title: The significance of crack-resistance curves to the mixed-mode fracture toughness of human cortical bone.
abstract: The majority of fracture mechanics studies on the toughness of bone have been performed under tensile loading. However, it has recently been shown that the toughness of human cortical bone in the transverse (breaking) orientation is actually much lower in shear (mode II) than in tension (mode I); a fact that is physiologically relevant as in vivo bone is invariably loaded multiaxially. Since bone is a material that derives its fracture resistance primarily during crack growth through extrinsic toughening mechanisms, such as crack deflection and bridging, evaluation of its toughness is best achieved through measurements of the crack-resistance or R-curve, which describes the fracture toughness as a function of crack extension. Accordingly, in this study, we attempt to measure for the first time the R-curve fracture toughness of human cortical bone under physiologically relevant mixed-mode loading conditions. We show that the resulting mixed-mode (mode I+II) toughness depends strongly on the crack trajectory and is the result of the competition between the paths of maximum mechanical driving force and "weakest" microstructural resistance.
authors.affiliation: Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Zimmermann
authors.forename: Maximilien E
authors.initials: ME
authors.lastname: Launey
authors.forename: Robert O
authors.initials: RO
authors.lastname: Ritchie
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000473:pathology*; D005264:Femoral Fractures / Q000473:pathology; D050723:Fractures, Bone / Q000473:pathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D013314:Stress, Mechanical
references.citation: Nat Mater. 2006 Jan;5(1):52-5
references.pmid: 16341218
references.citation: Acta Biomater. 2010 Apr;6(4):1505-14
references.pmid: 19941980
references.citation: J Biomech. 2003 Sep;36(9):1343-53
references.pmid: 12893043
references.citation: Nat Mater. 2008 Aug;7(8):672-7
references.pmid: 18587403
references.citation: J Biomech. 2005 Jul;38(7):1517-25
references.pmid: 15922763
references.citation: Biomaterials. 2009 Oct;30(29):5877-84
references.pmid: 19573911
references.citation: J Biomed Mater Res. 2000 Sep 5;51(3):504-9
references.pmid: 10880095
references.citation: J Biomech. 1996 Aug;29(8):1023-31
references.pmid: 8817369
references.citation: Nat Mater. 2003 Mar;2(3):164-8
references.pmid: 12612673
references.citation: Bone. 2008 Nov;43(5):798-812
references.pmid: 18647665