Engineering Commons^™

Relationship Between Electrochemical Reaction Processes And Environment-Assisted Crack Growth Under Static And Dynamic Atmospheric Conditions, Fritz Friedersdorf, Carlos Hangarter, Nate Brown, Steve Policastro, Matt Merrill

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

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) …

Investigation Of Electrochemically-Induced Repassivation Of Al 7075-T6 And Al 2024-T3 As A Function Of Applied Stress And Galvanic Corrosion, Monica Trueba, Stefano P. Trasatti, Daniele Guastaferro, Michele Ferri, Marina Cabrini

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

The repassivation behavior of Al alloys 7075-T6 and 2024-T3 was investigated by means of pitting scan (PS) technique (Fig. 1) (Trueba, Trasatti, 2015). The effect of mechanical load and galvanic coupling was estimated by considering principally the electrochemical characteristics of the reverse curve, namely the pit transition potential (Eptp), the associated current density (iptp) and the steepness. The load levels explored were mostly below the elastic limit, using four point bent-beam (4PBB) stress-corrosion test specimens (ASTM G39-99). CRES 304 or Ti6Al4V alloy were physically joined with Al sheet for simulating stress-induced galvanic corrosion. Different experimental variables (e.g. irev, [Cl-], pH, …

Examination And Prediction Of Corrosion Fatigue Damage And Inhibition, Sarah E Galyon Dorman, Justin W Rausch, Saravanan Arunachalam, Scott A Fawaz

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

The United States Department of Defense (DoD) estimated that the annual cost of corrosion, the unintended material degradation due to the environment, to weapon systems and infrastructure in 2010 exceeded $21 billion, and that the number was likely to continue to rise. Unfortunately, as the warfighters demand more from their systems, corrosion prevention and control is frequently traded during the acquisition cycle for weapon system performance. As a result, the DoD remains entrenched in a find-and-fix corrosion management philosophy which is expensive and unsustainable. Better standardized fatigue laboratory procedures are need to help the DoD develop (1) a fundamental understanding …

Understanding Small Crack Effects On Failure & Threshold Diagrams, Daniel Kujawski

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

It is well recognized that crack length has significant effects on both the monotonic failure stress and cyclic threshold stress conditions. Existing experimental data indicates that LEFM predicts correctly the failure and threshold stresses only for relatively long cracks. For small/short cracks, the LEFM overestimates both the failure and threshold stresses. Usually, an argument has been made that LEFM is violated in terms of a crack length with respect to the crack-tip plastic zone that results in overestimating the failure stress for small cracks. On the other hand, the Kitagawa diagram has been used to experimentally illustrate the connection between …

Environmental Assisted Cracking Of Pipeline Steels In Co2 Containing Environment, Marina Cabrini, Sergio Lorenzi, Fabio Maria Bolzoni

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

Buried pipelines are susceptible to Environmental Assisted Cracking (EAC) in three different conditions: Stress Corrosion Cracking in the presence of Carbonate-Bicarbonate (CB-SCC), Near Neutral Stress Corrosion Cracking (NN-SCC) and Hydrogen Embrittlement (HE). Both CB-SCC and NN-SCC involve in their mechanism the presence of CO2 and/or its dissociated species dissolved in moisture under the coating, while the generic term of HE refers to the phenomena of brittle fracture taking place for entry of atomic hydrogen inside the metal lattice, owing to the applied cathodic protection.

Historically the CB-SCC was the first established form of stress corrosion on pipelines in the 60s, …

Mechanical & Chemical Driving Force Affecting Crack Nucleation, K. Sadanand, Asuri K. Vasudevan

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

Load history has been known to affect fracture and stress corrosion behavior. The degree to which it affects depends on the severity of the load history. It is known that shop peening can retard the SCC lives markedly in steels. Similarly, prestraining can reduce the KIscc and plateau velocity in high strength steels.

These types of experiments are difficult to quantify their effects on the SCC behavior. One can analyze the prestarining effects in a better way by analyzing the effects of single overloads followed by constant applied load to study the behavior. Such experiments can be done by observing …

Material Weakening Due To Corrosion In Hardened Bearing Steels, R.H. Vegter, M. Ersson, Bo Han

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

In rolling and ball bearings, materials are designed to withstand extremely high loads for long operation times. Most bearing steels are hardened steels with high carbon content that typically can function up to the Very High Cycle Fatigue regime (>1010 load cycles). The loads under which this occurs are given by the fatigue limit, which is a parameter that does depend on the strength of the material, but is commonly seen as a fixed parameter Therefore, material weakening is playing an important role when components fail as a result of rolling contact fatigue loading. In this paper, the effects …

Predicting Fatigue Crack Initiation In Metals Using Dislocation Dynamics Simulations, Veera Sundararaghavan, Christian Heinrich

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

The presented work aims at deepening the understanding of the initiation of fatigue cracks in metals. The work is based on an argument of Mura and Nakasone [1] where an energy criterion is used to predict the initiation of a fatigue crack from a slip band. The discussion is based on the evolution of dislocation networks, as these are the prime cause for permanent deformation in metals. Using high performance computing, 3D dislocation dynamics simulations [2] are performed over several cycles to study the growth of the dislocation arrangement. Then the evolution of energy in the system is determined, including …

Micromechanisms Of Fracture Propagation In Glassy Polymers, Matteo Ciccotti, Matthieu George, Yannick Nziakou, Guillaume Fischer, Anne-Caroline Genix, Bruno Bresson, Stéphane Roux

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

While most glassy polymers are nominally brittle at macroscopic scales, they are known to exhibit plastic deformation in indentation, scratching, and microcutting when the loaded region is sufficiently small. The same applies to the micrometer size process zone at the tip of a propagating crack. While the presence and approximate size of this microscale plastic zone is well described by the Dugdale model, the prediction of the toughness of these materials is not possible without accounting for the details of the local large strain field and the work hardening behaviour of these polymers, which can be inferred from their response …

A Perspective On Environmentally-Induced Cracking, R.M. Latanision, A.K. Vasudevan

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

The premature failure of engineering alloys in service is often associated with exposure to unintended environmental chemistry. High strength carbon steels and stainless steel will fail prematurely if exposed under tensile stress to absorbed atomic hydrogen. This is known as hydrogen embrittlement. Similarly, when aluminum alloys are exposed to liquid mercury, they are likely to crack prematurely if tensile stresses are present This is an example of liquid metal embrittlement. Silicate glass cracks in the presence of water, a phenomenon known as static fatigue of glass. Plastics fail prematurely in the presence of organic solvents. Service environments that contain soluble …

A Method For Corrosion-Fatigue Life Prediction, Daniel Kujawski

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

It is well recognized that environment has significant effects on the failure of cyclically loaded members/structures Existing experimental data indicates that fatigue life is much shorter in corrosive environment that in more inert environment such as a dry air or vacuum. This paper presents a method and strategy to predict/estimate life under corrosion-fatigue. A corrosion fatigue factor k_corr is defined as the ratio of the fully-reversed stress amplitude in air, (_a)_air, over that in corrosive environment, (_a)_corr, for a given fatigue life in terms of a number of cycles to …

Conference Program, A.K. Vasudevan, Ronald Latanision, Henry Holroyd, Neville Moody

International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures

No abstract provided.