Effects of particle size and oxide shell on variable stiffness performance of phase-changing materials

Phase-changing materials have recently found use as particulate fillers to engender stiffness-changing behavior in composites. In the transition from solid to liquid particles, the composite modulus can be significantly reduced, and then raised again as the particles are allowed to solidify. While the general effect of stiffness tuning in phase-changing composites has been demonstrated in a range of studies and applications, the most drastic stiffness ranges are provided by fusible metallic alloys, which are commonly subject to the formation of oxide shells on their surfaces. In this work, we examine the effect these oxide surfaces have on variable-stiffness performance, and investigate the corresponding role of particle size. In particular, we study particles of a low-melting-point metallic alloy, Field's Metal, and we also present a facile method of manufacture that allows for control of particle size. We then manufacture a set of stiffness-changing composites using these particles and characterize mechanical performance, with the aim of controlling particle size to increase the total stiffness ratio while resisting material failure.