Embedded Shape Memory Alloy Research Articles

Effect of Embedded Shape Memory Alloy (SMA) on the Low-velocity Impact Behaviour of Stringer Stiffened Composite Plates

Effect of Embedded Shape Memory Alloy (SMA) on the Low-velocity Impact Behaviour of Stringer Stiffened Composite Plates

Thermo-aeroelastic analysis of triangular composite plate with embedded shape memory alloy at supersonic flow

This work investigates the effectiveness of a shape-memory alloy (SMA) in controlling the instabilities of triangular composite plates under supersonic flow. Lagoudas’ quadratic polynomial hardening theory models the SMA effect. First-order piston theory was used for the aerodynamic modeling, and the reference-temperature method was used for modeling the thermal heating. The buckling and post-buckling behaviors were studied for different boundary conditions with four different layups. In addition, buckling and post-buckling of the composite plate, with and without shape memory alloy wire, has been studied. The effect of SMA wire on aeroelastic instabilities is accurately studied. The embedded SMA wire significantly increased the stability region (postpone divergence and flutter velocities) and buckling temperature. Also, the time responses of the triangular composite plate are determined at different Mach numbers, showing that by increasing the Mach number, the SMA wire can control or decrease the vibration amplitudes.

Topology optimization design of recoverable bistable structures for energy absorption with embedded shape memory alloys

In this work, multistable mechanical metamaterials with recoverable capabilities are designed for high energy absorption and resistance to repetitive impacts. Based on the known curved beam with energy dissipation characteristics, the shape memory alloys (SMAs) curved beam is added and optimized to achieve recoverability of the bi-layer beam structure. To simultaneously achieve bistable characteristics and recoverability in the designed metamaterial, the optimization model is formulated to maximize the energy absorption capacity of the structure while constraining the peak and valley forces. To solve this complex and highly nonlinear topological optimization problem with stringent constraints, the topological design of the SMAs layer is represented using a limited number of design variables along with the material-field series expansion strategy, and the optimization problem is subsequently solved using a non-gradient-based optimization algorithm. Finite element simulation results demonstrated that the optimized design possesses a substantial capacity for energy absorption. Additionally, the design structure can recover to its initial state from buckling induced by the initial load by regulating the external temperature. Different multistable metamaterials, including those designed to prevent repetitive impacts, have been further developed based on the designed recoverable high-energy-absorbing bistable unit cells, utilizing combinations of varying energy absorption capacities.

Safe Supervisory Control of Soft Robot Actuators.

Although soft robots show safer interactions with their environment than traditional robots, soft mechanisms and actuators still have significant potential for damage or degradation particularly during unmodeled contact. This article introduces a feedback strategy for safe soft actuator operation during control of a soft robot. To do so, a supervisory controller monitors actuator state and dynamically saturates control inputs to avoid conditions that could lead to physical damage. We prove that, under certain conditions, the supervisory controller is stable and verifiably safe. We then demonstrate completely onboard operation of the supervisory controller using a soft thermally actuated robot limb with embedded shape memory alloy actuators and sensing. Tests performed with the supervisor verify its theoretical properties and show stabilization of the robot limb's pose in free space. Finally, experiments show that our approach prevents overheating during contact, including environmental constraints and human touch, or when infeasible motions are commanded. This supervisory controller, and its ability to be executed with completely onboard sensing, has the potential to make soft robot actuators reliable enough for practical use.

Inexpensive monolithic additive manufacturing of silicone structures for bio-inspired soft robotic systems

In soft robotics, the fabrication of extremely soft structures capable of performing bio-inspired complex motion is a challenging task. This paper introduces an innovative 3D printing of soft silicone structures with embedded shape memory alloy (SMA) actuators, which is completed in a single printing cycle from CAD files. The proposed custom-made 3D printing setup, based on the material extrusion (MEX) method, was used in conjunction with a cartesian pick and place robot (CPPR) to completely automate the fabrication of thick silicone skins (7 mm) with embedded shape memory alloy actuators. These structures were fabricated monolithically without any assembly tasks and direct human intervention. Taking advantage of the capability to 3D print different geometries, three different patterns were fabricated over the silicone skin, resulting in remarkable dynamic motions: an out-of-plane deformation (jumping of the structure from the x-y plane to the x-z plane) was achieved for the first-time employing silicone skin, to the best of the author’s knowledge. In addition, two process parameters (printing speed and build plate temperature) and the extruded silicone curing mechanisms were investigated to enhance the printing quality. This paper aims to advance the role of additive manufacturing in the field of soft robotics by demonstrating all the benefits that a low-cost, custom-made silicone 3D printer can bring to the table in terms of manufacturing soft bio-inspired structures.

One-shot additive manufacturing of robotic finger with embedded sensing and actuation

A main challenge in the additive manufacturing (AM) field is the possibility to create structures with embedded actuators and sensors: addressing this requirement would lead to a reduction of manual assembly tasks and product cost, pushing AM technologies into a new dimension for the fabrication of assembly-free smart objects. The main novelty of the present paper is the one shot fabrication of a 3D printed soft finger with an embedded shape memory alloy (SMA) actuator and two different 3D printed sensors (strain gauge and capacitive force sensor). 3D printed structures, fabricated with the proposed approach, can be immediately activated after their removal from the build plate, providing real-time feedback because of the embedded sensing units. Three different materials from two nozzles were extruded to fabricate the passive elements and sensing units of the proposed bioinspired robotic finger and a custom-made Cartesian pick and place robot (CPPR) was employed to integrate the SMA spring actuator into the 3D printed robotic finger during the fabrication processes. Another novelty of the present paper is the direct integration of SMA actuators during the 3D printing process. The low melting thermoplastic polycaprolactone (PCL) was extruded: its printing temperature of 70 °C is lower than the SMA austenitic start temperature, preventing the SMA activation during the manufacturing process. Two different sensors based on the piezoresistive principle and capacitive principle were studied, 3D printed and characterized, showing respectively a sensitivity ratio of change in resistance to finger bending angle to be 674.8 frac{Omega }{^circ mathrm{Angle}} and a capacitance to force ratio of 0.53 frac{mathrm{pF}}{mathrm{N}}. The proposed manufacturing approach paves the way for significant advancement of AM technologies in the field of smart structures with embedded actuators to provide real-time feedback, offering several advantages, especially in the soft robotics domain.

Highly Dynamic Bistable Soft Actuator for Reconfigurable Multimodal Soft Robots

AbstractMatching the rich multimodality of natural organisms, i.e., the ability to transition between crawling and swimming, walking and jumping, etc., represents a grand challenge in the fields of soft and bio‐inspired robotics. Here, a multimodal soft robot locomotion using highly compact and dynamic bistable soft actuators is achieved. These actuators are composed of a prestretched membrane sandwiched between two 3D printed frames with embedded shape memory alloy (SMA) coils. The actuator can swiftly transform between two oppositely curved states and generate a force of 0.3 N through a snap‐through instability that is triggered after 0.2 s of electrical activation with an input power of 21.1 ± 0.32 W (i.e., electrical energy input of 4.22 ± 0.06 J. The consistency and robustness of the snap‐through actuator response is experimentally validated through cyclical testing (580 cycles). The compact and fast‐responding properties of the soft bistable actuator allow it to be used as an artificial muscle for shape‐reconfigurable soft robots capable of multiple modes of SMA‐powered locomotion. This is demonstrated by creating three soft robots, including a reconfigurable amphibious robot that can walk on land and swim in water, a jumping robot (multimodal crawler) that can crawl and jump, and a caterpillar‐inspired rolling robot that can crawl and roll.

Design and Control of SLPM-Based Extensible Continuum Arm

Abstract As an important branch of reconfigurable robots, extensible continuum robots are soft and light, with the flexibility of movement and high adaptability in complex environments. These robots have very broad applications in a variety of fields, including military reconnaissance, geological exploration and rescue operations. In this paper, a high folding ratio, flexible, and compact extensible continuum arm is designed using a novel combination of parallel and deployable mechanisms. We present the spherical-linkage parallel mechanism (SLPM) as a flexure hinge. The analysis suggests that the SLPM is highly flexible and meets the requirements for many DoFs (degrees-of-freedom) needed in various fields. The folding ratio of the SLPM was 72.73. Following this, we present an SLPM compliant module powered by a set of embedded shape memory alloy (SMA) springs. These can change the internal elasticity of the module as temperature changes, thereby varying the stiffness. Moreover, the control system is designed to enable real-time cooperation between multiple motors and carries out simulations for deployable motion. The extensible continuum arm prototype was manufactured and its performance was tested in complex environments. From the results, it is shown that the arm can be utilized for rescue during disasters as well as investigation and repair of aircraft engines.

Experimental analysis of fiber-reinforced laminated composite plates with embedded SMA wire actuators

Shape memory alloy (SMA) wires are effective smart actuators since they provide relatively large actuation force and strain in a very limited space. Embedding SMA wires in flexible laminated composite plates or shells allows for creating active structures for morphing applications. However, the design of such structures is challenging due to the nonlinear thermomechanical coupling of SMA materials, the adhesion of the SMA actuators to the resin, the effect of temperature on the adhesion strength, the heat transfer between the SMA wires and the surrounding laminate, and the convection boundary conditions. This paper presents an experimental analysis of smart fiber-reinforced composite laminated plates with embedded SMA wires, focusing on the relationship between the applied electric current, measured temperature of the SMA wires, and the resulting tip deflection. A temperature-based control method was developed to achieve the required wire temperature and tip deflection as quickly as possible. Results showed that the fiber-orientation angle of the composite plies and the convection boundary conditions have significant effects on the structure’s actuation. With cyclic actuation, damage starts around the heated SMA wires and can grow to cause delamination at areas between neighboring SMA wires and yielding of the matrix material, resulting in permanent deformation.

Mechanical behavior and recoverable properties of CFRP shape memory alloy composite under different prestrains

This paper explored a prestressed CFRP/SMA composite system, which can be applied to add prestress to the civil structural members. The composite system was composed of carbon fiber reinforced polymer (CFRP) sheets and the embedded shape memory alloy (SMA) wires. The prestress in CFRP sheets was formed by the recovery of SMA wires. Four groups of fully composite (Type I) specimens were fabricated to bear a unidirectional static load to investigate their tensile mechanical properties. Three groups of partial composite (Type II) specimens and five groups of SMA wire specimens were used to study their recoverability. The static test results showed that two main failure modes of the Type I specimens were observed, and the strength of the material was affected by the structural form of the composite. The recovery test results showed that the SMA wire could generate different levels of recovery stress under various amounts of prestrain, and the maximum recovery stress can reach 394.2 MPa for the SMA wire with 6% prestrain by heating it to 131℃. More importantly, the recovery stress can be introduced into the CFRP sheets. In addition, an analytical model for predicting the stress–strain relationship and material strength of the fully composite was proposed, and an improved segmented recovery stress–temperature model of the SMA wire under constraint conditions was also put forward. The results indicated that the calculated values are in good agreement with the experimental values, and the proposed model can effectively predict the mechanical and recoverable properties of the composites.

A structural design approach for a droop nose morphing demonstrator with shape memory alloy patches

An innovative concept has been devised for assisting an actuator to morph a Droop Nose (DN) structure, which is comprised from the skin and three longitudinal omega stringers. The concept is based on the development of a suitable composite patch, with embedded shape memory alloy (SMA) wires, and the appropriate design of a DN configuration for morphing purposes. The integration of composite patches, to the DN structure, has a dual innovative role: (a) it can either provide/extend the morphing capabilities of the structure, in terms of displacement or (b) it can reduce the required actuation forces for obtaining morphing of the DN structure. For determining the most suitable DN configuration, for the application, a sensitivity analysis, with the aid of ANSYS finite element (FE) software and a design of experiments (DoE) approach, has been carried out. The investigated parameters (geometrical and lamination characteristics) are selected to vary the stiffness of the DN structure. Additionally, a numerical parametric FE model, of the SMA patch and its configuration, is developed and analysed. The developed FE models simulated the shape memory effect of SMA wires considering their activation temperature and hence their thermo-mechanical behaviour. Eventually, a possible integration of the SMA patches to the DN structure is proposed and the respective remarks are highlighted.

Flutter performance of shape memory alloy-embedded 3D woven flexible composite plate under subsonic flow

Recently, 3D composites have gained prominence over 2D composites due to their remarkable through-the-thickness reinforcement that enhanced performances of structures subject to multi-directional stress conditions. However, it is at the expense of reduced in-plane properties. 3D composites also increased damage tolerance due to their high impact and delamination resistance properties, which are susceptible in 2D composites. In aeronautics, both are major concerns in primary structures such as lifting and control surfaces due to high vibrational loads from the airflow. Advancements in the aeroelasticity of aircraft structures show an increasing trend in using smart materials with composite structures for improved aeroelastic performance. An example is combining shape memory alloys (SMAs) with composites for improving damping, stiffness, and vibrational characteristics by utilizing stress generation and strain accommodation properties of SMAs in response to temperature and load, respectively. Published works are mostly numerical in nature, and experimental research is noticeably lacking as aeroelasticity is multidisciplinary and involves both structural and aerodynamic methodology. In this work, 3D composites with embedded SMA wires (for improved in-plane properties) are evaluated in terms of flutter performance in wind tunnel flutter testing under low airspeed conditions. Three 3D orthogonal interlock configurations with a different interlocking pattern of yarns with SMA wire were considered. These 3D configurations are layer-to-layer (L2L), through-the-thickness (TT), and a modified interlock (MF) structure that provides the strongest grip to SMA wire than L2L and TT. The effect of SMA positioning, at mid and near to trailing and leading edges of the cantilevered composite plate, on the aeroelastic flutter properties is also investigated. Results showed that activating SMA wires embedded in 3D structures have significantly improved post-flutter properties while there is a decrement in flutter speed and flutter frequency due to increased flexibility of deflected plate in the airflow by SMA-induced stresses. Among 3D structures, L2L with SMA near to trailing edge showed significant improvement in post-flutter properties by decreasing 22.2% in twist limit cycle oscillation (LCO) amplitude while L2L with SMA at mid showed a decrement of 9.5% for bending LCO amplitude. Hence, this work showed that embedding SMA is beneficial for mitigating the post-flutter vibrations but at the consequence of reduced flutter speed and frequency of flexible composite plate.

A nonlinear aerothermoelastic model for slender composite beam-like wings with embedded shape memory alloys

This paper reports the formulation of an aerothermoelastic tool developed to investigate the behavior of flexible beam-like wings made of a hybrid adaptive material. Here, hybrid materials are defined as laminated composites additionally reinforced with embedded shape memory alloy wires. As main novelties, the proposed model couples geometrical, material, and aerodynamic nonlinearities to the thermal dynamics of SMA wires undergoing Joule’s effects, thereby establishing a multi-physical nonlinear problem. Geometrical nonlinearities were taken into account via an FE model of a 2D Timoshenko’s beam experiencing large deformations. Material nonlinearities were incorporated by a semi-empirical micro-mechanical model that computes the properties of hybrid laminates. To complement, nonlinear aerodynamic effects were introduced via an unsteady strip theory method in the time-domain, along with a nonlinear stall model and an assumption of follower aerodynamic forces. A set of numerical aerothermoelastic cases was performed by assuming various layups and SMA temperatures, with the objective of tailoring the aeroelastic response of hybrid wings. These cases were shown to lead to a considerable reduction in both post-flutter oscillations and post-divergence amplitudes as the SMA temperature increases. The outcomes have indicated compelling evidences on the applicability of embedded SMAs for structural, shape or aeroelastic control of flexible wings.

A unified modeling method for dynamic analysis of GPLs-FGP sandwich shallow shell embedded SMA wires with general boundary conditions under hygrothermal loading

In this research, the dynamic analysis of graphene platelets (GPLs) reinforced functionally graded porous (FGP) sandwich shallow shell embedded shape memory alloy (SMA) wires with general boundary conditions under hygrothermal loading is conducted. Four different porosity distributions of FGP reinforced with four various GPLs dispersion patterns are considered. Based on the Brinson formulation, the constitutive equation of the SMA is established. The energy functional of the sandwich shallow shell is constructed by employing the Hooke’s law and the first-order shear deformation theory (FSDT). Ultimately, the dynamic characteristics of the sandwich shallow shell are obtained by solving the energy functional with the Rayleigh-Ritz method. After the verification of accuracy and reliability, parametric studies on the effects of material properties, geometrical parameters, and boundary conditions are investigated.

Thermal buckling of trapezoidal composite laminated plates with embedded shape memory alloys

AbstractThe present work deals with thermal buckling of trapezoidal composite plates with embedded shape memory alloy (SMA) wires. In order to estimate the thermomechanical behavior of SMAs, Brinson's model is applied. The thermal buckling equations are derived based on first‐order shear deformation theory, and then solved by means of two‐dimensional generalized differential quadrature method. A parametric study is performed to demonstrate the influence of some parameters such as volume fraction and pre‐strain of SMA wires, the geometric properties, lay‐up configuration, as well as boundary conditions on the critical buckling temperature of trapezoidal composite plates. Numerical results state that the positive effects of SMA wires are restricted to a limited range of thickness and temperature. Results also show that SMA wires can play a destructive role in the thermal buckling behavior of trapezoidal plates, depending on the geometry of the structure, stacking sequence of layers, and boundary conditions.

Introduction and comprehensive theoretical framework of analysis of Smart Plate retrofitted reinforced concrete members (SPRRCs)

Several reasons result in the need for retrofitting of existing reinforced concrete structures, and extensive effort is devoted to invent and implement different methods for strengthening RC members. One of the leading rehabilitation techniques is attaching FRP strips, but FRP materials’ low ductility has caused several issues such as FRP-structure debonding, boundary layer cracking, and brittle behaviour of the strengthened RC members. To overcome these drawbacks, the Smart Plate (SP) which is a ductile retrofitting cover, is proposed for the first time. This cover is formed by embedding Shape Memory Alloy (SMA) wires in an elastomeric substrate. The SMAs exhibit certain properties, including superelasticity, shape memory effect, and temperature-dependent behaviour, while the elastomer can withstand severe stretches. To investigate SP-retrofitted RC beams (SPRRC) characteristics, at first, a computer program has been developed based on the fiber analytical method to analyse the strengthened concrete members. The program is verified against experimental and finite element method (FEM) data for ordinary, FRPRC, SMARC and SPRRCs members. Following verification, the program and FEM are implemented to conduct a comprehensive analysis of the influential parameters affecting the behaviour of SPRRCs including SMA percentage and working temperature. As a result, the SPRRCs show improved stiffness and strength compared to ordinary beams. They also behave in a ductile way contrary to FRP-strengthened beams. The FMA program and the FEM simulations both indicate that the SMA phase transition temperature significantly alters the performance of SPRRCs. Moreover, FMA and FEM outcomes approve that the smart plate is less likely to debond from the strengthened structural member, which is a remarkable advantage. Additionally, a parametric study is conducted, and a characteristic moment–curvature diagram is proposed, which approves the merits of using SP as an alternative retrofitting cover. These advantages are the significant enhancement in moment capacity, yielding moment, ultimate curvature, and ductility.

Shape memory alloy based 3D printed composite actuators with variable stiffness and large reversible deformation

Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft polymer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufacturing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators.

Evaluation of the Mechanical Properties of Glass/Epoxy Composite by Embedding Shape Memory Alloy and Nanoclay

Embedding smart materials in the composite to enhance mechanical strength have become a research hotspot owing to their unique properties. The present research also focus on novel way to fabricate composite by embedding Shape Memory Alloy (SMA) wire and montmorillonite (MMT) nanoclay by varying clay concentration (0-7 wt.%). The extent of dispersion of nanoclay in epoxy resin was studied using Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD). Fabricated samples were examined for tensile, flexural and impact characteristics. Scanning Electron Microscopy (SEM) was used to study the adhesion, delamination and damage occurred within the composite due to tensile loading. Results shows that the tensile strength, flexural strength and impact energy of SMA/MMT/glass/epoxy composite was improved by 23%, 21% and 57% respectively, when it was compared with composite with glass/epoxy composite.

On the free vibration and design optimization of a shape memory alloy hybrid laminated composite plate

A shape memory alloy (SMA) is a temperature-dependent smart material that can be used to tune the stiffness of structures in a thermal environment. In the present article, vibrations of hybrid laminated composite plates reinforced with shape memory alloy fibers under temperature change are studied. Parametric free vibration analysis is conducted to study the effect of the SMA volume fraction, SMA fibers prestrain, length-to-width ratio, and thickness-to-length ratio on the fundamental natural frequency and critical thermal buckling temperature of the hybrid plate subject to fully clamped and fully simply supported boundary conditions. With the objective of maximizing the fundamental natural frequency of the hybrid plate, for the first time, simultaneously, the optimum stacking sequence of the hybrid plate and the best layers to embed the shape memory alloy fibers are found. Interestingly, the study shows that the notion of embedding SMA fibers in the composite plate does not guarantee an increase in the fundamental natural frequency. Depending on the stacking sequence and the layers in which the SMA fibers are embedded, adverse effects might happen. It is shown that inserting the SMA fibers in layers close to the mid-plane maximizes the fundamental natural frequency of the plate.

Experimental investigation of sandwich panels with hybrid composite face sheets and embedded shape memory alloy wires under low velocity impact

AbstractThis experimental study was conducted to investigate the behavior of hybrid composite sandwich panels with superelastic shape memory alloy (SMA) wires under low velocity impact (LVI). Square‐shaped sandwich panels were made few of a foam core and hybrid composite structures with carbon fiber and glass fiber, in which prestrained superelastic SMA wires were embedded between the layers. The sandwich panels had symmetrical and asymmetrical lay‐ups and SMA wires were placed between the layers with different states. LVI tests were performed by drop weight impact testing machine. Moreover, damaged areas of the panels were estimated using thermography. The experimental results showed that the impact performance of the panels improved after embedding SMA wires. The presence of the SMA within the composite sandwich structure prevented the full perforation of the samples and reduced the internal delamination area. The utilization of SMA wires embedded in front face sheet, which is subject to the direct impact, is more effective than the utilization of wire in the back face layer. It was also found that increasing the layers of the back face and asymmetrication of the structure were more effective than the use of SMA wires in the symmetric structure in improving the panel impact resistance.