UnitcellDB

UnitcellDB is a submodule of the lattice design tool UnitcellHub. It contains a database of simulated meso-scale lattice properties (including geometric and structural/thermal performance) for more than 13,000 point designs. All properties were generated using UnitcellHub's UnitcellEngine: for more details regrading geometry definitions, simulation details, etc., see http://github.com/unitcellhub/unitcellengine. The UnitcellDB database is stored in the open source HDF5 database format within the file unitcelldb.h5. The quickest way to get started viewing the database is with HDFView; however, for more detailed interrogation and interaction, an HDF5 tool like Python's pytable is required (see the examples folder for more details).

Database contents

The primary data in UnitcellDB are geometric, effective linear elastic mechanical, and effective thermal properties. Here, "effective" refers to the homogenized, macro-scale properties of a lattice structure and thus are only valid where the length-scale of the lattice unitcell is much smaller than that of the macroscopic structure. The database was constructed by sampling 18x unitcell types (show below) across a range of geometric variations (aspect ratio and thickness). In general, the properties are normalized to be length-scale and material agnostic. The primary exception to this is for the linear elastic mechanical properties, as Poisson's ratio cannot be fully normalized out; thus, a Poisson's ratio is specified. Currently, all data are with respect to a material with Poisson's ratio of $\nu$=0.3, which is relevant to most metallics and glassy-state polymers.

Database structure

The UnitcellDB database structure consists of a primary data table called design. Each element in the design table corresponds to a lattice point design and contains the fields in the below table. Unless specified otherwise, the property normalization scheme is as follows:

• Geometric distances (such as length and width) have arbitrary scaling. To convert to absolute units, all geometric distances must be multiplied by the same scaling factor. For example, if length=5 and width=2 and we want a unitcell with length 10 mm, then we multiple all normalized geometric parameters by 2x. So, in this case, for a length of 10 mm, the width is 2*2=4 mm.
• Stiffness-based mechanical properties (elastic and shear modulii) are normalized by the elastic modulus of the base material. For example, if we're interested in aluminum lattices, we can convert the stiffness property Emin to absolute units by multiplying it by 68 GPa (the elastic modulus of aluminum).
• Conductance-based thermal properties are normalized by the thermal conductance of the base material. For example, if we're interested in aluminum lattices, we can convert the conductance property homogenizedConduction matrix to absolute units by multiplying it by 152 W/mK (the thermal conductance of Aluminum 6061).

Field	Category	Dependence	Description
image	General	Derived	200x200x4 table of integers corresponding to an rgba image of the lattice unitcell.
date	General	Derived	Creation date in the form of the vector [year, month, day, hour, minute, second].
unitcell	Geometry	Specified	String defining the unitcell name (such as "Body centered cubic", "Octet", or "Gyroid").
form	Geometry	Specified	String defining the unitcell type (such as "walledtpms" -- Thin-walled Triply Periodic Minimal Surface -- or "graph" -- unitcells defined by nodal points and beam/plate connections
length	Geometry	Specified	Normalized length of the unitcell (distance along the x-direction).
width	Geometry	Specified	Normalized width of the unitcell (distance along the y-direction).
height	Geometry	Specified	Normalized height of the unitcell (distance along the z-direction).
thickness	Geometry	Specified	Normalized thickness of the primary unitcell feature (such as the strut or plate thickness).
radius	Geometry	Specified	Fillet radius for feature connection points normalized by the thickness property.
relativeDensity	Geometry	Derived	Relative density of the unitcell (volume of material within the unitcell normalized by the total volume of the unitcell bounding box).
relativeSurfaceArea	Geometry	Derived	Relative surface area of the unitcell (surface of the material within the unitcell normalized by the total surface area of the unitcell bounding box).
youngsModulus	Material	Specified	Elastic modulus of the base material. This property is redundant, as it has already been incorporated into the normalized properties, but is reported for consistency purposes.
poissonRatio	Material	Specified	Poisson's ratio of the base material.
conductance	Material	Specified	Conduction coefficienct of the base lattice material. This property is redundant, as it has already been incorporated into the normalied properties, but is reported for consistency purposes.
homogenizedCompliance	Mechanical	Derived	A 6x6 table corresponding to the normalized homogenized compliance matrix with respect to tensorial strains (rather than engineering strains). The row/column ordering correspond to ["xx", "yy", "zz", "xy", "yz", "xz"].
homogenizedStiffness	Mechanical	Derived	A 6x6 table corresponding to the normalized homogenized stiffness matrix with respect to tensorial strains (rather than engineering strains). The row/column ordering correspond to ["xx", "yy", "zz", "xy", "yz", "xz"].
Emin	Mechanical	Derived	Minimum possible normalized elastic modulus for any possible loading direction.
EminDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of minimum elastic modulus.
Emax	Mechanical	Derived	Maximum possible normalized elastic modulus for any possible loading direction.
EmaxDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of maximum elastic modulus.
Gmin	Mechanical	Derived	Minimum possible normalized shear modulus for any possible shear plane and loading direction.
GminDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of minimum shear modulus.
GminNormal	Mechanical	Derived	Length 3 vector specifying the shear plane normal for minimum shear modulus.
Gmax	Mechanical	Derived	Maximum possible normalized shear modulus for any possible shear plane and loading direction.
GmaxDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of maximum shear modulus.
GmaxNormal	Mechanical	Derived	Length 3 vector specifying the shear plane normal for maximum shear modulus.
numin	Mechanical	Derived	Minimum possible Poisson's ratio for any possible shear plane and loading direction.
numinDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of minimum Poisson's ratio.
numinNormal	Mechanical	Derived	Length 3 vector specifying the shear plane normal for minimum Poisson's ratio.
numax	Mechanical	Derived	Maximum possible Poisson's ratio for any possible shear plane and loading direction.
numaxDirection	Mechanical	Derived	Length 3 vector specifying the loading direction of maximum Poisson's ratio.
numaxNormal	Mechanical	Derived	Length 3 vector specifying the shear plane normal for maximum Poisson's ratio.
Kmin	Mechanical	Derived	Minimum possible normalized bulk modulus for any possible load direction.
KminDirection	Mechanical	Derived	Length 3 vector specifying the load direction of minimum bulk modulus.
Kmax	Mechanical	Derived	Maximum possible normalized bulk modulus for any possible load direction.
KmaxDirection	Mechanical	Derived	Length 3 vector specifying the load direction of maximum bulk modulus.
vonMisesWorst11	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a uniaxial unit macroscopic stress $\sigma$xx.
vonMisesWorst22	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a uniaxial unit macroscopic stress $\sigma$yy.
vonMisesWorst33	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a uniaxial unit macroscopic stress $\sigma$zz.
vonMisesWorst12	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a shear unit macroscopic stress $\sigma$xy.
vonMisesWorst23	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a shear unit macroscopic stress $\sigma$yz.
vonMisesWorst33	Mechanical	Derived	Worst case von Mises stress within the lattice when subjected to a shear unit macroscopic stress $\sigma$xz.
vonMisesWorst	Mechanical	Derived	Worst case local von Mises stress when loaded by a unit macroscopic stress state applied in the worst case possible direction. This is effectually the worst case stress amplification within the lattice structure.
vonMisesWorstDir	Mechanical	Derived	Length 6 unit vector specifying macroscopic stress state that results in the worst case von Mises stress local to the unit cell.
anisotropyIndex	Mechanical	Derived	Anisotropy index based on the definition in "Visualising elastic anisotropy: theoretical background and computational implementation" by Nordmann et al., 2018.
homogenizedConduction	Thermal	Derived	A 3x3 table corresponding to the normalized conduction matrix.