Dynamic compaction induced heterogeneity in boron carbide powder

To investigate the impact-induced heterogeneous responses caused by particle rotation and slip in the process of powder compaction, dynamic compression experiments of Boron carbide powders with two packing densities (i. e. 1.22 and 1.11 g/cm3) are conducted by the mini-split Hopkinson pressure bar (mini SHPB) device combining with the simultaneous and in-situ X-ray imaging system. The compaction front, characterized as the impact -induced heterogeneous deformation, is observed and analyzed by the digital image correlation (DIC) method based on the images recorded by the simultaneous X-ray imaging system. The distribution of the contrast ratio of X-ray images is applied to demonstrate the propagation of compaction, and it shows a clear compaction front. The mean rotation degree and the shearing resistance at the compaction band are discussed in detail to describe the particle state during compaction. The results illustrate a relatively stable compaction process in denser sample A and an unstable one in looser sample B, which account for the abnormal evolutions of compaction density and porosity when comparing these two samples. A relaxation-diffusion model is then obtained based on the equivalent shear strain activation mechanism to describe the forming of the compaction front. The shearing diffusion resistance, a generalized driving force for compaction front shifting, is introduced to investigate par-ticles' movement at the compaction front, which is more powerful for describing the compaction degree of powder. The results might help improve contact extent and sintering of powders.