A simple, phenomenological model is presented for crack extension in a double cantilevered beam model. It invokes a continuum description of the beam per se, but postulates a discrete spring mechanism (which bonds the two halves to the beam) to provide a model of local failure. This in turn allows the prediction of global failure. Solutions to the mathematical model are obtained by the Rayleigh-Ritz method. Several interesting physical phenomena, which have been observed by previous investigators in wholly discrete models, are also predicted by the present model. These include lattice trapping, rapid fracture, and spontaneous bond healing.