Some Advances in Understanding of Environmental Fatigue

A research program has yielded advances in understanding of numerous aspects of environmental crack propagation in aerospace aluminum alloys. From one perspective, the objective of this program was to quantitatively establish governing crack-tip-mechanics conditions and damage mechanisms pertinent to environmental crack propagation, using a combination of (1) high-spatial-resolution experimentation and (2) computational simulation based on continuum-mechanics mathematical models employing multiple length scales. From a slightly different perspective, the central goals of this research were to (1) develop means of accurate prediction of crack-tip stresses and plastic strains for incorporation into micromechanical descriptions of crack growth, (2) validate crack-tip-mechanics models by means of high-spatial-resolution experiments, and (3) resolve physical characteristics of damage attributable to accumulation of hydrogen at fatigue-crack tips.