Mechanical behaviour of a hot pressed aluminum nitride under uniaxial compression

Failure strength of a hot pressed aluminum nitride (AlN) is measured as a function of strain rate under uniaxial compression. At low strain rates (10(-6) 10(-2) s(-1)), the material is found to exhibit a weak strain rate sensitivity and at higher strain rates (10(2) 10(3) s(-1)), a strongly strain rate sensitive behaviour is observed. The quasi-static failure strength is found to be around 2.81 GPa and it increases to 5.25 GPa at a strain rate of 2200 s(-1). During high strain rate testing, the specimen fractured into columnar fragments by axial splitting. Microscopic examination of the fractured surfaces revealed a typical brittle fracture with a combination of inter and intragranular failure modes. Based on the experimental results and microscopic observations, a micromechanical model has been developed to predict the constitutive behaviour of these ceramics under uniaxial compression. The model predictions of failure strength are shown to to be in agreement with the experimental observations. (C) 1998 Chapman & Hall.