Electroactive polymer (EAPs)-based technologies have shown promise in areas such as artificial muscles, aerospace, medical devices and soft robotics because of large electromechanical actuation at relatively high speed. The promises of EAPs have led us to study EAP-based grippers. The in-plane actuation of P(VDF-TrFE-CTFE) is converted into bending actuation using unimorph configurations, where one passive substrate layer is attached to the active polymer. On-demand segmented folding is harnessed from this pure bending actuation by creating notch samples with an aim to implement them for applications like soft robotics gripper. In this paper, we studied the effect of various design parameters of notched folding actuators to establish a design reference and maximize the actuation performance of EAP based devices. Both finite element analysis (FEA) and micromechanics based analytical study is performed to investigate the effect of actuator parameters on the folding actuation of notched samples. The notched configuration has been analyzed via FEA for the non-uniform deformations and stress-fields. FEA analysis shows the importance of notch positioning to maximize the electromechanical performance. On the other hand, analytical study has proposed a design curve for the selection of proper notch parameters (e.g. notch length and Young’s Modulus) to maximize the actuation performance. Finally, based on the FEA and analytical analysis, a human finger inspired ‘finger-like’ biomimetic actuator is realized by assigning multiple notches to the structure.
In this study, we investigate the hierarchical microarchitecture formation of magnetic barium hexaferrite (BF) platelets in polydimethylsiloxane (PDMS) using electric and magnetic field assembly technique. First, external fields are applied to the colloidal solution to form the microstructure before curing the composites. After microstructure formation, the composites are thermally cured to freeze the microstructure. We investigate two different cases in this study-(1) magnetic field processed composites and (2) multi-field processed composites, which were processed under both magnetic and electric fields. We observe that macro-chains formed due to simultaneous application of electric and magnetic fields had a much higher length compared to the macro-chains formed due to just magnetic field. For both cases individual BHFs are found to be oriented in the direction of the external field. The analysis of SEM microstructures using ImageJ and MATLAB showed that at least two different levels of hierarchies are present in the microstructure for both cases, which are referred to as BHF stacks and micro-chains. From the experimental quantitative microstructure analysis, BHFs are found to be slightly better oriented (magnetic easy-axis direction in relation to the external field) at all scales for the electric and magnetic field processed composites compared to just the magnetic field processed composites. Magneto-electrohydrodynamics modeling of the polymer-particulate mixture predicts a similar behavior. Computational simulations are performed wherein particulates, subjected to both DEP forces resulting from an applied electric field, and magnetic dipole interactions in response to applied magnetic field, are allowed to form quasi-equilibrium structures before locking in a final structure to represent curing. Results from simulation confirms the finding on longer macro-chain formation similar to the experiment for the case of magnetic and electric fields compared to just magnetic field. Analysis of the microstructures from simulation also confirms that multiple levels of hierarchies are present in the composites’ microstructure for both cases. In future, quantifying the corresponding metrics at each level of hierarchy will help to better understand the microstructure and can be served as input to the model and also used to validate the model.
This study demonstrates how to judiciously use two different external fields to engineer a polymer- based composite that responds to both electric and magnetic fields. Specifically, we demonstrate the electric and magnetic alignment of M-type Barium Hexaferrite (BF) in polydimithylsiloxane (PDMS) to obtain a multifunctional composite whose electrical and magnetic properties depend on the orientation of the BF. First, the BFs are electrically aligned in the polymer matrices by applying an AC electric field. From optical microscopy (OM) imaging, the optimal electrical alignment conditions are determined, and those parameters are used to fabricate the composites. After the composite is electrically aligned and partially cured, magnetic field is then applied. Under the magnetic field, BFs are further aligned in-plane and out-of-plane along their magnetic c-axis within the chains that formed during electrical aligning. Following complete cure, the microstructures from the OM image show parallel chain formation. Vibrating Sample Magnetometry (VSM) and XRD results confirm BFs are crystallographically aligned along their magnetic c-axis. The textured BF-PDMS composites are found to have anisotropic magnetic and dielectric properties. The possibility of electrical alignment of magnetic particles will open up new doors to manipulate and design particle-modified polymers for different applications.
Magnetorheological elastomers (MREs) are state-of-the-art elastomagnetic composites comprised of magnetic particles embedded in an elastomer matrix. MREs offer enormous flexibility given that elastomers are easily molded, provide good durability, exhibit hyperelastic behavior, and can be tailored to provide desired mechanical and thermal characteristics. MRE composites combine the capabilities of traditional magnetostrictive materials with the properties of elastomers, creating a novel material capable of both highly responsive sensing and controlled actuation in real-time.
This work investigates the response of MRE materials comprised of varying mixtures of 40 and 10 micron iron particles. Samples are tested in compression yielding a compressive modulus and measure of the shear stiffness <i>via</i> Mooney plots. Samples are also tested using a tunable vibration absorber (TVA) designed specifically for this experiment. The TVA loads the samples in oscillatory shear (10-100Hz) under the influence of a magnetic field.
In all samples, results show increases in the material's stiffness under the application of a magnetic field as evidenced by the frequency response function of the TVA system. Increases in stiffness of 50% at 0.15T were achieved with samples containing 30%-40 micron particles and 30%-40micron + 2%-10 micron particles. This yields a ratio of over 300%/T. The two-particle MRE appeared not to have reached saturation suggesting further stiffness enhancement was possible beyond the saturated single-particle 40 micron sample. However, this may be a result of the larger iron content. Results also suggest variation in the behavior of two-versus single-particle MRE behavior as evidenced by the shear modulus found in compression, but results are inconclusive. MRE materials made with nanoparticles of hard magnetic barium ferrite show stiffness increases of 70%/T which is comparable to MREs having larger iron particles.