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Wang G.,Defence Materials Technology Center, Australia | Wang G.,University of Queensland | Croaker P.,University of New South Wales | Dargusch M.,Defence Materials Technology Center, Australia | And 4 more authors.
Computational Materials Science | Year: 2017

Grain refinement of an Al-2Cu alloy using ultrasonic treatment was investigated numerically. A finite element model coupling fluid flow and heat transfer was developed and validated by comparing the results of both numerical simulations and physical experiments. The model successfully describes hydrodynamic fields generated by ultrasonic treatment and its influence on heat transfer. The simulations were used to study the influence of the duration of ultrasonic treatment and the associated acoustic streaming on convection and the resulting temperature distribution. It was revealed that a relatively cold sonotrode applied during ultrasonic treatment for up to 4 min created a casting environment that promoted crystal nucleation and enabled their growth and survival during transport of these grains into the bulk of the melt by strong convection. The enhanced convection established a low temperature gradient throughout the melt which favours the formation of an equiaxed grain structure. Therefore, the convection induced by acoustic streaming plays a critical role in facilitating nucleation, growth, and transport of grains. © 2017 Elsevier B.V.

Cartwright B.K.,Pacific Engineering Systems International | Lex Mulcahy N.,Pacific Engineering Systems International | Chhor A.O.,Pacific Engineering Systems International | Thomas S.G.F.,Defence Materials Technology Center, Australia | And 4 more authors.
Journal of Manufacturing Science and Engineering, Transactions of the ASME | Year: 2015

To reduce combat casualties, military helmets are designed to provide protection against projectiles. Modern combat helmets are constructed of relatively lightweight composite materials that provide ballistic protection to the soldier. The manufacture of most composite helmets is labor intensive and involves the manual application and smoothing of individual layers of reinforcement to a concave mold surface. The recently developed double diaphragm deep drawing thermoforming process turns as-purchased, flat-form composite materials into structurally efficient three-dimensional shapes. Using this process, prototype shells have been produced and subsequently tested structurally. The success of the outcome has been greatly assisted through the use of specialized virtual prototyping techniques to provide insight into the thermoforming process of the shells and subsequently their structural performance by accounting for the actual fiber orientations of those finished shells. Copyright © 2015 by ASME.

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