Project A4: Design of structures for dynamic loading conditions
	Target: Understanding the role of structure on time-invariant properties
•	Project Chief Investigators: Christopher Hutchinson (Project Leader), Peter Hodgson, Mark Hoffman, Michael Ferry
•	Senior Researchers/Research Associates: Monash: Yuri Estrin, post-doc, May 2008, Deakin: post-doc, early 2008.
•	Research Students (to be recruited in 2008): UNSW: PhD student, Monash: PhD student
•	Research Assistants Visiting Scholars, Hons Students etc: UNSW: Timothy Burgess, Kai Dick Lau, Greig Kurniawan
•	External Collaborators: Yves Bréchet (Grenoble, France)
Project Summary
Many engineering applications require materials to perform under sustained and dynamic mechanical loadings. In these applications, the material properties must be stable under the loading conditions for the expected lifetime of the material. Often this stability in properties is translated to a question of stability in microstructure and the materials scientist usually implements approaches to retard the kinetics microstructural change to solve this problem. In systems subject to sustained mechanical loadings, the driving forces for microstructural change are not easily identified. In these cases, the external input of mechanical energy must be explicitly incorporated into both questions of the driving forces for microstructural change and any approaches to stabilization of microstructure.
This field is not very well developed for external mechanical forcing and consequently, neither is the design principles for stabilization of materials properties subject to fatigue or creep loadings or sustained deformation such as that experienced during an automobile crash. At present, principles based on quasi-static loadings are used; for example, assuming that designing for creep resistance is the same as designing for elevated temperature yield stress or extrapolating the strain-rate dependence of deformation under low strain-rates to very high strain-rates. Recent experiments have shown this to be incorrect.
Project Progress: Technical Details, Targets and Research Outcomes
This overall aim of this project is to contribute to the understanding of the fundamental principles governing microstructural change in systems subject to an external mechanical forcing. An understanding of these principles is to be used in the design of new light alloys with improved creep, fatigue and medium-high strain-rate deformation behaviour.
This project is divided into two streams based on the mode of mechanical loading: monotonic or cyclic. The monotonic loading stream consists of two sub-projects:
a)	Intermediate strain-rate effects (20-1000s-1) on the deformation behaviour of light alloy systems. This project is geared towards the design of materials for applications where crashworthiness is a primary requirement.
b)	Creep behaviour of Al alloys. This project is concerned with elucidating design principles for microstructures subject to sustained and simultaneous thermal and mechanical loading.
The cyclic loading stream (fatigue) also consists of two projects, addressing the two aspects of fatigue failure of materials; fatigue crack nucleation and growth:
a)	Cyclic hardening of model Al alloys. This project is concerned with the effects of solute and precipitates on the accumulation of damage during cyclic loading and the subsequent fatigue crack nucleation.
b)	Fatigue crack growth in nanocrystalline Al Alloys. This project is concerned with the fatigue crack growth behaviour in Al alloys with a particular emphasis on the effects of grain size and grain boundary character.