In the recent past, bistable laminates have been widely studied for their potential in wing morphing applications. The existence of multiple stable states makes them extremely viable as structural elements. However, for successful deployment, these laminates must be integrated into a larger mechanism. For integration, the bistable laminates are required to be clamped to a larger structure without the loss of bistability. In this work, an attempt has been made to understand the effect of integration (i.e., using different structural constraints and clamping) on the bistability and the snapthrough performance of a special class of hybrid bistable symmetric laminates (HBSLs). The structural analysis has been carried out using FEA software ABAQUS. Subsequently, a conceptual design of a morphing wing is proposed based on the insights gained from the numerical analysis that uses two HBSLs as skin with a corrugated core. Finally, using the analysis guidelines, two HBSL skins and a circular corrugated core are manufactured and integrated to show the possibility of using such bistable laminates as skin.
In this article two numerical approaches for the shape prediction of a composite wing panel under the combined actuation of a Shape memory alloy (SMA) wire and a Macro fiber composite (MFC) bimorph has been developed. The first approach is a Euler-Bernouilli beam theory based linear finite element iterative scheme and the second approach is a Timoshenko beam theory based nonlinear finite element iterative scheme that takes into account the von Karman strains. The force due to the SMA wire is modeled as a follower force. It is shown that both the techniques developed are capable taking into account this non conservative follower force, while accounting for any additional arbitrary loading. The numerical schemes developed in this paper are validated using the existing techniques while elucidating the lacuna in the existing methods.
Magnetoelectric (ME) materials have presented themselves appealing towards sensing and energy harvesting applications. Comprehensive studies under linear and nonlinear material behavior have been performed on symmetric ME laminates subjected to homogeneous deformations. However, studies on unsymmetric laminates working under bending action are sparse, despite their advantages like low resonant frequencies. A finite element (FE) model is thus developed in this work based on Mindlin plate theory to quantify the ME coupling under an applied magnetic loading in quasi-static and resonant conditions. Due emphasis has been given to the material nonlinearity of the ferromagnetic phase and the resulting ME coupling in bending and axial as well as torsional modes has been studied. The influence of the frequency of applied AC magnetic field, the magnitude of the bias field and their orientation relative to the plate axes and the effect of plate width are explored for free-free and cantilever conditions. The developed model is also validated against data available in literature. The results illustrate that the cantilever configuration offers a two-fold advantage of high ME coupling and low resonant frequency.
Nano-piezoelectric energy harvesters, due to their ability to convert mechanical vibrations to electrical current, are apt candidates for self-powered NEMs devices. Further, these are strain based electrical potential generators and can be used in tactile devices for accurate position sensing. ZnO, due to its piezoelectric properties and semiconducting nature is the ideal candidate for such applications. This paper proposes an analytical model to explain the potentials generated due to ZnO nano-films on being subjected to different forms of static loading. The model also incorporates the effect of different boundary conditions imposed on the nano-film. A perturbation theory based approach has been used to generate the analytical model. Initially, the strains are calculated ignoring the piezoelectric effect. Later, the electromechanical coupling is taken into consideration and the potentials have been calculated as a second order effect. The finite element simulation results agree with the theory to an accuracy of 5%. The profiles for piezoelectric potential distribution agree also well with the simulations. These piezoelectric potential profiles can also be used in smart materials for obtaining the required deformation in a specimen by applying a similar electrical potential across it.
Macro fiber Composite (MFC) finds its application in active control, vibration control and sensing elements. MFC can be laminated to surfaces or embedded in the structures to be used as an actuator and sensors. Due to its attractive properties and applications, it may be subjected to continuous loading, which leads to the deterioration of the properties. This study is focused on the fatigue lifetime of MFC under tensile and compressive loading at room temperature. Experiments were performed using 4 point bending setup, with MFC pasted at the center of the mild steel beam, to maintain constant bending stress along MFC. MFC is pasted using vacuum bagging technique. Sinusoidal loading is given to sample while maintaining R=0.13 (for tensile testing) and R=10 (for compressive testing). For d31 and d33 type of MFC, test was conducted for the strain values of 727 μ strain, 1400 μ strain, 1700 μ strain and 1900 μ strain for fatigue under tensile loading. For fatigue under compressive loading, both d33 and d31, was subjected to minimum strain of -2000 μ strain. Decrease in the slope of dielectric displacement vs. strain is the measure for the degradation. 10 percent decrease in the slope is set as the failure criteria. Experimental results show that MFC is very reliable below 1700 μ strain (R=0.13) at the room temperature.
1-3 piezocomposites are very attractive materials in underwater and biomedical applications. These materials may be subjected to high electric field (2kV/mm) under continuous operation leading to deterioration in the output parameters such as remnant, saturation polarization and strain. Hence in this work, an experimental study is carried out to understand the fatigue behavior of 1-3 piezocomposites for various fiber volume fraction subjected to cyclic electric field (2kV/mm, 50Hz) up to 106 cycles. A uni-axial micro-mechanical model is developed to predict the fatigue behaviour of 1-3 piezocomposite. The novelty of this model is, the remnant polarization and strain are chosen as internal variables which is also dependent on the damage.The simulated results are compared with the experimental observations, it is observed that the proposed micro-mechanical model is able to predict the material degradation with increase in number of cycles of operation. A parametric study is also conducted for various fiber volume fraction of 1-3 piezocomposite as function of fatigue cycle it shows that the amplitude of dielectric hysteresis and butterfly loop decreases with increase in the number of cycles. The fatigue behavior has a substantial effect in the performance parameters such as coercive field, remnant polarization and the asymmetric strain behavior of 1-3 piezocomposite. This fatigue study explores the utilities of 1-3 piezocomposites in transducer applications by providing insight into the device design.
In this paper, rate-dependent switching effects of ferroelastic materials are studied by means of a micromechanically
motivated approach. The onset of domain switching is thereby initiated as soon as a related
reduction in energy per unit volume exceeds a critical value. Subsequent nucleation and propagation of
domain walls during switching process are incorporated via a linear kinetics theory. Along with this micromechanical
model, intergranular effects are accounted for by making use of a probabilistic ansatz; to be
specific, a phenomenologically motivated Weibull distribution function is adopted. In view of finite-element-based
simulations, each domain is represented by a single finite element and initial dipole directions are
randomly oriented so that the virgin state of the particular bulk ceramics of interest reflects an un-poled
material. Based on a staggered iteration technique and straightforward volume averaging, representative
stress versus strain hysteresis loops are computed for various loading amplitudes and frequencies. Simulation
results for the rate-independent case are in good agreement with experimentally measure data reported
in the literature and, moreover, are extended to rate-dependent computations.
Piezoceramic materials show nonlinear behavior when they are under high electrical and mechanical field. The nonlinearity is increasing when loading becomes rate or frequency dependent. In addition to understand quasi-static characteristics, dynamic behaviors of piezoelectric materials are also important in some special application. In this paper rate dependent behaviour of tetragonal perovskite type piezoceramic materials is simulated using a three-dimensional micromechanical model. Energy equation is used for the onset of domain switching with taking in to account the probability functions that have been used for the assumption of domain switching under critical electromechanical field. Also, rate dependent properties of piezoceramics are investigated by implementing various frequencies of cyclic loading during the simulations in which nucleation and propagation of domains during polarization switching have been modeled with the help of linear kinetics relations. Different amplitudes of alternating loadings are also applied with changing frequencies in order to understand the macroscopic behavior of piezoelectric and ferroelectric materials such as coercive field and remnant polarization and strain characterization under various loading situations. PIC 151 is chosen as a sample piezoelectric material because of the experimental data that the material has been already observed in some experiments in the literature. The results of simulations have been given in electric displacement versus electric field hysteresis and mechanical strain versus electrical field butterfly curves under different amplitude and frequencies of high electrical field with comparison of experimental ones.
Piezoelectric materials exhibit nonlinear behavior when subjected to large electric or mechanical loads. This strong nonlinear behavior is induced by localized polarization switching at the domain level. In this work, certain piezoelectric materials having tetragonal perovskite type microstructure characteristics are simulated using micromechanical approach in which linear constitutive and nonlinear switching models are done in each and every grain of the material. Uniaxial loading is applied in the simulation. The effect of different domain switchings (90° or 180° domain switching for tetragonal perovskite structure) due to energy differences, different probability functions, different statistical random generators and material parameters are analysed. The response of the bulk ceramics is predicted by averaging the response of individual grains that are considered to be statistically random in orientation. The observed strain and electric displacement hysteresis loops for the piezoelectric and ferroelectric materials are compared with previous experimental works described in the literature.