Issue 37

S. Vantadori et alii, Frattura ed Integrità Strutturale, 37 (2016) 215-220; DOI: 10.3221/IGF-ESIS.37.28 215 Focussed on Multiaxial Fatigue and Fracture Two-parameter fracture model for cortical bone Sabrina Vantadori, Andrea Carpinteri, Giovanni Fortese, Camilla Ronchei, Daniela Scorza University of Parma, Dept. of Civil-Environmental Engineering and Architecture, Parco Area delle Scienze 181/a, 43124 Parma – Italy sabrina.vantadori@unipr.it , http://orcid.org/0000-0002-1904-9301 Filippo Berto University of Padua, Dept. of Management and Engineering, Stradella San Nicola 3, 36100, Vicenza - Italy NTNU, Department of Engineering Design and Materials, Richard Birkelands vei 2b, 7491, Trondheim – Norway A BSTRACT . The analysis of the bone fracture behaviour is fundamental for prevention, diagnosis and treatment of traumas. In the present paper, an experimental analysis of the fracture behaviour of a bovine femoral cortical bone is carried out, where specimens are extracted from a diaphysis. Fracture toughness is computed by employing a two-parameter fracture model originally proposed for concrete. In order to take into account the possibility of crack deflection (kinked crack) due to osteons orientation, a modified version of such a model is here discussed. The fracture toughness results are then compared with those reported in the literature, related to a femur of an 18-month-old bovine. K EYWORDS . Cortical Bone; Fracture Toughness; Quasi-brittle Material; Two-parameter Model. I NTRODUCTION one is a specialised tissue which has both metabolic and mechanical functions [1-3]. The load-bearing capacity of bone is limited up to a certain extent, beyond which it fails [4]. The analysis of the fracture behaviour of bone is fundamental for prevention, diagnosis and treatment of traumas. Basic parameters which represent the structure and functions of bone have to be measured, such as its fracture toughness. In the present paper, an experimental analysis of the fracture behaviour of a bovine femoral cortical bone is carried out, where specimens are extracted from a diaphysis. The experimental campaign is conducted to determine the fracture toughness, by employing a two-parameter fracture model originally proposed for concrete [5], that is, for a quasi-brittle material showing a nonlinear slow crack growth before the peak load is reached. In bones, such a behaviour is produced by the mechanism of extrinsic toughening categorised in four classes [6]: (i) constrained microcracking; (ii) crack deflection and twist; (iii) uncracked-ligament bridging; (iv) collagen-fibril bridging. Such a two-parameter fracture method is based on experimental data obtained from three-point bending tests on single edge-notched specimens, and employs linear elastic fracture mechanics Mode I expressions. However, for the bone material, it cannot be applied in its original formulation since the crack starting from notch may deflect. In order to understand the cause of such a deflection under Mode I loading (three-point bending), the bone microstructure level has to be briefly examined [7,8]. In cortical bone, it is represented by osteons (Fig. 1). The osteons B

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