Fracture Mechanisms of Bone: A Comparative Study between Antler and Bovine Femur
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Fracture Mechanisms of Bone: A Comparative Study between Antler and Bovine Femur P.Y. Chen1, F.A. Sheppard2, J.M. Curiel2, and J. McKittrick1,2 1 Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093-0418, U.S.A. 2 Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A.
ABSTRACT In this study, fracture toughness of North American elk (Cervus elaphus canadensis) antler and bovine femur were measured using four-point bending tests on single-edge notched compact samples (ASTM C1421). Tests were conducted on crack growth directions longitudinal and transverse to the long axis of antler and bone in both dry and hydrated conditions to study the effects of fiber orientation and hydration. Fracture toughness results in the transverse orientation were much higher than that in the longitudinal orientation and increased with degree of hydration for both antler and bovine femur. The fracture toughness of antler was ~ 50% higher than that of bovine femur. The highest fracture toughness value was obtained from the hydrated antler in the transverse orientation, which reached 10.31 MPa·m1/2 compared to that measured from bovine femur, which was 6.35 MPa·m1/2. The crack propagation and fracture surface were characterized using scanning electron microscopy. Toughening mechanisms, including crack deflection by osteons, uncracked ligament bridging, and microcracks formation, are observed and discussed. Comparisons between antler and bone are made.
INTRODUCTION Deer antlers, one of the fastest growing tissues in the animal kingdom, have a main function in intraspecific combat and have been designed for sustaining high impact loading and bending moment without fracture [1,2]. Antlers have a similar microstructure as mammalian long bones, composed primarily of type-I collagen fibrils and carbonated apatite crystals, arranged in osteons in the compact bone and a lamellar structure in the cancellous bone. However, there are distinct differences between antler and bone. First, antlers have lower mineral content (~ 30 vol%) compared to bones (~ 40 vol%) [3]. Secondly, antlers consist mainly of young primary osteons whereas most adult limb bones consist of secondary osteons and older interstitial bone [4]. There are limited reports on the mechanical properties of antlers [5-10]. Antler was found to have the lowest mineral content and consequently the lowest elastic modulus, roughly half that of the bovine femur [5]. Red deer antler had similar ultimate tensile strength as bovine femur, ranging between 100 and 140 MPa; however, the strain at failure (8-10%) and work of fracture (6186 J/m2) for antler were 4-5 times greater than bovine femur [3]. Numerous studies on the fracture properties of bone were performed at various conditions, such as microstructure, orientation, hydration, strain rate, age, and diseases [11-19]. However, the fracture toughness of antler has not been studied. In the present work, we report the frac
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