Materials used in demanding environments are regularly exposed to intense pressure, stretching and compression. To ensure their safety and reliability in industries such as aerospace, automotive and construction, it’s important to understand the science of how they fail under stress.
Metal failure typically begins with the formation of micro-cracks which occur in a process called void coalescence. Tiny empty spaces, or voids, exist within metals which grow and merge when the metal is subjected to forces beyond its limits.
“This ultimately contributes to the material’s failure, or complete loss of load-bearing capacity,” explained Tianfu Guo and Mark Wong, Senior Principal Scientists at the A*STAR Institute of High Performance Computing (A*STAR IHPC).
While the mechanisms of metal failure under slow, steady stress (static loading) are well understood, void behaviour during high-speed impacts (dynamic loading) has yet to be explored deeply.
“Since the material experiences strain at high rates, voids can merge more rapidly than under static conditions, which in turn might lead to quicker crack formation and potentially catastrophic failure,” said Guo and Wong.
In response, the team developed micromechanical models and simulations to predict when voids inside materials would coalesce under dynamic conditions. To achieve this, they developed a new mathematical framework, incorporating stress triaxiality (T), the Lode parameter (L), and stress rate (κ), to identify exactly when these microscopic voids would begin to coalesce. Their findings revealed a critical threshold called the ‘ductile-brittle’ transition point, which highlights the material's behaviour under varying dynamic loading conditions.
They found that this transition depends on the rate of stress applied and how stress is distributed inside the metal. “The interplay between the speed of loading and the material’s microstructure revealed behaviours that were not evident under static conditions,” Guo and Wong noted.
By mapping these stress conditions, the researchers were able to distinguish between regions where the material is prone to coalescence and those that resist it, providing valuable insights into how and where failure is most likely to occur. This could enable safer engineering designs, improving the reliability of critical structures in the future. The team’s next chapter focuses on applying their computational models to more complex materials, such as the composites used in aerospace engineering. They also aim to explore how extreme environmental factors—such as high temperatures and chemical exposure—affect the coalescence process.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Institute of High Performance Computing (A*STAR IHPC).
