How To: Units, Geometry, & Materials¶

Units¶

The default Unit System is MKS or MeterKilogramSecond. We allow the following customizations:

Specify custom unit for geometry through the Scenario unit (default MKS)
Specify custom unit for loads (default MKS)
Specify custom unit for materials (default MKS)

Unit System Keywords	Mass	Force	Stress	Length	Temperature	Energy
MeterKilogramSecond	kg	N	Pa	m	K	J
CentimeterGramSecond	g	dyne	dyne/cm²	cm	K	dyne·cm
MillimeterMegagramSecond	Mg	N	MPa	mm	K	mJ
FootPoundSecond	slug	lbf	lbf/ft²	ft	Ra	lbf·ft
InchPoundSecond	lbf s²/in (slinch)	lbf	psi	in	Ra	lbf·in

Geometry¶

Geometry is specified through a Model object.

MeshModel created from a surface mesh can be defined in two ways:

By specifying a filename to define mesh from a file (STL, PLY)

auto mesh_geometry = Intact::MeshModel("beam.stl");
mesh_geometry.instance_id = "beam";

By constructing mesh face-by-face

// define an empty mesh
auto mesh_geometry = Intact::MeshModel();
mesh_geometry.instance_id = "fixed_boundary";

// add vertices to the mesh and get the vertex id as output
auto v0 = mesh_geometry.addVertex({0.0, 0.0, 0.0});
auto v1 = mesh_geometry.addVertex({1.0, 0.0, 0.0});
auto v2 = mesh_geometry.addVertex({0.0, 1.0, 0.0});

// add faces defined by the vertex id
mesh_geometry.addFacet(v0, v1, v2);

Meshes can be refined, usually for finer interpolation of results during visualization, using the MeshModel::refine method with refinement_level argument. refinement_level is the largest allowed triangle edge as a ratio of the bounding box diagonal.

// mesh geometry created above is further refined
mesh_geometry.refine(0.02);

Structural Material Properties¶

IsotropicMaterialDescriptor to create an Isotropic material. (Unit system is MeterKilogramSecond)

density is the material density
youngs_modulus is the elastic modulus
poisson_ratio is the Poisson ratio

auto steel_structural = std::make_shared<Intact::IsotropicMaterialDescriptor>();

// Set the density to 7845 kg/m^3, modulus to 200 GPa and poison ratio to 0.29
steel_structural->density = 7845
steel_structural->youngs_modulus = 200e9
steel_structural->poisson_ratio = 0.29

OrthotropicMaterialDescriptor to create an Orthotropic material. Orthotropic materials are often used to represent composites and wood, where the material properties along one axis are significantly different from the properties along the other axes. (Unit system is MeterKilogramSecond)
- density is the material density
- Ex is the elastic modulus in the material’s x-direction
- Ey is the elastic modulus in the material’s y-direction
- Ez is the elastic modulus in the material’s z-direction
- Gxy is the shear modulus in the xy plane
- Gxz is the shear modulus in the xz plane
- Gyz is the shear modulus in the yz plane
- vxy is the poisson ratio in the xy plane
- vxz is the poisson ratio in the xx plane
- vyz is the poisson ratio in the yz plane
- transform is the optional material transform to arbitrarily rotate the axes along which the material properties are defined. Specified as a list of 9 floating point numbers corresponding to a 3x3 matrix. Note the first 3 floating point numbers corresponds to the first row.
```
// Create an orthotropic material (Red Pine)
auto material = std::make_shared<Intact::OrthotropicMaterialDescriptor>();
material->density = 460.0;             // kg/m³
material->Ex = 11.2e9;                 // Pa
material->Ey = 492.8e6;                // Pa
material->Ez = 985.6e6;                // Pa
material->Gxy = 907.2e6;               // Pa 
material->Gxz = 1.08e9;                // Pa 
material->Gyz = 123.2e6;               // Pa 
material->vxy = 0.315;
material->vxz = 0.347;
material->vyz = 0.308;
material->transform = {1.0, 0.0, 0.0,
                       0.0, 1.0, 0.0,
                       0.0, 0.0, 1.0}  // transform is optional
```

Thermal Material Properties¶

ThermalMaterialDescriptor to create a thermal material. (Unit system is MeterKilogramSecond)

density is the material density
conductivity is the conductivity of the material
specific_heat is the specific heat of the material

auto thermal_material = std::make_shared<Intact::ThermalMaterialDescriptor>();

// Set the density, conductivity, and specific heat of the material
thermal_material->density = 2700.0;    // kg/m^3
thermal_material->conductivity = 170;  // W/(m·K)
thermal_material->specific_heat = 500; // J/(kg·K)

Component and Assembly¶

A Component is created as a MaterialDomain and takes three inputs

A Model object (MeshModel specifically)
A material name
A ScenarioDescriptor object (see Simulation Setup)

auto bar1_structural = Intact::MaterialDomain(mesh_geometry, "Steel", structural_scenario);
auto bar2_structural = Intact::MaterialDomain(mesh_geometry, "Red Pine", structural_scenario);

Assembly is a std::vector of components that are bonded together

Intact::Assembly structural_assembly = {bar1_structural, bar2_structural};