- ItemExplosive Welding of Aluminum Plates: Experiments, Evaluation, and Modeling(UNIVERSITY OF CALIFORNIA SAN DIEGO, 2019) Arnett, KevinExplosive welding is a field with a wide variety of applications of great value, such as corrosion resistant cladding and bi-metallic joints. It occupies a special place in the available metal joining techniques. Dissimilar metal welding is possible in metal pairings that don’t support other conventional bonds, and it can produce superior area welds regardless of the metal parts to be joined. The objectives of this dissertation were to further the understanding of explosive welding in general, as well as the empirical understanding of welding of Aluminum 6061-O, and to investigate the use of LS-DYNA’s Multi-Material Arbitrary Lagrangian-Eulerian formulation as a potential tool for the design of explosive welds. In the course of the work, the theory on formation of bond interfacial waves was identified as an area where there was not an apparent consensus, and this was addressed in light of both recent works and information from this study. For this dissertation, an experimental program of explosive welding tests, mechanical weld verification, and metallurgical observation were undertaken in order to add to the data available for this type of welding. Nine different explosive welding tests were conducted covering four scenarios, which were combinations of different explosive thicknesses and flyer inclination angles. Tensile shear tests with digital image correlation were used to test the welds, and optical microscope, Scanning Electron Microscope, and Transmission Electron Microscope images were used to investigate the nature of the bond. The numerical investigation was conducted and compared to both experiment and initial modeling results. The results reinforce the need for well-developed and material specific welding windows, adding additional data for the joining of Aluminum 6061-O. The endorsement of the continuous Kelvin-Helmholtz jet wake as the source of instability was supported with modeling results. The Multi-Material Arbitrary Lagrangian Eulerian modeling with Euler-Lagrange Coupling was demonstrated to yield results comparable to research codes for welding parameters, to be able to capture jetting, and provide meaningful temperature results. Bond interfacial waves were characterized with some success as well, concluding that this modeling technique is a viable means to assist in the design of explosive welds.
- ItemProduct Support in a Maintenance Free Operating Period Strategy(USMA, 2021) Bellocchio, Andrew; Pegues, Kathryn; Chetcuti, StevenApplication of a Maintenance Free Operating Period (MFOP) strategy in a fleet of vertical lift aircraft has profound implications to product support. Previous approaches to MFOP focused on estimating the operating period’s probability of success with modeling techniques and improving results using design elements such as inherent reliability. These approaches were aircraft centric and neglected aspects of the sustainment system external to the airframe. Key external facets addressed are the establishment of metrics that adequately measure MFOP performance as a stochastic process, optimization of the recovery period through a systems approach, transition to risk-based maintenance using high fidelity diagnostic and prognostic systems, establishment of an architecture to facilitate quality data consumed by a digital twin, and construction of maintenance policies suited for MFOP. The study concluded that robust product support surrounding the aircraft provides the best likelihood to achieve MFOP strategy success while delivering an efficient recovery period.
- ItemThe Effects of Transitioning an Undergraduate Mechanical Engineering Course from Shorter and More Frequent Class Periods to Longer and Fewer In-Class Sessions(ASEE, 2019) Miller, Matthew Louis; Rigney, Jeffrey Michael; Arnold, Daniel; Flaherty, DavidClass frequency and duration are fundamental parameters within engineering education across nearly all pedagogical methods. Optimizing these factors enables programs to achieve a higher level of learning in the classroom while providing for more efficient time management. The objective of this paper is to document the perceived effect on students and instructors when transitioning from a traditional 40 lesson course with 55 minutes duration, to one comprised of 30 lessons at 75 minutes in length. This analysis limits research to a mechanical engineering curriculum at the United States Military Academy at West Point, NY. Major assessment performance under the new structure was compared with historical results to provide objective qualitative comparison. Anonymous student feedback was also collected at the midpoint and end of each course. Survey questions centered on perceived information absorption and synthesis, impact on problem solving opportunities, and the effect of variation in classroom contact time. Changes in course syllabi to accommodate the 75 minute structure generally resulted in no net gain or loss of new material to the original curriculum, though outliers did occur and are discussed in more detail. Class size averaged 18 students over four different courses, ranging from Helicopter Aeronautics to Vehicle Dynamics. Course size averaged 34 students with a total of 135 students enrolled across all courses. The change in course structure demonstrates potential opportunity for both greater depth and application of learning in the classroom as well as increased schedule flexibility. Conversely, the heightened implications of students missing class and the administrative feasibility of such a shift can be problematic. Instructor assessment of student learning and student feedback through end-of-course evaluations will be presented in this paper, as well as recommendations for future instructors wishing to apply similar changes.
- ItemAtmospheric Flow Validation for Contaminant Transport(Sandia National Laboratories, 2019) Lance, Blake W.; Brown, Alexander L.; Dowding, Kevin J.; Clemenson, Michael D.; Elkins, ChrisPresentation on atmospheric flow validation for contaminant transport.
- ItemNumerical Methods for Simulating Multiphase Electrohydrodynamic Flows with Application to Liquid Fuel Injection(University of Colorado, 2010) Van Poppel, Bret P.Over the past decade, there has been a growing amount of attention paid to the emissions from small engines in the size range of 200 cm3 or smaller. In 2002 the EPA published a study claiming small engine emissions were responsible for 9% Hydrocarbons (HC), 4% Carbon monoxide (CO), 3% NOx, and 2% particulate matter from all mobile sources in the United States . As a result, there is considerable interest in controlling emissions for these small engines. One of the main reasons small engines produce high emissions is that they are carbureted. Carburetors mix fuel with air for combustion, but they are incapable of providing precise fuel timing. These deﬁciencies lead to partial combustion and decreased fuel eﬃciency while increasing emissions. Direct fuel injection may reduce the incidence of these pollutants. However, the cost of implementation is a barrier to large scale adoption. Fuel injectors used in the automotive industry are too costly to be implemented on small engines, with the average cost falling in the range of $35 dollar per unit (USD). In order to keep the production cost proﬁtable, costs will have to be substantially lower.