Temperature and rate dependent debonding behaviors of precision glass molding interface

The glass-to-mold adhesion in precision glass molding could severely degrade the quality of molded optics and shorten the lifespan of the precious molds. Since the consequences of adhesion take effect during the separation between glass and molds, it is important to investigate the debonding behaviors of a typical glass molding interface. To this end, here we perform a probe tack test procedure for borosilicate glass BK7, where debonding is conducted at molding temperature and specific velocity. We fully characterize the debonding behaviors using the peak adhesion stress σ_max and the work of debonding W_deb. Experiments show that when temperature is decreased from 690°C to 655°C at 10 μm/s, σ_max continuously increases, while W_deb first increases but then sharply decreases. When the debonding velocity is increased from 10 to 50 μm/s at 680°C, σ_max also increases while W_deb overall decreases. Therefore, the debonding behaviors are highly temperature and rate dependent. More importantly, depending on the debonding conditions, three debonding types are identified, that is, the cohesive bulk deformation, the cohesive-interfacial transition and the interfacial fracture. The cohesive type can be converted into the interfacial fracture, by either decreasing temperature or increasing the debonding velocity. Based on the W_deb criterion, the three debonding regimes can be clearly distinguished. Finally, analyses on the temperature and velocity experimental results are unified by incorporating the reduced crack velocity a_Tv_c. The dependences of both viscoelasticity and W_deb on a_Tv_c qualitatively explain the transition condition for different debonding types. Concerning these findings, the work of debonding not only supplements the characterization of adhesion strength, but also throws insightful light on revealing the debonding mechanisms.