Experiments on snap buckling, hysteresis and loop formation in twisted rods

V.G.A. Goss, G.H.M. van der Heijden, J.M.T. Thompson & S. Neukirch

We give results of large deflection experiments involving the bending and twisting of 1 mm diameter nickel-titanium alloy rods, up to 2 m in length. These results are compared to calculations based on the Cosserat theory of rods. Details of this theory, formulated as a boundary value problem are presented. The mathematical boundary conditions model the experimental setup. The rods are clamped in aligned chucks and the experiments are carried out under rigid loading conditions. An experiment proceeds by either twisting the ends of the rod and then adjusting the amount of slack, or fixing the slack and varying the amount of twist. In this way commonly encountered phenomena such as snap-buckling, the formation of loops, and buckling into and out of planar configurations are investigated. The effect of gravity is discussed.

keywords: twisted rods, rod experiments, snap buckling, loop formation, snarling, hockling, welded boundary conditions

Experimental Mechanics 45, 101-111 (2005)