Wong Ngai-ning. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 65-67). / Abstracts in English and Chinese. / Abstract --- p.ii / Content --- p.iv / List of Table --- p.v / List of Figures --- p.v / Acknowledgement --- p.vii / Dedication --- p.viii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Related work --- p.2 / Chapter 1.2 --- Background --- p.6 / Chapter 1.3 --- Contribution --- p.23 / Chapter 1.4 --- Thesis roadmap --- p.24 / Chapter 2 --- The Capacitance method --- p.25 / Chapter 2.1 --- Theoretical Comparison --- p.29 / Chapter 3 --- Collision detection --- p.32 / Chapter 3.1 --- Searching the hierarchy --- p.33 / Chapter 3.2 --- Neighborhood algorithm --- p.35 / Chapter 3.3 --- Regional sphere tree update --- p.38 / Chapter 4 --- Implementation --- p.41 / Chapter 4.1 --- System Architecture --- p.41 / Chapter 4.2 --- Multi-contact latency --- p.45 / Chapter 5 --- Result and Analysis --- p.46 / Chapter 5.1 --- Pre-computation --- p.46 / Chapter 5.2 --- Relation matrix Establishment --- p.47 / Chapter 5.3 --- Sphere tree construction --- p.49 / Chapter 5.4 --- Regional sphere tree update --- p.50 / Chapter 5.5 --- Graphic result --- p.52 / Chapter 6 --- Conclusion and Future work --- p.62 / Chapter 6.1 --- Conclusion --- p.62 / Chapter 6.2 --- Future work --- p.64 / Reference --- p.65 / Appendix A --- p.68 / Appendix B --- p.70

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by I-Wei Chen. / Ph.D.

by Ng, Hiu Tung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 121-123). / by Ng, Hiu Tung. / Acknowledgement --- p.i / Abstract --- p.ii / Table of Contents --- p.iv / List of Figures --- p.viii / List of Tables --- p.xi / Chapter Chapter One --- Introduction --- p.1 / Chapter 1.1 --- Non-destructive testing techniques --- p.2 / Chapter 1.1.1 --- Liquid penetration technique --- p.2 / Chapter 1.1.2 --- Electrical methods (Eddy current testing) --- p.3 / Chapter 1.1.3 --- Ultrasonic testing --- p.4 / Chapter 1.1.4 --- Radiography --- p.5 / Chapter 1.1.5 --- Magnetic methods --- p.6 / Chapter 1.2 --- The development of Barkhausen and magnetoacoustic emissions --- p.7 / Chapter 1.2.1 --- Barkhausen emission --- p.7 / Chapter 1.2.2 --- Magnetoacoustic emission --- p.8 / Chapter 1.3 --- The advantages of using Barkhausen and magnetoacoustic emission over the other nondestructive techniques --- p.10 / Chapter Chapter Two --- Fundamental concept in ferromagnetic materials --- p.12 / Chapter 2.1 --- Ferromagnetism --- p.12 / Chapter 2.1.1 --- Curie point --- p.13 / Chapter 2.1.2 --- Hysteresis loop --- p.14 / Chapter 2.2 --- Magnetic domains --- p.17 / Chapter 2.2.1 --- Magneto static energy --- p.17 / Chapter 2.2.2 --- Structure of domain wall --- p.19 / Chapter 2.2.3 --- Domain wall motion --- p.21 / Chapter 2.2.4 --- Domain nucleation --- p.22 / Chapter 2.3 --- Magnetostriction --- p.28 / Chapter 2.3.1 --- Spontaneous magnetostriction --- p.28 / Chapter 2.3.2 --- Saturation magnetostriction --- p.29 / Chapter 2.3.3 --- Field-induced magnetostriction --- p.29 / Chapter 2.3.4 --- Magnetostriction of polycrystalline --- p.30 / Chapter 2.4 --- Effect of stress on magnetic properties --- p.36 / Chapter 2.4.1 --- Stress --- p.36 / Chapter 2.4.2 --- Effect of stress on the magnetization --- p.37 / Chapter 2.4.3 --- Effect of stress on the magnetostriction --- p.38 / Chapter 2.5 --- Eddy current shielding --- p.41 / Chapter Chapter Three --- Barkhausen emission and magnetoacoustic emission --- p.42 / Chapter 3.1 --- Barkhausen emission --- p.42 / Chapter 3.1.1 --- The wall potential energy model of Barkhausen emission --- p.43 / Chapter 3.1.2 --- Typical BE profiles --- p.45 / Chapter 3.2 --- Magnetoacoustic emission --- p.48 / Chapter 3.2.1 --- Magnetoacoustic emission model --- p.48 / Chapter 3.2.2 --- Typical MAE profiles --- p.50 / Chapter Chapter Four --- Instrumentation --- p.52 / Chapter 4.1 --- Introduction --- p.52 / Chapter 4.2 --- Experimental setup for Barkhausen emission --- p.53 / Chapter 4.3 --- Experimental setup for magnetoacoustic emission --- p.56 / Chapter 4.4 --- Specimen treatment --- p.58 / Chapter 4.4.1 --- Furnace --- p.58 / Chapter 4.4.2 --- Instron loading machine --- p.60 / Chapter 4.4.3 --- Optical microscopy --- p.60 / Chapter 4.4.4 --- Vicker's hardness tester --- p.61 / Chapter Chapter Five --- Effect of field frequency and strength on Barkhausen emission in mild steel and nickel --- p.66 / Chapter 5.1 --- Introduction --- p.66 / Chapter 5.2 --- Experiments --- p.67 / Chapter 5.3 --- Results and discussions --- p.68 / Chapter 5.4 --- Conclusions --- p.76 / Chapter Chapter Six --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in steel bar --- p.77 / Chapter 6.1 --- Introduction --- p.77 / Chapter 6.2 --- Experiments --- p.81 / Chapter 6.3 --- Results and discussions --- p.84 / Chapter 6.3.1 --- BE profiles --- p.84 / Chapter 6.3.2 --- MAE profiles --- p.85 / Chapter 6.3.3 --- Optical microscopy and hardness measurements --- p.85 / Chapter 6.4 --- Conclusions --- p.92 / Chapter Chapter Seven --- Effect of residual stress on Barkhausen and magnetoacoustic emissions in a nickel bar --- p.93 / Chapter 7.1 --- Introduction --- p.93 / Chapter 7.2 --- Experiments --- p.96 / Chapter 7.3 --- Results and discussions --- p.97 / Chapter 7.3.1 --- Hardness and optical microscopy measurement --- p.97 / Chapter 7.3.2 --- BE profiles --- p.98 / Chapter 7.3.3 --- MAE profiles --- p.99 / Chapter 7.4 --- Comparison of nickel and mild steel --- p.106 / Chapter 7.5 --- Conclusions --- p.108 / Chapter Chapter Eight --- Effect of dynamic stress on Barkhausen emission in mild steel --- p.109 / Chapter 8.1 --- Introduction --- p.109 / Chapter 8.2 --- Experiments --- p.110 / Chapter 8.3 --- Results and discussions --- p.112 / Chapter 8.4 --- Conclusions --- p.118 / Chapter Chapter Nine --- Conclusions --- p.119 / References --- p.121

Abstract not available

The deformation mechanisms and contact response of TiN-based thin films deposited onto a soft substrate using a physical vapour deposition (PVD) technique is still an area of both technological importance and considerable discussion. These coatings are commonly applied to various kinds of steel cutting tools, creating surfaces with enhanced tribological properties. However, no extensive systematic study of the deformation mechanisms in these thin film systems has been performed to date. In the present study, the effect of the coating microstructure, indenter geometry, coating thickness and substrate hardness on the deformation mechanisms in both TiN and TiAlN coatings of varying thickness deposited onto ductile steel substrates has been investigated using a combination of nanoindentation and microstructural analysis, including focused ion beam (FIB) milling and transmission electron microscopy (TEM). Different modes of cracking, such as columnar and transverse cracking, as well as shear steps at the coating/substrate interface, were observed. The microstructure of the TiN coatings was found to be very important in controlling their modes of deformation. Thicker coatings were seen to contain more equiaxed grains, so less columnar shearing occurred and inclined cracks were found to be a more dominant fracture type in the thicker coating. Also, it was found that soft substrates absorbed most of the energy from indentation by plastic deformation. It was found that both the TiN and TiAlN/TiN dual-layer coatings exhibited broadly similar mechanisms of deformation. The epitaxial interface between the TiAlN and TiN in the dual-layer coating did not appear to affect the deformation behaviour. As a further investigation of the overall deformation behaviour for the coating/substrate systems studied, a DualBeam FIB was used to generate three dimensional images of the indented regions which provided additional information on the crack morphology. For the first time, a systematic study of the deformation behaviour of TiN and TiAlN coatings upon indentation has been carried out. FIB milling was demonstrated to be a highly appropriate technique for characterization of the deformation behaviour of these coatings, allowing detailed, high resolution microstructural investigations to be performed in both two and three dimensions.

In this paper, a numerical method is used to predict the response of an elastic body during a collision in which both normal and tangential impulses are important. Results are compared with those from simplified prediction procedures, which stem from the assumptions that the energy-returning capacity of the normal deformation mechanism is constant and the tangential compliance is neglected. The finite-element predictions indicate the importance of the tangential compliance for elastic collisions wherein friction forces are significant. The results of both methods of prediction point up the roles of friction and inertia coupling in determining the normal velocity ratio (the "coefficient of restitution"). / Graduation date: 1992

An elastohydrodynamic analysis of a rotary lip seal is performed numerically, incorporating both the fluid mechanics of the lubricating film and the elastic deformation of the lip, by solving the Reynolds equation with flow factors. Asperities on the lip surface dominate the behavior of the flow field in the lubricating film and the elastic deformation of the lip. Since previous analyses treated those asperities deterministically, they required very large computation times. The present approach is much less computationally intensive because the asperities are treated statistically. Since cavitation and asperity orientation play important roles, these are taken into account in the computation of the flow factors. An asperity distortion analysis is introduced to obtain a more realistic model of the complex variations in the asperity distribution on the surface of the seal. Results of the analysis show how the operating parameters of the seal and the characteristics of the asperities affect such seal characteristics as the thickness of the lubricating film, reverse pumping rate, power dissipation and load carrying capacity.

In recent impact and penetration mechanical tests, steel projectiles (AISI4340) were impacted into targets like concrete with striking velocities (1200 m/s to 1500 m/s). Results indicated a material removal from the nose of the projectile, phase changes of the projectile materials, a reduction in the length of the projectile, and a blunting of the nose shape. These observations cannot be explained by current theories and numerical integration code that are used to study impact and penetration mechanics. Thus, the objectives of the thesis research are to (a) formulate and characterize the mechanisms responsible for the material erosion of the impacting projectile and the mass loss from the nose region; and (b) to determine the physical properties of alloy steels that are important to penetration mechanics from ab initio methods. The results can be used to design new projectile materials that can provide the desired penetration characteristics. These objectives are accomplished by investigating two related problems. The first problem is to formulate simplified models that can explain the penetration mechanics. The new models include the varying cross-section nose, changes of yield stress behind the shock wave and high strain rate phase transitions. Nose erosion effects, and time-dependent penetration path can be determined by integrating ODEs. A cavity expansion theory model is used to obtain the target resistance that is responsible slowing and deforming the penetrating projectile. The second problem concerns the determination of the constitutive relations from ab initio methods. The equation of state (EOS) and magnetic moments for alloy steels are investigated by using a special quasirandom structure technique and ab initio methods. Specifically, EOS for an interstitial disordered alloy Fe1-x-yNixCy is developed. First, the EOS of iron and phase transition of iron are studied and validated. Second, Nickel is considered to investigate the substitutional disordered alloy Fe1-x-yNixCy. Third, Carbon is placed at an interstitial position in the substitutional disordered alloy. These investigations will form foundation for future work involving new projectile with steel nose and shank made of multifunctional structural energetic materials.

Nanowires are an exciting class of novel materials that have potential applications in areas including biological sensing, photonics, and electronics. The promise of these future applications relies on the production of nanowires of controlled size, shape, and crystal structure, in reasonable quantities, and further, ultimately requires that the nanowires be mechanically stable in the application environment. This research is aimed at understanding the mechanical behavior of metallic nanowires, through the use of atomistic simulations. At the nanometer scale, where the surface-area-to-volume ratio is substantial, the effects of free surfaces have a primary influence on the physical properties of a material. Surface energy arises from unsatisfied bond coordination at the surface of a solid and results in a surface stress as the surface atoms contract into the bulk of the material to increase their local electron density. The magnitude of surface energy and surface stress is dependent on the orientation of the surface and the compliance of the structure. In bulk materials, the effects of surfaces are negligible; however, at the nanometer scale, surface effects become quite significant. In metallic nanowires, these surface effects strongly influence mechanical properties, and the characteristics of plastic deformation. The mechanical testing of nanowires is precluded by the difficulties of accurately applying and measuring forces on the nanometer scale. For this reason, computational simulations are a primary tool for investigating the mechanical behavior of nanowires. In this work, we have performed atomistic simulations to examine the mechanical response of silver nanowires. We have conducted studies to determine the deformation characteristics of experimentally observed nanowire geometries subjected to tensile and bending loads. We have also developed a technique to probe the energetics of mechanical deformation, in order to elucidate the energetically favored deformation pathways in nanowires. Our results show that nanowires may be tailored for specific mechanical requirements based on geometry and free surface orientation and provide insight to the effect of free surfaces in the mechanical deformation of nanometer scale structures.

In order to study suspensions of deformable particles, a hybrid numerical technique was developed that combined a lattice-Boltzmann (LB) fluid solver with a finite element (FE) solid-phase solver. The LB method accurately recovered Navier-Stokes hydrodynamics, while the linear FE method accurately modeled deformation of fluid-filled elastic capsules for moderate levels of deformation. The LB/FE technique was extended using the Message Passing Interface (MPI) to allow scalable simulations on leading-class distributed memory supercomputers. An extensive series of validations were conducted using model problems, and the LB/FE method was found to accurately capture proper capsule dynamics and fluid hydrodynamics. The dilute-limit rheology was studied, and the individual normal stresses were accurately measured. An extension to the analytical theory for viscoelastic spheres [R. Roscoe. J. Fluid Mech., 28(02):273-93, 1967] was proposed that included the isotropic pressure disturbance. Single-body deformation was found to have a small negative (tensile) effect on the particle pressure. Next, the rheology and microstructure of dense suspensions of elastic capsules were probed in detail. As elastic deformation was introduced to the capsules, the rheology exhibited rapid changes. Moderate amounts of shear thinning were observed, and the first normal stress difference showed a rapid increase from a negative value for the rigid case, to a positive value for moderate levels of deformation. The particle pressure also demonstrated a decrease in compressive stresses as deformation increased. The corresponding changes in microstructure were quantified. Changes in particle self-diffusivity were also noted.