Large deflection deformation behavior of a Zr-based bulk metallic glass for compliant spinal fixation application

A novel compliant spinal fixation designed based on the concept of compliant mechanisms can reduce the stress-shielding effect and adjacent segment degeneration (ASD) effectively, but propose higher requirements for the properties of the used materials. Bulk metallic glasses (BMGs), as a kind of young biomaterials, exhibiting excellent comprehensive properties, which are attractive for compliant spinal fixation. Here, according to the practical service condition of the basic elements in compliant spinal fixation, large deflection deformation behaviors of Zr61Ti2Cu25Al12 (at.%, ZT1) BMG beam, including elastic, yielding and plastic were investigated systematically. It was shown that the theoretical nonlinear analytical solution curve as the benchmark not only with the capacity to predict the nonlinear load-deflection relation within the elastic deformation regime, but also assists to capture the yielding event roughly, which can be used as a powerful design tool for engineers. To capture the beginning of the yielding event exactly, bending proof strength (sigma p,0.05%) accompanied with tiny permanent strain of 0.05% was proposed and determined for BMGs in biomedical implant applications, which is of significance for setting the allowable operating limits of the basic flexible elements. By approach of interrupted loading-unloading cycles, plastic deformation driven by the bending moment can be classified into two typical stages: the initial stage which mainly characterized by the nucleation and intense interaction of abundant shear bands when the plastic strain below the critical value, and the second stage which dominated by the progressive propagation of shear bands and coupled with the emergence of shear offsets on tensile side. The plasticity of BMG beam structures depends on the BMG's inherent plastic zone size (rp). When the half beam thick-ness less than that of the rp, the plastic deformation of BMGs will behave in a stable manner, which can be acted as the margin of safety effectively.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

A novel compliant spinal fixation based on compliant mechanisms is designed to effectively reduce stress-shielding effect and adjacent segment degeneration (ASD), but it requires high properties of the used materials. Bulk metallic glasses (BMGs), as young biomaterials, demonstrate excellent comprehensive properties, making them attractive for compliant spinal fixation. In this study, the large deflection deformation behaviors of Zr61Ti2Cu25Al12 (at.%, ZT1) BMG beam were systematically investigated, including elastic, yielding, and plastic deformations. The theoretical nonlinear analytical solution curve predicts the load-deflection relation within the elastic deformation regime and assists in capturing the yielding event, serving as a powerful design tool for engineers. To accurately capture the beginning of the yielding event in biomedical implant applications, the concept of bending proof strength (sigma p,0.05%) with tiny permanent strain of 0.05% was proposed and determined, which is significant for setting the allowable operating limits of the basic flexible elements. The plastic deformation driven by the bending moment can be classified into two stages: the initial stage characterized by nucleation and intense interaction of shear bands, and the second stage dominated by the progressive propagation of shear bands and emergence of shear offsets. The plasticity of BMG beam structures depends on the BMG's inherent plastic zone size (rp), and when the half beam thickness is less than that of rp, the plastic deformation of BMGs behaves in a stable manner, effectively serving as the margin of safety.