SUMMARYIn this study, the passive pitching due to wing torsional flexibility and its lift generation in dipteran flight were investigated using (a) the non-linear finite element method for the fluid-structure interaction, which analyzes the precise motions of the passive pitching of the wing interacting with the surrounding fluid flow, (b) the fluid-structure interaction similarity law, which characterizes insect flight, (c) the lumped torsional flexibility model as a simplified dipteran wing, and (d) the analytical wing model, which explains the characteristics of the passive pitching motion in the simulation. Given sinusoidal flapping with a frequency below the natural frequency of the wing torsion, the resulting passive pitching in the steady state, under fluid damping, is approximately sinusoidal with the advanced phase shift. We demonstrate that the generated lift can support the weight of some Diptera.

Dynamic shear-band-evolution processes in a bulk-metallic glass (BMG), an emerging class of materials, were captured by a state-of-the-art, high-speed, infrared camera. Many shear bands initiated, propagated, and arrested before the final fracture in tension, each with decreasing temperature, and shear-strain profiles. A free-volume-exhaustion mechanism was proposed to explain the phenomena. The results contribute to understanding and improving the limited ductility of BMGs, which otherwise have superior mechanical properties.

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Raman microprobe spectroscopy was used to measure the crack tip stress distribution in single-crystalline silicon using a wedge-loaded double cantilever beam (dcb) specimen. The wedge was advanced until the crack just propagated. After the crack arrested, the stresses were measured between 3 and 20 pm directly ahead of the crack. An average value of -0.43 was obtained for the slope of log stress vs log distance from the crack tip, rather than the theoretical value of -0.5. The value of K1 was determined from (1) the intercept of this curve and (2) the slope of stress against 1 / 6 . The values were in good agreement. The average experimental value of KI was determined to be 0.71 MPa.ml", compared to literature values for the K l c ranging from silicon of 0.8 to 0.94 MPa.ml". The value measured with the Raman is the arrest value of KI and is expected to be lower from kinetic energy considerations associated with wedge-loaded dcb specimens. [