Elastic and thermodynamic properties of the shape-memory alloy AuZn

The current work reports on the elastic shear moduli, internal friction, and the specific heat of the B2 cubic ordered alloy AuZn as a function of temperature. Measurements were made on single-crystal and polycrystalline samples using Resonant Ultrasound Spectroscopy (RUS), semi-adiabatic calorimetry and stress-strain measurements. Our results confirm that this alloy exhibits the shape-memory effect and a phase transition at 64.75 K that appears to be continuous (second-order) from the specific heat data. It is argued that the combination of equiatomic composition and a low transformation temperature constrain the chemical potential and its derivatives to exhibit behavior that lies at the borderline between that of a first-order (discontinuous) and a continuous phase transition. The acoustic dissipation does not peak at the transtion temperature as expected, but shows a maximum well into the low-temperature phase. The Debye temeprature value of 219 K, obtained from the low-temperature specific heat data is in favorable agreement with that determined from the acoustic data (207 K) above the transition.Comment: 25 pages, 6 figures, submitted to Phys. Rev.

Conceptual Design for Long-Endurance Convertible Unmanned Aerial System

This research is aimed at analysing the effect of design parameters on critical aerodynamic performance of convertible unmanned aerial vehicle (UAV) with vertical take-off and landing (VTOL) capabilities and providing a sizing tool for its conceptual design. The research was based on new aerodynamic models specifically developed and validated for convertible aircraft, performed using mission-based optimisation techniques. To accommodate a wide range of convertible aircraft configurations, a non-linear lifting-line method was used to efficiently analyse different combinations of lifting surface and propeller arrangements. Propeller loads were calculated using a blade element momentum approach and corrected for high incidence angle conditions according to numerical and experimental studies. Propeller-wing interactions were considered by modifying local boundary conditions at wing sections immersed in propeller slipstream. Previous studies have suggested that the design of convertible aircraft is sensitive to typical mission requirements, notably the endurance breakdown between near-hover flight and cruise flight. A clear sizing law for wing and propeller according to given mission specification could greatly improve the understanding of compromises between hover and high speed flight