Statistical modeling for the corrosion fatigue of aluminum alloys 7075-T6 and 2024-T3

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Publication Type dissertation
School or College College of Engineering
Department Mechanical Engineering
Author Arriscorreta, Carlos A.
Title Statistical modeling for the corrosion fatigue of aluminum alloys 7075-T6 and 2024-T3
Date 2012-05
Description It is well known that corrosion and simultaneous cyclic loading have a detrimental impact in the integrity of devices or structures. Understating these mechanisms is critical to ensure safety of aircraft. This work presents an extensive literature review on issues of corrosion mechanisms including pitting, exfoliation and intergranular attack. Moreover, models for phases of life and pitting corrosion are presented. Relevant definitions related to these failure modes are presented. The nucleation of fatigue cracks from corrosion pits was investigated by evaluating the effects of two variables on the fatigue life of dog-bone specimens of aluminum alloys 7075-T6 and 2024-T3. The specimens were exposed to different levels of corrosion in an acidified saline solution of 3.5% NaCl. In addition, the specimens were exposed to concomitant fatigue and corrosion until failure by fracture occurred. SEM analysis indicated that fatigue cracks formed/nucleated from each pit, and subsurface mechanisms of degradation were identified associated with the pitting nucleation sites including subsurface pitting, cracking, tunneling and intergranular attack. Failure data were analyzed by ANOVA methods and three transformations were evaluated to minimize the variance, including natural log, inverse square root and power with a lambda of 1/3. Contour and surface plots were developed to show how these variables impact the response of cycles to failure for the conditions evaluated. The effects of stress are more detrimental than corrosion time on the fatigue life of the specimens for the values previously defined by the DOE matrix. The research reported herein presents a methodology for accelerated corrosion fatigue of high strength aluminum alloys in an acidified saline environment. Subsequently a statistical based methodology to assess the impact of multiple variables into the fatigue life of specimens is presented. Statistical models are developed to assess the effect of two variables, stress and corrosion time into the fatigue life of the specimens. Stress levels were chosen to simulate conditions of current aircraft, such as fuselage bulkheads in the F-16. Development of statistical models to predict the behavior of materials will increase our ability to predict and prevent catastrophic structural failures thereby increasing the safety of our aircraft structures.
Type Text
Publisher University of Utah
Subject Aluminum alloys; Corrosion; Fatigue; Intergranular corrosion; Pitting corrosion; 7075-T6; 2024-T3
Subject LCSH Aluminum alloys -- Corrosion fatigue
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Carlos A. Arriscorreta 2012
Format Medium application/pdf
Format Extent 7,435,175 bytes
Identifier us-etd3/id/634
Source Original in Marriott Library Special Collections, TN7.5 2012 .A77
ARK ark:/87278/s63t9xzv
Setname ir_etd
Date Created 2012-05-02
Date Modified 2016-08-26
ID 194803
Reference URL https://collections.lib.utah.edu/ark:/87278/s63t9xzv