@article{chen_li_gigax_hunter_fensin_zikry_2024, title={How are microstructural defect interactions linked to simultaneous intergranular and transgranular fracture modes in polycrystalline systems?}, volume={188}, ISSN={["1873-4782"]}, url={https://doi.org/10.1016/j.jmps.2024.105674}, DOI={10.1016/j.jmps.2024.105674}, abstractNote={The major objective of this investigation is to fundamentally understand and predict how intergranular (IG) and transgranular (TG) fracture modes nucleate and propagate in f.c.c. polycrystalline systems due to defects, such as total and partial dislocation densities and grain boundary (GB) structures and misorientations. A dislocation density crystalline plasticity (DCP) formulation based on the evolution and interaction of total and partial dislocation densities was integrated with a recently developed fracture approach to investigate the fracture nucleation and propagation of simultaneous multiple fracture events, including both IG and TG fracture events. The aggregate grains and GB orientations and morphologies are based on EBSD measurements that are representative of polycrystalline copper aggregates with a broad range of random high angle and low angle GBs. The predictions indicate that dislocation density pileups induce IG fracture due to interrelated stress, slip, and total and partial dislocation density accumulations and interactions for both high angle GBs (HAGBs) and low angle GBs (LAGBs). TG fracture nucleation and propagation occurred due to normal stress accumulations, which exceeds the fracture stress, along cleavage planes. Furthermore, it is shown how IG cracks transition from the GB plane to the cleavage planes as cracks nucleate and propagate. Accumulated plastic zones due to different slip system activities can impede and blunt crack propagation and fronts. These plastic zones form due to high Lomer and Shockley partial dislocation densities. These predictions, which are consistent with experimental observations, provide a fundamental understanding of how simultaneous failure modes initiate and propagate for physically representative microstructures.}, journal={JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS}, author={Chen, Muh-Jang and Li, Nan and Gigax, Jonathan and Hunter, Abigail and Fensin, S. and Zikry, Mohammed A.}, year={2024}, month={Jul} }
 @article{arcari_zikry_callahan_horton_chen_2024, title={Modeling hydrogen diffusion in precipitation hardened nickel-based alloy 718 by microstructural modeling}, volume={6}, ISSN={["2191-0316"]}, DOI={10.1515/corrrev-2024-0013}, abstractNote={Abstract Environmentally assisted cracking can significantly affect the performance of high strength alloys and limit material selection to minimize the risk of subcritical crack growth in service. UNS N07718 is widely used in marine service applications and under a variety of conditions, such as: alternate immersion, different levels of cathodic protection, and freely corroding galvanic couples, because of its demonstrated corrosion and fracture resistance in these environments. In this work we developed a representative model of the material microstructure including the metal grains, the material texture, and the precipitates along the grain boundaries and within the grains. The microstructural model was subjected to the boundary conditions identified at the notch root of a fracture mechanics sample and the results are used as input for a simulation of hydrogen diffusion from the surface of the notch, assuming the material has been introduced to a hydrogen producing environment. The diffusion of hydrogen was modeled by Fick’s law and included both hydrostatic stress and mobile dislocation velocity as driving forces. The influence of immobile dislocations was also modeled to account for the irreversible trapping. The results show that hydrostatic stress and immobile dislocation trapping can significantly alter the highest concentration of hydrogen and its location within the microstructure towards the fracture process zone. Mobile dislocation velocity has a small influence in determining the hydrogen distribution near the fracture process zone.}, journal={CORROSION REVIEWS}, author={Arcari, Attilio and Zikry, Mohammed A. and Callahan, Patrick G. and Horton, Derek J. and Chen, Muh-Jang}, year={2024}, month={Jun} }
 @article{xie_chen_gigax_luscher_wang_hunter_fensin_zikry_li_2023, title={A fundamental understanding of how dislocation densities affect strain hardening behavior in copper single crystalline micropillars}, volume={184}, ISSN={["1872-7743"]}, DOI={10.1016/j.mechmat.2023.104731}, abstractNote={Under mechanical loading, the strain hardening behavior of crystalline face-centered cubic (FCC) metals is of critical importance in determining fracture behavior and overall mechanical performance. While strain hardening is typically accompanied by a decrease in ductility, it can also simultaneously enhance the material's resistance to plastic deformation and improve its load bearing capacity. Hence, we conducted a detailed study using copper (Cu) single-crystal micropillars as a model system to investigate and delineate the relationship between strain hardening and defect behavior. We employed in situ compression in a scanning electron microscope (SEM) and dislocation density-based crystal plasticity (DCP) modeling. The strain hardening rate varied with the compression crystallographic orientation, ranging from negligible values (of approximately 80 MPa) to relatively high hardening rates (of approximately 1150 MPa) for nominal strains of up to 15%. Various analysis methods were applied, including slip trace characterization, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission Kikuchi diffraction (TKD). These techniques allowed us to identify the distributions of active slip systems, dislocation structures after compression, and correlated internal lattice rotations. Furthermore, the DCP model was developed to specifically understand how serration events are related to dislocation-density evolution or strain bursts, and this was validated with the micropillar experiments. This integrated experimental and modeling investigation offers valuable insights and predictions regarding the evolution of both total and partial dislocations, including Hirth and Lomer junctions, as well as lattice rotations.}, journal={MECHANICS OF MATERIALS}, author={Xie, Dongyue and Chen, Muh-Jang and Gigax, Jonathan and Luscher, Darby and Wang, Jian and Hunter, Abigail and Fensin, Saryu and Zikry, Mohammed and Li, Nan}, year={2023}, month={Sep} }
 @article{chen_xie_li_zikry_2023, title={Dislocation-density evolution and pileups in bicrystalline systems}, volume={870}, ISSN={["1873-4936"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85149441852&partnerID=MN8TOARS}, DOI={10.1016/j.msea.2023.144812}, abstractNote={A dislocation-density crystalline plasticity (DCP) framework based on total and partial dislocation densities interactions was used to investigate the behavior of Cu/Pb bicrystals with a focus on GB effects. The modeling predictions were validated with bicrystal compression micropillar experiments. A key new aspect of the modeling approach is to account for partial dislocation-densities. A GB formulation that is directly linked to GB energies was used to monitor GB transmission and blockages, such that pileups can be monitored and predicted at the GB interfaces for misorientations. The predictions indicate that pileups can form due to fully and partially blocked slip-rates and perfect and partial dislocation-densities. As the nominal strain increases from five to fifteen percent, dislocation-densities and pileups significantly increase by almost an order of magnitude. The proposed validated approach provides a microstructural scale predictive framework that accounts for a myriad of defects related to the interactions of partial and perfect dislocation densities that interact at highly misoriented GBs; it is these interactions that are critical to the formation and evolution of dislocation-density pileups that can lead to physically limiting stress accumulations in bicrystals.}, journal={MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING}, author={Chen, Muh-Jang and Xie, Dongyue and Li, Nan and Zikry, Mohammed A.}, year={2023}, month={Apr} }
 @article{arcari_horton_chen_zikry_2023, title={Precipitate and dislocation-density interactions affecting strength and ductility in inconel alloys}, volume={8}, ISSN={["1573-4803"]}, url={https://doi.org/10.1007/s10853-023-08822-8}, DOI={10.1007/s10853-023-08822-8}, journal={JOURNAL OF MATERIALS SCIENCE}, author={Arcari, Attilio and Horton, Derek and Chen, Muh-Jang and Zikry, Mohammed A.}, year={2023}, month={Aug} }
 @article{phillips_chen_islam_ryu_zikry_2023, title={Predicting and Controlling Ribbing Instabilities of Carbon Nanotube-PDMS Thin-Film Systems for Multifunctional Applications}, volume={7}, ISSN={["1527-2648"]}, url={https://doi.org/10.1002/adem.202300582}, DOI={10.1002/adem.202300582}, abstractNote={The manufacturing of thin films with structured surfaces by large‐scale rolling has distinct advantages over other techniques, such as lithography, due to scalability. However, it is not well understood or quantified how processing conditions can affect the microstructure at different physical scales. Hence, the objective of this investigation is to develop a validated computational model of the symmetric forward‐roll coating process to understand, predict, and control the morphology of carbon nanotube (CNT)–polydimethylsiloxane (PDMS) pastes. The effects of the thin‐film rheological properties and the roller gap on the ribbing behavior are investigated and a ribbing instability prediction model is formulated from experimental measurements and computational predictions. The CNT–PDMS thin‐film system is modeled by a nonlinear implicit dynamic finite‐element method that accounts for ribbing instabilities, large displacements, rolling contact, and material viscoelasticity. Dynamic mechanical analysis is used to obtain the viscoelastic properties of the CNT–PDMS paste for various CNT weight distributions. Furthermore, a Morris sensitivity analysis is conducted to obtain insights on the dominant predicted characteristics pertaining to the ribbing microstructure. Based on the sensitivity analysis, a critical ribbing aspect ratio is identified for the CNT–PDMS system corresponding to a critical roller gap.}, journal={ADVANCED ENGINEERING MATERIALS}, publisher={Wiley}, author={Phillips, Matthew and Chen, Muh-Jang and Islam, Md Didarul and Ryu, Jong and Zikry, Mohammed}, year={2023}, month={Jul} }
 @article{islam_perera_black_phillips_chen_hodges_jackman_liu_kim_zikry_et al._2022, title={Template‐Free Scalable Fabrication of Linearly Periodic Microstructures by Controlling Ribbing Defects Phenomenon in Forward Roll Coating for Multifunctional Applications}, volume={9}, ISSN={2196-7350 2196-7350}, url={http://dx.doi.org/10.1002/admi.202201237}, DOI={10.1002/admi.202201237}, abstractNote={Abstract}, number={27}, journal={Advanced Materials Interfaces}, publisher={Wiley}, author={Islam, Md Didarul and Perera, Himendra and Black, Benjamin and Phillips, Matthew and Chen, Muh‐Jang and Hodges, Greyson and Jackman, Allyce and Liu, Yuxuan and Kim, Chang‐Jin and Zikry, Mohammed and et al.}, year={2022}, month={Aug}, pages={2201237} }
 @article{granger_chen_brenner_zikry_2022, title={The Challenges of Modeling Defect Behavior and Plasticity across Spatial and Temporal Scales: A Case Study of Metal Bilayer Impact}, volume={12}, ISSN={["2075-4701"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85144831580&partnerID=MN8TOARS}, DOI={10.3390/met12122036}, abstractNote={Atomistic molecular dynamics (MD) and a microstructural dislocation density-based crystalline plasticity (DCP) framework were used together across time scales varying from picoseconds to nanoseconds and length scales spanning from angstroms to micrometers to model a buried copper–nickel interface subjected to high strain rates. The nucleation and evolution of defects, such as dislocations and stacking faults, as well as large inelastic strain accumulations and wave-induced stress reflections were physically represented in both approaches. Both methods showed similar qualitative behavior, such as defects originating along the impactor edges, a dominance of Shockley partial dislocations, and non-continuous dislocation distributions across the buried interface. The favorable comparison between methods justifies assumptions used in both, to model phenomena, such as the nucleation and interactions of single defects and partials with reflected tensile waves, based on MD predictions, which are consistent with the evolution of perfect and partial dislocation densities as predicted by DCP. This substantiates how the nanoscale as modeled by MD is representative of microstructural behavior as modeled by DCP.}, number={12}, journal={METALS}, author={Granger, Leah and Chen, Muh-Jang and Brenner, Donald and Zikry, Mohammed}, year={2022}, month={Dec} }