Rings in Taylor Spatial Frame: Mechanical testing and finite element analysis.

Taylor Spatial Frame (TSF) is a type of hexapod external ring fixation system. TSF rings are supplied as half rings, whole full rings and two third rings in different sizes. In this work, these components as well as bolted full rings made of two half rings were tested in compression in two or three directions. Tests were simulated by Finite Element (FE) method using 3D solid elements, which were validated against the experimental results. Load-deflection curves and values for stiffness and ultimate loads are presented for each case from both tests and FE analyses. Load-stiffness curves are also presented for each test. The followings were demonstrated by the results: (1) a significant difference between bolted and whole full rings in their respective stiffness behaviour, the clear advantage being with the whole full rings, (2) a variation in stiffness of bolted rings when loaded across their different diameters, (3) a potential problem in the TSF rings: having the same cross section and thickness, smaller rings are stronger than larger ones, whereas in fact the larger ones ought to be stronger due to patient's weight and that (4) the lowest stiffness was exhibited when a 2/3 ring was loaded parallel to the line joining its open ends.