19 research outputs found
Infill topology and shape optimisation of lattice-skin structures
Lattice-skin structures composed of a thin-shell skin and a lattice infill
are widespread in nature and large-scale engineering due to their efficiency
and exceptional mechanical properties. Recent advances in additive
manufacturing, or 3D printing, make it possible to create lattice-skin
structures of almost any size with arbitrary shape and geometric complexity. We
propose a novel gradient-based approach to optimising both the shape and infill
of lattice-skin structures to improve their efficiency further. The respective
gradients are computed by fully considering the lattice-skin coupling while the
lattice topology and shape optimisation problems are solved in a sequential
manner. The shell is modelled as a Kirchhoff-Love shell and analysed using
isogeometric subdivision surfaces, whereas the lattice is modelled as a
pin-jointed truss. The lattice consists of many cells, possibly of different
sizes, with each containing a small number of struts. We propose a penalisation
approach akin to the SIMP (solid isotropic material with penalisation) method
for topology optimisation of the lattice. Furthermore, a corresponding
sensitivity filter and a lattice extraction technique are introduced to ensure
the stability of the optimisation process and to eliminate scattered struts of
small cross-sectional areas. The developed topology optimisation technique is
suitable for non-periodic, non-uniform lattices. For shape optimisation of both
the shell and the lattice, the geometry of the lattice-skin structure is
parameterised using the free-form deformation technique. The topology and shape
optimisation problems are solved in an iterative, sequential manner. The
effectiveness of the proposed approach and the influence of different
algorithmic parameters are demonstrated with several numerical examples.Comment: 20 pages, 17 figure
Design and Optimization of Functionally-graded Triangular Lattices for Multiple Loading Conditions
Aligning lattices based on local stress distribution is crucial for achieving
exceptional structural stiffness. However, this aspect has primarily been
investigated under a single load condition, where stress in 2D can be described
by two orthogonal principal stress directions. In this paper, we introduce a
novel approach for designing and optimizing triangular lattice structures to
accommodate multiple loading conditions, which means multiple stress fields.
Our method comprises two main steps: homogenization-based topology optimization
and geometry-based de-homogenization. To ensure the geometric regularity of
triangular lattices, we propose a simplified version of the general rank-
laminate and parameterize the design domain using equilateral triangles with
unique thickness per edge. During optimization, the thicknesses and orientation
of each equilateral triangle are adjusted based on the homogenized properties
of triangular lattices. Our numerical findings demonstrate that this proposed
simplification results in only a slight decrease in stiffness, while achieving
triangular lattice structures with a compelling geometric regularity. In
geometry-based de-homogenization, we adopt a field-aligned triangulation
approach to generate a globally consistent triangle mesh, with each triangle
oriented according to the optimized orientation field. Our approach for
handling multiple loading conditions, akin to de-homogenization techniques for
single loading conditions, yields highly detailed, optimized, spatially varying
lattice structures. The method is computationally efficient, as simulations and
optimizations are conducted at a low-resolution discretization of the design
domain. Furthermore, since our approach is geometry-based, obtained structures
are encoded into a compact geometric format that facilitates downstream
operations such as editing and fabrication
A brick in the wall: Staggered orientable infills for additive manufacturing
International audienceAdditive manufacturing is typically conducted in a layer-by-layer fashion. A key step of the process is to define, within each planar layer, the trajectories along which material is deposited to form the final shape. The direction of these trajectories triggers an anisotropy in the fabricated parts, which directly affects their properties, from their mechanical behavior to their appearance. Controlling this anisotropy paves the way to novel applications, from stronger parts to controlled deformations and surface patterning.This work introduces a method to generate trajectories that precisely follow an input direction field while simultaneously avoiding intra- and inter-layer defects. Our method results in spatially coherent trajectories - all follow the specified direction field throughout the layers - while providing precise control over their inter-layer arrangement. This allows us to generate a staggered layout of trajectories across layers, preventing unavoidable tiny gaps from forming tunnel-shaped voids throughout a part volume.Our approach is simple, robust, easy to implement, and scales linearly with the input volume. It builds upon recent results in procedural generation of oscillating patterns, generating a signal in the 3D domain that oscillates with a frequency matching the deposition beads width while following the input direction field. Trajectories are extracted with a process akin to a marching square