**2. Model Creation and Validation**

Particle flow code in two dimensions (PFC2D), a program based on DEM, is used to model soda-lime glass and random distributions of circular particles are adopted to achieve an isotropic material. The particle contact behaviors of the model are expressed by flat-joint bonds, which is detailed in the authors' previous work [1]. The interactions and movements of the circular particles can be simulated by PFC2D. It allows finite displacement and rotations of discrete bodies, including complete detachment, and recognizes new contacts automatically as the calculation progresses.
