This constraint may be used in 2D/3D. The node is expected to come in contact with another solid system. This constraint is nonlinear because the status of contact varies with load. The node status is either released, in sliding contact or in sticking contact. The normal to the target surface determines the side of contact. A specific order of node numbering is required to determine the side of contact. In 3D element the normal will have the same direction as determined by the right hand rule of the direction of rotation used to number the element local nodes in the same order listed in the constraint control card. In 2D elements the normal direction is determined by the cross product , where is the vector originated from the first local node to the second one as in the same order listed in the constraint control card.