Real-time visualization of dynamic fractures in porcine bones and the loading-rate effect on their fracture toughness

We visualized, in real time, the dynamic fracture behaviors in porcine cortical bone from humerus and porcine trabecular bone from nasal bone at a high loading rate using high-speed synchrotron X-ray phase-contrast imaging (PCI). Dynamic three-point bending loading was applied on notched bone specimens by a modified Kolsky compression bar and images of the entire fracture events were recorded with an ultra-high-speed camera. Experiments at a quasi-static loading rate on material testing system (MTS) were also performed to identify the loading-rate effects on the fracture toughness of the two types of bone. Three-dimensional synchrotron X-ray computed tomography was conducted to examine the initial microstructures in the bone specimens before mechanical loading. At the dynamic loading rate, the onset locations of crack initiation were found to be independent from the bone types. The deleterious effect of dynamic loading rate on bone's fracture toughness was verified in this study and the crack was found to propagate at higher speeds in cortical bone than in trabecular bone. In a comparison of the observed more torturous crack paths at the quasi-static loading rate, cracks in dynamically loaded bone specimens generally followed the paths with less in-plane deflections and out-of-plane twists. However, our experimental results also indicated that, although the extent was diminished at dynamic loading rate, the crack deflections at osteon cement lines still played a role as a major toughening mechanism to dynamic fractures in transversely orientated cortical bone.