Elongations of magnetoactive elastomers (MAEs) under ascending–descending uniform magnetic fields were studied experimentally using a laboratory apparatus specifically designed to measure large extensional strains (up to 20%) in compliant MAEs. In the literature, such a phenomenon is usually denoted as giant magnetostriction. The synthesized cylindrical MAE samples were based on polydimethylsiloxane matrices filled with micrometer-sized particles of carbonyl iron. The impact of both the macroscopic shape factor of the samples and their magneto-mechanical characteristics were evaluated. For this purpose, the aspect ratio of the MAE cylindrical samples, the concentration of magnetic particles in MAEs and the effective shear modulus were systematically varied. It was shown that the magnetically induced elongation of MAE cylinders in the maximum magnetic field of about 400 kA/m, applied along the cylinder axis, grew with the increasing aspect ratio. The effect of the sample composition is discussed in terms of magnetic filler rearrangements in magnetic fields and the observed experimental tendencies are rationalized by simple theoretical estimates. The obtained results can be used for the design of new smart materials with magnetic-field-controlled deformation properties, e.g., for soft robotics.
We investigated magnetic-field-induced modifications of the surface roughness of magnetoactive elastomers (MAEs) with four material compositions incorporating two concentrations of ferromagnetic microparticles (70 wt% and 80 wt%) and exhibiting two shear storage moduli of the resulting composite material (about 10 kPa and 30 kPa). The analysis was primarily based on spread optical reflection measurements. The surfaces of all four materials were found to be very smooth in the absence of magnetic field (RMS roughness below 50 nm). A maximal field-induced roughness modification (approximately 1 μm/T) was observed for the softer material with the lower filler concentration, and a minimal modification (less than 50 nm/T) was observed for the harder material with the higher filler concentration. All four materials showed a significant decrease in the total optical reflectivity with an increasing magnetic field as well. This effect is attributed to the existence of a distinct surface layer that is depleted of microparticles in the absence of a magnetic field but becomes filled with particles in the presence of the field. We analyzed the temporal response of the reflective properties to the switching on and off of the magnetic field and found switching-on response times of around 0.1 s and switching-off response times in the range of 0.3–0.6 s. These observations provide new insight into the magnetic-field-induced surface restructuring of MAEs and may be useful for the development of magnetically reconfigurable elastomeric optical surfaces.
Магнитодеформация представляет собой изменение размеров и формы образца под действием однородного внешнего магнитного поля. Исследование данного эффекта в различных материалах позволяет изучить природу магнитных и механических взаимодействий в них. Большой интерес вызывает магнитодеформация и с инженерной точки зрения для конструирования новых приборов и устройств микросистемной техники. В магнитоактивных эластомерах, содержащих магнитные микрочастицы в полимерной матрице, обнаружена гигантская деформация под действием внешнего магнитного поля. Общепризнанные методы измерения магнитодеформации в магнитоактивных мягких материалах в настоящее время практически отсутствуют. В статье описана установка, разработанная для исследования магнитoмеханических характеристик магнитоактивных эластомеров, и продемонстрированы ее экспериментальные возможности. Установка позволяет измерить деформации в диапазоне от 0 до 12.5 мм с разрешением 1 мкм. Получаемые при помощи данной установки деформационные кривые необходимы для разработки актюаторных и сенсорных устройств на основе магнитоактивных эластомеров и улучшения технологий их изготовления.Ключевые слова: магнитоактивные эластомеры, магнитострикция, магнитодеформации, ферромагнетики, микрочастицы. УДК 537.622.4; 53.098 https://doi.
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