Strain and damage sensing performance of functionally graded nanocomposite lattices enabled by DLP 3D printing

Abstract

This research examines the mechanical and piezoresistive characteristics of geometrically graded octet and kelvin lattices fabricated via Digital Light Processing (DLP) additive manufacturing technique. The geometrically graded lattice structures feature varying unit cell sizes with constant relative density (20, 30, and 40 %), and are composed of electrically conductive nanocomposite photoresin loaded with 0.05 phr multi-walled carbon nanotubes (MWCNTs). Under monotonic compression, the peak stress and energy absorption of the graded octet lattice are found to rise with increasing level of gradation, reporting enhancements in the latter properties by factors of up to 2.6 and 2.0, respectively, in comparison to their non-graded counterparts of equal weight. In contrast, the graded kelvin lattice structures show lower enhancements in energy absorption of up to 1.2 times the non-graded equivalent. The piezoresistive response of both octet and kelvin lattices is characterized by a sharp initial drop in electrical resistance followed by a nonlinear response that shows signatures related to distinct failure processes observed in the studied structures. The initial gauge factor of the lattice structures is found to increase with increasing level of gradation and relative density. The geometric gradients also enhance the structure’s recoverability, allowing the struts in the softer layers to fold and unfold during cyclic compressive loading, yielding enhanced cyclic stability in piezoresistive behavior. The findings of this study suggest that the adoption of functional geometry gradients in nanocomposite lattices can assist in achieving enhanced energy absorption and strain/damage sensing functionalities under various loading conditions.

Keywords

• Additive manufacturing
• Digital light processing
• Octet lattice
• Kelvin lattice
• Architected Material
• Piezoresistive sensing