Issue 37

S. Vantadori et alii, Frattura ed Integrità Strutturale, 37 (2016) 215-220; DOI: 10.3221/IGF-ESIS.37.28 219 Specimens No. Elastic modulus E (MPa) Fracture toughness S IC K (MPa m 1/2 ) FA-1 13692.54 4.09 FA-2 14393.65 3.68 FP 14038.29 3.74 FM-1 14253.00 3.92 FM-2 13488.94 3.85 FL 14042.47 3.91 FP-long1 12371.99 2.14 FP-long2 12370.47 1.99 Table 1 : Elastic modulus and fracture toughness. (a) FA-1 FL (b) FP-long1 FP-long2 Figure 3 : Fracture: (a) Mixed Mode for transversal specimens FA-1 and FL; (b) pure Mode I for longitudinal specimens. C ONCLUSIONS n the present paper, the behaviour of a compact bone in terms of fracture toughness has been analysed. Fracture toughness has experimentally been evaluated through specimens obtained from the femur diaphysis of a bovine. The influence of local biaxial stress state on fracture behaviour has been analysed by employing two specimen types. As a matter of fact, when the osteons alignment is perpendicular to the loading direction (transversal specimens), the stress state is biaxial due to normal stresses produced by bending and shear stresses, at the cement line interface between osteons and interstitial lamellae. On the other hand, when the osteons alignment is parallel to the loading direction (longitudinal specimens), the stress state is uniaxial. Then fracture toughness values have been computed by a modified version of the Two-Parameter Model originally formulated for crack propagating under Mode I. Such a modified version is here proposed for Mixed Mode (Mode I and Mode II). The theoretical results obtained are compared with some data available in the literature, by highlighting that the value of the near-tip stress-intensity factor of a kinked crack can be considerably lower than that for a straight crack of the same length. R EFERENCES [1] An, H.Y., Draughn, R.A., Mechanical testing of bone and the bone-implant interface, CRC Press, Boca Raton, (2000). [2] Marks, S.C., Popoff, S.N., Bone cell biology: the regulation of development, structure, and function in the skeleton, Am. J. Anat., 183 (1988) 1-44. [3] Keaveny, T.M., Hayes, W.C., Mechanical properties of cortical and trabecular bone, CRC Press, Boca Raton, (1993). [4] Li, S., Abdel-Wahab, A., Silberschmidt, V.V., Analysis of fracture processes in cortical bone tissue, Eng. Frac. Mech., 110 (2013) 448-458. DOI: 10.1016/j.engfracmech.2012.11.020 [5] Jenq, Y., Shah, S., J., Two parameter fracture model for concrete, Eng. Mech., 111 (1985) 1227-1241. I