Grain-size Induced Strengthening and Weakening of Dislocation-free Polycrystalline Gas Hydrates

Sediment-hosted gas hydrates have profound impacts on global energy sources and climate change. Their mechanical properties play a crucial role in gas recovery and understanding their evolution in nature, however, the deformation mechanisms of gas hydrates have not yet been elucidated owing to the difficulties in experimental measurements. Direct molecular dynamics simulations of the material instability of polycrystalline methane hydrates under mechanical loading have been carried out. The results show an unexpected ductile ultimate strength as a result of crossover from strengthening to weakening in polycrystals. The Hall-Petch type strengthening behavior arises from grain-junction mediated failure mechanism while the inverse Hall-Petch type weakening originates from grain boundary mediated deformation mechanism.