An experimental approach on fracture behavior of cortical bones

The transverse and longitudinal crack propagationbehaviors in bovine cortical bone were studied using stable crack growth andfatigue test methods. Twenty five Compact Tension (CT) specimens of corticalbone were prepared in specific directions. In stable crack growthexperiment, the ASTM standard is no longer applicable due to the geometry ofthe CT specimens and anisotropy of the materials. The relationship betweenthe stress intensity factor and crack length was established by means ofnumerical method. In order to identify the location of crack tip duringcrack propagation, Digital Image Correlation (DIC) method was used. As thecrack deflected largely when propagating in the transverse direction, thetransverse fracture toughness was analyzed with J integral. The results showthat the fracture toughness of cortical bone increases with crack extensionin a certain range, i.e. cortical bone exhibits rising resistance curve(R-curve). And the fracture toughness in the transverse direction is muchhigher than that in longitudinal direction, which indicates that the R-curveis anisotropic. The fatigue test shows that fatigue crack propagationbehavior in cortical bone is also anisotropic. Crack grow rate in thelongitudinal direction is greater than that in transverse direction. It isalso found that the fatigue crack growth rate decreases with the increase ofstress intensity factor range at the initial stage of crack extension.