SM12L_12682:Thu:0950:213
XXI International Congress of Theoretical and Applied Mechanics
Warsaw, Poland, August 15-21, 2004

On the Concept of “Dynamic (In)Stablility of Quasi - Static Paths”

Joao A. C. Martins (1), F. M. F. Simoes (1), A. Pinto da Costa (1), Isabel Coelho (2)
1. Instituto Sup. Técnico, Department of Engineering Civil and ICIST, Lisboa, Portugal
2. CMAF-UL, Lisboa, Portugal


A concept of dynamic stability of quasi-static paths is proposed that takes into account the existence of fast (dynamic) and slow (quasi-static) time scales. A change of variables is performed that replaces the (fast) physical time $t$ by a (slow) loading parameter $\lambda$, whose rate of change with respect to time, $\epsilon=d\lamda/dt$, is decreased to zero. This leads to a system of dynamic equations defining a singular perturbation problem: the highest order derivative with respect to $\lambda$ appears multiplied by $\epsilon$. The proposed definition is essentially a continuity property with respect to the smallness of initial perturbations (as in Lyapunov stability) and loading rate $\epsilon$ (as in singular perturbation problems). Three mechanical examples (the Ziegler and Shanley columns and a pin-on-flat friction apparatus) are presented to illustrate similarities and differences between ?dynamic stability of quasi-static paths? and Lyapunov stability of some related equilibrium configurations or dynamic trajectories.



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