A critical analysis of fracture toughness determination methods in glass or glass-ceramic matrix composites

The production of glass or glass-ceramic matrix composites is a promising method to obtain, from a brittle and flaw sensitive material, significant fracture toughness improvements. Fracture propagation in glass is modified by the presence of a secondary phase, which could be ceramic or metallic, particulate or fibrous. Fracture toughness becomes the fundamental property to be investigated, and an exact determination method is needed. In this work several determination methods are briefly explained, particularly relating to glass matrix composites. Chevron notch beam flexural method appears to be the most accurate and flexible, but experimental conditions are complex. Direct indentation methods appear useful for particulate reinforced glasses, but need a calibration step. Flexural tests on indented specimens appear to be promising, in spite of calibration need, as experimental apparatus is simple and indent-induced cracks are undoubtedly sharp, thus approximating the actual flaws in glasses.