Mechanical Engineering - Ph.D. / Sc.D.
http://hdl.handle.net/1721.1/7848
2016-04-11T03:40:28ZExperimental investigation of optimal heat removal from a surface
http://hdl.handle.net/1721.1/102212
Experimental investigation of optimal heat removal from a surface
Kozlu, Hamdi
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1989.; Includes bibliographical references (leaves 121-129).
1989-01-01T00:00:00ZSub-Tg̳, solid-state, plasticity-induced bonding of polymeric films and continuous forming
http://hdl.handle.net/1721.1/101816
Sub-Tg̳, solid-state, plasticity-induced bonding of polymeric films and continuous forming
Padhye, Nikhil, Ph. D. Massachusetts Institute of Technology
If two pieces of a glassy polymer are brought into intimate contact (within molecular proximity) at temperatures well below their glass transition temperature (Tg) negligible adhesion, due to lack of inter-diffusion of macromolecules, will be noted. Because polymer chains are kinetically trapped well below the Tg, the time-scales for relaxations in the glassy state are extremely large, and the system is effectively frozen with respect to any long range diffusive motion. This thesis shows the discovery of a new phenomenon of solid-state, plasticity-induced bonding at temperatures well below Tg which take on the order of a second, by subjecting amorphous polymers to active plastic deformation. In spite of the glassy regime, the bulk plastic deformation triggers requisite molecular mobility of polymer chains to cause inter-penetration across the interface. Quantitative levels of adhesion and morphology of the fractured interfaces validate the sub-Tg, plasticity-induced, molecular mobilization causing bonding. The absence of bonding during compression of films in a near hydrostatic setting (which inhibits plastic flow), and between an 'elastic' and a 'plastic' film, further establishes the explicit role of plastic deformation in this newly reported sub-Tg solid-state bonding. Other components of this thesis comprise the design and fabrication of machines to perform continuous forming and sub-Tg, solid-state bonding of polymer films. A peel-test fixture has also been designed and developed to improve the T-peel test for determination of mode-I fracture toughness of thin and flexible adhered laminates. This research has been conducted as a part of an ongoing activity at the Novartis-MIT Center for Continuous Manufacturing at MIT.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.; In title on title-page, double-underscored "g" appears as subscript. Cataloged from PDF version of thesis.; Includes bibliographical references (pages 271-310).
2015-01-01T00:00:00ZHarmonic poly-actuator : design and control of a new piezoelectric mechanism
http://hdl.handle.net/1721.1/101538
Harmonic poly-actuator : design and control of a new piezoelectric mechanism
Torres, James, Ph. D. Massachusetts Institute of Technology
Piezoelectric devices, e.g. piezoelectric stack actuators, have several salient features inherent to their structure. They are efficient, have a high bandwidth, and their capacitive loading allows for static loads to be maintained with virtually no power consumption. The major preventative drawback that limits more widespread use is the small strain, on the order of 0.1%. For marco-scale applications, the displacement must be amplified, typically through mechanical or frequency leveraging. Both have inherent limitations: mechanical devices can increase the stroke but is naturally limited; and frequency devices relies on friction and is limited to nanopositioning. In this thesis, we investigate combining a unique mechanical amplification with a frequency amplification device that does not rely on friction to produce an arbitrarily large stroke linear actuator. The first stage of amplification aims to achieve the greatest displacement amplification without sacrificing force capabilities. The second stage relies on the coordinated actuation of multiple copies of the mechanically amplified device to produce a long stroke, smooth force poly-actuator. The theoretical design concepts for each stage of amplification are explicitly derived. The mechanical amplification device uses rolling contact joints to maintain stiff connections to transmit the force without losses due to friction; and the frequency amplification uses a sinusoidal Transmission interface to exploit a passive balancing of undesirable non-linearities, proven by harmonic analysis. A unique control algorithm is developed to produce a wide variety of capabilities. The theoretical findings are supported by experimental prototypes. The mechanical amplification device produces a comparable energy density while amplifying the displacement by an additional factor 10. The proof-of-concept poly-actuator prototype can continually produce +/-100 Newtons of force over a stroke of 200 mm. We conclude with simulations, which are verified through physical experiments, used to estimate several performance metrics for comparison.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 127-132).
2015-01-01T00:00:00ZEfficient multiscale methods for micro/nanoscale solid state heat transfer
http://hdl.handle.net/1721.1/101537
Efficient multiscale methods for micro/nanoscale solid state heat transfer
Péraud, Jean-Philippe M. (Jean-Philippe Michel)
In this thesis, we develop methods for solving the linearized Boltzmann transport equation (BTE) in the relaxation-time approximation for describing small-scale solidstate heat transfer. We first discuss a Monte Carlo (MC) solution method that builds upon the deviational energy-based Monte Carlo method presented in [J.-P. Péraud and N.G. Hadjiconstantinou, Physical Review B, 84(20), p. 205331, 2011]. By linearizing the deviational Boltzmann equation we formulate a kinetic-type algorithm in which each computational particle is treated independently; this feature is shown to be consequence of the energy-based formulation and the linearity of the governing equation and results in an "event-driven" algorithm that requires no time discretization. In addition to a much simpler and more accurate algorithm (no time discretization error), this formulation leads to considerable speedup and memory savings, as well as the ability to efficiently treat materials with wide ranges of phonon relaxation times, such as silicon. A second, complementary, simulation method developed in this thesis is based on the adjoint formulation of the linearized BTE, also derived here. The adjoint formulation describes the dynamics of phonons travelling backward in time, that is, being emitted from the "detectors" and detected by the "sources" of the original problem. By switching the detector with the source in cases where the former is small, that is when high accuracy is needed in small regions of phase-space, the adjoint formulation provides significant computational savings and in some cases makes previously intractable problems possible. We also develop an asymptotic theory for solving the BTE at small Knudsen numbers, namely at scales where Monte Carlo methods or other existing computational methods become inefficient. The asymptotic approach, which is based on a Hilbert expansion of the distribution function, shows that the macroscopic equation governing heat transport for non-zero but small Knudsen numbers is the heat equation, albeit supplemented with jump-type boundary conditions. Specifically, we show that the traditional no-jump boundary condition is only applicable in the macroscopic limit where the Knudsen number approaches zero. Kinetic effects, always present at the boundaries, become increasingly important as the Knudsen number increases, and manifest themselves in the form of temperature jumps that enter as boundary conditions to the heat equation, as well as local corrections in the form of kinetic boundary layers that need to be superposed to the heat equation solution. We present techniques for efficiently calculating the associated jump coefficients and boundary layers for different material models when analytical results are not available. All results are validated using deviational Monte Carlo methods primarily developed in this thesis. We finally demonstrate that the asymptotic solution method developed here can be used for calculating the Kapitza conductance (and temperature jump) associated with the interface between materials.
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.; Cataloged from PDF version of thesis.; Includes bibliographical references (pages 193-199).
2015-01-01T00:00:00Z