nD

An nD material (n-dimensional) describes the full 2D/3D stress–strain law at the Gauss point of a continuum element. Shells, bricks and tetrahedra all need one.

🔧 Grasshopper component

nDAlpaca4d ▸ 00_Material

Inputs

MatNameMaterial NameText(empty)Label for the material. Cosmetic.

ENumber210000000Young's modulus, in kN/m².

GNumber80760000Shear modulus, in kN/m².

νNumber0.3Poisson's ratio.

RhoNumber7850Density, in kg/m³.

ColourColour(empty)The colour the material is drawn in when Model View colours the elements by material.

Left empty, Model View gives each material a colour of its own. Display only: the analysis never reads it.

MatNameMaterial NameText(empty)Label for the material. Cosmetic.

ExNumber210000000Young's modulus along x, in kN/m².

EyNumber210000000Young's modulus along y, in kN/m².

EzNumber210000000Young's modulus along z, in kN/m².

GxyNumber80760000Shear modulus in the xy plane, in kN/m².

GyzNumber80760000Shear modulus in the yz plane, in kN/m².

GzxNumber80760000Shear modulus in the zx plane, in kN/m².

NuXyNumber0.3Poisson's ratio xy.

νYzNumber0.3Poisson's ratio yz.

νZxNumber0.3Poisson's ratio zx.

RhoNumber7850Density, in kg/m³.

ColourColour(empty)The colour the material is drawn in when Model View colours the elements by material.

Left empty, Model View gives each material a colour of its own. Display only: the analysis never reads it.

Outputs

MaterialMaterialnD material, for a Plate Fiber Section, an SSP Brick or a Tetrahedron.

Note

G on the isotropic unit is not written to OpenSees — ElasticIsotropic derives its shear modulus from E and ν. Alpaca4d keeps G on the material because the same material object may also be read for section properties.

Note

Rho is in kg/m³, and it is what gives shells and solids their mass.Shells, bricks and tetrahedra take no mass input of their own — OpenSees reads the density straight off this material. Alpaca4d converts it to the solver's mass unit when the deck is written.

Before 0.11 that conversion was missing, so every shell and solid was a thousand times too heavy and modal frequencies came out about 31.6 times too low. Static results were never affected — density only feeds the mass matrix, and self-weight is applied as explicit nodal loads by Gravity Load.

A switcher component: pick the unit in the drop-down under it, or right-click it ▸ Units:

• ElasticIsotropic — the same stiffness in every direction.
• ElasticOrthotropic — different stiffness along three orthogonal directions, for timber, composite panels, or plates that behave differently in-plane and out-of-plane.

📈 When to use it

Use it when

• The element is a shell, a brick or a tetrahedron.
• You need direction-dependent stiffness — timber panels, laminates, ribbed slabs smeared into an orthotropic plate → use ElasticOrthotropic.

Do not use it when

• The element is a beam → use a Uniaxial material.
• You want a standard isotropic grade → the Material Database will produce one directly.

🔗 Relation to OpenSees

nDMaterial ElasticIsotropic   $matTag $E $nu $rho
nDMaterial ElasticOrthotropic $matTag $Ex $Ey $Ez $nuXy $nuYz $nuZx $Gxy $Gyz $Gzx $rho

For the orthotropic material on shells, the axes are those of the shell section — axes 1 and 2 of Local Axes in Model View. On solids they are the global axes. On shells, set Local X Axis on the ASD Shell component so every face agrees on which direction Ex refers to.