We study the percolation aspects of diffusional “Coble” creep on heterogeneous grain boundary networks, assuming free grain boundary sliding. A novel percolation threshold is obtained for the honeycomb lattice when two representative types of grain boundaries are randomly distributed, $p_{\mathrm{cc}}=0.5416\pm 0.0036$. The creep viscosity diverges near the percolation threshold with power-law exponents $t=1.69\pm 0.09$ and $s=1.88\pm 0.12$, different from the standard conduction and rigidity percolation exponents. The moments of both the force and flux distributions all conform to finite-size scaling at $p_{\mathrm{cc}}$, but with new exponents. These new scaling behaviors seen in the creeping system are proposed to arise from the unique coupling of both force and flux balances in the network.

• Received 13 October 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.035701