Artifactual nonlinearity due to wear grooves and friction in four-point bending experiments of cortical bone.

This research article investigates the cause of inconsistent linear responses in four-point bending tests on cortical bone samples. The study found that visible grooves on the bone surface and friction at the load and support points were largely responsible for the non-linear outcomes.

Objective of the Research

• The objective of the research was to determine why the force-deflection response was nonlinear during four-point flexural fatigue of beams of cortical bone. This nonlinearity could impact the accuracy and effectiveness of the experiments.

Methodology

• The researchers selected beams of cortical bone from the mid-diaphysis of equine third metacarpus for the tests.
• They analysed the beams under different conditions and loads, aiming to identify and isolate the factors affecting the linearity of force-deflection response.

Findings

• The study found that grooves forming on the surface of the bone beam during the test, caused by the load noses and supports, were primarily responsible for the nonlinearity.
• An additional geometric nonlinearity was detected at large deflections via finite element modeling. However, this could be minimized by using the smallest diameter load noses and supports, as recommended in the ASTM 790 standard.

Recommendations

• The team discovered that low-level frictional constraints at load noses and supports, caused by the bending process, could impact results. They recommend that this should be avoided by using roller-bearing supports and load noses, or an equivalent method.
• This adjustment can ensure more accurate observations and the collection of reliable data in subsequent testing.