Emergence of crack tip plasticity in semi-brittle -Fe

Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*

Journal of Applied Physics, 135(7), p.075102_1 - 075102_7, 2024/02

https://doi.org/10.1063/5.0178940

Fracture of body centred cubic (bcc) metals and alloys below the ductile-to-brittle transition temperature is brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plasticdeformation; hence, brittle fracture is chosen over plastic deformation. Although this view is true from a macroscopic point of view, such brittle fracture is always accompanied by small-scale plastic deformation in the vicinity of the crack tip, i.e. crack tip plasticity. This short paper investigates the origin of this plasticity using atomistic modeling with a recently developed machine-learning interatomic potential of -Fe. The computational results identified the precursor of crack tip plasticity, i.e. the group of activated atoms dynamically nucleated by fast crack propagation.

Hierarchical aggregation in a complex fluid; The Role of isomeric interconversion

Massey, D.*; Williams, C. D.*; Mu, J.*; Masters, A. J.*; Motokawa, Ryuhei; Aoyagi, Noboru; Ueda, Yuki; Antonio, M. R.*

Journal of Physical Chemistry B, 127(9), p.2052 - 2065, 2023/03

https://doi.org/10.1021/acs.jpcb.2c07527

Interaction between an edge dislocation and faceted voids in body-centered cubic Fe

Yabuuchi, Kiyohiro*; Suzudo, Tomoaki

Journal of Nuclear Materials, 574, p.154161_1 - 154161_6, 2023/02

https://doi.org/10.1016/j.jnucmat.2022.154161

In nuclear materials, irradiation defects cause degradation of mechanical properties. In these materials, the relationship between dislocations and voids is particularly important for mechanical strength. Although only spherical voids have been studied in the past, this study focuses on faceted voids, which are observed simultaneously with spherical voids. In the current study, molecular dynamics was used to analyze the effect of faceted voids in the irradiation hardening of pure iron. Specifically, we clarified the difference in obstacle strength and interaction processes between spherical voids and faceted voids, and that even faceted voids show differences in interaction depending on their crystallographic arrangement with dislocations.

Molecular dynamics simulation to elucidate effects of spatial geometry on interactions between an edge dislocation and rigid, impenetrable precipitate in Cu

Tsugawa, Kiyoto*; Hayakawa, Sho*; Okita, Taira*; Aichi, Masaatsu*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Computational Materials Science, 215, p.111806_1 - 111806_8, 2022/12

https://doi.org/10.1016/j.commatsci.2022.111806

Cleavages along {110} in bcc iron emit dislocations from the curved crack fronts

Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*

Scientific Reports (Internet), 12, p.19701_1 - 19701_10, 2022/11

https://doi.org/10.1038/s41598-022-24357-5

Body-centered-cubic (bcc) transition metals, such as -Fe and W, cleave along the {100} plane, even though the surface energy is the lowest along the {110} plane. To unravel the mechanism of this odd response, large-scale atomistic simulations of curved cleavage cracks of -Fe were conducted in association with stress intensity factor analyses of straight crack fronts using an interatomic potential created by an artificial neural network technique. The study provides novel findings: Dislocations are emitted from the crack fronts along the {110} cleavage plane, and this phenomenon explains why the {100} plane can be the cleavage plane. However, the simple straight crack-front analyses did not yield the same conclusion. It is suggested that atomistic modeling, at sufficiently large scales to capture the inherent complexities of materials using highly accurate potentials, is necessary to correctly predict the mechanical strength. The method adopted in this study is generally applicable to the cleavage problem of bcc transition metals and alloys.

Machine learning molecular dynamics simulations toward exploration of high-temperature properties of nuclear fuel materials; Case study of thorium dioxide

Kobayashi, Keita; Okumura, Masahiko; Nakamura, Hiroki; Itakura, Mitsuhiro; Machida, Masahiko; Cooper, M. W. D.*

Scientific Reports (Internet), 12(1), p.9808_1 - 9808_11, 2022/06

https://doi.org/10.1038/s41598-022-13869-9

no abstracts in English

TEM observation and MD simulation of frank partial dislocation climbing in Al-Cu alloy

Chen, J.*; Yoshida, Kenta*; Suzudo, Tomoaki; Shimada, Yusuke*; Inoue, Koji*; Konno, Toyohiko*; Nagai, Yasuyoshi*

Materials Transactions, 63(4), p.468 - 474, 2022/04

https://doi.org/10.2320/matertrans.MT-M2021233

In situ electron irradiation using high-resolution transmission electron microscopy (HRTEM) was performed to visualize the Frank loop evolution in aluminium-copper (Al-Cu) alloy with an atomic-scale spatial resolution of 0.12 nm. The HRTEM observation along the [110] direction of the FCC-Al lattice, Frank partial dislocation bounding an intrinsic stacking fault exhibited an asymmetrical climb along the 112 direction opposed to those in the reference pure Al under an electron irradiation, with a corresponding displacement-per-atom rate of 0.055-0.120 dpa/s. The asymmetrical climb of the partial dislocation was described as pinning effects due to Cu-Cu bonding in Guinier-Preston zones by a molecular dynamics simulation.

Self-learning hybrid Monte Carlo method for isothermal-isobaric ensemble; Application to liquid silica

Kobayashi, Keita; Nagai, Yuki; Itakura, Mitsuhiro; Shiga, Motoyuki

Journal of Chemical Physics, 155(3), p.034106_1 - 034106_9, 2021/07

https://doi.org/10.1063/5.0055341

no abstracts in English

Brittle-fracture simulations of curved cleavage cracks in -iron; A Molecular dynamics study

Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito

AIP Advances (Internet), 10(11), p.115209_1 - 115209_8, 2020/11

https://doi.org/10.1063/5.0026659

The mechanism of their brittle fracture of BCC metals is not fully understood. In this study, we conduct a series of three-dimensional molecular dynamics simulations of cleavage fracture of -iron. In particular, we focus on mode-I loading starting from curved crack fronts. In the simulations, brittle fractures are observed at cleavages on the {100} plane, while the initial cracks become blunted on other planes as a result of dislocation emissions. Our modeling results agreed with a common experimental observation, that is, {100} is the preferential cleavage plane in bcc transition metals.

Dynamic observation and theoretical analysis of initial O molecule adsorption on polar and -plane surfaces of GaN

Sumiya, Masatomo*; Sumita, Masato*; Asai, Yuya*; Tamura, Ryo*; Uedono, Akira*; Yoshigoe, Akitaka

Journal of Physical Chemistry C, 124(46), p.25282 - 25290, 2020/11

https://doi.org/10.1021/acs.jpcc.0c07151

The initial oxidation of different GaN surfaces [the polar Ga-face (+c) and N-face (-c) and the nonpolar (100) ()plane] under O molecular beam irradiation was studied by real-time synchrotron radiation X-ray photoelectron spectroscopy and DFT molecular dynamics calculation. The results predict that triplet O either dissociates or chemisorbs at the bridge position on the +c-surface, while on N-terminated -c-surface the O2 molecule only undergoes dissociative chemisorption. On the -GaN surface, although the dissociation of O is dominant, the bond length and angle were found to fluctuate from those of O molecules adsorbed on the polar surfaces. The computational model including both the surface spin and polarity of GaN is useful for understanding the interface between GaN and oxide layers in metal-oxide electronic.