A beam network model is used to study the nucleation and propagation of cracks in uniaxially loaded materials consisting of randomly cross-linked fibers with statistically distributed failure thresholds. The failure behavior of such materials
is investigated and, for different degrees of disorder, the fraction of cross links required to achieve an optimal strength-to-weight ratio is determined. In the absence of disorder, this problem has a trivial analytical solution (no cross links), which however turns out the worst possible arrangement for strongly disordered materials and/or for large system sizes.