This paper describes the stress recovery behaviour of an Fe-17Mn-5Si-10Cr-4Ni-1(V, C) (mass%) shape memory alloy used for prestressing of civil structures. The prestressing due to the shape memory effect was simulated by a series of tests with pre-straining of the material followed by heating and cooling back at constant strain. Different pre-strain and heating conditions were examined. Moreover, the response due to additional mechanical and thermal cyclic loading has been investigated. These results were used to predict the partial prestress loss in a structure due to variable loading during operation. Finally, a heating test at constant strain was performed after the cyclic loading to check the possibility of reactivating the prestress lost during an exceptionally high load.
The dissipated cycle energy of magnetorheological (MR) dampers operated at constant
current results from controllable hysteretic damping and from almost current
independent, small viscous damping. Thus, the emulation of Coulomb friction and
linear viscous damping necessitates current modulation during one vibration cycle
and therefore current drivers. To avoid this drawback, a cycle energy control
(CEC) approach is presented which controls the hysteretic MR damper part such
that the total MR damper energy equals the energy of optimal linear viscous
damping by constant current during one cycle. The excited higher modes due to the
hysteretic damping part are partially damped by the MR damper viscous part.
Simulations show that CEC copes better with damper force dynamics and constraints
than emulated linear viscous damping due to the slow control force dynamics
of CEC which are given by cable amplitude dynamics. It is demonstrated that
CEC of MR dampers with viscosity of approximately 4.65% of the optimal modal
viscosity performs better than optimal linear viscous damping. The reason is
that this damper viscosity represents an optimal compromise between maximum
energy spillover to higher modes due to the controllable hysteretic part which
produces more cable damping and maximum viscous damping of these higher
modes. Damping tests on a cable with an MR damper validate the CEC approach.
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