Use Of Smart Structures Research Articles

Edible Origami Actuators Using Gelatin-Based Bioplastics.

The potential of ingestible medical devices can be greatly enhanced through the use of smart structures made from stimuli-responsive materials. While hydration is a convenient stimulus for inducing shape changes in biomaterials, finding robust materials that can achieve rapid actuation, facile manufacturability, and biocompatibility suitable for ingestible medical devices poses practical challenges. Hydration is a convenient stimulus to induce shape changes in smart biomaterials; however, there are many practical challenges to identifying materials that can achieve rapid actuation and facile manufacturability while satisfying constraints associated with biocompatibility requirements and mechanical properties that are suitable for ingestible medical devices. Herein, we illustrate the formulation and processability of a moisture-responsive genipin-crosslinked gelatin bioplastic system, which can be processed into complex three-dimensional shapes. Mechanical characterization of bioplastic samples showed Young's Modulus values as high as 1845 MPa and toughness values up to 52 MJ/m3, using only food-safe ingredients. Custom molds and UV-laser processing enabled the fabrication of centimeter-scale structures with over 150 independent actuating joints. These self-actuating structures soften and unfold in response to surrounding moisture, eliminating the need for additional stimuli or actuating elements.

Tailorable activation of thermoresponsive composite structures incorporating wavy heaters via hybrid manufacturing

The activation method of thermoresponsive materials greatly affects the practical use of smart structures composed thereof. Despite extensive research that relies on methods using high ambient temperatures or planar heaters, the efficient and tailorable activation of relatively thick thermoresponsive composite structures remains challenging. Herein, we present a concept of embedding a wavy heater into a thermoresponsive material matrix to form a composite structure with parametrically designed thermal activation behavior, through a facile manufacturing approach combining 3D-printing and laser-cutting. We develop a numerical model to predict the transient heat transfer for varying wavy shapes of heater, and experimentally validate the numerical results. The exploration of the design space using the numerical model shows a reduction of up to 82% in heating time using the wavy design compared with the flat design. Finally, we demonstrate experimentally the stiffness tuning in thermoresponsive composite structures. This work paves the way for large-scale thermoresponsive composite structures with applications in aerospace and architecture.

Soft ionic liquid multi-point touch sensor.

The development of electronic skin (e-skin) and soft tactile sensing has recently attracted great interest. Here we report for the first time on a novel ionic liquid (IL) based soft pressure sensor with multi-point touch detection capability using 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]+[BF4]−) as a highly conductive sensing medium. The sensing mechanism is attributed to the repopulation of charge cations and anions in aqueous solution under pressure. The sensor can detect two dimensional touching positions with a sensitivity of −0.28% kPa−1. Our sensor showed good stability and temperature independence thanks to the incompressibility of IL in the range of touch pressure and the appropriate signal measurement configuration. We successfully demonstrated the sensor's capability to detect multi-point human touch with different pressure levels. Our simple design with smart structures and ease of fabrication processes enable the development of a soft and low-cost sensor with multiple-point sensing capabilities on a single chip.

Stiffness control of cylindrical shells under axial compression using piezocomposite actuators—An experimental investigation

ABSTRACTThe present study explores the modification and control of prebuckling stiffness of cylindrical shells for their potential use in smart structures. The effects of surface-bonded microfiber composite actuator patches on cylindrical shells subjected to axial compression are studied experimentally. The actuators are placed such that the distance separating them is less than the observed axial and circumferential buckling wavelengths. Strain gauge sensors are used to measure the axial strains at discrete locations on the cylindrical shell. Experimental results indicate that the actuation effect can reduce the local strains as well as improve the overall stiffness of the structure. The results obtained in this study potentially have a significant impact in space applications.

Compressive Strength and Microstructure of 0–3 Lead Zirconate Titanate Ceramic-Portland Cement Composites

Lead zirconate titanate (PZT)-Portland cement (PC) composites have been reported to have good potential for use in smart structures. In this work, PZT-PC composites containing 40%, 50% and 60% of PZT by volume were produced and their mechanical and hydration properties were investigated. Compressive strengths of those typically used in normal concrete were found for all PZT-PC composites, with measured values of 41.5–45.0 MPa. Hydration products of Portland cement detected by thermal analysis were calcium silicate hydrates (the main cement hydration product), calcium hydroxide and ettringite. Furthermore, calcium silicate hydrates and ettringite can also be observed surrounding the PZT grains in the SEM micrograph.

The use of smart structures in the realization of effective semi-active Control systems for vibration reduction

The realization of semi-active actuators by smart structures is discussed. Semi-active actuators have the advantage of consuming much less power than direct-active actuators and are appropriate for the utilization in vibration problems encountered in aeronautical applications, where the loads are in general too high for direct-active actuators to perform. The development of a compact actuator device of this class, from the design phase to the validation tests, is presented.

Analytical modeling of active structural acoustic control

AbstractSince the reduction of disturbing noise is highly important in industrial and civil engineering, much research and development has been done in this field over the past decades. The application of smart structures provides a way to reduce unwanted noise radiation. A smart structure is an integrated system consisting of the passive base structure attached with actuators and sensors. Piezoelectric ceramics are widely used as sensors and actuators, because they can easily be bonded on or imbedded into conventional structures. An often used concept for noise reduction is active structural acoustic control (ASAC). This concept means that the noise radiation will be reduced by minimizing or changing the vibrational behavior of a structure using additional actuator forces. The development and industrial use of smart structures for ASAC requires efficient and reliable simulation and design tools. Usually the design process of smart structures is based on numerical methods. In order to verify numerical techniques, the paper presents an analytical reference solution for an ASAC system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Adhesive Layer Effects in Surface-Mounted Piezoelectric Actuators

The role of the adhesive layers in active panels with surface-mounted (bonded) piezoelectric layers is studied. The investigation focuses on the strain transfer mechanism between the active layers and the host structure, the stress concentrations involved, and the influence of the geometrical and mechanical properties of the adhesive layers on the static response of the panel. The analysis is based on the High-Order approach and uses 2D elasticity to model the adhesive layers. The mathematical formulation is derived using variational principles, compatibility requirements, and the piezoelectric constitutive equations. Confirmation of the analytical model is achieved through an experimental study that reveals good agreement between the theoretical predictions and the behavior of the active structure. Numerical results are presented for a typical piezoelectric active panel and compared to detailed 2D finite element analysis. The results reveal the high-order effects and the stress concentrations in the transition zone near the edge of the panel and indicate that a careful selection of the adhesive's properties can improve the behavior of the structure and reduce the severity of the stress concentrations involved. The paper concludes with a summary and recommendations for the analysis, design, and use of smart structures with bonded actuators.

Smart Structure Integrity Monitoring Using Transient Response

Structural integrity monitoring is a critical process in ensuring safe operation of structures. Damage that is not detected continuously and corrected immediately can cause additional damage and eventually catastrophic failures. In ensuring safe operation, real time damage detection is necessary and is realisable through the use of smart structures. In this paper, a new non-destructive testing method to detect damage in structural connections using piezoelectric actuating/sensing devices is proposed. A thin beam with one end fixed and the other subjected to a variety of boundary conditions is used to investigate the feasibility of this method. The method involves first flexurally exciting the beam and measuring its resulting transient response using a piezoelectric device, and then determining any change in its one variable boundary condition by comparing the measured response to that of a fixed-fixed (or secure) condition. The size of the difference in responses indicates the degree of extent of the boundary change. The proposed transient response approach uses information that is unobtainable using current steady-state harmonic based methods. Results of experiments show significant differences in the transient responses of secure and damaged beam connections.