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Book Determination of Damage Initiation Mechanisms in Aerospace Alloys Due to Stress Corrosion Cracking Via In situ Microscale Characterization Techniques

Download or read book Determination of Damage Initiation Mechanisms in Aerospace Alloys Due to Stress Corrosion Cracking Via In situ Microscale Characterization Techniques written by Remelisa P. Esteves and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aluminum alloys are used on aerospace vehicles due to their high strength-to-weight ratio, formability and machinability. However, they become vulnerable to stress corrosion cracking (SCC) during their service life.SCC is primarily caused by the material’s stress condition, a suitable corrosive environment and material susceptibility. It is also influenced by a mixture of electrochemical, mechanical, and chemical factors. Due to the complexity of SCC, tools with better resolution and sensitivity are needed to better understand the impact and interaction of the contributing factors. A vast amount of research has been done to study SCC behavior, but the scale of characterization must be reduced to elucidate the key initiation mechanisms. In this work, it is shown that SCC initiation was detected early via micro-digital image correlation (micro-DIC) prior to the crack being discernible in microscopy images. The initial effort to monitor stress corrosion cracking in AA7075-T6 involved using a pixel resolution of 3.825 microns/pixel, frame rate of 10-15 min/image and an airbrush nozzle diameter of 0.3 mm for the speckle pattern, which led to the detection of crack initiation at 98% failure load. By using a pixel resolution that is 6 times smaller, a frame rate of up to 60 times less time per image, and an airbrush nozzle that is 2 times smaller, the first observation of strain concentration marking the eventual failure region of the AA7075-T6 sample was detected as early as 58% failure load. When the micro-DIC technique was applied to study SCC behavior in additively manufactured AlSi10Mg, the first observation of localized strain marking the eventual failure region of the sample was detected at 78% failure load. X-ray synchrotron tomography was used to qualitatively assess the hydrogen bubble and precipitate formation and to quantitatively assess the post initiation crack growth in AA7075-T651. With improved micro-DIC parameters and correlation with experimental outcomes from x-ray synchrotron tomography, multiple factors contributing to SCC can be assessed to better understand the mechanisms of SCC initiation. Correlations of material exposure time and load with SCC initiation can provide data for developing corrosion control strategies and new and improved alloys or heat treatment, as well as understanding SCC behavior in alloys made through unconventional means, such as additive manufacturing. The impact of this work lies in the life extension of alloys and greater reusability and fatigue life extension of aerospace vehicles.

Book Development of Multi scale Characterization Techniques for Stress Corrosion Cracking of Aerospace Alloys

Download or read book Development of Multi scale Characterization Techniques for Stress Corrosion Cracking of Aerospace Alloys written by Nicholas Reed and published by . This book was released on 2021 with total page 70 pages. Available in PDF, EPUB and Kindle. Book excerpt: Corrosion presents an inherent challenge in the safe and effective use of metallic aerospace structures for extended periods of time. Progress in the fundamental understanding of corrosion initiation and propagation under stress requires a multi-scale approach that leverages experiments to develop predictive models. Although there exists a large amount of research results tracking the corrosive processes of anodic dissolution and hydrogen embrittlement, the amount of available data and modeling of the micro-scale initiation of corrosion is sparse. This work leverages a suite of characterization techniques to systematically analyze an aerospace grade aluminum alloy AA7075-T6, providing important multi-scale data for correlation with overall corrosion progression. Samples were exposed to 3.5% NaCl solution at various exposure times under loading with a micro-tensile system. Optical microscopy, Raman spectroscopy and Energy Dispersive X-ray Analysis provided spatial maps of the visual and chemical alloy signatures before, during, and after failure, to analyze and track the progression of corrosion. An experimental setup for in-situ Digital Image Correlation (DIC) was developed to provide strain maps to study local concentrations around corrosion pits and quantify the impact on the material tensile performance. The material morphology and composition from these measurements identified localized oxide formations at a high spatial resolution that can be used to quantify the corrosion rates. Meanwhile, in-situ DIC measurements provided results showing stress concentrations formed by the corrosion pits and the reduced mechanical performance with exposure. The results demonstrate that multiple factors affect corrosion susceptibility and material deterioration, and highlight the need to overcome experimental challenges in quantifying these factors distinctly. This work demonstrates the capacity for highly detailed analysis of corrosion initiation and propagation in affected alloys using the processes outlined in the systematic study. The outcomes provide a pathway to address methods for maintaining the integrity of these alloys and extending their lifespan.

Book Stress corrosion Cracking of Aluminum Alloys

Download or read book Stress corrosion Cracking of Aluminum Alloys written by F. H. Haynie and published by . This book was released on 1966 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report deals with the stress-corrosion cracking of aluminum alloys, and it represents an effort by DMIC to expand on the information contained in DMIC Memorandum 202, 'Stress-Corrosion Cracking of Aluminum Alloys', dated February 15, 1965. DMIC Report 228 begins by presenting a comprehensive definition of stress-corrosion cracking. This is followed by sections dealing with (1) the historical development and growth in awareness of the problem, (2) the mechanisms involved, and (3) the theory of stress-corrosion cracking. A section on experimental techniques is presented. These techniques include test methods used to determine the susceptibility of alloys to stress-corrosion cracking, as well as more refined methods of studying the fundamental mechanisms of the problem. Different evaluation methods, applicable to obtaining the different objectives of stress-corrosion testing, are also presented. All of the foregoing serve as background to the sections on stress-corrosion-cracking behavior of aluminum alloys and preventive measures. (Author).

Book Influence of the Microstructure on Mechanical Properties and Damage Mechanisms in Al Si Cu Alloys by Using 2D and 3D In situ Analysis

Download or read book Influence of the Microstructure on Mechanical Properties and Damage Mechanisms in Al Si Cu Alloys by Using 2D and 3D In situ Analysis written by Zaidao Li and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 2D and 3D characterization and image analysis have been performed to measure the microstructural changes associated with: different Sr, Fe and Mn levels, the casting process (Gravity Die Casting vs. Lost Foam Casting, LFC) and the solution heat treatments in A319 alloy. The evolution of microstructure in Al-Si-Cu alloy with different alloying elements addition was also studied by thermal analysis. The microstructure consists of hard inclusions, i.e. eutectic Si, iron-intermetallics and Al2Cu phases, and pores. The effect on mechanical properties of the alloys has been monitored by Vickers hardness measurement and tensile tests. Surface damage observations are performed on A319 alloys with different Fe content during in-situ tensile test, which allows following the development and localization of the deformation and cracks. Digital image correlation measurement and fractography highlighted the role of iron-intermetallics in the cracks initiation and propagation. Tensile tests on LFC A319 samples with two different heat treatment conditions were performed in-situ under Laboratory Computed Tomography. Strain measurements from digital volume correlation and observed damage mechanisms show that cracks initiate at hard inclusions in the areas with sufficient stress concentrations, which are mainly provided by large pores, and often propagate through the fracture of Al2Cu, iron-intermetallics, as well as through Si particles rather than by their decohesion from the matrix.

Book Damage Mechanisms and Life Assessment of High Temperature Components

Download or read book Damage Mechanisms and Life Assessment of High Temperature Components written by Ramaswamy Viswanathan and published by ASM International. This book was released on 1989 with total page 497 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Stress corrosion Cracking

Download or read book Stress corrosion Cracking written by Russell H. Jones and published by ASM International(OH). This book was released on 1992 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: Details the many conditions under which stress-corrosion cracking (SCC) can occur, the parameters which control SCC, and the methodologies for mitigating and testing for SCC, plus information on mechanisms of SCC with experimental data on a variety of materials. Contains information about environmen

Book Stress corrosion Cracking Materials Performance and Evaluation

Download or read book Stress corrosion Cracking Materials Performance and Evaluation written by Russell H. Jones and published by . This book was released on 2017 with total page 473 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second edition serves as a go-to reference on the complex subject of stress corrosion cracking (SCC), offering information to help metallurgists, materials scientists, and designers determine whether SCC will be an issue for their design or applications; and for the failure analyst to help determine if SCC played a role in a failure under investigation. Research conducted over the last 20 years warranted new coverage on crack tip chemistry analysis and modeling, SCC of low strength steels in alcohol, SCC in new high strength steels, new data in SCC of stainless steels and nickel-based alloys, SCC of copper alloys in potable water, and hydrogen induced cracking of aluminium alloys. Additional case studies and a section on high strength low alloy steels were added. An appendix of relevant standards pertaining to SCC is also included. The book details the many conditions under which SCC can occur, the parameters which control SCC, and methodologies for mitigating and testing for SCC, plus information on the mechanism of SCC with experimental data on a variety of materials. It contains information about the environmental, mechanical, microstructural and chemical aspects of SCC to help predict and prevent component failure. Chapters include coverage of SCC in these materials: carbon, and low-alloy steels; high-strength steels; stainless steels; nickle-base alloys; copper alloys; magnesium alloys; titanium alloys; zirconium alloys; uranium alloys; amorphous alloys; and glasses and ceramics.

Book A Fundamental Investigation of the Nature of Stress corrosion Cracking in Aluminum Alloys

Download or read book A Fundamental Investigation of the Nature of Stress corrosion Cracking in Aluminum Alloys written by F. H. Haynie and published by . This book was released on 1967 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Several experimental techniques are used to study the mechanisms of stress-corrosion cracking in high purity aluminum alloys. The effect of metallurgical variables such as alloying elements (Cr, Ag, Cu) and heat treatments on a 4.2Zn-3.3Mg aluminum alloy are determined. Techniques used in this study include electrode polarization, autoradiographic studies, microstress studies, electron microscopy (replica and transmission), metioscopy, and standard stress-corrosion testing methods. As a result of these studies, an electrochemical theory for the mechanism of stress-corrosion cracking which involves the strain induced absorption of hydrogen is found to be consistent with the observations.

Book Spatially Resolved In situ Monitoring of Crack Growth Via the Coupling Current in Aluminum Alloy 5083

Download or read book Spatially Resolved In situ Monitoring of Crack Growth Via the Coupling Current in Aluminum Alloy 5083 written by Krystaufeux Williams and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The work discussed in this dissertation is an experimental validation of a body of research that was created to model stress corrosion cracking phenomenon for 304 stainless steels in boiling water reactors. This coupled environment fracture model (CEFM) incorporates the natural laws of the conservation of charge and the differential aeration hypothesis to predict the amount of stress corrosion crack growth as a function of many external environmental variables, including potential, stress intensity, solution conductivity, oxidizer concentrations, and various other environmental parameters. Out of this approach came the concept of the coupling current; a local corrosion current that flows from within cracks, crevices, pits, etc... of a metal or alloy to the external surface. Because of the deterministic approach taken in the mentioned research, the coupling current analysis and CEFM model can be applied to the specific problem of SCC in aluminum alloy 5083 (the alloy of interest for this dissertation that is highly sought after today because of its corrosion resistance and high strength to weight ratio). This dissertation research is specifically devoted to the experimental verification of the coupling current, which results from a coupling between the crack's internal and external environments, by spatially resolving them using the scanning vibrating probe (SVP) as a tool. Hence, through the use of a unique fracture mechanics setup, simultaneous mechanical and local electrochemical data may be obtained, in situ.The SVP is an alternating current device designed to obtain highly localized potential gradients (with a best resolution of microns) in a solution conductivity of 100s of [mu]S/cm. In order to enhance resolution of the SVP maps as much as possible, without being too far away from the desired test conditions of 0.6M saltwater (utilized in the lab as a substitute for seawater), dilution of the saltwater by an order of magnitude (0.06 M) was used throughout all experiments unless otherwise noted. Initial experiments of localized corrosion events from 10s of micron to mm-sized galvanic couples were first mapped in order to obtain confidence in the ability to map the current flowing through the solution above a stress corrosion crack. Furthermore, because of these feasibility studies, the current density that flows between an alloys matrix to or from an intermetallic compound can be spatially mapped as well.Standard fracture mechanics of AA5083-H116 bend bars were performed in diluted saltwater (0.06M) to obtain the critical fracture toughness for cracking in air and in saltwater. During loading in a bending test setup, standard load and crack mouth opening signals were obtained until the sample broke, or until the crack arrested. It was discovered that when the data was analyzed by plotting the load as a function of crack mouth opening displacement, the critical stress intensity (air), or threshold stress intensity (electrolyte) could be determined by identifying the decreasing of unload/reload slopes from a constant value. Transitions to and from different characteristic zones of cracking (different characteristics for different environments) are observed in the provided light and scanning electron microscopy images.The posited existence of the coupling current provides a different and more convenient marker for analyzing stress corrosion cracking, corrosion fatigue, and other forms of localized corrosion attack involving applied loads. For the first time, through the research in this dissertation, the positive current flowing from a crack were mapped, in situ, providing the changes in the anodic current density through the solution as a function of position. A collage of SVP maps were constructed on a grand scale according to their observed location with the light microscope by using features (such as the notch, or the growing crack) from the larger SVP maps taken at lower fracture toughness values with less resolution. These larger maps were then lined up with the extremes of the same features in smaller, SVP maps taken at a later time with a new location and higher resolution to keep up with the advancing crack tip. From that collage, a crack length vs. time graph was plotted to examine the characteristics of the crack growth. Finally, a crack growth rate vs. fracture toughness trend was constructed to compare with the CEFM and other studies on stress corrosion cracking of AA5083.In order to accommodate the expansion of the CEFM to predict crack growth in heavily sensitized AA5083 specimens, more electrochemical data (i.e., polarization scans taken from recent literature and compiled in this dissertation) was needed. The experimental findings from this dissertation also contributed to the model's expansion with the spatial analysis of the crack internal and external environments. Future work will incorporate testing of the more sensitive specimen orientations, acoustic emission analysis for probing micro-fracture processes, and coating effectiveness for SCC mitigation.

Book Mechanisms of Stress

Download or read book Mechanisms of Stress written by S. P. Lynch and published by . This book was released on 1977 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metallographic and fractographic observations of sub-critical crack growth in a precipitation-hardened AlZn-Mg alloy in liquid-metal, aqueous, and water-vapour/air environments suggest that stress-corrosion cracking and liquid-metal embrittlement in this alloy involve a common mechanism. Sub-critical crack growth in all these environments can produce entirely dimpled fracture surfaces and, in liquid-metal and aqueous environments, crack growth can occur extremely rapidly. It is proposed that stress-corrosion cracking and liquid-metal embrittlement in aluminium alloys (and possibly other materials) can be explained on the basis that chemisorption of environmental species facilitates nucleation of dislocations at crack tips. Such a process would produce sub-critical crack growth with less blunting at crack tips than in inert environments and, hence, would explain observations that dimples on fracture surfaces after SCC are smaller and shallower than those on overload fractures. The results suggest that neither dissolution nor hydrogen-embrittlement processes occurred during stress-corrosion cracking in aluminium alloys. (Author).

Book De alloying and Stress corrosion Cracking Final Report

Download or read book De alloying and Stress corrosion Cracking Final Report written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This research program has had two major areas of focus that are related: (1) alloy corrosion and (2) the role of selective dissolution in the stress corrosion cracking of alloy systems. These interrelated issues were examined using model systems such as Ag-Au and Cu-Au by conventional electrochemical techniques, in situ scanning tunneling microscopy (STM), in situ small angle neutron scattering (SANS), ultrahigh speed digital photography of fracture events, and computer simulations. The STM and SANS work were specifically aimed at addressing a roughening transition known to occur in alloy systems undergoing corrosion at electrochemical potentials greater than the so-called critical potential. Analytical models of de-alloying processes including the roughening transition were developed that specifically include curvature effects that are important in alloy corrosion processes. Stress-corrosion experiments were performed on the same model systems using rapid optical and electrochemical techniques on 50[micro]m--250[micro]m thick sheets and small diameter wires. The primary goal of this work was to develop a fundamental understanding of the corrosion and electrochemistry of alloys and the stress-corrosion cracking processes these alloys undergo. Computer simulations and analytical work identified surface stress and an important parameter in environmentally assisted fracture. The major results of the research on this program since the summer of 1993 are briefly summarized.

Book Damage Precursor Identification Via Microstructure Sensitive Nondestructive Evaluation

Download or read book Damage Precursor Identification Via Microstructure Sensitive Nondestructive Evaluation written by Brian John Wisner and published by . This book was released on 2017 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: Damage in materials is a complex and stochastic process bridging several time and length scales. This dissertation focuses on investigating the damage process in a particular class of precipitate-hardened aluminum alloys which is widely used in automotive and aerospace applications. Most emphasis in the literature has been given either on their ductility for manufacturing purposes or fracture for performance considerations. In this dissertation, emphasis is placed on using nondestructive evaluation (NDE) combined with mechanical testing and characterization methods applied at a scale where damage incubation and initiation is occurring. Specifically, a novel setup built inside a Scanning Electron Microscope (SEM) and retrofitted to be combined with characterization and NDE capabilities was developed with the goal to track the early stages of the damage process in this type of material. The characterization capabilities include Electron Backscatter Diffraction (EBSD) and Energy Dispersive Spectroscopy (EDS) in addition to X-ray micro-computed tomography (Îơ-CT) and nanoindentation, in addition to microscopy achieved by the Secondary Electron (SE) and Back Scatter Electron (BSE) detectors. The mechanical testing inside the SEM was achieved with the use of an appropriate stage that fitted within its chamber and is capable of applying both axial and bending monotonic and cyclic loads. The NDE capabilities, beyond the microscopy and Îơ-CT, include the methods of Acoustic Emission and Digital Image Correlation (DIC). This setup was used to identify damage precursors in this material system and their evolution over time and space. The experimental results were analyzed by a custom signal processing scheme that involves both feature-based analyses as well as a machine learning method to relate recorded microstructural data to damage in this material. Extensions of the presented approach to include information from computational methods as well as its applicability to other material systems are discussed.