EXPERIMENTAL STUDY OF THE HIGH VELOCITY EXPANSION AND FRAGMENTATION OF PMMA RINGS

The dynamic fracture and fragmentation of brittle solids under impact loading are important research subjects. However, the experimental study on the tensile fracture and fragmentation of brittle solids is relatively limited. A technique using liquid-driving expansion ring setup was developed for the dynamic tensile fracture and fragmentation testing of brittle materials. This technique was used to study the fragmentation properties of PMMA rings at different expansion velocities. From the observations of the fracture morphology and the residual internal cracks of the recovered fragments, it is concluded that the fracture of the rings is caused by the circumferential tensile stress. The unloading stress waves from the fracture points of the fragments inhibit the further development of other cracks close to the fracture points by unloading the tensile stress in the tension regions. The PMMA ring expansion process was captured using ultrahigh speed camera. The specimen surface expansion velocity was measured using laser interference device DISAR (displacement interferometer system for any reflector). The strain history and fracture strain of ring were captured using the strain gauge on the specimen. Preliminary experimental results conducted on PMMA rings show that: (1) In the range of tensile strain rate $150\mathrm{~}500s^{-1}$, the dynamic failure strain of PMMA is lower than that under the quasi-static tensile loading, which means that PMMA became brittle under higher strain rate loading; (2) Higher loading rates resulted in the more fragments and the smaller size of the PMMA rings; (3) The “non-dimensional fragment size vs. strain rate” data fall between the theoretical fragmentation predictions for ductile material and brittle material.