  We study the transverse cracking of the 90 degree ply in [0/90] cross-ply
laminates by means of a discrete element method. To model the 90 degree ply a
two-dimensional triangular lattice of springs is constructed where nodes of the
lattice model fibers, and springs with random breaking thresholds represent the
disordered matrix material in between. The spring-lattice is coupled by
interface springs to two rigid bars which represent the two 0 degree plies in
the model, which could be sublaminate as well. Molecular dynamics simulation is
used to follow the time evolution of the model system. It was found that under
gradual loading of the specimen, after some distributed cracking, segmentation
cracks occur in the 90 degree ply which then develop into a saturated state
where the ply cannot support additional load. The stress distribution between
two neighboring segmentation cracks was determined, furthermore, the dependence
of the microstructure of damage on the ply's thickness was also studied. To
give a quantitative characterization of stiffness degradation, the Young
modulus of the system is monitored as a function of the density of segmentation
cracks. The results of the simulations are in satisfactory agreement with
experimental findings and with the results of analytic calculations.
