A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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    A Review of Metastable Beta Titanium Alloys
    (MDPI, 2018-06-30) Kolli, R. Prakash; Devaraj, Arun
    In this article, we provide a broad and extensive review of beta titanium alloys. Beta titanium alloys are an important class of alloys that have found use in demanding applications such as aircraft structures and engines, and orthopedic and orthodontic implants. Their high strength, good corrosion resistance, excellent biocompatibility, and ease of fabrication provide significant advantages compared to other high performance alloys. The body-centered cubic (bcc) β-phase is metastable at temperatures below the beta transus temperature, providing these alloys with a wide range of microstructures and mechanical properties through processing and heat treatment. One attribute important for biomedical applications is the ability to adjust the modulus of elasticity through alloying and altering phase volume fractions. Furthermore, since these alloys are metastable, they experience stress-induced transformations in response to deformation. The attributes of these alloys make them the subject of many recent studies. In addition, researchers are pursuing development of new metastable and near-beta Ti alloys for advanced applications. In this article, we review several important topics of these alloys including phase stability, development history, thermo-mechanical processing and heat treatment, and stress-induced transformations. In addition, we address recent developments in new alloys, phase stability, superelasticity, and additive manufacturing.
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    PERFORMANCE OF ELECTRIC MEDIUM-SIZED VARIABLE-RPM ROTOR AND SHROUDED ROTOR
    (2022) Ryseck, Peter Christian; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Electric variable RPM rotors are increasingly being used for propulsion and control of unmanned air vehicles. As these vehicles scale to carry heavier payloads of 50 to 400 lbs (20 to 180 kgs) in the group 2 and 3 UAS category, there are concerns about their aerodynamic performance and handling quality degradation. Therefore, there is a need to develop a systematic experimental testing procedure to measure loads on these systems to evaluate performance and augment Computational Fluid Dynamic (CFD) validation tools. In this work, a universal electric powered test rig is designed and fabricated for hover and wind tunnel tests of open and shrouded rotors. Steady hover results are validated using blade element momentum theory. These predictions incorporate an empirical correction approach in conjunction with an interpolation scheme to capture Reynolds number variation along the span of the blade and variation with RPM. Results show good agreement with the interpolation method for the low Reynolds number rotor tested (Re_tip<500,000). For the variable RPM rotor, transient step and chirp inputs are also presented. System identification showed linear frequency responses between thrust and torque with RPM and RPM-square in hover. Therefore, when modeling this rotor, steady inflow appears adequate in the frequency range of interest (0.4 to 60 rad/sec). In addition to an open rotor, the electric motor-rotor test stand was used to test a shrouded rotor in hover and forward flight to systematically compare performance results. Test data showed the shrouded rotor gained 15% thrust for the same power in hover with the best configuration. For low speed forward flight, lift-to-drag ratio was found to increase by 8 to 10% for the shrouded rotor system over the isolated rotor.