Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002. / Includes bibliographical references (v. 2, p. 104-109). / Anand & Gurtin (2002) have recently developed a continuum theory for the elastic-viscoplastic deformation of amorphous solids. Their theory is motivated by and builds on the work of Parks, Argon, Boyce, Arruda, and their co-workers (e.g. Boyce et al., 1988; Arruda & Boyce, 1993) on modeling the plastic deformation of amorphous polymers. The theory of Anand & Gurtin (2002) carefully accounts for restrictions placed on constitutive assumptions by frame-indifference and by a new mathematical definition of an amorphous material based on the notion that the constitutive relations for such materials should be invariant under all rotations of the reference configuration and, independently, all rotations of the relaxed configuration. Also, they explicitly account for the dependence of the Helmholtz free energy on the plastic deformation in a thermodynamically consistent manner, a dependence which leads directly to a backstress in the underlying flow rule. In addition to the standard kinematic and stress variables, their theory contains two internal variables: a variable s > 0 that represents an isotropic intermolecular resistance to plastic flow; and an unsigned variable 7 that represents the local free-volume. In this thesis, we extend the work of Anand & Gurtin (2002) to model the deformation and fracture response of amorphous glassy polymers which exhibit both a ductile mechanism of fracture associated with large plastic stretches and subsequent chain scission and a brittle mode of fracture. / (cont.) For polymers such as polycarbonate (PC), the brittle fracture mode is characterized by a mechanism of elastic cavitational failure, which results in cleavage-type fracture similar to that observed in brittle fracture of metals. In contrast, polymers such as polymethylmethacrylate (PMMA) and polystyrene (PS) exhibit a brittle mode of fracture characterized by craze initiation, flow, and breakdown. To model crazing, we introduce a continuum constitutive relation which contains the three ingredients of crazing - initiation, widening, and breakdown - in a suitable statistically-averaged sense. We allow for local inelastic deformation due to shear yielding in possible concurrence with that due to crazing, and introduce a craze initiation criterion based on the local maximum principal tensile stress reaching a critical value which depends on the local mean normal stress. After crazing has initiated, our continuum model represents the transition from shear-flow to craze-flow by a change in the viscoplastic flow rule, in which the dilational inelastic deformation associated with craze-plasticity is taken to occur in the direction of the local maximum principal stress. Finally, for situations in which the local maximum tensile stress is positive, craze-breakdown and fracture is taken to occur when a local tensile plastic craze strain reaches a critical value. We apply our model to the techologically important polymer, polymethylmethacrylate ... / by Brian Paul Gearing. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 120-125). / In many applications, mobile robots are required to travel on outdoor terrain at high speed. Compared to traditional low-speed, laboratory-based robots, outdoor scenarios pose increased perception and mobility challenges which must be considered to achieve high performance. Additionally, high-speed driving produces dynamic robot-terrain interactions which are normally negligible in low speed driving. This thesis presents algorithms for estimating wheel slip and detecting robot immobilization on outdoor terrain, and for estimating traversed terrain profile and classifying terrain type. Both sets of algorithms utilize common onboard sensors. Two methods are presented for robot immobilization detection. The first method utilizes a dynamic vehicle model to estimate robot velocity and explicitly estimate longitudinal wheel slip. The vehicle model utilizes a novel simplified tire traction/braking force model in addition to estimating external resistive disturbance forces acting on the robot. The dynamic model is combined with sensor measurements in an extended Kalman filter framework. A preliminary algorithm for adapting the tire model parameters is presented. The second, model-free method takes a signal recognition-based approach to analyze inertial measurements to detect robot immobilization. Both approaches are experimentally validated on a robotic platform traveling on a variety of outdoor terrains. Two detector fusion techniques are proposed and experimentally validated which combine multiple detectors to increase detection speed and accuracy. An algorithm is presented to classify outdoor terrain for high-speed mobile robots using a suspension mounted accelerometer. The algorithm utilizes a dynamic vehicle model to estimate the terrain profile and classifies the terrain based on spatial frequency components of the estimated profile. The classification algorithm is validated using experimental results collected with a commercial automobile driving in real-world conditions. / by Christopher Charles Ward. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 63-64). / In this thesis, I designed and simulated an actuator mechanism for generating a moment within a compliant (soft) body system. The moment produces vibrational waves throughout a compliant material, and these vibrations are utilized to create biomimetic locomotion. The prototype actuator was developed for use in a fish tail, but it is hope that the actuation system can be applied in other robotic structures. The primary goals of this project included making gains in energy efficiency over previous embodiments, creating a compliant actuator that does not interfere with the natural body vibrations, and creating a system that can easily be modified to be used in a wide variety of soft-bodied systems. The system is also scalable to the size of the structure being actuated. / by Sean Andrew Mellott. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (p. 163-172). / The widespread use of improvised explosive devices (IEDs) against American and coalition forces in the ongoing Iraqi and Afghani conflicts has caused a dramatic increase in the number of traumatic brain injury (TBI) cases seen in recent years. The skull acts as the first and primary line of defense for the brain. Researching this structure's protective capabilities and shortcomings is therefore critical to 1) understanding how blunt impact loads and blast waves are propagated through the skull and transmitted into the brain, and 2) improving and evaluating future combat protection systems. This doctoral study is aimed at mechanically characterizing and modeling the two major constituents of the skull: cortical and trabecular bone. The mechanical behavior of these two materials over a wide range of strain rates is identified through both a review of the existing literature data and our own experimental investigations. For the behavior of compact bone two separate viscoelastic rate-sensitivity regimes are identified and modeled with a Maxwell-Weichert model containing one linear elastic and two linear viscoelastic branches in parallel. The rate-dependent plasticity of the material is further shown to obey a simple power law relationship and the overall material behavior is captured in a generalized three-dimensional viscoelastic, viscoplastic constitutive model formulation. For validation, the three-dimensional constitutive model is implemented as a subroutine within a commercial nonlinear finite element program. Given the similar composition of both cortical bone and the solid portion of trabecular bone, the compact bone constitutive model is subsequently employed in modeling the trabeculae of cancellous bone within two complementary microstructural frameworks. The first approach utilized is to create three-dimensional solid bone models of trabecular architecture directly from micro computed tomography (CT) scans of cancellous bone biopsy samples. The original samples from which these micro CT scans were obtained are then tested experimentally and the resulting stress-strain curves are found to show excellent agreement with the micromechanical model predictions. Successful simulation of specimen loading was found to be contingent upon extracting the trabecular structure from micro CT data in such a way that matched the relative density of the resulting specimen mesh to the experimentally recorded value. Analysis of both the experimental and simulation results further demonstrates that 1) local distributions in strut relative density are highly influential in the determining the compressive strength of trabecular bone and 2) the formation of macroscopic, multi-strut shear bands is responsible for the initial plateau and post-yield softening exhibited by trabecular bone in uniaxial compression. 3 The second microstructural approach employed is to model the trabecular network with an idealized representative volume element (RVE) and apply periodic boundary conditions. This latter approach allows for rapid investigation of the effects of relative density and strain rate in determining trabecular bone's mechanical properties. Specifically, Young's modulus is found to vary in a nearly quadratic manner with relative density and compressive strength is shown to have a power law relationship to relative density with an exponent of 1.5. In addition, compressive strength is shown to have a power law dependence upon strain rate with an exponent of 0.055. These relationships and the magnitude of the values predicted are all found to closely match the experimental trends and values reported in the literature. / by Timothy Paul Mahal Johnson. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 161-162). / Much of the previous research into magnetohydrodynamics has involved large-scale systems. This thesis explores the miniaturization and use of devices to convert the power dissipated within an expanding gas flow into electricity. Specific properties, such as high surface tension, allow for unique possibilities in the design of such devices. The material covered includes a brief derivation of the theory describing steady well-developed MHD flows within circular and rectangular channels. Numerical simulations are used to elucidate the relationships derived theoretically and to enable future design without the reliance upon such simulation. Fabricated devices are experimentally observed to determine the agreement with the modeled behavior. Finally, a design is proposed that is predicted to be a viable generator as well as a means for further examining the unanswered questions raised by the research performed in this thesis. / by Jay J. Fucetola. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (leaves 33-34). / Mechanical forces are known to directly influence the structure and function of living cells in a frequency-specific manner, however, the mechanism behind this frequency sensitivity remains unknown. The effects of high frequency mechanical perturbations were investigated in cultured capillary endothelial cells using a piezoelectric actuator. The actuator was used to displace fibronectin-coated coverslip on which the cells were cultured the associated displacement of sub-cellular regions was examined using surface-bound microbeads in conjunction with real-time light microscopy and image analysis. The role of different cytoskeletal microtubules and microfilaments in the cellular response to stress was examined using specific chemical disruptors (nocodazole and cytochalasin D, respectively); the level of prestress (preexisting tension) in the cell was altered by addition of the constrictor agent, thrombin. The results showed that the experimental method is effeqtive for determining the effects of chemical disruptors on the mechanical oscillatory behavior of cells. Specifically, in the presence of nocodazole, absolute displacement of beads on cells peaked at 1100 Hz whereas it peaked at approximately 200 Hz in the presence of cytochalasin-D. Finally, error inherent in the original system was reduced by refocusing the cells and beads on the microscope and optimizing image exposure time, which both yielded more definitive results. This optimized technique may be useful for future studies analyzing changes in cell structure and cellular biochemistry in response to different frequencies of mechanical stimulation. / by Jack Yu. / S.B.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 36-37). / This is an analysis assessing the installation costs of different solar power plant technologies and the current commercial availability for installation on the Island or Roatàn. Commercial large-scale power plants have been in use for decades and their technical feasibility has been documented as well as their high installation costs. Roatàn is currently seeking alternatives for powering their island. This thesis explores the initial costs of the solar power options currently available to the island, focusing on the large energy storage requirements needed for the island to be powered entirely off of sunlight. / by Ethan Huwe. / S.B.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008. / Includes bibliographical references (leaf 71). / A Kanban Production System is designed to help a factory line meet fluctuating demands for multiple part types. Based on the parameter settings of the Control-Point Policy, the optimum Kanban levels are obtained. The simulation software Simul8 was used to model the factory line and the Kanban system. Using the optimum Kanban levels, the Kanban system will act as an automatic production scheduling system that will indicate clearly when and how much of each part-type should be produced. Use of this system will avoid unnecessary inventory and changeover cost incurred by the existing Kanban system used by the factory line. Key words: Kanban, Control-Point Policy, Optimization Disclaimer: The content of the thesis is modified to protect the real identity of the attachment company. Company name and confidential information are omitted. / by Kaizhao Lee. / M.Eng.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 26). / The Atlantic Marine Engine, designed and manufactured by Lunenburg Foundry of Lunenburg, Nova Scotia, is a historically significant gasoline marine engine from the beginning of the 20th century. The Atlantic and other similar engines transformed the American and Canadian fishing industries with their power and reliability. A project to recreate a historic J model, single cylinder, two-cycle "make and break" engine is ongoing at MIT's Pappalardo Laboratory by a number of students. This thesis will focus on making progress towards a completed engine with the design and fabrication of the engine base. The fabrication will continue to use a traditional sandcasting process, but will explore the viability of using computer-aided design and manufacturing (CAD/CAM) processes to make high quality patterns out of high-density polyurethane foam. / by Kyle Joba-Woodruff. / S.B.

Massachusetts Institute of Technology. Dept. of Mechanical Engineering. Thesis. 1945. B.S. / MIT Institute Archives copy bound: Hickey, Thomas R. and Stephenson, Thomas I., III. The performance of a diesel engine using benzol as a fuel (1945) -- Hoigné, Emilio. Comparative economy in a small industrial plant of purchased power vs. power generated from process steam (1945) -- Howkins, John S., Jr. Design of recording interferometer (1945) -- Lenhard, Charles Ferd and Nietert, Robert William. Effect of piston contour on friction and lubrication (1945) -- McDowell, John R., III and Swartz, Paul W. Starting tests on a diesel engine (1945) -- Meade, William J., Jr. and McKay, William J. Performance tests on a two-stage air compressor (1945). / Bibliography: leaf 49. / by Thomas R. Hickey and Thomas I. Stephenson, III. / B.S.