Phase field fracture models to predict crack initiation and propagation in anti-reflective coatings

The performance of optical coating systems are frequently limited by the formation of defects and cracks, hence deteriorating the optical properties, film integrity and durability. Typical anti-reflective coating systems consist of inorganic low index and high index thin oxide films (e.g., SiO2 and ZrO2) on polymeric substrates that can be subjected to complex strain states induced by environmental effects such as thermal excursions or even by the manufacturing process. Any crack in the multi-layer stack is likely to be problematic in terms of optical performance and visual comfort for the wearer and also in terms of the mechanical durability of the stack. To overcome this limitation, the development of predictive tools is essential to improve the design of coatings systems while complementing experimental analyses. Thus, in this work, we performed numerical simulations by means of phase field fracture models relying on the finite element method and the energy minimization principle. Specifically, we developed and implemented a modelling strategy that can be applied as a readily usable dimensioning tool with a potential to optimize and predict the mechanical behaviour of optical coating systems upon crack initiation and propagation.