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A novel flexure-based biaxial compression/shear apparatus has been designed, built, and utilized to conduct tribological studies of interfaces relevant to MEMS. Aspects of our new apparatus are detailed and its capabilities are demonstrated by an investigation of two interfaces for MEMS applications. Tribological tests may be performed with normal and tangential forces in the µN to N range and relative sliding displacements in the nm to mm range. In this testing range, the new experimental apparatus represents an improvement over existing techniques for tribological studies at the small scale. / Singapore-MIT Alliance (SMA)

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Friction, wear, and lubrication have direct influence on performance, reliability, and service life of mechanical systems with moving components. The useful life of these systems and their efficiency can be improved by improving the surface properties/ performance at sliding interfaces. Further, the usage of materials for sliding systems is limited in extreme environments, such as high temperature, and space, etc., due to their limited surface properties. This thesis focuses on the development of a new class of composites with superior surface properties, i.e., low friction and high wear resistance for extreme environmental conditions. Alumina, a well understood material for its tribological performance, is a merit choice for applications where high wear resistance is required, such as pump bearings, seal rings, valve seats, piston components, gears, cutting tool inserts and artificial joints. We propose to develop a novel alumina based ceramic composite to enhance its surface and tribological properties using a powder compaction technique. The newly developed composites will be characterized by X-ray Diffraction (XRD), Fourier Transform Infrared spectroscope (FTIR), Optical microscope, Environmental Scanning Electron Microscope (E-SEM), Goniometer and Surface profilometer. In-situ formation of high temperature stable phases, effect of sintering temperature, and percentage of reinforcement on phase formation will be studied. Investigation of effect of sintering temperature and percentage of reinforcement on density, porosity, and grain size will be conducted. The composites will be characterized for their tribological properties (friction and wear). The mechanisms for modified friction and wear will be proposed. The process parameters and compositions will be optimized. XRD results confirmed the formation of Al18B4O33, and AlB2 and FTIR confirmed the presence of B2O3. Increase in sintering temperature and wt % of boron affected the porosity, grain size, and hardness of the composites. The coefficient of friction was lower for the composites compared to pure alumina ceramic. The coefficient of friction decreased with increase in sintering temperature. The wear mechanism was found to be micro-fracture using ESEM and SEM studies.

Industrial demands for more efficient machine tool systems have been significantly increased. In order to obtain high performance machine tool systems, researchers are focused on enhancing functioning of various components of machine tool systems. Feed drives are important component of the most of machine tool systems such as computer numerical control (CNC) machines for achieving desirable performance. An essential research stream of current interest aiming enhancement of feed drive performance is construction of control methods that help to decrease tool positioning errors in the system. An effective approach for mitigation or reduction of positioning errors is modeling, identifying, and compensating friction in appropriate manner. In addition, accurate modeling of feed drive systems is essential in elimination of these positioning errors. In this thesis, the precision control of feed drives is studied using several different control methods. Firstly, the feed drive type that has common use in machine tools is chosen to be main focus for this research, namely ball screw drive. Different dynamic models of ball screw drive are shown in detail. In addition, some of the nonlinearities that affect ball screw dynamics such as friction affects are discussed. Friction modeling needs to be performed realistically and accurately in order to design an effective compensator to cancel friction effects. In general, the friction models are divided into two categories; classic (static) and dynamic friction models. In this thesis, we present details of these models and derive linear parametrization of the key ones. Based on the derived linear parametric models, we design a least-squares on-line friction estimator and adaptive friction compensation scheme. The performance of these designs are verified via simulation and real-time experimental tests. Noting that the parameters of the base rigid body model, i.e., inertia and viscosity constants, need to be known precisely for effective high precision control tasks, including the aforementioned adaptive schemes. The second part of the thesis focuses on off-line identification of these key base model parameters. In this part, we present a real-life case study on identification of plant and built-in controller parameters and a simulator design based on this identification for a grinding CNC machine used in a gear manufacturing company.

Polyvinylidene Fluoride (PVDF) is a common piezoelectric polymer. It is widely utilized because of its advantageous mechanical, chemical, and electromechanical properties. An interesting application for its properties lies in using it as an actuator, specifically for a microgripper device. The microgripper has many applications such as surgeries, microassembly, and micromanipulation. The friction force is an important criterion that greatly affects the gripping. This research studies the frictional behavior of the PVDF and effects of applied electrical potential. Approaches include tribological investigation of the polymer associated with surface properties. The surface characterization was conducted using a profilometer and an Atomic Force Microscope (AFM). In addition, the application of a PVDF material as a microgripper is addressed along with the design of the gripper. It was found that the friction could be turned-on and off because of external applied electrical potential. Such behavior was associated with the microstructure, where dipoles were aligned in an electrical field. Such active-friction has not been reported in the past. This work opens new areas of research in fundamental friction that benefits the design and development of small devices such as a microgripper.

A novel surface modifying technique, friction stir processing¡]FSP¡^, has been developed for fabrication of surface composite. Al-Al2O3 surface composites with different volume fractions of particles were successfully fabricated. The Al2O3 particles were uniformly distributed in the aluminum matrix. The surface composites have excellent bonding with the aluminum alloy substrate. The microhardness of the surface composite reinforced with 40 vol% Al2O3 of ~50nm, average particle size was ~150 HV, almost doubt that of the 5083 Al alloy substrate¡]86HV¡^. The distribution curves showed that the SD was increased steeply when the volume fractions of Al2O3 particles of SZ attained to about above 30 vol%. In addition, it is difficult to reduce the grain size of SZ stirring with powder by increasing traveling speed or adding more volume fractions of Al2O3 particles because the processing temperature is higher than 0.5 Tm.

We applied the Friction-Stir Process (FSP) to make the ZrO2 /5083 Al alloy composite material, and analyzed its physical properties in different aspects. Different weight percents of nanometer composite materials, ZrO2/Al, with well distributed strengthening grains were manufactured with the FSP which was used for five runs on ZrO2 along with the matrix material, aluminum, at 505¢XC, and created reactants of Al3Zr, tetragonal D023 structure, and Al2O3, identified with X-ray diffraction analysis. The grain size of 5083 Al-alloy could be finer, around 2.6£gm, by the FSP. This study suggests that increasing the addition of ZrO2 into the Al matrix could make the grain size of aluminum finer. We found that the Al grain size would be able to down to 0.66£gm, as 15.3 wt% of ZrO2 powder was reached. The mechanical properties of the Al-matrix material could be also modified by adding ZrO2 that reduces the ductility but boosts the strength of the matrix material. When we put 15.3 wt% of ZrO2 powder, 5083 Al-alloy attained the hardness of 158Hv, almost twice of hardness of the original alloy material, and its yield strength also increased from 125MPa to 400MPa as well.

Al-Al2O3 precipitated alloys and Al-Zn solid solution alloys fabricated by friction stir process are investigated in this study. The mechanical specimen cutting from stir zone were tested by Instron machine. Micro-structure was observed by Scanning Electron Microscopy and Transmission Electron Microscopy. Phase composition was measured by X-ray diffraction. Different Grain sizes sample were obtained at condition with constant traverse speed of 1.0mm/s, different RPM(500rpm, 550rpm, 700rpm, 1500rpm and 1500rpm with subsequent annealing treatment) and pin shape. Mechanical properties and ductility improvement on grain size effect are discussed in this research. In Al/Al2O3 composite materials, mechanical strength is enhanced by Al2O3 precipitation distributed homogeneously in Al matrix and ductility is improved simultaneously by increment of work hardening rate due to interaction between obstacles and dislocations. In Al-Zn solid solution alloys, ductility enhancement takes place not only in refining grain sizes but also occurs obviously with different weight fraction of Zn addition.