Coefficient of thermal expansion of Nd-Fe-B magnetic particle polymer composites – experiments and stochastic finite element modeling

Abstract

Polymer composites containing magnetic fillers show great potential for various applications, including energy storage and medical devices. To aid in the engineering and design of these components, a thorough understanding of the thermal behavior of these inhomogeneous and often highly anisotropic materials is essential, particularly in terms of their coefficient of thermal expansion (CTE). To explore this, the authors produced magnetic composites using compression molding and casting techniques. The epoxy polymer matrix was modified with a commercial thickening agent, and isotropic magnetic particles were added as functional fillers. The microstructural morphology of the composites, including the distribution, dispersion, and alignment of the magnetic fillers, was analyzed through microscopy techniques like scanning electron microscopy. Furthermore, the glass transition temperature of both the polymer matrix and the composites was measured using differential scanning calorimetry (DSC). The CTEs of both the polymer matrix and the composites were experimentally determined using a custom-designed setup and analyzed through stochastic finite element analysis (SFEA). Five modeling scenarios were considered to predict the CTEs of the composite systems: fully random distribution, randomly aligned distribution, a ‘bonded’ interface contact, and a ‘no-separation’ interface contact for the in-plane directions of particles. For the out-of-plane direction, the randomly aligned distribution with ‘no-separation’ contact was also explored. Among the in-plane direction scenarios, the case with ‘bonded’ interface contact and randomly aligned distribution yielded the lowest CTE, while the case with fully random distribution and ‘no-separation’ interface contact resulted in the highest CTE. Finally, the experimental and SFEA modeling results were compared and discussed.