), are also called on to support mechanical stresses. As a result, the integrity of these joints is critical to the success of the mission. The analytical challenge for investigating these components lies in the presence of a partial shrink fit, that is, a shrink fit in which the length of contact between mating cylinders does not equal the entire length of at least one of the components. Such a design leads to stress distributions that are impossible to calculate using standard shrink fit theory that is analytically tractable. Arguably more important, however, is the varying radial deflection profile along the length of the liner that results from the partial shrink fit. For the success of these experiments, uniform implosions are deemed to be highly beneficial; thus, determining how to predict and compensate for liner deflection profiles is crucial. The primary issues at hand include the following: mechanics of the interference fits, physical description of the contact surfaces between the liner and glide planes, joint void (gap) description, and material property effects. Furthermore, for the original shrink fit design of ATLAS, liner geometry alterations were investigated for potential performance improvement, particularly for the elimination of joint interface gaps and lower stress magnitudes. For the modified ATLAS design that included components designed to compress and distort other elements, effects of localized geometry modifications were investigated for the same purposes. Composite liners, i.e., liners with two constituent materials, were also examined, along with potential problems such as cylindrical out-of-roundness on the precision scale. To investigate these issues, finite element analysis models have been created and compared to experimental data. A measurement technique has been developed to compare radial deflection profiles of diamond turned thin-walled shrink fit test specimens to finite element models of corresponding geometry. Verification of the computer generated finite element models with experimental results could provide tremendous aid in accurately predicting the shape, deflection, and stress distribution of such cylindrical elements.
Force modeling and deflection compensation of miniature ball end mills
(2003-07-25) Clayton, Stuart Harold; Dr. Ronald Scattergood, Committee Member; Dr. Thomas Dow, Committee Chair; Dr. Gregory Buckner, Committee Member
The primary objective of this research is to increase the quality and productivity of precision milling operations. More specifically, increased accuracies and reduced costs are desired for die fabrication of injection molds when small flexible tools are required. The problem with miniature tools is their radial compliance. Typical machining forces in die materials such as hardened steels can cause significant tool deflection. When features on the order of 100 μm are desired, tool deflections can cause form errors exceeding 20% of the desired geometry. There were two main goals of this research: 1) to develop an accurate cutting force model and 2) to design and implement a spindle actuation system utilizing real-time forcefeedback machining. The first goal was to gain knowledge and understanding of the machining process by predicting cutting forces for miniature tools. The second goal involved the design of a closed loop actuated spindle system that can manipulate a tool path in one dimension. A precision actuated spindle allows real-time implementation of deflection compensation algorithms to reduce geometric form errors from tool deflection. The results from this research indicate that machining forces for miniature ball end mills are both predictable and repeatable. Experimental tests were conducted using a variety of two-flute ball end mills, workpiece materials, chip areas, upfeeds, and tool tilts. It was shown that the cutting force model provides a complete dynamic understanding of the machining forces and paves the way for the actuation system that was built into the tool spindle. Two different control algorithms were tested and proven successful as feature errors were reduced with each technique. The first algorithm involved an open loop technique where the force model was used to create an altered tool path that compensated for tool deflection. This was accomplished by predicting the machining forces, dividing by the appropriate tool stiffness to obtain deflection, and superimposing the deflection onto the original tool path. The second algorithm entailed closed loop control with forcefeedback machining using a newly designed PZT actuated spindle. The machining forces, which were used to predict tool deflection, were measured with a force transducer. The tool was moved in response to the deflection using a PID controller that regulated the voltage to a pair of PZT actuators. Errors produced from tool deflection were reduced with both control techniques. Experimental results showed that both control techniques, open and closed loop, reduced errors. The open loop compensation methods reduced error by approximately 65%, while the closed loop compensation methods reduced errors by 80%.
Integrated AlN/diamond heat spreaders for silicon device processing
(2002-08-19) Saripalli, Yoganand N; Dr. Carl Osburn, Committee Member; Dr. Ronald Scattergood, Committee Member; Dr. Jag Kasichainula, Committee Chair
Diamond with its very high thermal conductivity is an excellent choice for spreading heat produced during the operation of all electronic devices and in particular, high power and high frequency devices. Hitherto, diamond heat spreaders have been bonded to silicon devices using metallization and soldering layers. However, the interfacial thermal resistances at the interfaces decrease the effective thermal conductivity of the bonded heat spreader. Although direct growth of diamond on Si is expected to reduce the interfacial resistance, it has not been attempted. Contamination of the device wafers from carbon, oxygen and other impurities by diffusion during the growth of diamond could be a limiting factor. Moreover, diamond oxidizes above 600°C in the presence of oxygen and may not be stable during oxidation and other high temperature steps in silicon device processing. Growth of diamond by CVD is not defect free and contains voids that decrease the thermal conductivity. Hence, a buffer layer of AlN that fills these voids and thereby reduce the thermal resistance is thought to be beneficial. The growth and characterization of AlN and diamond films on the backside of Si (100) wafer with silicon nitride on the device side is investigated. AlN films were deposited by pulsed DC reactive magnetron sputtering at 600°C. Diamond film was deposited by microwave plasma chemical vapor deposition at 900°C. The films were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for crystalline quality, by scanning electron microscopy (SEM) for morphology, and by infrared thermography for heat spreading characteristics. The heat spreading characteristics of the wafer with the composite AlN/diamond films were found to be superior to that of wafers with no heat spreaders or to the wafers with either single layer diamond or single layer AlN heat spreaders. Deep level transient spectroscopy (DLTS) and secondary ion mass spectroscopy (SIMS) were performed on the samples with and without the heat spreader for determining the concentration of the impurities. The results showed that the purity of the wafers is not altered. The device characteristics were studied by fabrication of Schottky diodes on the wafers with the composite AlN/diamond heat spreader and compared with that of devices on wafers with no heat spreader. The device characteristics were found to be similar and unaffected by integration with AlN/diamond heat spreader. Thus, the integration of AlN/diamond heat spreaders with silicon device processing has been shown to be successful.
Live Axis Turning
(2005-12-06) Buescher, Nathan P; Dr. Jeffrey Eischen, Committee Member; Dr. Ronald Scattergood, Committee Member; Dr. Thomas Dow, Committee Chair
The goal of this research is to develop a new method to create Non-Rotationally Symmetric (NRS) optical surfaces that overcomes the limitations of the current techniques and is fast, accurate and inexpensive. The term Live-Axis turning (LAT) has been coined to describe a lightweight, linear-motor driven, air bearing slide that can be used to fabricate NRS surfaces. The system described was developed at the Precision Engineering Center (PEC) in an effort to create a long-range fast tool servo to fabricate future NASA optics. The slide designed for the system is a triangular cross-section, lightweight (0.6 kg) honeycomb aluminum slide driven by a linear motor (64 N maximum force) resulting in an acceleration capability of 10 g. Additionally, a damper was added to the system to investigate the effects of physical damping on surface quality. The LAT axis was mounted on a Nanoform 600 diamond turning machine and both flat surfaces and tilted flat surfaces were machined to assess the performance of the system, which has a rise time of less than 2 msec. The 12.5 mm diameter flat surfaces had surface finishes of 16 nm without damping and 14 nm with damping, with both having a figure error of less than ½ wave. 25 mm diameter tilted flat surfaces, using a maximum stroke of +/- 1 mm at 5 Hz, had a surface finish of 24 nm without damping and 20 nm with damping. The figure error for the damped and undamped parts was +/- 25 microns.
Processing and Characterization of Aluminum-Steel Composite Metal Foams
(2009-06-27) Vendra, Lakshmi Jyotshna; Dr. Larry Silverberg, Committee Member; Dr. Mohammed Zikry, Committee Member; Dr. Ronald Scattergood, Committee Member; Dr. Afsaneh Rabiei, Committee Chair
Composite Metal Foam (CMF), a new material belonging to the class of advanced cellular and porous materials, has been successfully processed using Gravity Casting technique for the first time at NC State University. This material comprises of steel hollow spheres and a solid Aluminum alloy matrix. The complete characterization of the material included mechanical testing such as monotonic compression, compression-compression fatigue, micro hardness, nano hardness and higher strain rate compression. The energy absorption behavior of the material under static compression has been studied extensively. Experimental results show that Al-steel CMF not only has a higher energy absorption capability than that of other commercially available metal foams produced from similar materials, but also possess a higher strength to density ratio. The microstructural analysis of the material was used to study and explain the formation of different phases at the Aluminum-Steel interface and their effect on the deformation behavior of the composite foam under compression. The effect of processing temperature on the microstructure of the composite metal foam and specifically on the sphere-matrix interface was studied by experimental means. The mechanical properties of the ternary phases formed in the microstructure of the composite foam were characterized using micro and nano-hardness tests. The phases were chemically characterized and formulated using Energy Dispersive Spectroscopy analysis and Al-Fe-Si alloy ternary phase diagrams. The fatigue behavior of the composite metal foams was studied under compression-compression fatigue loading and the results were compared with those of other closed cell metal foams. The elastic modulus of the foams was evaluated using experimental and analytical techniques and the results were found to be in good agreement. Composite metal foams were also processed using a higher solidification rate with water cooling. The effect of alterations in microstructure on the mechanical properties of the composite metal foams was studied and results presented. As the result of high strength, the increase in energy absorption of the composite metal foam samples ranges over thirty times compared to that of 100% Al foams and over six times compared to that of 100% steel foams.