Microstructurally small fatigue crack growth in thin, aluminum-alloy, pressure vessel liner

Abstract

Motivation to decrease weight and cost of composite-overwrapped pressure vessels used in space exploration leads to designs that challenge the current qualification standards and methods for predicting fatigue life of the structures. Namely, as thickness of the metallic, overwrapped liners is reduced (potentially to tens of grains through-thickness), plastic deformation extends to the liner bounds, and linear elastic fracture parameters become invalid for fatigue crack growth characterization. In this case, fatigue crack growth is likely governed by microstructural features of the material. Life predictions should ultimately reflect this microstructural dependence. In this work, we design a study that involves both experimental and computational modeling aspects to gain three-dimensional perspective of the microstructural features influencing fatigue crack growth in a thin aluminum alloy reminiscent of a metallic liner material. High-energy X-ray diffraction microscopy is explored as a method for characterizing microstructural morphology, including crystallographic orientations, in a volume of material containing a microstructurally small fatigue crack. Initial work involves a feasibility study of the material form (rolled sheet versus actual liner material) to be used in the proposed experimental study. An outlook on future work of the study is provided.