  We investigate the effect of thermal fluctuations on the critical stress and
the micro-structure of damage preceding macroscopic fracture of Lennard-Jones
solids under a constant external load. Based on molecular dynamics simulations
of notched specimens at finite temperature, we show that the crystalline
structure gets distorted ahead of the crack in the secondary creep regime. The
damage profile characterizing the spatial distribution of lattice distortions
is well described by an exponential form. The characteristic length of the
exponential form provides the scale of damage which is found to be an
increasing function of the temperature: At low temperature damage is strongly
localized to the crack tip, while at high temperature damage extends to a
broader range leading to more efficient relaxation of overloads. As a
consequence, the stress intensity factor decreases with increasing temperature.
The final macroscopic failure of the system occurs suddenly which is initiated
by the creation of vacancies and voids. The creep strength exhibits the inverse
square root scaling with the notch size corrected by the extension of the
process zone.
