Abstract
Assessment of bone quality is an emerging solution for quantifying the effects of bone pathology or treatment. Perhaps one of the most important parameters characterising bone quality is the toughness behaviour of bone. Particularly, fracture toughness, is becoming a popular means for evaluating bone quality. The method is moving from a single value approach that models bone as a linear-elastic material (using the stress intensity factor, K) towards full crack extension resistance curves (R-curves) using a non-linear model (the strain energy release rate in J-R curves). However, for explanted human bone or small animal bones, there are difficulties in measuring crack-extension resistance curves due to size constraints at the millimetre and sub-millimetre scale. This research proposes a novel “whitening front tracking” method that uses videography to generate full fracture resistance curves in small bone samples where crack propagation cannot typically be observed. Here we present this method on sharp edge notched samples (<1 mm×1 mm×Length) prepared from four human femora tested in three-point bending. Each sample was loaded in a mechanical tester with the crack propagation recorded using videography and analysed using an algorithm to track the whitening (damage) zone. Using the “whitening front tracking” method, full R-curves and J-R curves could be generated for these samples. The curves for this antiplane longitudinal orientation were similar to those found in the literature, being between the published longitudinal and transverse orientations. The proposed technique shows the ability to generate full “crack” extension resistance curves by tracking the whitening front propagation to overcome the small size limitations and the single value approach.
Highlights
The interest in measuring fracture toughness behaviour of bone tissue is increasing within the bone research community as it is a quantitative way to evaluate an important bone quality parameter
Bone tissue fracture toughness behaviour is likely to differ with sample size, due to the predominance of different hierarchical structures or defects at different sample sizes
We present a new method for generating crack extension resistance curves in notched small bone samples, i.e. with crosssectional dimensions of 1 mm61 mm or less, tested in three-point bending combined with videography
Summary
The interest in measuring fracture toughness behaviour of bone tissue is increasing within the bone research community as it is a quantitative way to evaluate an important bone quality parameter. Fracture toughness measurement techniques have been used in an increasing number of studies to quantify the fracture resistance of bone [1,2,3,4,5,6,7,8] These studies were able to provide a good estimate of bone fracture toughness in terms of the critical stress intensity factor (Kc) and/or the critical strain energy release rate (JIntegral) while they were pushing fracture toughness testing to the limits; in many cases, samples only a few millimetres in size were investigated due to size and shape constraints of available tissue samples (Table 1) [1,2,3,4,5,6,7,8]. Because of the small dimensions e.g. the femur of small rodent mammals (rats: 30–40 mm long and 3–4 mm diameter; mice: ,15 mm long and 1–2 mm diameter), generating a crack resistance curve (R-curve) is very difficult and generally only a single-value Kc is measured instead [9]
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