Smart Structure Applications Research Articles

Smart Multi-Responsive Biomaterials and Their Applications for 4D Bioprinting.

The emergence of 4D printing has become a pivotal tool to produce complex structures in biomedical applications such as tissue engineering and regenerative medicine. This chapter provides a concise overview of the current state of the field and its immense potential to better understand the involved technologies to build sophisticated 4D-printed structures. These structures have the capability to sense and respond to a diverse range of stimuli, which include changes in temperature, humidity, or electricity/magnetics. First, we describe 4D printing technologies, which include extrusion-based inkjet printing, and light-based and droplet-based methods including selective laser sintering (SLS). Several types of biomaterials for 4D printing, which can undergo structural changes in various external stimuli over time were also presented. These structures hold the promise of revolutionizing fields that require adaptable and intelligent materials. Moreover, biomedical applications of 4D-printed smart structures were highlighted, spanning a wide spectrum of intended applications from drug delivery to regenerative medicine. Finally, we address a number of challenges associated with current technologies, touching upon ethical and regulatory aspects of the technologies, along with the need for standardized protocols in both in vitro as well as in vivo testing of 4D-printed structures, which are crucial steps toward eventual clinical realization.

Self-aware active metamaterial cell 3D-printed in a single process

Metamaterials are capable of attenuating undesired mechanical vibrations within a narrow band-gap frequency range; however, real-world applications often require adjustments due to varying loads and frequency content. This study introduces a self-aware, thermo-active metamaterial, 3D-printed in a single process using thermoplastic material extrusion. The adjustment of the natural frequency and band-gap region is achieved through resistive heating of conductive paths, which alters the stiffness of the base cell’s resonator. Additionally, these conductive paths facilitate the detection of the resonator’s excitation frequency and temperature, thereby eliminating the need for external sensors. This dynamic adaptability, experimentally demonstrated by achieving a band-gap tuning range from 505 Hz to 445 Hz with a 17 °C temperature difference, highlights the potential of these metamaterials for applications in smart structures across the aerospace, civil, and automotive industries.

Response Properties of Electrorheological Composite Hydrophilic Elastomers Based on Different Morphologies of Magnesium-Doped Strontium Titanate.

As smart materials, electrorheological elastomers (EREs) formed by pre-treating active electrorheological particles are attracting more and more attention. In this work, four Mg-doped strontium titanate (Mg-STO) particles with spherical, dendritic, flake-like, and pinecone-like morphologies were obtained via hydrothermal and low-temperature co-precipitation. XRD, SEM, Raman, and FT-IR were used to characterize these products. The results showed that Mg-STOs are about 1.5-2.0 μm in size, and their phase structures are dominated by cubic crystals. These Mg-STOs were dispersed in a hydrogel composite elastic medium. Then, Mg-STO/glycerol/gelatin electrorheological composite hydrophilic elastomers were obtained with or without an electric field. The electric field response properties of Mg-doped strontium titanate composite elastomers were investigated. We concluded that dendritic Mg-STO composite elastomers are high-performance EREs, and the maximum value of their energy storage was 8.70 MPa. The significant electrorheological performance of these products is helpful for their applications in vibration control, force transducers, smart structures, dampers, and other fields.

Electro-thermal actuation in recycled aggregate concrete with rapid self-reinforcement via smart cement-based composites

With the growing call for low-carbon and environmentally friendly materials, recycled aggregate concrete (RAC) holds great promise for sustainable development. Nevertheless, significant challenges exist with respect to the material’s poor flexural carrying capacity. Development of an effective method for improving the flexural carrying capacity of RAC under a specific deflection deformation is important for enhancing the range of its structural applications. In this study, an intelligent structural optimisation strategy for compounding RAC with carbon-fibre (CF) reinforced cement-based composites (CFRCs) to realize rapid self-reinforcement via electro-thermal actuation is proposed. As a smart component, CFRC was first researched to investigate its electrical, mechanical, and microscopic properties. The optimal properties were obtained in specimens incorporating 0.5 vol%, CFRC0.5. CFRC0.5 exhibits an electrical resistivity of approximately 0.39 Ω∙m, accompanied by 65.3 % and 33 % increases in flexural and compressive strengths, respectively, when compared to the control mixture without CF. Furthermore, CFRC0.5 can maintain outstanding stability after multiple electro-thermal cycles. Analysis via microscopic characterisation revealed that a satisfactory conductive network can be formed at 0.5 vol% CF. Furthermore, CFs with excellent dispersity are particularly advantageous in improving the mechanical biting force within the cement matrix and restraining the further formation and expansion of microcracks. Thus CFRC0.5 was designed and fabricated as a pre-stress controller to realise rapid structural self-reinforcement, resulting in a 38.6 % improvement in the flexural carrying capacity of the RAC under specific midspan deflection conditions. Additionally, a response behaviour model for midspan deflection with temperature differential was established, showing an excellent correlation between the experimental results and theoretical simulation. This findings from this study highlight the significance of leveraging intelligent techniques to realise rapid self-reinforcement capabilities in concrete structures, facilitating their potential application in smart and adaptive structures.

Effect of hybrid ratio on shape memory properties of graphene oxide‐carbon/glass fiber composites prepared based on vacuum infiltration hot‐press forming experimental system

AbstractShape memory composites now have a wide range of applications in aerospace, medical devices, and smart structures. Seven graphene‐carbon oxide/glass fiber (GO‐CF/GF) hybrid reinforced shape memory composites were prepared using vacuum infiltration hot pressing system (VIHPS) and the shape memory properties of the materials were investigated in 100°C test. By comparing and analyzing the microstructure and shape memory properties of composites containing different volume fractions of GFs, the mechanism of the influence of different hybrid contents of GFs on the organizational properties and shape memory properties was investigated. The results show that when the reinforcement of the composites were all carbon fibers, the composites had the largest elasticity modulus, harder material and the fixation rate of 77.15%, the recovery rate of 95.17%, the porosity of 0.80% and the shape recovery force of 7.98 N. When the reinforcement of the composites were glass fibers, the composites had the smallest elasticity modulus, softer material and the fixation rate of 94.89%, the recovery rate of 77.21%, the porosity of 13.56% and the recovery force of 2.28 N. The results of this test can lay a foundation for subsequent research on fibers with different mixing ratios.Highlights The GO‐CF/GF/EP prepared by VIHPS has excellent shape memory properties. Fiber hybrid ratio affects the composite's porosity and its properties. Fiber hybrid ratio affects the composite's shape fixation, recovery, and memory force. The shape fixation of G6 decreases the lowest with test cycles. Carbon fiber content changes the zero‐stress plane of GO‐CF/GF/EP.

Nonlinear dynamic analysis of opto-electro-thermo-elastic perovskite plates

AbstractPhotostrictive materials have attracted tremendous interest as the new generation of smart materials that can achieve a direct conversion from optical energy to mechanical energy. Understanding their nonlinear mechanical properties under light illumination is of paramount significance for their realistic optomechanical applications. This article proposes a novel opto-electro-thermo-elastic constitutive model that can consider the effects of photostriction, photothermal temperature, and electrostriction for metal halide perovskite crystals and investigates the nonlinear static and dynamic responses of the perovskite plates. The nonlinear governing equations are established based on the first-order shear deformation theory and von Kármán nonlinearity and are numerically solved by the differential quadrature method. A detailed parametric investigation is performed to analyze the effects of light and electricity on the nonlinear mechanical behaviors of perovskite plates. It is concluded that light illumination leads to the presence of optical stress and thermal stress in the perovskite plates, giving rise to increased static and dynamic deformations and stresses, as well as reduced postbuckling and free vibration characteristics. The research findings pave the way for the optomechanical applications of perovskite-based smart materials and structures.

Swift 4D printing of thermoresponsive shape-memory polymers using vat photopolymerization

Shape-memory polymers (SMPs) are smart materials that have gained significant attention in recent years owing to their widespread application in smart structures and devices. Digital light processing (DLP), a vat-photopolymerization-based technique, is a significantly faster technology for printing a complete layer in a single step. The current study reports a facile and fast method for the 3D printing of SMP-based smart structures using a DLP 3D printer and a customized resin. A liquid crystal (LC, RM257) was combined with the resin to introduce shape-memory properties. The combination of LCs in photocurable resin provides the opportunity to directly 3D-print thermoresponsive structures, avoiding the complexity of SMP resin preparation. The structures were printed with different geometries, and the shape-memory response was measured. Lattice structures were fabricated and programmed to obtain tunable mechanical properties. Furthermore, the strain-sensing response was measured to demonstrate the utility of these lattice structures as smart patches for joint-movement sensing. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors.

Free-Form Liquid Crystal Elastomers via Embedded 4D Printing.

Liquid crystal elastomers (LCEs) are a class of active materials that can generate rapid, reversible mechanical actuation in response to external stimuli. Fabrication methods for LCEs have remained a topic of intense research interest in recent years. One promising approach, termed 4D printing, combines the advantages of 3D printing with responsive materials, such as LCEs, to generate smart structures that not only possess user-defined static shapes but also can change their shape over time. To date, 4D-printed LCE structures have been limited to flat objects, restricting shape complexity and associated actuation for smart structure applications. In this work, we report the development of embedded 4D printing to extrude hydrophobic LCE ink into an aqueous, thixotropic gel matrix to produce free-standing, free-form 3D architectures without sacrificing the mechanical actuation properties. The ability to 4D print complex, free-standing 3D LCE architectures opens new avenues for the design and development of functional and responsive systems, such as reconfigurable metamaterials, soft robotics, or biomedical devices.

Electro-mechanical vibro-acoustic characteristics of submerged functionally graded piezoelectric plates with general boundary conditions

The present paper focuses on studying the underwater electro-mechanical vibro-acoustic characteristics of functionally graded piezoelectric material (FGPM) plates with general boundary conditions. For this purpose, the collocation points method is firstly developed to handle vibro-acoustic coupling, which can directly calculate the virtual work of secondary sound pressure via an easy double integral, without pre-simplifying the complex quadruple integral. The proposed FGPM plate model is established in the framework of first-order shear deformation theory (FSDT) and second type constitutive equations of piezoelectric materials, and the macroscopically inhomogeneous electro-mechanical properties are considered by means of Voigt model. The multi-physical fields including electric, mechanical and acoustic fields are uniformly extended in Chebyshev polynomials. Meanwhile, penalty function method is introduced to satisfy the arbitrary mechanical and electric constraints. All energy formulations are processed by Rayleigh-Ritz procedure and a standard governing equation is finally derived. Based on the proposed unified model, the convergence and accuracy for solving vibration and acoustic radiation of FGPM plates are validated firstly. Additionally, the influence of some key parameters on underwater vibro-acoustic characteristics of FGPM plates is fully examined. The results of this paper may provide a reference for future application of FGPM-based smart structures.

Design and manufacture of lead-free eco-friendly cement-based piezoelectric composites achieving superior piezoelectric properties for concrete structure applications

A complex-ion doping strategy fabricates lead-free BCZT ceramic. The excellent properties (d33 ∼ 577 pC/N, Kt ∼ 52%, TC ∼ 110 °C, d∗33 ∼ 620 pm/V, εr ∼ 1820, tanδ ∼ 0.02) were obtained in BCZT ceramic. The in-situ Raman spectroscopy and PFM were conducted to reveal the mechanisms for the superior properties achieved. BCZT ceramics were manufactured for cement-based piezoelectric composites, including 0–3, 2-2 and 1–3 types. 0–3 type (50% BCZT) showed the properties (d33 ∼ 46 pC/N, εr ∼ 310 and Kt ∼ 18.1%). 2-2 and 1–3 types exhibited good piezoelectric properties (d33 ∼ 285 pC/N, εr ∼ 720 and Kt ∼ 33.4% for 2-2 type; d33 ∼ 238 pC/N, εr ∼ 485 and Kt ∼ 29.5% for 1–3 type). Temperature-dependent electrical properties of BCZT-cement composites were systematically explored. Additionally, BCZT ceramic was designed and fabricated for PCD vibration energy harvesting. The output voltage (∼4.9 V) and output power (∼2.4 mW) were obtained. This work underpins the significance of lead-free BCZT ceramic and cement-based piezoelectric composites, and promotes their applications in smart structures.

Thermo-mechanical modeling of semicrystalline triple shape memory polymers

Compared with amorphous shape memory polymers (SMPs), semicrystalline SMPs have more diverse shape memory effects (SMEs) which promotes their application in smart structures. To reveal the driving mechanism of the triple SMEs of semicrystalline SMPs, our study focuses on developing the constitutive model under the condition of finite deformation. In the paper, a thermo-mechanical constitutive model under consideration of the second law of thermodynamics is developed based on the theory of thermodynamics with internal state variables. The model can be used to describe the nonequilibrium response of the amorphous and semicrystalline components in the vicinity of the glass transition, melting, and crystallization. To verify the validity of model, numerical simulation is carried out for a thermo-mechanical shape memory cycle which can be divided into a two-step programing process and a two-step recovery process. The comparison between the model results and the test data shows good agreement.

Book Review of Self-Sensing Concrete in Smart Structures

Self-Sensing Concrete in Smart Structures, published by Elsevier, is the first English monograph in the field of self-sensing concrete and its smart structures. The monograph contains 11 chapters in 3 parts. The first part describes in detail the structure, composition, preparations, testing methods, sensing properties, sensing mechanisms, and smart structures of self-sensing concrete. The second part gives the results of the authors’ systematic research in the field of self-sensing concrete materials and smart structures from 2000 to 2014, including the self-sensing concrete with carbon fiber, nickel powder, and carbon nanotubes. The third part discusses the future challenges and countermeasures for the development of self-sensing concrete and its smart structures. The monograph not only provides a comprehensive introduction to the basic principles of self-sensing concrete and the research cases of self-sensing concrete-based smart structures applications, but also presents a series of representative innovative researches results of selfsensing concrete and its smart structures, as well as plans and deploys the future research and applications of self-sensing concrete and its smart structures. This monograph can provide guidance and reference for scientific researchers and engineers in the field of concrete materials and structures as well as smart materials and structures.

Bifurcation Point Analysis of a Magnetostrictive Sandwich Composite Plate Subjected to Magnetic Field and Axial Force

This article studies parametric vibration and dynamic instability of a rectangular and symmetric magnetostrictive sandwich composite plate (MSCP) on a visco-Pasternak medium. The MSCP consists of three layers; a magnetostrictive layer considers the core and composites as its upper and lower faces. The MSCP subjected to temperature change, parametrically exciting force, and magnetic load is studied with consideration to geometrical von Karman nonlinearity. Based on the energy method and first shear deformation theory (FSDT), Hamilton’s principle is used to achieve the system’s governing equations and boundary conditions. In the next step, the partial differential equation is transformed into ordinary differential equations by applying the Galerkin technique. Then the equation of motion is solved using the multiple-scale method. Numerical results illustrate the stability of the sandwich plate is significantly related to the magnetostrictive parameters. In addition, the effects of significant parameters, such as the effect of amplitude response and parametric excitation or detuning parameter, coupled with the effect of foundation, thickness ratio, aspect ratio, and temperature increment on vibration characteristics, bifurcation points behavior and stability of the systems are charted, plotted and discussed. The innovation of this article is the use of magnetostrictive material in sandwich plates and the development of its mathematical relationships. It is anticipated that the results of this research can contribute to the development of future smart structural applications subjected to in-plane axial forces.

Complex dispersion relations and evanescent waves in periodic magneto-electro curved phononic crystal plates

This paper presents a novel semi-analytical method to consider complex dispersion relations and evanescent wave characteristics in periodic magneto-electro-electric curved phononic crystal plates, based on the plate theory and Bloch-Floquet theorem. Generalized elastodynamic wave equation considering the magneto-electric effects in cylindrical coordinate system is established and discretized with the curved higher-order spectral elements. Then, the proposed approach is validated by the analysis of accuracy and convergence. The influence of magneto-electro coupling effect on dispersion relations are discussed. Significant parameters of the periodic curved phononic crystal are studied systematically, which fundamentally determines the tunability of complex dispersion relations of various guided wave modes including propagative wave modes, purely evanescent wave modes, evanescent edge wave modes, and complex wave modes. It is witnessed that propagative wave modes lead the bandgap to the emergence, variation, and closure with the change of significant parameters. And evanescent wave modes dominate two individual patterns of bandgaps. When the radius angle or curvature changes, the polarization of bandgaps appears. Furthermore, complex wave modes are generated with the increase of curvature resulting in strengthening the attenuation of propagative wave modes. The variation of lattice ratio can separate the intersection point of two propagative wave modes, which induces the opening of two bandgaps and the attenuation of evanescent wave modes. The results of this work provides may benefit the multi-functional development and application of smart materials and structures.

Active Disturbance Rejection Control for Piezoelectric Smart Structures: A Review

The piezoelectric smart structures, which can be labeled as the cream of the crop of smart structures without overstatement, are strongly impacted by a large number of uncertainties and disturbances during operation. The present paper reviews active disturbance rejection control (ADRC) technologies developed for application in piezoelectric smart structures, focusing on measurement, analysis, estimation, and attenuation of uncertainties/disturbances in systems. It first explained vast categories of uncertainties/disturbances with their adverse influences. Then, after a brief introduction to the application of basic ADRC in smart structures, a thorough review of recently modified forms of ADRC is analyzed and classified in terms of their improvement objectives and structural characteristics. The universal advantages of ADRC in dealing with uncertainties and its improvement on the particularity of smart structures show its broad application prospects. These improved ADRC methods are reviewed by classifying them as modified ADRC for specific problems, modified ADRC by nonlinear functions, composite control based on ADRC, and ADRC based on other models. In addition, the application of other types of active anti-disturbances technologies in smart structures is reviewed to expand horizons. The main features of this review paper are summarized as follows: (1) it can provide profound understanding and flexible approaches for researchers and practitioners in designing ADRC in the field and (2) light up future directions and unsolved problems.

Reliability analysis of smart laminated composite plates under static loads using artificial neural networks

The applications of smart structures with integrated piezoelectric elements have been expanding in the last few decades due to the abilities of such structures to withstand mechanical loads and operate as sensors or actuators using their electromechanical coupling. The available manufacturing techniques can result in uncertainties in the structure's geometric parameters, which, coupled with uncertainties in material properties, can lead to unexpected failures or unreliable performance. This paper presents a reliability analysis of a smart laminated composite plate made of a graphite/epoxy cross-ply substrate with a piezoelectric fiber-reinforced composite (PFRC) actuator layer under static electrical and mechanical loads. A coupled finite element (FE) model was developed in COMSOL Multiphysics, from which nondimensional stresses and displacements were calculated. To investigate the effects of randomness in the material and geometric properties, an artificial neural network (ANN) model was developed and trained using generated FE data. Monte Carlo Simulation (MCS) and First- and Second-Order Reliability Methods (FORM/SORM) were then used to shed light on the significance of considering randomness in the various material and geometric parameters and the effect of such uncertainty on the resulting nondimensional stresses and displacements. A coefficient of variation (CV) study identified the piezoelectric stress coefficient as the most significant contributing factor to the variation of all nondimensional parameters. Variation in the nondimensional parameters also increases under the application of an electric load. ANN-based FORM, SORM, and MCS all indicate a pattern of low probability of failure until a threshold value of about 3% of input parameter variation is reached, beyond which there is a rapid nonlinear increase in failure probability with increasing input parameter variation.

Dynamic analysis of porosity dependent functionally graded sigmoid piezoelectric (FGSP) plate

This paper analyzes the vibration behaviour of the functionally graded sigmoid piezoelectric (FGSP) plate subjected to electrical and mechanical loading of a porous and non-porous plate. The sigmoid law is used for the variations of material properties along with the direction of thickness with different porosity types, i.e. even and uneven types. The plate incorporates the geometrical nonlinearity with von Kármán strains and First-order shear deformation theory (FSDT) based displacement field. For getting the nonlinear governing equation from Hamilton's principle or energy principle and higher-order numerical formulation with nine nodded isoperimetric elements and the six degrees of freedom per node. The perfect FGSP plate shows multi-periodic excitation with two strong attractors for SSSS boundary conditions, while quasi-periodic responses and 3-T periodic responses are observed for CCCC and CFFF boundary conditions. For evenly distributed porous SSSS FGSP square plate, the center displacement increases with an increase of the porosity from 0.2 to 0.4, while for un-evenly distributed porous center displacement reduces with a rise of the porous exponent from 0.2 to 0.4. The current analysis outcomes can be used for perfect and porous functionally graded piezoelectric smart structure applications under different electromechanical loading environments.

A Highly Accurate Method for Deformation Reconstruction of Smart Deformable Structures Based on Flexible Strain Sensors.

Smart deformable structures that integrate designing, sensing, and controlling technology have been widely applied in the fields of aerospace, robotics, and biomedical engineering due to their multi-functional requirements. The deformation reconstruction method essential for security monitoring and shape controlling, especially for the large deflection deformation, remains a challenge on accuracy and efficiency. This paper takes a wind tunnel’s fixed-flexible nozzle (FFN) plate as the research object to develop a highly accurate deformation reconstruction method based on sensing information from flexible strain sensors. The mechanical behaviors of the FFN plate with large deflection deformation, which is modeled as a cantilever beam, are studied to analyze the relationship of the strain and moment. Furthermore, the large deflection factor and shell bending theory are creatively utilized to derive and modify the strain–moment based reconstruction method (SMRM), where the contour of the FFN plate is solved by particular elliptic integrals. As a result, structural simulation based on ABAQUS further demonstrates that the reconstruction error of SMRM is 21.13% less than that of the classic Ko-based reconstruction method (KORM). An FFN prototype accompanied by customized flexible sensors is developed to evaluate the accuracy and efficiency of the SMRM, resulting in a maximum relative error of 3.97% that is acceptable for practical applications in smart deformable structures, not limited to the FFN plate.

Recent Progress in 3D Printing of Smart Structures: Classification, Challenges, and Trends

3D Printing of Smart Structures Three-dimensional (3D) printing revolutionizes the smart structures manufacturing. Recent progress in 3D printing methods, materials, and applications of various smart structures are summarized and discussed from a manufacturing perspective in article number 2000271 by Congcong Luan, Yong He and co-workers. The cover is inspired by a traditional Chinese fable, namely Calabash Brothers, where different color calabashes possess different capabilities. Herein, different calabashes represent different smart structures manufactured by 3D printing methods.

Sustainability of Civil Structures through the Application of Smart Materials: A Review.

Every year, structural flaws or breakdowns cause thousands of people to be harmed and cost billions of dollars owing to the limitations of design methods and materials to withstand extreme earthquakes. Since earthquakes have a significant effect on sustainability factors, there is a contradiction between these constraints and the growing need for more sustainable structures. There has been a significant attempt to circumvent these constraints by developing various techniques and materials. One of these viable possibilities is the application of smart structures and materials such as shape memory and piezoelectric materials. Many scholars have examined the use of these materials and their structural characteristics up to this point, but the relationship between sustainability considerations and the deployment of smart materials has received little attention. Therefore, through a review of previous experimental, numerical, and conceptual studies, this paper attempts to draw a more significant relationship between smart materials and structural sustainability. First, the significant impact of seismic events on structural sustainability and its major aspects are described. It is then followed by an overview of the fundamentals of smart material’s behaviour and properties. Finally, after a comprehensive review of the most recent applications of smart materials in structures, the influence of their deployment on sustainability issues is discussed. The findings of this study are intended to assist researchers in properly addressing sustainability considerations in any research and implementation of smart materials by establishing a more explicit relationship between these two concepts.