Homogeneous oriented magnetic field for developing biaxial fractal-like magnetorheological materials.

This research describes the design and fabrication of an electromagnetic quadrupole installed inside a biaxial tensile test bench to induce magnetic field effects whose orientation can be adjusted to either 45° or 90° to develop magnetorheological elastomer (MRE) materials subjected to a biaxial stress condition. The objective of the quadrupole is to generate a homogeneous and oriented magnetic field in the central zone of the specimen. To achieve this, we used computational tools to simulate magnetic fields and applied the fundamentals of electrical machine design. The quadrupole can produce a uniform magnetic field ranging from 0 to 120 mT with a minimal gradient within the central area of the specimen. This feature allows us to comprehensively analyze the specimen under the influence of a uniform and controllable magnetic field. The quadrupole effectively aligns the microparticles within the polymeric matrix during the MRE curing process, resulting in a fractal structure with an average dimension of 1.78. While examining the MRE specimen's molecular structure, we observed fractal micro-particle clusters oriented at 45° and 90° from the positive x-axis. Because of the unexpected specimens' fractal molecular structures, we calculated their fractal dimension (FD-Avg), standard deviation (FD-Sd) and lacunarity (FD-Lac) to investigate a possible relationship between fractal dimensions and the specimens' physical properties. Consequently, we discovered that the molecular structure and physical properties, such as the shear modulus of the MRE specimens, are related to the resulting fractal dimensions using data collected from biaxial tests that consider material softening and its residual deformation effects. Our findings elucidate, for the first time, how the fractal dimension obtained from MRE specimens can be used to determine some of their physical properties. • Novel design of an electromagnetic quadrupole capable of generating a homogeneous magnetic field. • Quadrupole core assembly optimized for biaxial testing with partial winding. • Excellent agreement between predicted and measured magnetic flux density. • Successful magnetic alignment in elastomer curing. • An expression that relates the fractal dimension of the MRE with the material static shear modulus was proposed. [ABSTRACT FROM AUTHOR]