Impact of characteristic length and loading rate upon dynamic constitutive behavior and fracture process in alumina ceramics

Understanding the impact performance of ceramic materials requires accurate corresponding relationship be-tween mechanical response and fracture behavior. In this study, constitutive behaviors of alumina ceramics were successfully determined via split-Hopkinson pressure bar (SHPB) system coupled with high-speed camera to track the deformation and failure process. Failure strength of alumina demonstrated a strong dependency on strain rate beyond a critical value (namely transition strain rate). Inelastic deformation in the dynamic stress-strain curves implied that degradation of modulus does occur. The incorporating such degradation (damage evolution) in modulus enabled a more accurate evaluation of transition strain rate as a function of characteristic length of specimen. On-line observation revealed that longitudinal cracks dominated the failure process of alumina with negligible interfacial friction. However, interfacial friction became significant with the decreased characteristic length, thus the inclined cracks dominated fracture in alumina. It was found that the effect of interfacial friction can be minimized by lowering the impact velocity to maintain the uniaxial loading status in SHPB loads. Finally, it is suggested that an aspect ratio of 1.0 for the specimen should be suitable for alumina due to its insensitivity to interfacial friction within the achievable strain rate.

Automated summary

Understanding the relationship between mechanical response and fracture behavior is crucial for evaluating the impact performance of ceramic materials. In this study, the constitutive behaviors of alumina ceramics were determined using the split-Hopkinson pressure bar (SHPB) system and high-speed camera. It was found that the failure strength of alumina is highly dependent on the strain rate, particularly beyond a critical value. Incorporating the degradation of modulus in the evaluation enabled more accurate determination of the transition strain rate.