Topology Optimization Requirementsin the Age of Additive Manufacturing

Dr. Andreas VlahinosPrincipal at Advanced Engineering Solutions

andreas@aes.nu

Topology Optimization Roundtable

Hilton Crystal City at Washington DC

February 20, 2018

Current State• Design Automation “brakes down” with current Topology

Optimization tools• CAD reconstruction is not trivial (Sub-D, Altair/Inspire,

PTC/Freestyle, Dassault Systems 3DX, SANDIA)• Why bother with CAD/NURBS?

– Size optimization, morphing, post-processing– High quality mesh for validation step– In the age of MBD/MBE we need:

• Accurate mass properties• Semantic GD&T• Automated Assembly Tolerance Analyses• Inspection/Verification & process definition for metrology (QIF)• Technical Data Package (TDP) for NASA & DOE projects

• Why bother with Facets/.stl– Validation step becomes easy (re-mesh skin and then volume)– File size matters (i.e. larger number lattice members)– Cellular Lattice generation

Topology Optimization Output

CAD Reconstruction is not Trivial Sub-Divisional Surface Modeling with PTC/Freestyle

Sub-D models are great for:Geometry morphing, MBD and Meshing for Validation

Frame Lattice Generation• Lightweight structural panels, energy absorption

devices, thermal insulation, porous implants• Infill / Conformal Lattices: ANSYS SpaceClaim,

Materialise Magics, Simpleware, Paramount Industries, NetFabb / Autodesk, PTC AM, 3DXpert

• Mature Topology Optimization codes use element mesh (!) to generate lattice structures

• We need smart lattice generation coupled to Topology optimization– Lattice element size based on the density field– Node repositioning / rezoning base on density field– Smooth transition between solid & lattice– Consideration of Stress Concentration with homogenization

Smooth transition between solid & lattice based on the density field

Requires strong geometry kernel

Useful Topology Optimization Features • Manufacturing constraints

– Symmetry / pattern grouping / periodic patterns– Minimum /Maximum Member Size Control– Draw direction constraints for AM, extrusion, casting,

stamping, radial filling, machining, etc.– Sheet metal – Additive manufacturing (slopes for support-less

elements) • Multiphysics

– Structural, Thermal, Fluid, Electromagnetics• Optimization Constraints

– Stress, deflection, natural frequency, temperature– Global and local buckling (lattice elements)

• Robustness evaluation– Load magnitude uncertainties (μ, σ)– Load Orientation uncertainties (μ, σ)– Material properties uncertainties (μ, σ)

•

Infill with Minimal Surfaces Callophrys Rubi butterfly - Calcite particles

• Nature is a great designer• Minimal surfaces unlock Natures

maximum structural efficiencies• There are three fundamental minimal

surfaces:– P structures cosX+cosY+cosZ=t (Primitive)– D surface cosZsin(X+Y)+sinzcos(X-Y)=t (Diamond)– G surface sinXcosY+sinYcosZ+cosXsinZ=t (Gyroid)

• The unit cells of the P, D and G nodal surfaces (t=0) are periodic

• Great infill structure– It doesn’t need supports– Great compression strength– Heat exchanger capability

Thickness of Minimal Surfaces based on the density field

• Primitive– Schwarz P Faceted Lattice

• Diamond– Schwarz D Faceted Lattice

• Gyroid– Gyroid Faceted Lattice

Design Optimization is more than Topology• Topology Optimization – Finds best distribution

of material for stiffness or compliance• Sizing Optimization – Design variables are

dimensions of any elements properties like beam section, shells thickness and composites orientation etc.

• Shape Optimization – Finds the best possible shape. DV are perturbation vectors on FE domainsTopography Optimization - Find the location and shape of bead patterns to stiffen panel structures. Nodes move normal to shells

• Topometry Optimization – DV are all element properties i.e. all lattice structure sections

• Freeform Optimization – Finds the best location and shape of rib patterns that stiffen solid structures

Early Adaptors used TO & ALM in Critical Components

Monday, March 12, 2018 2015 Automotive Simulation World Congress 12

Jan 6, 2014, SpaceX launched its Falcon 9 rocket with a 3D-printed Main Oxidizer Valve (MOV) body

• Metamaterial is a synthetic composite material with a structure such that it exhibits properties not usually found in natural materials

• Sometimes we need to design the structure at a microscopic level and build it with multi-material metal 3D printers

• Examples of mechanical metamaterials• Materials with negative Poisson's ratio (auxetics) Defense applications• Material with negative stiffness, longitudinal and volume compressibility transitions• Pentamode metamaterials or meta-fluids that have finite bulk but vanishing shear

modulus• Material with zero coefficient of thermal expansion• Acoustic or phononic metamaterials can exhibit acoustic properties not found in

nature, such as negative effective bulk modulus

Synthesis of Metamaterials usingTopology Optimization & Lattices

Geometry / FEM• CAD Part with PMI• Lattice Structure• Support Structure• FEM Mesh• Physics definitions

3D Printer• Control Software• Printability Checks• Layer thickness• Disposition path• Build orientation• Print Preview• …

Material Selection• Alloy composition• Powder diameter• Powder compaction• Service active trace elements• …

Multi Physics Simulation for

Characterization of Additive

Manufacturing Materials

Material Performance Field• Modulus of elasticity Ex(x,y,z)• Poisson’s ratio• Coefficient of thermal expansion• Density• Yield strength• Ultimate strength• Fatigue strength• Residual stress distribution• Distortion of the part• Damping• Thermal conductivity• etc.

Processes Settings • Laser power• Pulse rate• Spot size• Velocity• Spacing

Fundamental Challenge Characterization of Additive Manufacturing Materials

What material properties should I use in TO?