Effect of fatigue-induced microdamage on the compressive properties of bovine trabecular bone
Abstract
Understanding the effect of microdamage accumulation on the failure mechanisms of bone is important
for treatment and prevention in degenerative diseases such as osteoporosis. The common sites of fracture
in osteoporotic patients – arm, vertebra, hip – have large proportions of trabecular bone, which make
them of particular interest. Degenerative bone diseases disrupt bone’s natural remodeling ability, meaning
the microdamage which is normally repaired begins to accumulate, increasing a patient’s risk of fracture.
The current study aims to investigate the effect of microdamage accumulation on subsequent monotonic
tests-to-failure using cored bovine trabecular bone samples. Various levels of microdamage were induced
via pre-determined quantities of compressive fatigue loading on cored samples, which were subsequently
tested in a uniaxial, compressive, test-to-failure. A parabolic relationship was found in the yield strain
(from the test-to-failure) plotted against the reduction in modulus from fatigue loading, as well as in the
normalized yield stress (from the test-to-failure) plotted against the reduction in modulus from fatigue
loading. These results support the hypothesis that increases in yield strain at low quantities of fatigue
induced damage could be attributed to a microdamage stress relieving mechanism in which small
microdamage sites nucleate rather than growing larger sites. The results are indicative that a critical
amount of this proposed mechanism exists, after which point further microdamage accumulation becomes
detrimental to the mechanical properties obtained in subsequent compressive testing-to-failure. Once this
critical amount of fatigue-induced damage is induced, a significant decrease in the subsequent yield strain
is noted representing the growth and coalescence of few, large microdamage sites that become
responsible for yielding in the test-to-failure.
X-ray micro-computed tomography was used in an attempt to characterize damage propagation during
post-yield loading of select trabecular bone samples during monotonic failure testing. Qualitative three
dimensional imaging suggests that two distinct damage propagation types may exist: the first appearing to
originate from the centre of trabeculae, while the second appears to originate from trabecular surfaces.