Dynamic Fracture Toughnesses of Reaction‐Bonded Silicon Nitride

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Abstract
Dynamic fracture toughness specimens consisting of 5.1‐mm thick, modified wedge‐loaded, tapered double‐cantilever‐beam (WL‐MTDCB) specimens, which are side‐grooved on one side, were used to establish the room‐temperature dynamic fracture toughness, K ID vs crack velocity, a , relations of two reaction‐bonded silicon nitrides. The measured dynamic crack extension histories were then used to drive a dynamic finite‐element code in its generation mode which computes the dynamic stress intensity factors for a given crack extension. Results indicate that the K ID vs a relations of reaction‐bonded silicon nitrides do not follow the general trend in those relations of brittle polymer and steel. The slow initial crack velocity which was reported for glass was observed again in silicon nitride and resulted in a nonunique K ID vs a relation, in contrast to the unique K ID vs a material properties reported for brittle polymers and metals.

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