The stress analysis environment provides the means to override materials for any component. The default material provided in Inventor templates is not defined for simulation purposes. When modeling your components, use materials that are appropriate and defined, particularly if you are going to use simulation.
Inventor materials are maintained through the Styles and Standards editor. You can modify existing materials or define new ones according to your need. You can access the editor from the Assign Materials dialog box or by clicking Manage tab Styles and Standards panel Styles Editor .