Effective Behavior of Dual-Phase Interpenetrating Composites Comprising an Additively Manufactured Smart Nitinol Core

Abstract

Interpenetrating phase composites (IPCs) are novel multifunctional co-continuous composite materials in which each constitutive phase forms a self-supporting cellular structure. In this study, 3D IPCs comprising an elastic-plastic second phase are computationally analyzed with architected shape memory alloy (SMA) microstructure. The SMA functional phase consists of nitinol (NiTi) in a variety of architected topologies for which a user-defined material subroutine (UMAT) implemented in the finite element software Abaqus is used for the constitutive material behavior of architected NiTi in IPCs. Whereas the reinforcement consists of elastic-plastic AlSi10Mg for which the material data is sourced from in-house experiments. Architecture topologies including several beam or strut-based and mathematically-driven surfaces known as triply periodic minimal surfaces (TPMS) are considered for the NiTi functional phase. TPMS architectures promote several multifunctional attributes and reduce the effect of stress concentrations within the composite. Schoen I-WP (IWP), Schoen Gyroid (G), Schwarz Diamond (D), and Schwarz Primitive (P) are solid-network-based TPMS architectures that are considered, whereas strut-based architectures include Diamond* (DS), Kelvin Cell (K), Octet (O) and Truncated Octahedron (TO). Co-continuous composites are modeled as representative volume elements (RVEs) and their functional properties are evaluated based on the volumetric homogenization technique with idealized periodic boundary conditions (PBCs). Effective mechanical properties consist of effective elastic stiffness including uniaxial, bulk, and shear moduli, Poisson’s ratio, and NiTi phase transformation parameters (austenite-to-martensite phase transformation) along with effective strain recovery upon unloading are evaluated. These functional properties are analyzed and compared based on the architecture of the NiTi functional phase and its volumetric fraction (VF), considering different loading conditions. The result shows that the elastic stiffness significantly depends on the morphology of functional phase which varies monotonically with the concentration of NiTi microstructure. Furthermore, an exponentially increasing trend in overall strain recovery is recorded as a function of NiTi SMA concentration which results from the superelasticity of Nitinol. Among the topologies considered for NiTi phase, IPCs possessing Kelvin cell and Diamond topologies resulted in higher effective axial stiffness, while Octet struts with shear stiffness. Whereas, most of the TPMS topologies are superior in providing better hydrostatic stiffness when compared with strut topologies. Moreover, Primitive, Kelvin cell, and IWP showed the highest strain recovery. Experimental data sourced from two different studies in the literature are replicated to ensure the accuracy of finite element simulations.

Date of Award	Aug 2023
Original language	American English
Supervisor	Wael Zaki (Supervisor)