Design of Switching Damping Control for Smart Structure Self-Powered Adaptive Damping Control

This paper presents a new damping control circuit which named adaptive VSPD [1] (adaptive velocity-controlled switching piezoelectric damping) that can be used to vary control voltage of VSPD damping circuit with the amplitude variation and be self-powered itself as well. Since the voltage source in the VSPD damping control circuit may cause a stability problem at small vibrations, an adaptive voltage source can be designed to purposely solve this problem. The design concept of an adaptive VSPD unit is not only to dampen the residual vibration but also to maintain the system stability by incorporating an adaptive control voltage. In fact, the energy needed for the extra voltage source within the control circuit can be provided by the storage capacitor and the energy stored can be harvested from the structure vibration energy. With this design, the damping performance can be maximized while maintaining system stability at the same time and also does not add complexity to the circuit. All the theoretical modeling, simulation and experimental results will all be detailed in this paper.

Experimental Study of a Self-Excited Piezoelectric Energy Harvester

In the present experimental work, we explore the possibility of using piezoelectric based fluid flow energy harvesters. These harvesters are self-excited and self-sustained in the sense that they can be used in steady uniform flows. The configuration consists of a piezoelectric cantilever beam with a cylindrical tip body which promotes sustainable, aero-elastic structural vibrations induced by vortex shedding and galloping. The structural and aerodynamic properties of the harvester alter the vibration amplitude and frequency of the piezoelectric beam and thus its electrical output. This paper presents results of energy-harvesting tests with one configuration of such a self-excited piezoelectric harvester using a PZT bimorph. In addition to the electrical voltage output, the strain on the surface of beam close to its clamped tip was also measured The measured strain and voltage output were perfectly correlated in the frequency range containing the first natural mode of vibration of the system. It was observed that about 0.24 mW of electrical power can be attained with this harvester in a uniform flow of 28 m/s.

Experimental and Numerical Analysis of Recovery Stress in Ni47Ti44Nb9 Shape Memory Alloys: Application to Tightening

Ni47Ti44Nb9 Shape Memory Alloys (SMAs) are widely considered for tightening applications. The alloy is composed of a NiTi SMA matrix containing niobium precipitates. A specific thermomechanical treatment strongly increases the transformation hysteresis in these alloys, what improves the tightening efficiency. Tightening pressures exhibited by Ni47Ti44Nb9 rings are experimentally investigated. Strain gage measurements allow to monitor the tightening pressure using a home test bed. Evolutions with temperature are recorded. A thermo-mechanical constitutive law, specific for Ni47Ti44Nb9, is proposed. It is based on the Mori-Tanaka scale transition technique by considering the precipitates as elastic-plastic inclusions embedded in the SMA matrix. The resulting effective law is implemented, and validated in ABAQUS via UMAT subroutine. Experimental tests are simulated by Finite Element Modeling, and comparisons are performed.

Cyclic Behavior of Concrete Confined by Active and Passive Jackets

Shape memory alloy (SMA) wire jackets for concrete are distinct from the conventional jackets of steel or FRP since they provide active confinement that can be easily archived due to the shape memory effect of SMAs. This study uses NiTiNb SMA wires of 1.0 mm diameter to confine concrete cylinder with the dimension of 300 mm × 150 mm (L × D). The NiTiNb SMAs have a relative wider temperature hysteresis than NiTi SMAs and, thus, are more applicable for severe temperature-variation environment which civil structures are exposed to. Steel jackets of passive confinement are also prepared to compare the cyclic behavior of active and passive confined concrete cylinders. For this purpose, monotonic and cyclic compressive loading tests are conducted to obtain axial and circumferential strain. The both of strains are used to estimate volumetric strains of concrete cylinders. Also, plastic strains from cyclic behavior are also estimated. For the NiTiNb SMA jacketed cylinders, the monotonic axial behavior differs from the envelope of cyclic behavior; this should be studied in future. The plastic strains of the active confined concrete show a similar trend to those of the passive confinement. The trend of plastic strain of this study does not match with that of CFRP (Carbon Fiber Reinforce Polymer) jackets. For the volumetric strain, the active jackets of the NiTiNb SMA wires provide more energy dissipation than the passive jacket of steel.

Analysis of Wrinkled Membranes Bounded With Macro-Fiber Composite (MFC) Actuators

In this paper we focus on a study which involves quantifying the effects of Macro Fiber Composite (MFC) actuators on the pattern and magnitude of wrinkles in a membrane when exposed to various loadings. An ABAQUS finite element code is employed for this research. The membrane in this study has a rectangular shape which is clamped at one edge and is free to move in the horizontal direction at the other edge. MFC actuators are bounded to the membrane to make a bimorph configuration.

Modeling the Behavior of Crystallizable Shape Memory Polymers Subject to Inhomogeneous Deformations

The constitutive model for the mechanics of crystallizable shape memory polymers (CSMP) has been developed in the past [1, 2]. The model was developed using the theory of multiple natural configurations and has been successful in addressing a diverse class of problems. In this research work, the efficacy of the developed CSMP model is tested by applying it to the torsion of a cylinder, which is an inhomogeneous deformation. The crystallization of the cylinder is studied under two different conditions i.e. crystallization under constant shear and crystallization under constant moment.

The Modelling of Hysteresis in Magnetorheological Dampers Using a Generalised Prandtl-Ishlinskii Approach

The major drawback of magnetorheological dampers (MR) lies in their non-linear and hysteretic force-velocity response. To take full advantage of the operating characteristics of these devices a high fidelity model is required for control analysis and design. In this contribution the ability of a generalised PI operator-based model to represent the characteristics of a commercially available MR damper is examined. This approach allows the user to define the PI operator to best match the hysteresis characteristics. For the MR damper the force-velcoity hysteresis characteristic is ‘S’ shaped and constrained. Two possibilities will be examined here for the generalised play operator; an hyperbolic tan function and a symmetric sigmoid function.

Thermal Robustness Assessment of a Rigidized Space Inflatable Boom via Experimental Modal Analysis and Finite Element Modeling

The following paper presents the results of a thermal robustness assessment of a rigidized space inflatable boom. Modal testing is performed at three different environmental temperatures; spanning a range of 38°C, with the purpose of characterizing dynamic behavior and assessing changes in bending frequencies. Experimental results show that the natural frequencies of the boom shift only marginally within the tested bandwidth. A finite element model is developed in parallel with experiments to determine compatibility with beam theory. The resulting simulation shows that linear beam theory can be used to predict bending frequencies and frequency response function magnitudes with very good accuracy.

Towards Self-Sensing of DEAP Actuators: Capacitive Sensing Experimental Analysis

Dielectric Electro-Active Polymers (DEAP’s) have become attractive material for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. The materials ability to act as both and actuator and a sensor enable DEAP actuators to have “self-sensing” capabilities. This advancement provides low cost actuator systems that do not require external sensors for feedback control. This paper explores the capacitive sensing capabilities of a DEAP actuator under loading conditions typical for pumping and valve applications. The capacitive sensing capabilities of the actuator are tested using a method similar to that used by Jung et al. [1] which uses the DEAP actuator as a variable capacitor in a high pass filter circuit. This sensing circuit produces a direct voltage output when the actuator is displaced. The sensing response of this system is experimentally investigated under mechanical loading. The sensor is shown to have an effective sensitivity of .041 (V/Vexc) / mm. In addition, the initial results of a dual sensing and actuating system are presented.

A Design Method for Shape Memory Alloy Actuators Accounting for Cyclic Shakedown With Constrained Allowable Strain

The high energy density actuation potential of SMA wire is tempered by conservative design guidelines set to mitigate complex factors such as functional fatigue (shakedown). Shakedown causes problems of stroke loss and interface position drift between the system and the SMA wire under higher stress levels if the wire does not undergo a pre-installation shakedown procedure. Limiting actuation strain has been reported as reducing shakedown as well as increasing fatigue life. One approach to limit actuation strain is using a mechanical strain limiter which sets a fixed Martensite strain position — useful for the development of in-device shakedown procedures which eliminates time consuming pre-installation shakedown procedures. This paper presents a new graphical design approach for SMA wire actuators which accounts for shakedown with the use of mechanical strain limiters to enable higher stress designs to maximize actuator performance. Experimental data on the effect of strain limiters along with stroke and work density contours form the basis for the new graphical design method. For each independent mechanical strain limiter, the maximum of the individual post-shakedown austenite curves at a range of applied stress are combined into a conglomerate stabilization design curve. These curves over a set of mechanical strain limiters provide steady state performance prediction for SMA actuation, effectively decoupling the shakedown material performance from design variables that affect the shakedown. The use and benefits of this new design approach are demonstrated with a common constant force actuator design example. This new design approach, which accounts for shakedown, supports design of SMA actuators at higher stresses with more economical use of material/power, and enables the utilization of strain limiters for cost saving in-device shakedown procedures.