This command is used to define local material directions. If $\bar{\mathbf y} = (\bar{y}_x, \bar{y}_y, \bar{y}_z)$ has been defined the local and z-axis ($\bar{\mathbf z}$) is computed as:

$\displaystyle{ \hat{\mathbf z} = \frac{\hat{\mathbf x} \times \bar{\mathbf y}}{\vert \hat{\mathbf x} \times \bar{\mathbf y} \vert}}$

If $\bar{\mathbf y}$ has not been defined the local z-axis ($\bar{\mathbf z}$) is equivalent to:

$\displaystyle{ \hat{\mathbf z} = \hat{\mathbf n}}$

where $\hat{\mathbf n}$ is the local element face normal. Note that this option only works if the structure is modeled with one single element in its thickness direction. Once $\hat{\mathbf z}$ has been computed $\hat{\mathbf y}$ is calculated as:

$\displaystyle{ \hat{\mathbf y} = \hat{\mathbf z} \times \hat{\mathbf x}}$

All direction parameters can either be constants or defined as functions of the local coordinate $(x,y,z)$.