Stress-Induced Melting Controlled Failure Mechanisms of Methane Hydrate.

Methane hydrate, a kind of nonstoichiometric crystalline, attracted worldwide attentions as a promising substitute energy. Its Dissociation is thought to be dominated by thermodynamic conditions, yet its intrinsic deformation behavior remains elusive, notably at the nanoscale. Here, substantial regional melting is found during nanoindentation on methane hydrate, supported by both molecular-scale dynamic simulations and mesoscale low-field nuclear magnetic resonance signals, revealing previously unknown failure mechanisms of methane hydrate. Stress-induced regional melting is also identified to form a short, dumb, and multivariant "least resistance path" for the nanoindentation tip to penetrate into methane hydrate, distinct from hexagonal ice. Results confine the elastic modulus of methane hydrate to 9.8 ± 0.6 GPa, similar in orders of magnitude to hexagonal ice (12.8 ± 1.0 GPa) under 173.15 K. However, its hardness is 261.4 ± 24 MPa, nearly half that of hexagonal ice (526.6 ± 62 MPa). The discovery challenges the prevailing wisdom that elastic modulus reliably predicts hydrogen-bonding phase-reversible crystals, and asserts that hexagonal ice is a poor proxy for methane hydrate, at least from the mechanical perspective. The findings also enlighten new clues to model the stability of ice-contained methane hydrate settings in high-latitude hydrate provinces, along with palaeo-methane-release capacity during glaciation-to-interglaciation transitions.