Finite element and experimental studies on deformation behavior of nanoglass and metallic glass structures

Abstract

Metallic glasses (MGs) have gained much attention due to many attractive mechanical properties such as high elastic limit, high strength, excellent corrosion resistance, and significant fracture toughness (Schuh et al., 2007) making them a potential candidate for structural as well as functional applications including medical implant, micro/nano electromechanical devices and cellular structures for packing purposes (Telford, 2004; Miracle et al., 2008; Schuh et al., 2007; Liu et al., 2014; Liu et al., 2016). However, MGs exhibit localization of plastic strain in narrow bands, called as shear band, and fail in brittle manner under tensile loading due to unhindered propagation of crack inside a predominant band. The lack of tensile ductility in MGs impedes their employment as structural material (Schuh et al., 2007), which has motivated researchers to explore various strategies to improve plastic deformation in MGs such as synthesizing MG composites (Hofmann et al., 2008; Qiao et al., 2016; Wang et al., 2020), nanoglass (NG) architecture (Ivanisenko et al., 2018), NGMG laminate composites (Adibi et al., 2016; Sha et al., 2017) and MG cellular structures (Sarac et al., 2012; Sarac and Schroers, 2013b; Chen et al., 2014; Liu et al., 2016; Zhang et al., 2016). MG composites exhibit significant tensile ductility, but their strength is compromised considerably due to lower yield strength of the soft phases making them less viable choice (Schuh et al., 2007; Qiao et al., 2016). NGs which are synthesized from MGs have been reported to exhibit significantly large ductility under tensile loading (Wang et al., 2015). The laminate NG-MG composites with alternate layers of NGs and MGs have also been reported to show enhanced tensile ductility (Sha et al., 2017). Consequently, there has been considerable scientific curiosity in understanding the deformation and fracture behavior of these materials. A few experiments and atomistic simulations performed in the past have provided some insights on the underlying mechanics/mechanism of deformation and fracture in NGs (Sopu et al., 2009; Ritter et al., 2011; Adibi et al., 2013, 2014; Franke et al., 2014; Sha et al., 2014) and NG-MG composites (Adibi et al., 2016; Sha et al., 2017). Yet, there are several unresolved issues which need to be addressed for the safe deployment of these materials in actual applications. In particular, NGs are reported to be harder than MGs with identical composition (Nandam et al., 2017), and their hardness is noticed to drop with increase in load, though mechanistic reasons for these behaviors are not explained in the literature. In addition, the effect of mode mixity on the evolution of crack tip plasticity and the fracture toughness in NGs are not investigated till now. Further, the deformation behavior of NG-MG laminate composites transitions from localized to superplastic flow, though mechanistic reasons are not well understood. The cellular MG structures have also been synthesized and they showed enhanced plasticity, but the mechanics of the deformation behavior is not well understood. In the view of above discussion, indentation experiments and complementary finite element simulations are performed on NGs as well as MGs in this thesis. In addition, deformation behavior of NG-MG laminate composites and cellular MGs are analyzed through finite element simulations. The relevant background is briefly presented below.