Dynamic breakage of porous hexagonal boron nitride ceramics subjected to impact loading

Abstract

Based on the Split Hopkinson Pressure Bar (SHPB) device, a series of experiments have been conducted to reveal the intrinsic mechanism of dynamic breakage for hexagonal boron nitride ceramics (HBNC) under impact loading at strain rates ranging from 400 s−1 to 1000 s−1. Firstly, high speed camera and the digital image correlation (DIC) method are employed to trace the strain field on specimen surface. Evolution of number density of strain amplitude is found to obey the bimodal (two-peak) Weibull distribution. The first peak (peak 1) and the second peak (peak 2) owe respectively to deformations of the matrix part and the failure part of specimen. Secondly, by using the 4-units HgCdTe infrared detector, the in-situ instantaneous temperatures elevating at three positions on specimen surface are measured. Contributions of two main mechanisms, e.g. the plastic work and the macro fracture energy, to the elevated temperature are distinguished when taking the temperature profiles of strain rate 400 s−1 as reference. Relations of peak 2 to the elevated temperatures induced by the macro fractures (TIF) are then established and analyzed in details. The TIFs show linear relationship to 1/R, where R denotes the characteristic fragment size. The results should be helpful for temperature controlling in powder grinding and medical pill refining.