Mixed-mode fracture of human cortical bone.
Although the mode I (tensile opening) fracture toughness has been the focus of most fracture mechanics studies of human cortical bone, bones in vivo are invariably loaded multiaxially. Consequently, an understanding of mixed-mode fracture is necessary to determine whether a mode I fracture toughness test provides the appropriate information to accurately quantify fracture risk. In this study, we examine the mixed-mode fracture of human cortical bone by characterizing the crack-initiation fracture toughness in the transverse (breaking) orientation under combined mode I (tensile opening) plus mode II (shear) loading using samples loaded in symmetric and asymmetric four-point bending. Whereas in most structural materials, the fracture toughness is increased with increasing mode-mixity (i.e., where the shear loading component gets larger), in the transverse orientation of bone the situation is quite different. Indeed, the competition between the maximum applied mechanical mixed-mode driving force and the weakest microstructural paths in bone results in a behavior that is distinctly different to most homogeneous brittle materials. Specifically, in this orientation, the fracture toughness of bone is markedly decreased with increasing mode-mixity.
Zimmermann
Elizabeth A
EA
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Launey
Maximilien E
ME
Barth
Holly D
HD
Ritchie
Robert O
RO
D000368:Aged; D019245:Compressive Strength; D003198:Computer Simulation; D055119:Elastic Modulus; D005264:Femoral Fractures / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D005269:Femur / Q000000981:diagnostic imaging* / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011859:Radiography; D013314:Stress, Mechanical; D013718:Tensile Strength; D016474:Weight-Bearing