Fatigue of materials is an important engineering science topic since it is one of the predominant causes of mechanical failure observed in applications ranging from aerospace to automotive, marine and industrial fields. This award supports fundamental research to provide needed knowledge to understand fatigue damage incubation, initiation and evolution. Of particular interest in this research is the case of magnesium since its alloys have properties that could lead to significant advances in weight reduction and energy savings. Therefore, results of this research are expected to benefit the U.S. economy and society as it has the potential to improve the use of this very light metal alloys. The broader impact of this research targets the participation of academically underrepresented groups in STEM research and training. Specifically, students in the Community College of Philadelphia, which is the largest public institution in the city with a predominantly minority-based population, will be selected to conduct research with the investigators' group leveraging a comprehensive outreach plan focusing on the use of multiscale mechanics and simulation-based engineering.
The research approach supported by this award is based on the use of multiscale experimental mechanics coupled with physics-based computational modeling. Specifically, the problem of identifying reliable precursors to fatigue damage is addressed by performing experiments at a scale at which grain level information is important and is linked to mechanical fields such as deformation, as well as to microstructural parameters and their evolution including twinning-detwinning, dislocation activity, cracking and their interactions. Experimental measurements at the grain scale will include full field optical as well as acoustic nondestructive datasets, which can be directly correlated with the mechanical behavior and similar nondestructive measurements made at the macroscale. Such experimental information could provide a microstructure-sensitive explanation of macroscopically observed fatigue behavior effects including plastic anisotropy, tension-compression asymmetry and deformation banding. The experimental information will be also used to form novel computational procedures capable to model fatigue-induced changes in the material microstructure. Specifically, molecular dynamics will be used to study twin nucleation and thickening at the single crystal level. Furthermore, crystal plasticity simulations will be used to simulate spatially resolved twins and their interactions with slip systems and grain boundaries to validate observations made in magnesium polycrystals. Furthermore, crystal plasticity and continuum phase field models will be used to model experimentally observed and fatigue-induced localized strain formations which are related to damage initiation.
