准脆性单晶材料动态压痕试验研究

The micro-nanoindentation techniques can be used to determine the mechanical properties of small-sized samples that are hard to fabricate. The mechanical properties and failure mechanisms of quasi-brittle energetic single crystals have significant effect on their chemical and safety performance. The mechanical properties obtained by the quasi-static nanoindentation tests for brittle energetic single crystals cannot be directly used in the dynamic loading process. The dynamic and quasi-static microscopic failure mechanisms for RDX explosive crystals are very different. Till now, no dynamic indentation tests have been used in energetic materials. A dynamic indentation testing device consisting of a titanium alloy pressure bar and a Vickers diamond indenter is designed. A momentum trap is introduced to avoid multiple loading due to a single pressure bar. This device can deliver an indentation load with the pulse width of 80 μs and is then used to investigate the dynamic damage response of quasi-brittle single crystal materials such as sugar and RDX crystals. Comparative experiments between single indentation loading and multiple indentation loading are carried out for sugar crystals, and thus the deformation and damage model under indentation load is discussed. The dynamic hardness of sugar crystal is approximately 5.18 MPa. The RDX single crystal is very prone to fracture and fragment under indentation loading, and its dynamic hardness is 1.304 MPa. Compared with the RDX crystal, the plastic deformation ability of single sugar crystal is better. Radial and circumferential cracks of the indentation pit are observed using optical microscope. The crack growth mode of quasi-brittle crystal under dynamic indentation load is presented. For brittle materials, the generation of cracks is always accompanied with fragmentation. The dynamic indentation testing device used in the present study can expand the dynamic performance of more materials, in-depth understanding of the causes of cracks and propagation process.