Mechanical behaviours of periodic lattices

Abstract

This dissertation provide a comprehensive study of the mechanical properties
of lattice structures. Two types of topologies were considered including
two-dimensional triangular lattice and three-dimensional octet-truss lattice.
Prior analytical and numerical studies have shown that the triangular
lattice is one of the stiffest geometries of two-dimensional lattices. In
this work the modulus, tensile strength and fracture toughness of the lattice
have been measured experimentally using the specimens cut from an
Aluminium sheet. The dependence of the mechanical properties on the orientation of the lattice has also been revealed. It has been found that the
tensile strengths and fracture behaviours vary markedly with the lattice
orientation, while the modulus was almost isotropic. A significant property
anisotropy was also observed in the octet-truss lattices that its modulus
can be varied by 20% and the strength can be double when lattice orientation
was changed. The validity of linear elastic fracture mechanics (LEFM)
was examined on three-dimensional lattices. It shows that the LEFM can
be adequately adopted in the lattices with straight crack fronts, while a
curved crack front generates more complexity in the structure configuration
ahead of the crack tip, and results in a significant discrepancy in the
measured toughness compared to the models with linear crack fronts. Experimentation has been performed to characterise the fracture behaviour of
three-dimensional octet-truss lattices manufactured using a Selective Laser
Melting(SLM) technique. The fracture toughness and KR curves have been
measured. An increase in fracture resistance was observed during the crack
extension. Furthermore the influence of lattice orientation on the fracture
behaviour has been illustrated. It shows that a change in orientation will
result in a different crack path, but the effect on fracture toughness is small.
Numerical approaches were applied to simulate the progressive damage behaviour of the lattices, where a fairly well agreement was achieved between
the numerical predictions and experimental measurements.

Date of Award	28 Nov 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Martyn J Pavier (Supervisor)