  This article reports results concerning the fracture of a 2d triangular
lattice of atoms linked by springs. The lattice is submitted to controlled
strain tests and the influence of both porosity and temperature on failure is
investigated. The porosity is found on one hand to decrease the stiffness of
the material but on the other hand it increases the deformation sustained prior
to failure. Temperature is shown to control the ductility due to the presence
of cavities that grow and merge. The rough surfaces resulting from the
propagation of the crack exhibit self-affine properties with a roughness
exponent $\zeta = 0.59 \pm 0.07$ over a range of length scales which increases
with temperature. Large cavities also have rough walls which are found to be
fractal with a dimension, $D$, which evolves with the distance from the crack
tip. For large distances, $D$ is found to be close to 1.5, and close to 1.0 for
cavities just before their coalescence with the main crack.
