Abstract: Because of its good optical properties and exceptional compressive strength, lightweight borosilicate glass has been increasingly used in transparent armor applications. Due to its brittle nature, glass fails differently from ductile materials in the sense that fragmentation occurs instantly upon impact penetration ahead of the projectile tip. Therefore, the penetration resistance of glass armor typically is measured by the effective residual strength of predamaged glass under compression loading, which primarily is sustained by the interactions and accommodations of various-sized glass fragments in the comminuted zones under confinement from the surrounding intact body. As a result, a mechanistic description of this damage evolution process is needed to develop a predictive model for simulating glass strength for transparent armor applications. In the present study, a discrete element-based modeling framework has been established to understand and predict the transient compressive fragmentation and comminution failure processes within the confined borosilicate glass by explicitly resolving the experimentally observed dynamic initiation and propagation of local instabilities. The predicted results are found to aptly capture the most essential characteristic loading behaviors of the damaged glass, for which the effects of crucial material properties also were numerically evaluated.