Filipe Amarante dos Santos

Numerical simulation of superelastic shape memory alloys subjected to dynamic loads

Superelasticity, a unique property of shape memory alloys (SMAs), allows the material to recover after withstanding large deformations. This recovery takes place without any residual strains, while dissipating a considerable amount of energy. This property makes SMAs particularly suitable for applications in vibration control devices. Numerical models, calibrated with experimental laboratory tests from the literature, are used to investigate the dynamic response of three vibration control devices, built up of austenitic superelastic wires. The energy dissipation and re-centering capabilities, important features of these devices, are clearly illustrated by the numerical tests. Their sensitivity to ambient temperature and strain rate is also addressed. Finally, one of these devices is tested as a seismic passive vibration control system in a simplified numerical model of a railway viaduct, subjected to different ground accelerations.

Design and experimental testing of an adaptive shape-morphing tensegrity structure, with frequency self-tuning capabilities, using shape-memory alloys

The present paper explores the capabilities of a tensegrity-inspired tower with regard to frequency tuning by shape morphing. To change the configuration of the proposed structure, shape-memory-alloy (SMA) actuators are used. This actuation principle also takes advantage of the variation of the elastic modulus of SMAs associated with the martensitic transformation. The temperature modulation of the SMA wires is successfully achieved by Joule heating, through a proportional-integral-derivative controller, to change between a low-temperature shape and a high-temperature shape. The implementation of a short-time-Fourier-transform control algorithm allows for the correct identification of the dominant input frequency, associated with the dynamic excitation. This information is used to automatically change the configuration of the structure in order to shift its natural frequency away from that of the dynamic excitation. With this frequency tuning, one obtains a reduction of the accelerations throughout the structure up to about 80%. The good performance of the proposed control approach gives promising indications regarding the use of tensegrity systems, in combination with SMAs, for shape-morphing applications, and, in particular, for self-tuning structures.

A Mechanical Instrument to Evaluate Posture of the Spinal Column in Pregnant Women

Back pain is a very important problem in modern society. To better understand this problem we need instruments that evaluate the spinal column in a global way.

Adaptive underslung beam using shape-memory alloys for frequency-tuning

The present article addresses the study of an adaptive-passive beam structure with a shape-memory alloy based actuator. In order to mitigate adverse dynamic effects resulting from externally induced vibrations, the structure is able to automatically tune its natural frequency to avoid resonance. The adaptive-passive beam configuration is based on an underslung cable-stayed girder concept. Its frequency tuning is achieved by temperature modulation of the shape-memory alloy elements through a closed-loop control process based on a proportional-integral-derivative algorithm. The effectiveness of the proposed control solution is substantiated by numerical simulations and experimental tests on a small-scale prototype. The validated numerical model enables the simulation of the proposed control approach in a real-scale footbridge, subjected to a prescribed pedestrian loading. The results are very encouraging and show that, by activating the shape-memory alloy elements, the system is able to successfully shift its natural frequency and to mitigate the effects of induced vibrations.

Buckling Control Using Shape-Memory Alloy Cables

AbstractThis paper studies innovative restraining solutions based on lateral nickel-titanium (NiTi) shape-memory alloy (SMA) cables. Two novel control approaches are tested, which take advantage of superelasticity and the shape-memory effect. Superelasticity is employed in a passive control approach, using the restraining cables to increase the postbuckling resistance and recentering capabilities of a compressed column while dissipating energy. A numerical model to simulate this passive control system is also proposed and validated, adequately representing both its material and geometric nonlinearities. Additional parametric tests are performed, providing more insight into the good performance of the proposed system. The shape-memory effect (SME) is used in an active control approach, using the cables as actuators to counteract the buckling motion of the column. Experimental prototypes are built and tested in order to investigate the feasibility and effectiveness of these two control solutions, which aim ...

Toward an adaptive vibration absorber using shape-memory alloys, for civil engineering applications

This article explores the capabilities of a novel adaptive vibration absorber for civil engineering structures, with regard to frequency self-tuning, based on the temperature modulation of shape-memory alloy restitution elements. This real-time temperature modulation of shape-memory alloys, through Joule effect, enables to control the elastic modulus of these elements, by inducing thermal martensitic transformations, and allows for the adaptation of the stiffness of the absorber, in order to be continuously tunable for a wide frequency range. A series of simulations are performed, using numerical models of a lively footbridge, to give an additional insight into the high potentialities of this adaptive control approach in the mitigation of vibrations in civil engineering structures.