Papers by Keyword: Dynamic Instabilities

Abstract: The dynamic instability analysis of conveying fluid multi-walled carbon nanotubes (MWCNT) is analyzed. Based on the nonlocal elasticity theory, Donnells shell model, potential flow theory and the van der Waal interaction between walls, the governing equations are formulated. The small scale parameter and the internal fluid interaction effects on the dynamic behaviors of the MWCNT-fluid system as well as the instabilities induced by the fluid velocity are investigated. The critical velocity and the frequency-amplitude relationships are obtained with respect to physical and material parameters.

Abstract: The phenomena occurring during rapid crack propagation in brittle single crystals were studied by cleaving silicon specimens on the low energy cleavage planes under tensile and bending. The experiments revealed new phenomena not previously reported, and new crack path instabilities in particular. The well defined boundary conditions of the tested specimens and crack velocity measurements enabled rationalization of the observed phenomena and the velocity-surface instabilities relationship in particular. In contrast to amorphous materials, the observed instabilities are generated at relatively low velocity, while at high velocity the crack path remains stable. No evidences for mirror, mist, and hackle instabilities, typical in amorphous materials, were found.

Abstract: The dynamic instability behavior of delaminated composite plates under transverse excitations was investigated experimentally and analytically. An electromagnetic device, acting like a spring with alternating stiffness, was used to parametrically excite the delaminated composite plates transversely. An analytical method, combined with the finite element method, was used to determine the instability regions of the delaminated composite plates based on the modal parameters of the composite plate and the position, the stiffness of the electromagnetic device. The delamination size and position of composite plates were varied to assess their effects on the excitation frequencies of simple and combination resonances in instability regions. The experimental results were found to agree with the analytical ones.