Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects

• Ano de defesa: 2017
• Autor(a) principal: Cárdenas Barbosa, José Fernando
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Carregamento Dwell; Corrosão por fadiga; Corrosion fatigue; Crack growth rate determination; Crack length measurement techniques; Crack opening displacement method (COD); Determinação da taxa de propagação de trinca; Dwell carrying; Fatigue crack growth (FCG); Método de queda de potencial elétrico (QPE); Potential drop method (DCPD); Propagação de trinca por fadiga (PTF); Stress corrosion cracking (SCC); Técnicas de medição de trinca
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/18/18158/tde-27062017-111140/

Main extrinsic and intrinsic modifiers factors of crack growth rate in AA7050-T7451 were assessed in order to provide tools for aeronautical structures designers. These tools cover most necessary information to project aircraft\'s structures using the studied alloy, under damage tolerance philosophy. The experimental methodology consisted of use CT specimens, on TL and LT rolling direction to test its behavior under different conditions of stress ratio, force waveform, and the environment. The stress ratio values were 0.1 and 0.5, the force waveform used were sine and trapezoidal or Dwell under normal air laboratory conditions and salt fog 3.5%NaCl weight in order to simulate the marine environment. In Dwell tests, results were checked with the electrical potential drop technique (DCPD) in addition to the crack opening displacement (COD) method. Using the Walker coefficients, calculated on the present research, could be projected accurately the crack propagation behavior on Paris region and do fatigue life predictions using da/dN and S-N diagrams for different stress ratio values. The corrosion environment increases both crack growth rate and ΔKth due to oxides formation on the crack path that generates a crack closure effect. Dwell carrying makes decrease the crack growth rate by decreasing the slope of the Paris line on log (da/dN) versus log (ΔK) curve, instead of shifting down the line as occurs on titanium alloys. Rolling direction change from LT to TL increase the FCG rate in both threshold and Paris region, where the rate change use to be small.