• Prangnell, Philip
• Burnett, Tl
• Shanthraj, Pratheek
• Grant, Cameron
• Aboura, Yasser Al

Abstract

Intergranular Environmentally-Assisted Cracking (EAC) has recently been reported to be an issue of concern in<br/>new-generation 7000 series aluminium alloys, such as AA7085, when exposed to humid air. The cracking process<br/>occurs in a highly brittle manner almost exclusively along grain boundaries (GB’s) and has been attributed to<br/>hydrogen embrittlement, probably by GB decohesion within the stress field at the crack tip. Currently, how the<br/>highly heterogeneous grain structures found in these partially recrystallized materials impact the growth behaviour<br/>of microstructurally short cracks is poorly understood. In particular, there is expected to be a high sensitivity to<br/>the grain structure in the transition from initiation to sustained propagation, where the local mechanical driving<br/>force is very sensitive to the crack path. Volume Elements, VE's, with synthetic grain structures have been<br/>generated from real microstructure and texture data, so that the effects of important grain structure variables can<br/>be explored in crystal-plasticity simulations, to understand the extent to which typical grain-structural features<br/>affect the driving force for short-crack growth. Specifically, by considering the effect of different uncrystallised<br/>grain aspect ratios and embedding recrystallised grains in the model, the strain energy release rate has been<br/>calculated as a function of crack path. This has revealed large reductions and fluctuations in the driving force for<br/>short cracks in relation to the local grain structure encountered by the crack tip, which have been estimated by the<br/>model.

Topics

• impedance spectroscopy
• grain
• simulation
• aluminium
• crack
• aluminium alloy
• Hydrogen
• texture
• plasticity