The interaction between two small bubbles experiencing transient cavitation in a nonlinear Kelvin-Voigt fluid is investigated. The time-delay effect in the interaction is incorporated in the coupled Keller-Miksis model. The refined model predicts that bubbles with radii smaller than 2µm will be repelled by large bubbles, in contrast to predictions from previous models. The matching pressure needed to obtain same level of transient cavitation in different Kelvin-Voigt fluids is shown to depend mainly on the shear modulus and is insensitive to other parameters, which makes it a useful parameter to correlate the results. When the radii of the bubbles fall between 4µm and 6µm, the secondary Bjerknes force obtained with matching pressures shows only weak dependence on the shear modulus. For the pressure amplitudes investigated, equilibrium distances can be found between two bubbles when the equilibrium radius of one of the bubbles is in a narrow range around 2µm. The equilibrium distance decreases when the shear modulus is increased. A simple relation between the two quantities is established.

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The microstructures and physical properties of SAC0307 lead-free solder formed by an ultrasound-assisted semi-solid casting process were analyzed. The damages to a thin aluminium foil placed in the alloy melt at 226 • C showed strong effects of acoustic streaming. Significant erosion due to cavitation was found for powers higher than 450W. Numerical simulations of a collapsing cavitation bubble obtained the highest peak pressure and temperature when the ultrasonic power was around 550W. When the ultrasonic power was between 500W and 600W, sub-grains were observed and the crystal grains became equiaxed with the smallest average grain size of about 140µm. The highest tensile strength found in this range was about 36.6 MPa. The density was 7.35g/cm 3. The elongation at break was about 60%, which was 40% higher than the value obtained by traditional casting techniques.

A large quantity of oyster shell is generated every year in coastal regions. Instead of being dumped as waste, after crushing or grinding, oyster shell may be recycled for use in concrete. Herein, the use of crushed oyster shell (COS) in conjunction with fly ash (FA) and blastfurnace slag (BS) to produce marine concrete was studied. By varying the COS, FA and BS contents in the marine concrete, the combined effects of COS, FA and BS on the cube compressive strength, water penetration, cyclic wetting-drying chloride attack and long-term seawater attack resistances were evaluated. The results showed that the addition of proper amounts of COS, FA and BS has positive effects on the strength and durability of marine concrete, but excessive COS may have negative effects. Hence, the combined addition of COS, FA and BS up to a certain optimum COS content is a promising way of producing a higher performance and greener marine concrete.