A constraint that a function must satisfy along a boundary.
The boundary conditions are applied in the surface integral term of the integral equation for the field and consist of prescribed values of the solution and of the derivatives of the solution on the boundary. When the field values are specified the conditions are called Dirichlet conditions. When the derivatives are specified, the conditions are called Neumann conditions.
For elastic problems, the conditions at a solid-solid boundary are continuity of:
* 3 components of displacement, and
* 3 components of stress having an index referencing the normal to the boundary