title: Microscopic assessment of bone toughness using scratch tests.
abstract: Bone is a composite material with five distinct structural levels: collagen molecules, mineralized collagen fibrils, lamellae, osteon and whole bone. However, most fracture testing methods have been limited to the macroscopic scale and there is a need for advanced characterization methods to assess toughness at the osteon level and below. The goal of this investigation is to present a novel framework to measure the fracture properties of bone at the microscopic scale using scratch testing. A rigorous experimental protocol is articulated and applied to examine cortical bone specimens from porcine femurs. The observed fracture behavior is very complex: we observe a strong anisotropy of the response with toughening mechanisms and a competition between plastic flow and brittle fracture. The challenge consists then in applying nonlinear fracture mechanics methods such as theJ-integral or the energetic Size Effect Law to quantify the fracture toughness in a rigorous fashion. Our result suggests that mixed-mode fracture is instrumental in determining the fracture resistance. There is also a pronounced coupling between fracture and elasticity. Our methodology opens the door to fracture assessment at multiple structural levels, microscopic and potentially nanometer length scale, due to the scalability of scratch tests.
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
authors.forename: Amrita
authors.initials: A
authors.lastname: Kataruka
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
authors.forename: Kavya
authors.initials: K
authors.lastname: Mendu
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
authors.forename: Orieka
authors.initials: O
authors.lastname: Okeoghene
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
authors.forename: Jasmine
authors.initials: J
authors.lastname: Puthuvelil
authors.affiliation: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States; Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
authors.forename: Ange-Therese
authors.initials: AT
authors.lastname: Akono
keywords: Cortical bone; Fracture modes; Fracture toughness; Multi-scale testing; Scratch test; Size effect law