Buckling of coupled elastic rods

A simple physical system is studied which demonstrates the unfolding of a multiple bifurcation point. Two coupled elastic rods are subjected to a compressive load. The rods are joined such that their buckling directions are orthogonal. As the load is quasistatically increased from zero one of the two rods will buckle independently of the other. The “preferred” buckling mode is determined by two parameters, the length ratio and the stiffness ratio. The experimental system consists of two spring steel strips joined through a Teflon connector such that the buckling planes are orthogonal. The theoretical model consists of an analogous rigid rod and spring model which we assume retains the essential features of the continous system. Secondary bifurcation is essential to a continuous exchange of priority between the two buckling modes, and its role is examined for both imperfection-free and perturbed rod-spring systems. Our computational results are then compared with some experiments.