Light-activated Shape Memory Polymer Research Articles

Actuation of light-activated shape memory polymer laminated beams: theory and experiment

Actuation of light-activated shape memory polymer laminated beams: theory and experiment

Frequency manipulation of a light-activated shape-memory polymer-laminated cylindrical shell

A light-activated shape-memory polymer is a novel smart material that exhibits a dynamic Young's modulus when exposed to light. The non-contact actuation feature facilitates the lamination of a light-activated shape-memory polymer on host structures for realising frequency control. In this study, we investigated the natural frequency of a simply supported cylindrical shell coupled with light-activated shape-memory polymer patches located arbitrarily on the shell. Initially, we compared the natural frequency of a completely laminated cylindrical shell using two different approaches. Further, we analysed the effect of changes in the length and location of the light-activated shape-memory polymer patch pair on the natural frequency of the cylindrical shell. Based on the experimental results, we propose an optimal scheme, wherein several light-activated shape-memory polymer patch pairs are distributed on the surface of the shell, and the frequency control capability of the proposed scheme is evaluated comprehensively. The results verify that the optimal scheme has an adequate control effect on the natural frequency of the cylindrical shell.

Nature frequency manipulation of plates laminated with LASMP via Ritz method

Frequency control can be realized via laminating a novel smart material: light activated shape memory polymer (LASMP) whose Young’s modulus varies under light field. In this work, frequency control of plates with LASMP patches is studied. Validation is fulfilled by comparing present results with FEM results for both beams and plates. Furthermore, frequency analysis of plate with LASMP patch pair whose location or size varies is also investigated. Finally, the optimal frequency control scheme of the composite plate is presented and studied in detail. Results show that the optimal scheme has obvious control effect on natural frequency of the plate.

Nonlinear pull-in analysis of LASMP laminated micro-plate considering micro-scale effect

This research concentrates on pull-in behavior of a micro-plate laminated with a novel material: light activated shape memory polymer (LASMP). Under light exposure, this material can realize dynamic Young’s modulus. With this feature, a LASMP laminated micro-plate model considering micro-scale effect and geometric nonlinearity is proposed. Dynamic equations of the micro-plate system are derived via Hamilton principle and solved by Galerkin method whose accuracy is validated by FEM. Effect of size dependency and dynamic Young’s modulus of LASMP on pull-in behavior of the micro-plate are studied. Present study provided a technique to manipulate pull-in phenomenon of electrically actuated micro-plate.

A microbeam based piezoelectric energy harvester with LASMP

This work developed a piezoelectric micro-beam based energy harvester laminated with light activated shape memory polymer (LASMP). With noncontact mechanism and dynamic Young’s modulus of LASMP, natural frequency of the energy harvester can be tuned during light exposure. Based on modified couple stress theory, the governing equation of the size-dependent micro-beam is derived via Hamilton’s principle. Analytic solution of natural frequency and power output of the micro-beam is presented. Influence of size effect and dynamic Young’s modulus of LASMP on natural frequency and power output is investigated. Present research suggested that application of LASMP in micro-engineering is potential and effective.

Pull‐in analysis of microbeam laminated with LASMP

This work focuses on the pull-in phenomena of electrically actuated size-dependent microbeam laminated with the light-activated shape memory polymer, which can realise the Young's modulus variation under the light exposure. Based on the modified couple stress theory, a size-dependent microbeam model is developed. The dynamic governing equation of the microbeam is derived according to the Hamilton principle and solved by the Galerkin method and Runge–Kutta method numerically. The reliability and accuracy of the present method are validated experimentally. The static and dynamic pull-in behaviours of the microbeam are studied when the microbeam is under a purely direct current voltage and alternating current voltage, respectively. Influences of the size effect and dynamic Young's modulus on pull-in behaviour of the microbeam are discussed comprehensively. This research may be helpful and useful in electrostatically actuated microstructure applications and provide a theoretical foundation for designers and engineers.

Remote actuation of light activated shape memory polymers via D-shaped optical fibres

Shape memory polymers (SMPs) and their composites (SMPCs) can hold a programmed temporary shape and recover to their original shape once exposed to a particular external stimulus. The stimulus light has the advantage of being both an excitation energy source and a control signal carrier for remote actuation of SMP materials. Here we present the capability of D-shaped optical fibres to send near infrared (NIR) light into a light activated shape memory polymer composite (LASMPC) which generates the adequate photothermal effect necessary for the shape recovery process of relatively large samples. A D-shaped optical fibre enables dispersion of light through the polished area around the fibre than the dispersion of light through the tip of the fibre. Embedment of a D-shaped optical fibre in a LASMPC creates a single unit smart actuator, which can be remotely activated by light. Remotely controllable smart actuators can be located at any difficult to reach positions and controlled safely with light energy. It would be a breakthrough technology for biomedical, aerospace and many other engineering applications.

Microscopic control actions of LaSMP actuators on hemispherical shells

Light activated shape memory polymer (LaSMP) is one of novel shape memory polymers with dynamic strain and Young’s modulus when exposed to UV lights. This study investigates distributed microscopic control actions of LaSMP patches on hemispherical shells with free boundary. Based on strain models established in the experiments, governing equations of the spherical shell are defined and control forces in the meridional, circumferential and transverse directions are derived respectively. In case studies of LaSMP patch laminated on the shell by covering specific wavelength at each mode in the circumferential direction, the meridional and circumferential forces turn to zero. Then, the dominant transverse control forces and its components resulting from the bending moments and membrane forces are compared at different modes. Parametric analyses are carried out to evaluate the microscopic actuation effects of actuator position, thickness and shell radius, LaSMP thickness, etc. LaSMP induced meridional and circumferential microscopic membrane/bending control actions on hemispherical shells are evaluated. The analyses indicate that the transverse control forces increase with increasing of LaSMP patch thickness and decreasing of hemispherical shell thickness and radius. Then, the normalized control forces are derived by dividing LaSMP patch size. The parametric analyses confirm that the normalized control forces caused by membrane forces dominate the control effect and the best control position is near the boundary of hemispherical shell. This work provides an analysis procedure on estimating LaSMP vibration control actions and gives theoretical predictions for idealized LaSMP vibration control of hemispherical shells.

Frequency analysis of beams with LASMP using Ritz method

The present work concentrate on frequency analysis of beams laminated with light activated shape memory polymer (LASMP), whose Young’s modulus can be adjusted by light exposure. Based on this noncontact mechanism, stiffness of beams with LASMP can be manipulated so as to realize frequency control. Natural frequency of LASMP patch laminated beams with different boundary conditions is computed by present methodology and FEM for validation first. Then, influence of LASMP patch pair length and location on natural frequency of simply supported beam is evaluated numerically. This work is helpful and useful for frequency control of beams in practical applications.

Vibration Control of Hemispherical Shells with Light-Activated Shape Memory Polymers

Light-activated shape memory polymer (LaSMP) is a novel actuator with dynamic Young’s modulus and strain when exposed to ultraviolet lights, which can be used in noncontact vibration control. This study focuses on the vibration control effect of LaSMP patches on hemispherical shells with free boundaries. An LaSMP strain variation model is presented with experimental verifications. Based on the strain model, the control forces of LaSMP patches on hemispherical shells are introduced. The FEM method is used to obtain natural frequencies of the free hemispherical shell by solid modeling in ANSYS and proved by comparing numerical results with analytical and experimental results. Using the modal expansion method, the LaSMP vibration control of hemispheres is investigated, and independent modal responses are presented and evaluated. The results indicate that LaSMP patch can control vibrations of hemispherical shells by reducing vibration amplitudes. And the control effect is better for low modal vibration, as the LaSMP-induced strain is relatively smaller. By establishing the relationship between LaSMP actuator forces and modal amplitude reduction, this study offers an analytical tool and procedure for future LaSMP application to vibration controls of flexible structures.

Effects of selectively triggered photothermal particles on shape memory polymer composites: An investigation on structural performance, thermomechanical characteristics and photothermal behaviour

Light-activated shape memory polymer composites (LASMPCs) have the ability to facilitate breakthrough technological advancements in aerospace and space engineering applications since the shape memory effect can be remotely controlled by a light beam. Introduction of rare-earth organic complexes–based photothermal fillers such as Nd(TTA)3Phen and Yb(TTA)3Phen into thermally activated shape memory polymers has been reported as a convenient and commercially available approach to prepare light-activated shape memory polymer composites. Such light-activated shape memory polymer composites undertake selective photothermal stimulation due to light and applicable for macroscale and microscale applications. This article presents the effects of added rare-earth organic complexes of Nd(TTA)3Phen and Yb(TTA)3Phen, as well as glass fibre reinforcements on structural performance and shape memory behaviour of light-activated shape memory polymer composites. The physical and mechanical properties, as well as thermomechanical, shape memory, and photothermal behaviours, were systematically investigated. It has been found that the combination of photothermal fillers and glass fibre reinforcements has enhanced the capacity of light-activated shape memory polymer composites to apply for a wider range of large-scale engineering applications.

Frequency Control of Thin Plates with Light-Activated Shape-Memory Polymers

Light-activated shape-memory polymer (LaSMP) is a novel shape-memory material whose Young’s modulus can be manipulated with high-energy light irradiations. This study focuses on the frequency control of LaSMP-laminated simply supported thin plate by light-induced actuations. The governing equation of thin plate covered by LaSMP patch with arbitrary distribution is derived. The controlled frequency is solved numerically based on the Rayleigh–Ritz method and degenerates to an analytical solution of the fully laminated plate. The finite element method (FEM) is used to validate numerically solved analytical solutions, and FEM results are compared favorably with those solutions. Based on the numerical results of thin plate with partly covered LaSMP, the influences of LaSMP size and location on frequency control are investigated. The data suggest that the effect of frequency control is best when LaSMP is placed at the peak amplitude of the mode shapes with larger covering area. This study indicates that LaSMP can be a potential smart material for controlling frequency of thin plates by noncontact light actuations.

Dynamic analysis of a simply supported beam with LaSMP patches

Light-activated shape memory polymer (LaSMP) is a novel smart material, whose stiffness can be tuned by irradiating with UV light. By changing the Young’s modulus of LaSMP patches, the natural frequency of a simply supported beam laminated with LaSMP patches can be actively affected and the dynamic response of the beam can be influenced. Based on the stepped beam theory, dynamic equations were established for a simply supported beam laminated with LaSMP patches. The effect of LaSMP patch properties on the frequency variation of the first three modes was analyzed. It was found that the frequency variation range increases with increasing length. The strategy of locating the LaSMP patch pair on a single location was discussed first, and it was observed that when the LaSMP patch pair was located at antinodes of each mode, the widest frequency control range can be obtained. When multiple LaSMP patch pairs were considered, analytical results showed that the natural frequency ranges were 24.97% and 52.47% higher than by concentrating the patches on a single location for the second and third mode, respectively. When the controllable natural frequency range increases, the control capability of the LaSMP patch on the dynamic response of the beam structure increases as well. As a result, multiple LaSMP patches would have better potential for vibration control than single patches.

Ultraviolet-Activated Frequency Control of Beams and Plates Based on Isogeometric Analysis

A new light-activated shape memory polymer (LaSMP) smart material exhibits shape memory behaviors and stiffness variation via ultraviolet (UV) light exposures. This dynamic stiffness provides a new noncontact actuation mechanism for engineering structures. Isogeometric analysis (IGA) utilizes high order and high continuity nonuniform rational B-spline (NURBS) as basis functions which naturally fulfills C1-continuity requirement of Euler–Bernoulli beam and Kirchhoff plate theories. Compared with the traditional finite elements of beams and plates, IGA does not need extra rotational degrees-of-freedom while providing accurate results. The UV light-activated frequency control of LaSMP fully and partially laminated beam and plate structures based on the IGA is presented in this study. For the analysis of LaSMP partially laminated plates, the finite cell approach in the framework of IGA is proposed to handle NURBS geometries containing trimming features. The accuracy and efficiency of the proposed isogeometric approach are demonstrated via several numerical examples in frequency control. The results show that, with LaSMPs, broadband frequency control of beam and plate structures can be realized. Furthermore, changing LaSMP patch sizes on beams and plates further broadens its frequency control ranges. Studies suggest that: (1) the newly developed IGA combining finite cell approach is an effective numerical tool and (2) the maximum frequency manipulation ratios of beam and plate structures, respectively, reach 24.30% and 16.75%, which demonstrates the feasibility of LaSMPs-induced vibration control of structures.

Responses of rings with light-activated shape memory polymers regulated by neural network and phase shift

Light-activated shape memory polymer is able to hold the temporary shape and to change the permanent shape upon exposures of ultraviolet lights with specific wavelengths. The study aims to provide a non-contact and temperature-independent technique to suppress the vibration of rings using light-activated shape memory polymer. Forced responses of flexible rings laminated with light-activated shape memory polymer patches are evaluated. Dynamic equations of light-activated shape memory polymer–laminated rings are established first. With the modal expansion method, the modal force of light-activated shape memory polymer actuators is derived and then the modal responses (with or without control) are evaluated. A generic kth order and its simplified light-activated shape memory polymer constitutive equations are established based on the chemical kinetics. Light-activated shape memory polymer shows the dynamic stiffness when exposed to ultraviolet lights, and this feature is reflected in its constitutive equations influenced by light intensity, material constant, thickness, and so on. With these derivations, the relationship of light intensity and modal force is established and it exhibits a hysteresis phenomenon. The procedure of identifying the hysteresis model using the neural network is described. Then, the phase shift and neural network control techniques are, respectively, applied to enhance the control effects. The neural network vibration control (with a maximal reduction in 98.1%) is very effective to improve light-activated shape memory polymer’s actuation capability.

Light-induced vibration control of parabolic cylindrical shell panels

Parabolic cylindrical shell panel is useful in the aerospace. Light-activated shape memory polymer is a novel kind of smart materials. It is capable of offering a non-contact control way at the room temperature. In this study, the parabolic cylindrical shell panel laminated with light-activated shape memory polymer actuators is analyzed. First, the dynamic equations of the parabolic cylindrical shell panel coupled with light-activated shape memory polymer actuators are established; the modal control force of light-activated shape memory polymer actuators is derived with the modal expansion method. Then, the strain variation of light-activated shape memory polymer actuators is modeled based on the chemical kinetics. Furthermore, Young’s modulus of light-activated shape memory polymer actuators is measured through the biaxial tension experiments. The strain variation of light-activated shape memory polymer actuator with initial strain is also measured. The established strain model is validated by the experimental data of strain variation. In this case study, the snap-back control effects of the first four modes, that is, the (1,3), (1,4), (2,4), and (2,5) modes are evaluated. The study shows light-activated shape memory polymer actuators are effective to control the vibration of parabolic cylindrical shell panels. Light-activated shape memory polymer actuators have potential applications for the vibration control of double-curvature shells.

Quasi-linear viscoelastic modeling of light-activated shape memory polymers

In this article, we model the mechanical behavior of light-activated shape memory polymers with a view toward determining the effect of the viscoelasticity of the polymers with regard to their shape memory response. This study is a companion to our earlier investigation of both isotropic and anisotropic elastic light-activated shape memory polymers. The constitutive model is based on a multi-network approach consisting of two microstructural networks, the original network and the second network that is formed due to light irradiation. A single integral model is adopted to incorporate the viscoelastic response in the original and second networks. We study the response of viscoelastic light-activated shape memory polymers subject to uniaxial and biaxial tension. Parametric studies are carried out to obtain a better understanding of the effect of quantities such as relaxation time and the ratio of the relaxation modulus to the instantaneous modulus. A combination of the classical trapezoidal integration method, recursive scheme, and root-finding methods is adopted to solve the governing equations. Finally, the model is used to describe the stress relaxation behavior of light-activated shape memory polymer reported in the literature.

Frequency Control of Beams and Cylindrical Shells With Light-Activated Shape Memory Polymers

Light activated shape memory polymer (LaSMP) is a novel smart material. It realizes the shape memory function under the exposure of laser lights with two different wavelengths. During the exposure process, the stiffness of LaSMPs also changes. With this noncontact actuation feature, this study presents a new technique to manipulate frequencies of beams and cylindrical shells. Fundamental LaSMP mechanism and its stiffness manipulation are presented first. The LaSMP/elastic coupled dynamic equations of cylindrical shells coupled with LaSMPs are established first and then simplified to the governing equation of beams. In case studies, the natural frequency of a cantilever beam laminated with LaSMP patches is studied. Furthermore, the length of LaSMP patches is varied to broaden its frequency variation range. Results show that the maximum frequency change ratio reaches to about 24.5% on beams. A simply supported cylindrical shell laminated with LaSMPs on both the inner and outer surfaces is also analyzed and its frequency varies about 6% for the lowest (1,4) mode. Thus, adopting LaSMPs to manipulate the structural frequencies is a new noncontact actuation technique in vibration controls.

Light Activated Shape Memory Polymer Characterization—Part II

Presented are the experimental results of two light activated shape memory polymer (LASMP) formulations. The optical stimulus used to activate the materials is detailed including a mapping of the spatial optical intensity at the surface of the sample. From this, results of energy calculations are presented including the amount of energy available for transitioning from the glassy state to the rubbery state and from the rubbery state to the glassy state, highlighting one of the major advantages of LASMP as requiring less energy to transition than thermally activated shape memory polymers. The mechano-optical experimental setup and procedure is detailed and provides a consistent method for evaluating this relatively new class of shape memory polymer. A chemical kinetic model is used to predict both the theoretical glassy state modulus, as only the sample averaged modulus is experimentally attainable, as well as the through thickness distribution of Young’s modulus. The experimental and model results for these second generation LASMP formulations are then compared with earlier LASMP generations (detailed previously in Beblo and Mauck Weiland, 2009, “Light Activated Shape Memory Polymer Characterization,” ASME J. Appl. Mech., 76, pp. 8) and typical thermally activated shape memory polymer.

Light Activated Shape Memory Polymer Characterization

Since their development, shape memory polymers (SMPs) have been of increasing interest in active materials and structures design. In particular, there has been a growing interest in SMPs for use in adaptive structures because of their ability to switch between low and high stiffness moduli in a relatively short temperature range. However, because a thermal stimulus is inappropriate for many morphing applications, a new light activated shape memory polymer (LASMP) is under development. Among the challenges associated with the development of a new class of material is establishing viable characterization methods. For the case of LASMP both the sample response to light stimulus and the stimulus itself vary in both space and time. Typical laser light is both periodic and Gaussian in nature. Furthermore, LASMP response to the light stimulus is dependent on the intensity of the incident light and the time varying through the thickness penetration of the light as the transition progresses. Therefore both in-plane and through-thickness stimulation of the LASMP are nonuniform and time dependent. Thus, the development of a standardized method that accommodates spatial and temporal variations associated with mechanical property transition under a light stimulus is required. First generation thick film formulations are found to have a transition time on the order of 60 min. The characterization method proposed addresses optical stimulus irregularities. A chemical kinetic model is also presented capable of predicting the through-thickness evolution of Young’s modulus of the polymer. This work discusses in situ characterization strategies currently being implemented as well as the current and projected performance of LASMPs.