Deformation behaviour and damage accumulation of cortical bone specimens from the equine tibia under cyclic loading.

The research focuses on investigating how the bones in the lower legs (tibiae) of horses respond to repetitive load pressures. It emphasizes that despite its significance, fatigue behaviour of cortical bone is less examined compared to its static behaviour. The fatigue behaviour reveals that bone starts to weaken and lose strength under repetitive loading, leading to various microstructural damages.

Objective of Study

• The study aims to understand the fatigue behaviour of cortical bone, especially how it changes with continuous load. The main area of interest was the tibiae bone in horses.

Methodology

• The researchers performed load-controlled single-step tests on the cortical bone specimens from horses’ tibiae.
• The development of stress-strain hysteresis parameters over the bone’s lifetime was used to describe the cyclic deformation behaviour.

Findings

• The bone exhibits ‘cyclic softening,’ meaning that it continues to weaken as it is subjected to repetitive loads, especially towards the end of its lifetime.
• The microstructural damage accumulation resulting from cyclic loading causes reduction in stiffness and asymmetrical deformation of the bone under tension and cyclic compression.
• Microcrack formation and growth are the principal damage mechanisms, as revealed by light and scanning electron microscopy.
• The growth behaviour of these cracks is heavily influenced by microstructure, stress components, and local stress magnitudes.

Crack Formation and Growth

• When the local stresses are low or the mean stresses are compressive, the dominant influence is the shear stress components, which leads to shear failure at the bone’s inner interfaces.
• As the cracks grow longer (indicating higher stress amplitudes) or the mean stresses become tensile, the microstructure begins to be overlooked, and failure primarily occurs under the influence of normal stress components.
• This transition in damage mechanism is observable on the fracture and specimen surfaces.