Environmentally Assisted Cracking: Theory and Practice: Corrosion Fatigue and Cracking
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Tuesday 2:30 PM
March 21, 2023
Room: Sapphire 410B
Location: Hilton
Session Chair: Ting Zhu, Georgia Institute Of Technology; Xin Pang, Canmetmaterials, Natural Resources Canada
2:30 PM Invited
Multiscale Modeling of Fatigue Crack Growth and Environmental Effects: Ting Zhu1; 1Georgia Institute of Technology
Hydrogen embrittlement of metallic materials is widely observed, but remains a challenge for predictive computational modeling. This talk is focused on an ongoing effort toward the multiscale modeling of hydrogen-mediated fatigue crack growth in austenitic stainless steel. An interatomic potential of the Fe-Ni-Cr-H alloy system was developed to enable the atomistic simulations of hydrogen and dislocation interactions in stainless steel. A cyclic crystal plasticity model was formulated with guidance from the atomistic reaction pathway modeling of dislocation mobility. Our crystal plasticity finite element simulations revealed the effect of grain-level plastic deformation on fatigue crack growth. Further challenges and opportunities on predictive multiscale modeling of hydrogen embrittlement will be discussed.
3:00 PM
Atomic Mechanism of Near Threshold Fatigue Crack Growth in Vacuum as a Basis for Understanding Environmental Effects: Derek Warner1; Mingjie Zhao1; Wenjia Gu1; 1Cornell University
In many technologically relevant regimes, the process by which cracks grow remains unknown. A prime example is near-threshold fatigue crack growth in vacuum environments, which constitutes the foundation from which environmental effects can be understood. Here, I will report on atomistic simulations to cycle counts far beyond those analyzed previously by harnessing contemporary computational resources and a parallel implementation of the CADD concurrent multiscale approach. Our simulations show that fatigue crack growth arrests after an initial transient period, reconciling the standing discrepancy between model and experiment. We will then examine hypothesized mechanisms for near threshold fatigue crack growth in vacuum. Finding sustained crack growth to only occur when edge dislocations return to the crack tip on a slip plane behind the one on which they were emitted. This process transfers material away from the crack tip, supporting a long-ago hypothesized necessity for near threshold fatigue crack growth in vacuum.
3:20 PM
Measuring Crack Tip pH to Elucidate Corrosion Fatigue Susceptibility Differences between Al-Cu-Mg and Al-Zn-Mg-Cu Alloys: Gabby Montiel1; Jenifer Locke1; 1The Ohio State University
2xxx series (Al-Cu) and 7xxx series (Al-Zn) Al alloys are age-hardenable and widely used in aerospace industry. However, 7xxx alloys are more susceptible to corrosion fatigue (CF) in aqueous chloride environments. Literature establishes that the crack growth rate (da/dN) of 7xxx Al alloys is constant with decreasing fatigue loading frequency (f) at f below about 10 Hz, while 2xxx Al alloys have a decreasing da/dN with decreasing f in this same f range. Additionally, 7xxx Al alloys exhibit higher da/dN in aqueous chloride solutions than lab air, while the inverse is true for 2xxx Al alloys at f below approximately 1 Hz. This work aims to quantify CF crack growth rates as a function of f, while measuring crack tip pH in alloys with varying copper and zinc content to better understand the role of corroding Al-Cu-X secondary phase particles play in crack tip electrochemistry and CF behavior.
3:40 PM
Advancing the Understanding of the Impact of Atmospheric Environments on Corrosion Fatigue Crack Growth Rates of AA7085-T7451: Jenifer Locke1; Brandon Free1; Mary Cefaratti1; Sarah Dorman1; 1Ohio State University
This work aims to understand if conventional laboratory environment assisted cracking test environments of full immersion in aqueous solutions and lab air can properly estimate corrosion fatigue (CF) performance in atmospheric environments. To do this, constant ΔK, constant R, and varied fatigue loading frequency testing was performed on AA7085-T7451 with NaCl particles printed on the sample surface all while controlling RH and T levels to mimic aerospace environments. Testing measuring crack growth rate (da/dN) shows that for salt deposition levels between 50 and 300 μ/cm2, da/dN are similar to that measured in 0.06M NaCl. Interestingly, da/dN in the atmospheric environment is higher than that measured under full immersion in a solution of identical chemistry. Testing is ongoing between -40 and 25C to investigate the effect of T.
4:00 PM Break
4:20 PM
A Meshless Peridynamics Framework for Physics-based Modeling of Corrosion Crack Dynamics and Fracture: Srujan Rokkam1; Masoud Behzadinasab1; Max Gunzburger2; Sachin Shanbhag2; Nam Phan3; 1Advanced Cooling Technologies, Inc.; 2Florida State University; 3Naval Air Systems Command
Environmental assisted corrosion cracking is a major cause for structural damage in many engineering applications. In this work, we discuss a Peridynamic (PD) approach for physics-based modeling of corrosion damage phenomena which can be applied to model crack growth and failure due to either stress corrosion cracking (SCC) or corrosion fatigue (CF). PD approach is a reformulation of classical computational mechanics that enables modeling of crack growth problem without the need to re-mesh the domain. The presentation will focus on two aspects: (i) how multiphysics aspects of corrosion damage can be modeled using nonlocal PD approach, (ii) demonstration of corrosion crack dynamics in surrogate aluminum alloys. The developed framework is able to capture ductile damage behavior as well crack path dynamics without the drawbacks of conventional theories. This work was funded by U.S. Navy/NAVAIR STTR contract N68335-15C-0032, awarded to Advanced Cooling Technologies, Inc. The simulations used NSF-XSEDE allocation grants DMR180017.
4:40 PM
Modelling Environmentally Assisted Cracking (EAC) in Ni-based Superalloys: Sakina Rehman; 1
Ni-based turbine discs form a surface oxide layer when exposed to high temperatures and corrosive reagents. Growth of the oxide layer results in a γ´ precipitate depleted region at the oxide-matrix interface due to preferential transport of oxide-forming elements to the growing surface oxide. A mean-field model has been developed to predict the γ´ precipitate depletion zone in RR1000. Initial particle size distributions are divided into a series of discrete size classes, corresponding to the equilibrium phase fraction of γ´. A multicomponent diffusion driven growth-rate law is formulated to determine the dissolution rate of each discrete particle size class. The model is validated and agrees well with experimental depletion zone data. It is found that the γ` precipitates dissolve faster at the surface, and the rate of dissolution increases as the temperature approaches the solvus temperature. Increasing the solute concentration lead to a decreased dissolution rate of γ´ precipitates.