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Zhai J.,University of Akron | Luo T.,University of Akron | Gao X.,University of Akron | Graham S.M.,U.S. Naval Academy | And 3 more authors.
International Journal of Solids and Structures | Year: 2016

This paper presents a constitutive model, which combines the models proposed by Stewart and Cazacu (2011) and Zhou et al. (2014), to describe the ductile damage process in a commercially pure titanium (CP Ti) and to simulate its mechanical response. In particular, a Gurson-type porous material model is modified by coupling two damage parameters, accounting for the void damage and the shear damage respectively, into the yield function and the flow potential. The plastic anisotropy and tension-compression asymmetry exhibited by CP Ti are accounted for by a plasticity model based on the linear transformation of the stress deviator. The theoretical model is implemented in the general purpose finite element software ABAQUS via a user defined subroutine and calibrated using experimental data. Good comparisons are observed between model predictions and experimental results for a series of specimens in different orientations and experiencing a wide range of stress states. © 2016.

Williams K.,Center for Corrosion Science and Engineering | Williams K.,Pennsylvania State University | Bayles R.,Center for Corrosion Science and Engineering | Natishan P.,Center for Corrosion Science and Engineering | And 2 more authors.
ECS Transactions | Year: 2012

When as-received or sensitized AA5083 are immersed in an electrolyte, a growing crack creates a galvanic couple with the external surfaces according to the differential aeration hypothesis. Monitoring the resulting "coupling current" yields information about the mechanisms of crack advance. The purpose of this study is to determine if the scanning vibrating electrode technique (SVET) can be used to monitor the coupling current flowing through the solution from the crack to the external surfaces. If successful, this method, which maps potential as a function of probe position via a scanning vibrating probe (SVP), can be used to visualize and quantify the coupling current emanating from a growing stress corrosion crack in sensitized and unsensitized aluminum alloy samples to yield more localized information about the crack growth process. Preliminary feasibility studies were performed to map the current/potential in larger galvanic couples designed to simulate Cu-rich intermetallics dispersed in an aluminum matrix (as in the Cu-rich particles in AA2024 and Mgrich intermetallics in AA5083). A fracture mechanics apparatus, designed to apply a known stress intensity, was employed to reveal the onset of subcritical crack growth. The final goal is to combine the typical fracture mechanics testing with the SVET and acoustic emissions. We report on the progress that has been made in designing a customized four-point bend, fracture mechanics device that allows for simultaneous loading and electrochemical mapping. Future work will report data gathered from in-situ electrochemical and acoustic emissions testing on pre-cracked AA5083 specimens. © The Electrochemical Society.

Policastro S.A.,Center for Corrosion Science and Engineering | Hangarter C.M.,EXCET INC. | Horton D.J.,Center for Corrosion Science and Engineering | Wollmershauser J.A.,U.S. Navy | Roeper D.F.,EXCET INC.
Journal of the Electrochemical Society | Year: 2016

The electrochemical behavior of oxides of three Ti-based binary alloys, Ti99Co1, Ti99Sn1, and Ti99Cr1, are investigated using electrochemical impedance spectroscopy, Mott-Schottky analysis and cyclic voltammetry. It is found that native amorphous TiO2 can be doped in order to change the oxide's electronic properties and thereby reduce oxygen reduction rates in an alkaline solution, with the greatest reduction seen for the Ti99Sn1 alloy. © 2016 The Electrochemical Society.

Williams K.,Center for Corrosion Science and Engineering | Bayles R.,Center for Corrosion Science and Engineering | Macdonald D.D.,University of California at Berkeley
Advanced Materials and Processes | Year: 2013

A unique horizontal fracture mechanics device was developed to examine AA5083 bend bars mechanically and electrochemically using a scanning vibrational probe to detect and characterize the coupling current flowing from the crack to external surface, where it is annihilated by a cathodic charge transfer reaction (e.g., hydrogen evolution or oxygen reduction). Hence, the coupling current from the crack was spatially resolved while the specimen was actively loaded. The notch is active during loading and becomes more passive toward the end of the experiment. With knowledge from previous fracture mechanics studies on wedge-opening-load samples, the onset of subcritical crack growth was verified with the aid of an extensometer or clip gauge. Together with results of studies now underway, crack growth mechanisms may be more fully understood with regard to different sensitized alloys that undergo stress corrosion cracking.

Policastro S.A.,U.S. Naval Academy | Auyeung R.C.Y.,U.S. Navy | Martin F.J.,Center for Corrosion Science and Engineering | Rayne R.J.,U.S. Navy | And 4 more authors.
Journal of the Electrochemical Society | Year: 2012

A novel experimental technique for making electrochemical measurements on individual phase or isolated regions of a metal or alloy is reported. The technique, called Selective Masking by Photolithography (SMP), uses a hardened photoresist coating to mask the excluded portions of the sample and 355 nm laser pulses are employed to expose individual grains or regions of interest. The size of the exposed area can range from tens of microns to millimeters. Localized electrochemical DC and AC measurements and critical pitting temperature determinations for the two phases in a duplex stainless steel were used to show the utility and viability of SMP. © 2011 The Electrochemical Society.

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