title: Microscopic Origin of Strain Hardening in Methane Hydrate.
abstract: It has been reported for a long time that methane hydrate presents strain hardening, whereas the strength of normal ice weakens with increasing strain after an ultimate strength. However, the microscopic origin of these differences is not known. Here, we investigated the mechanical characteristics of methane hydrate and normal ice by compressive deformation test using molecular dynamics simulations. It is shown that methane hydrate exhibits strain hardening only if the hydrate is confined to a certain finite cross-sectional area that is normal to the compression direction. For normal ice, it does not present strain hardening under the same conditions. We show that hydrate guest methane molecules exhibit no long-distance diffusion when confined to a finite-size area. They appear to serve as non-deformable units that prevent hydrate structure failure, and thus are responsible for the strain-hardening phenomenon.
authors.affiliation: Environment and Resource System Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Jihui
authors.initials: J
authors.lastname: Jia
authors.affiliation: Environment and Resource System Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Liang
authors.affiliation: International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Tsuji
authors.affiliation: Environment and Resource System Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Sumihiko
authors.initials: S
authors.lastname: Murata
authors.affiliation: Environment and Resource System Engineering, Kyoto University, Kyoto 615-8540, Japan.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Matsuoka