Assessing variability in microstructural influence on fatigue crack growth behavior
The effect of microstructural variability has long been recognized as a major contributing factor in the scatter of published fatigue data. It is also acknowledged that these effects are generally more prevalent for short cracks and in the threshold region. A number of models exist to explain individual microstructural effects such as grain boundary influence, grain cluster, average grain size, porosity etc. It is the aim of the Aeronautics and Astronautics Fatigue Lab to develop an encompassing model that accurately predicts these effects. In order to develop this model a range of material data will be required to inform and validate the model simulation. It is the aim of this thesis to develop the methods required to generate suitable fatigue crack data and also image the crack propagation and strain fields. The methodology from ASTM E647 was used for the determination of crack growth data with the notable exception of the use of compression pre-cracking and relevant crack growth models for the ESE(T) specimen. Compression pre-cracking methods have been utilised as data have shown that standard pre-cracking methods may affect crack growth rate data and the determination of threshold values. High and low load ratio tests were conducted with closure accounted for, allowing for accurate determination of the fatigue crack growth threshold. High resolution DIC imagery was captured for a range of loads over a range of crack lengths and enabled the visualization of material strain fields. The imagery also allowed correlation between fatigue crack growth variability, closure data and the tortuosity of the crack surface.
Sangid, Purdue University.
Off-Campus Purdue Users:
To access this dissertation, please log in to our