A simple tractable model based on a thermomechanical approach of nodule ejection is developed. Our main purpose is to investigate the nodule critically according to the depth of the seed inside of the coating, in order to understand why the deepest nodules located close to the substrate interface are the most critical. A summary of the experimental results concerning the behavior of irradiated nodules is achieved. Then, the model is checked thanks to experimental data. A critical location of the nodules close to the top surface of the coating is found. A supplemental ingredient is added to understand why the nodules close to the substrate interface are critical.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.