SIMULATION OF CRACK-PROPAGATION IN TABLET FILM COATINGS CONTAINING PIGMENTS

A model originally developed to simulate crack propagation in structural steel has been evaluated for tablet film coatings containing pigments. The fracture mechanism is assumed to consist of hole formation around the pigment particles, growth and coalescence. The program allows both the visualisation of crack growth and the calculation of crack velocity. Simulations to investigate the effect of stress intensity factor indicate that the critical stress intensity factor for sustained crack growth in hydroxypropyl methylcellulose is of the order of 0.3 MPa m1/2 consistent with experimental findings. Simulations to investigate the effect of the particle size of pigments indicate that the crack velocity is highest at small particle sizes but becomes independent of size above 1-2-mu-m. In general, agreement with experiment both qualitatively and quantitatively is extremely good.