Monday, 11 October 2004 - 10:05 AM

This presentation is part of : Active Materials

Smart materials for nonlinear viscoelastic beam & columns: constitutive relations, simulations & probabilistic survival times

Harry H. Hilton and D. Michael McFarland. University of Illinois at Urbana-Champaign, 104 South Wright St., MC-236 316 Talbot Lab, 316 Talbot Lab., Urbana, IL 61801-2935

Analyses and numerical simulations are presented for beams and col-umns made of nonlinear generalized viscoelastic materials with imbedded smart materials. These structures are loaded by external loads and internal thermal distributions. Active control is exercised by smart material wires placed in the axial direction of the beams and columns, while simultaneously viscoelastic dissipative material properties provide passive control. The dependence of material properties on temperature distributions is taken into account resulting in even more pronounced non-homogenous media than those produced by the SMA alone. All mechanical properties are considered deterministic. However, non-deterministic failure property (delamination) experimental data is available allowing for probabilistic simulations of failure stress conditions as well as survival times.

Since viscoelastic failure conditions are known to degrade with time even at constant temperatures, viscoelastic structures possess finite life times. This concept has direct applications to missiles which have one shot flight times of prescribed durations. Consequently, the structure needs to be proportioned only to survive slightly longer than the time to reach its destination, thus resulting in lighter weight flight structures. The introduction of probability concepts as well as active and passive controls further reduces weight.

The attached graphs show typical results indicating that the longer a structural member survives, the higher its probability of failure. Additionally, in-creases in temperature increase the rate of relaxation modulus and failure condition degradation and hence increase failure probabilities and shorten lifetimes.

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