A novel technique for four-point bending of small bone samples with semi-automatic analysis

The design of this system takes into account the following parameters: the effects of excessive strain; specimen depth and width; span-depth ratio; overhang; rate of loading; measuring displacement from the crosshead position; radius of contact points; and the distance between the contacts. The contacts are radius edges rather than cylinders, although this is not to be recommended for multiple cycles because of wear problems, it does make the system as stiff as possible (allowance is made for this compliance). Equations are presented that allow the surface stress and strain to be calculated for each time point semi-automatically. The combination of stiff contacts and strain equations based on crosshead position not mid-span displacement is novel, this allows rapid analysis with minimum intervention from the user and gives results that are in agreement with those in the literature.