Tech Briefs

These advances may enable development of improved aerospace aluminum alloys.

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.

It is well known that with respect to fatigue, environment exerts a dominant and generally deleterious effect in that some environmental conditions (especially humidity) stimulate propagation of fatigue cracks in airframe and engine components. However, fundamental understanding of environmental fatigue remains elusive, making it necessary to engage in this and other related research in order to provide guidance for development of alloys, control of chemical and other environmental conditions, and fracture-mechanics-based prognosis of performance, all directed toward increasing the fatigue durability of engine and airframe components.