Abstract
An open question is the underlying mechanisms for a recent discovered nanocomposite, which composed of shape memory alloy (SMA) matrix with embedded metallic nanowires (NWs), demonstrating novel mechanical properties, such as large quasi-linear elastic strain, low Young’s modulus and high yield strength. We use finite element simulations to investigate the interplay between the superelasticity of SMA matrix and the elastic-plastic deformation of embedded NWs. Our results show that stress transfer plays a dominated role in determining the quasi-linear behavior of the nanocomposite. The corresponding microstructure evolution indicate that the transfer is due to the coupling between plastic deformation within the NWs and martensitic transformation in the matrix, i.e., the martensitic transformation of the SMA matrix promotes local plastic deformation nearby, and the high plastic strain region of NWs retains considerable martensite in the surrounding SMA matrix, thus facilitating continues martensitic transformation in subsequent loading. Based on these findings, we propose a general criterion for achieving quasi-linear elasticity.
Highlights
In this work, we investigate the interplay between plastic deformation and phase transformation during the mechanical pretreatment, aimed at revealing the underlying determinants of the quasi-linear behavior of the SMA-NWs composite
The interfaces between the SMA matrix and NWs in our finite element simulation are assumed as perfect bonding, as previous experiments showed that the microstructure of the composite consists of well dispersed and aligned Nb NWs embedded in the NiTi matrix with well-bonded interfaces, and there is no obvious debonding during deformation[7,14]
Pure martensite phase microstructure starts to form near the both ends of NWs at point D (Fig. 3(b)) and grow towards the interior of SMA matrix (Fig. 3(b), E)
Summary
We investigate the interplay between plastic deformation and phase transformation during the mechanical pretreatment, aimed at revealing the underlying determinants of the quasi-linear behavior of the SMA-NWs composite. The macro-strain dependent average volume fraction of the martensite phase in our model (Fig. 2(c)) shows a similar varying trend with that obtained from the relative intensity of the B19′-NiTi (001) diffraction peak (Fig. 2(d))[7]. All these results indicate that our FEM calculation predicts the mechanical response in excellent agreement with the experiments, which validates the implemented FEM model. This is because the simulated curve describes the mixed state of austenite-martensite phases, while the experimental result just present the B2 austenite phase estimated from the diffraction peaks of the B2-NiTi (211)[7]
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