Experimental and numerical investigation on the discrete fracture property and dynamic flexural response of aluminum nitride ceramics

Aluminum nitride (AlN) is a promising electronic material for high reliability electronic packaging structures. Quasi-static and dynamic flexural tests have been conducted on AlN to investigate its discrete fracture property and dynamic flexural response. AlN ceramics show complex discrete fracture properties, including stochastic fracture strength and failure modes, due to the randomly distributed pore defects in the bulk material. A novel inhomogeneous modelling technique coupled to Monte Carlo simulations was developed to describe the fracture behavior of AlN ceramics. The well comparable results between experimental observations and numerical simulations demonstrate that the proposed numerical technique can not only reproduce the stochastic strength of AlN, but also mimic the real failure modes under flexural loading. The dynamic bending tests were conducted based on the developed modified Split Hopkinson Pressure Bar (SHPB) device, which is validated through finite element numerical simulations. The highspeed photography technique and scanning electron microscopy (SEM) were utilized for fracture process recording and fractography analysis, identifying the flexural fracture mechanism of AlN under different loading conditions. The flexural strength of AlN demonstrates a nonnegligible positive correlation with loading speed. Post-mortem fractography studies show that the dominant fracture mechanism is intergranular fracture under quasi-static loading. However, both the intergranular and transgranular fracture mechanisms play a vital role in the dynamic failure process of AlN.