Rate dependent behaviors of nickel-based microcapsules

In this work, nickel-based microcapsules with liquid core were fabricated through an electroless plating approach. The quasi-static and high speed impact behaviors of microcapsules were examined by in-house assembled setups which are able to evaluate properties of materials and structures in microlevel accurately. Results indicated that the fabricated microcapsules showed strong rate sensitivity and the nominal strength of the capsule increased (up to 62.1%) with the increase in loading rates (up to 8200 s^-1). The reduced modulus of nickel-based microcapsules was three orders of magnitude larger than that of the traditional microcapsules. The findings revealed that the fabricated nickel-based microcapsules produced remarkable performances for both static and dynamic loading applications. A high speed camera with stereo microscope was used to observe the failure mode of the microcapsule during the impact, which is of great importance to study the mechanical behaviours of materials and structures. Different failure modes were identified as multi-cracks with more rough and tortuous fracture surfaces and debris were observed for the samples subject to impact loading. Finite element method was employed to further understand the physical phenomenon which fitted well with the experimental results. These results could inspire more fundamental studies on the core-shell microstructures and potential applications in multifunctional materials.