Equine cortical bone exhibits rising R-curve fracture mechanics.

The research article presents a study on the fracture properties of horse cortical bone. It reveals that the bone displays varying fracture toughness characteristics depending on the region of the cortex, exhibiting behavior similar to ceramic matrix composites.

Objective and Hypothesis of the Study

• The aim of the study was to explore the fracture mechanics of cortical bone, specifically in horses. The researchers hypothesized that the cortical bone’s fracture toughness varies depending on the region of the cortex, exhibiting what is called a ‘rising R-curve behavior’ (an increase in fracture toughness with crack length).

R-Curve Experiments and Methodology

• In order to test their hypothesis, the researchers carried out R-curve experiments on equine third metacarpal bones using standard fracture mechanics testing methods.
• They took compact type specimens from the dorsal (back) and lateral (side) areas from the middle part of the bone’s shaft, called the diaphysis. These specimens were tested for crack propagation perpendicular to the length of the bone.

Results and Observations

• The results of the tests confirmed the researchers’ hypothesis that the equine cortical bone displays a rising R-curve behavior during transverse crack propagation.
• There were notable regional differences in the crack growth initiation toughness (K0), the peak toughness (Kpeak), and the crack extension at peak toughness (deltaa)
• The lateral cortex showed higher initiation and peak toughnesses, while the dorsal cortex showed a greater extension at peak crack growth resistance.

Microstructure and Regional Dependence

• Using scanning electron microscopy, the scientists observed osteon (a structural unit in cortical bone) pullout in the fracture surfaces from the dorsal cortex and not in the lateral cortex.
• The significant differences in R-curves and the results from their microscopic analysis suggest that the fracture mechanisms at play in equine cortical bone are regionally dependent, confirming their initial hypothesis.

In conclusion, the study provides valuable insights into the fracture mechanisms of equine cortical bone and how they vary depending upon the region of the cortex. This research can form a basis for future studies into the biomechanical properties of other types of bones or species.