Atmospheric laboratory and outdoor testing of aluminum a lloy environment assisted cracking

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Relationship between electrochemical reaction processes and environment-assisted crack growth under static and dynamic atmospheric conditions

Environment-assisted cracking (EAC) of aluminum alloys in corrosive atmospheres is an important maintenance and safety issue for aerospace structures. EAC initiation and propagation are influenced by the interaction of load, environment, and alloy properties. For atmospheric corrosion, environmental conditions are dynamic; where temperature, relative humidity, and surface contaminants interact to control thin film electrolyte properties. Recent studies have determined that stage II stress corrosion crack (SCC) propagation, under atmospheric conditions is strongly dependent on humidity. SCC propagation in AA5083 and AA7075 alloys is a maximum during drying processes at intermediate humidity levels at or below the deliquescence relative humidity (DRH) for the applied corrosive salt. An improved understanding of the dependence of cracking on atmospheric conditions is important to testing material performance, establishing durable designs, and managing structural integrity. Please click Additional Files below to see the full abstract

Evaluation of chloride stress corrosion susceptibility of stainless steels

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The influence of dynamic atmospheric conditions on EAC and corrosion fatigue

Environment-assisted cracking (EAC) and corrosion fatigue (CF) of aluminum alloys in corrosive atmospheres are significant maintenance and safety issues for aircraft. It is well known that these cracking phenomena result from the combined effects of environment, mechanical loads, and material properties. The service life of an aircraft structure is dependent on various stages of degradation associated with formation of corrosion damage, crack nucleation, and crack propagation. Which of these stages limits the service life may be specific to a given component and can be dependent on a large number of factors, including environmental severity, mechanical loading, and protective coatings. Please download the file below for full content

Nonlinear Ultrasonic Measurements based on Pulse-Echo Method and Matched Filters Techniques

Cyclic loading of mechanical components promotes the formation of dislocation dipoles in metals, which can serve as precursors to crack nucleation and ultimately lead to failure. In the laboratory setting, an acoustic nonlinearity parameter has been assessed as an effective indicator for characterizing the progression of fatigue damage precursors. However, the need to use monochromatic waves of medium-to-high acoustic energy has presented a constraint, making it problematic for use in field applications. This paper presents a potential approach for field measurement of acoustic nonlinearity by using general purpose ultrasonic pulser-receivers. Nonlinear ultrasonic measurements during fatigue testing were analyzed by the using pulse-echo method, and matched filters were utilized to extract the fundamental and second harmonic waves fromthe signals, which were measured using wideband contact transducers. As in the case of the classic harmonic generation, the nonlinearity parameter indicates a strong correlation with fatigue cycles. Consideration has been given to potential nonlinearities in the measurement system, and tests have confirmed that measured second harmonic signals exhibit a linear dependence on the input signal strength, further affirming the conclusion that this parameter relates to damage precursor formation from cyclic loading.</p