Bending behavior of octet-truss lattice structures: Modelling options, numerical characterization and experimental validation

N Korshunova,G Alaimo,S.B Hosseini,M Carraturo,A Reali,J Niiranen,F Auricchio,E Rank,S Kollmannsberger

doi:10.1016/j.matdes.2021.109693

Abstract

Selective Laser Melting (SLM) technology has undergone significant development in the past years providing unique flexibility for the fabrication of complex metamaterials such as octet-truss lattices. However, the microstructure can exhibit significant variations due to the high complexity of the manufacturing process. Consequently, the mechanical behavior, in particular, linear elastic response, of these lattices is strongly dependent on the process-induced defects, raising the importance on the incorporation of as-manufactured geometries into the computational structural analysis. This, in turn, challenges the traditional mesh-conforming methods making the computational costs prohibitively large. In the present work, an immersed image-to-analysis framework is applied to efficiently evaluate the bending behavior of AM lattices. To this end, we employ the Finite Cell Method (FCM) to perform a three-dimensional numerical analysis of the three-point bending test of a lattice structure and compare the as-designed to as-manufactured effective properties. Furthermore, we undertake a comprehensive study on the applicability of dimensionally reduced beam models to the prediction of the bending behavior of lattice beams and validate classical and strain gradient beam theories applied in combination with the FCM. The numerical findings suggest that the octet-truss lattices exhibit size effects, thus, requiring a flexible framework to incorporate high-order continuum theories.

Highlights

Mechanical metamaterials have received much attention in the past decades [32,34]
Since in a three-point bending it is often desired to predict the mechanical behavior by dimensionally reduced beam models, we investigate more carefully the applicability of the beam models described in Section 3 to octet-truss lattice structures
We have shown and validated an efficient numerical framework to incorporate complex asmanufactured geometries in a direct image-to-analysis workflow

Summary

Introduction

One of the most common examples are octettruss lattices. These regular, periodic structures are attractive for many industries due to the possibility of largely decoupling the effective stiffness and strength from relative density [5,29,35,47]. One further advantage of the octet-truss lattices is the possibility to relate their mechanical properties to the truss topology and geometry [5,21,29,37]) This relation facilitates their design for specific applications, some geometrical constraints push traditional manufacturing techniques of octet-truss lattices to their boundaries. The design freedom comes at the cost of process com-

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