Abstract
This paper uses X-ray computed tomography to track the mechanical response of a vertebrate (Barnacle goose) long bone subjected to an axial compressive load, which is increased gradually until failure. A loading rig was mounted in an X-ray computed tomography system so that a time-lapse sequence of three-dimensional (3D) images of the bone’s internal (cancellous or trabecular) structure could be recorded during loading. Five distinct types of deformation mechanism were observed in the cancellous part of the bone. These were (i) cracking, (ii) thinning (iii) tearing of cell walls and struts, (iv) notch formation, (v) necking and (vi) buckling. The results highlight that bone experiences brittle (notch formation and cracking), ductile (thinning, tearing and necking) and elastic (buckling) modes of deformation. Progressive deformation, leading to cracking was studied in detail using digital image correlation. The resulting strain maps were consistent with mechanisms occurring at a finer-length scale. This paper is the first to capture time-lapse 3D images of a whole long bone subject to loading until failure. The results serve as a unique reference for researchers interested in how bone responds to loading. For those using computer modelling, the study not only provides qualitative information for verification and validation of their simulations but also highlights that constitutive models for bone need to take into account a number of different deformation mechanisms.
Highlights
Bone has a complex three-dimensional (3D) geometry, both in terms of its external shape and its internal structure
The purpose of the study was to investigate the range of deformation mechanisms that occur under axial loading in a typical vertebrate long bone
A B. leucopsis femur has been loaded to failure within a specially designed rig mounted in an X-ray computed tomography system
Summary
Bone has a complex three-dimensional (3D) geometry, both in terms of its external shape and its internal structure. Femora (thigh bone) support the transmission of load due to the weight of the owner’s body, which can be structurally thought of as a long beam-like cylinder With this geometry, it will have a distinct head, neck and shaft adapted to maximise mechanical strength at minimum weight (Brassey et al, 2013a, 2013b). Distribution of trabeculae in the femur is such that most of the bony trabeculae lie in the neck and tension–compression trabeculae lie in the medial cortex region This forms an efficient system to withstand stresses/forces under locomotion or other load bearing scenarios (Currey, 2000; Nagarajaa, Couseb & Guldberg, 2005; Rudman, Aspden & Meakin, 2006; Tomaˇs, 2006). The cement lines in the haversian canals are the first ones to fail, which spread across the lamellar region of osteons
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