Low Magnetic Field Induced Extrinsic Strains in Multifunctional Particulate Composites

The current paper reports on the quantification of the effect of magnetic field on the mechanical performance of ferromagnetic nanocomposites in situ during a basic standard tensile testing. The research investigates altering the basic mechanical properties (Modulus and Strength) via application of contact-less magnetic field, as primary attempt for a future composites strengthening mechanism. The nanocomposite specimens were fabricated using filament-based 3D printing and were comprised of ferromagnetic nanoparticle embedded thermoplastic polymers. The nanoparticles were iron particles dispersed at 21wt.% (10.2 Vol.%) inside polylactic acid (PLA) polymer, as characterized utilising optical microscopy and 3D X-ray computed tomography. The magnetic field was stationary and produced using permanent Neodymium round-shaped magnets available at two field strengths below 1 Tela. The 3D printing was a MakerBot Replicator machine operating based upon fused deposition method which utilised 1.75mm-diameter filaments made of the iron particles-based PLA composites. The magnetic field equipped tensile tests were accompanied with real-time digital image correlation technique for localized strain measurements across the specimens at 10-micron pixel resolution. It was observed that the lateral magnetic field induces slight Poisson’s effect on development of extrinsic strain across the length of the tensile specimens. However, the effect reasonably interferes with the evolution of strain fields via introduction of localised compressive strains attributed to accumulated magnetic polarisation at the magnetic particles at extrinsic scale. The theory overestimated the moduli by a factor of approximately 3.1. To enhance the accuracy of its solutions for 3D printed specimens, it is necessary to incorporate pore considerations into the theoretical derivations. Additionally, a modest 10% increase in ultimate tensile strength was observed during tensile loading. This finding suggests that field-assisted strengthening can be effective for as-received 3D printed magnetic composites in their solidified state, provided that the material and field are optimally designed and implemented. This approach could propose a viable method for remote field tailoring to strengthen the material by mitigating defects induced during the 3D printing process.