In this research, we connect fatigue crack growth to the microstructure in new and emerging materials, specifically single crystals and nanocrystalline material. By the use of digital image correlation, we can measure mixed mode displacements, anisotropic stress intensity factors, slip irreversibilities at the crack tip, crack closure effects, etc. When paired with microscopy, namely TEM and EBSD, we can specify the slip and fracture characterisitics of the material. In nanocrystalline NiCo, we showed that the material displayed superior resistance to fatigue crack growth (FCG), unlike previous studies, due to a stress relief heat treatment. This heat treatment stabilizes the microstructure resulting in dislocation mediated plasticity. Consequently the material achieves a balance between strength and ductility (combination of low internal stresses and nanoscale twins) thereby improving the FCG properties of the material.
Project Sponsors: Honeywell Aerospace Corporation, Critical Research Initiative at the University of Illinois, and US Department of Energy Nuclear Energy University Program
Collaborators: Garrett J. Pataky, Reginald F. Hamilton, Petros Sofronis, Huseyin Sehitoglu (University of Illinois, Urbana-Champaign); Thomas Niendorf, Hans J. Maier (University of Paderborn, Germany); and Richard G. Rateick (Honeywell)
Sangid MD, Pataky GJ, Sehitoglu H, Rateick RG, Niendorf T, Maier HJ, “Superior fatigue crack growth resistance, irreversibilities, and fatigue crack growth-microstructure relationship of nanocrystalline alloys,” Acta Materialia 59 7340-7355 (2011).
Pataky GJ, Sangid MD, Sehitoglu H, Hamilton RF, Maier HJ, Sofronis P, “Full field measurements of anisotropic stress intensity factor ranges in fatigue,” To appear in Engineering Fracture Mechanics (2012).