Old materials - new capabilities: lattice materials in structural mechanics

Lattice materials (LM) are a novel concept stemming from the combination of crystallography
and structural optimisation algorithms. Their practical applications have become
real with the advent of versatile additive layer manufacturing (ALM) techniques and the
development of dedicated CAD/CAE tools. This work critically reviews one of the major
claims concerning LMs, namely their excellent stiffness-to-weight performance. First, a brief
literature review of spatially uniform LMs is presented, focusing on specific strength of standard
engineering materials as compared with novel structures. An original modelling and
optimisation is carried out on a flat panel subject to combined shear and bending load. The
calculated generalised specific stiffness is compared against reference values obtained for a
uniform panel and the panel subjected to topological optimisation. The monomaterial, a spatially
repetitive solution turns out to be poorly suited for stiff, lightweight designs, because
of suboptimal material distribution. Spatially non-uniform and locally size-optimised structures
perform better. However, its advantage over manufacturable, topologically-optimised
conventional designs can at best be marginal (< 10%). Cubic-cell lattices cannot replace
conventional bulk materials in the typical engineering use. The multi-cell-type and multi-
-material lattice structures, albeit beyond the scope of this article, are more promising from
the point of view of mechanical properties. The possibility of approaching the linear scaling
reported in the recent litterature can make them an attractive option in ultra-low weight
designs.