Effect of low temperatures and anisotropy on fatigue crack behavior of aluminum alloys

This dissertation focuses on evaluating the crack growth behavior of two commonly used aircraft materials. The evaluation was conducted to explore the effects of low temperature and material anisotropy on the fatigue crack propagation behavior of 2024-T351 and 7075-T651 aluminum alloys.; The first chapter of this dissertation raises questions as to the need for data to be generated for aircraft alloys, in particular, the generation of fatigue data for the structural components operating in their natural thermal environment. Natural thermal environments change when the aircraft experiences its ground air ground flight cycle.; Chapter 2 briefly discusses the mechanical fatigue process from nucleation through propagation. Chapter 3 focuses on the variables which affect fatigue crack growth behavior. Low temperature and aircraft aluminum alloys are addressed in this section.; Chapters 4 and 5 describe the methodology and results of the fatigue crack growth tests. All fatigue crack growth tests were conducted according to ASTM standard E 647-93.; The material orientation did not have an effect on the fatigue crack growth behavior for the parameters of this study. However, the crack growth behavior was accelerated in the dry air environment compared to the dry nitrogen gas environment. The decrease in test temperature had a beneficial effect for both materials on the apparent threshold stress intensity and crack growth behavior. The fracture surface morphology for both materials tested experienced a lower energy fracture mode as the test temperature decreased.