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### Twenty-node brick element with reduced integration and incompressibility condition at the corner nodes (C3D20RI)
Keywords: ccx

This element is identical to the C3D20R element, except that in addition an isochoric condition is applied at the corner nodes of the element. This is guaranteed by creating a nonlinear multiple point constraint at each corner node of the element expressing that the Jacobian determinant of the deformation is equal to unity (J=1). Due to the nature of the shape functions only those nodes which are connected by an edge to a particular node enter its incompressibility condition.

The incompressiblity embodied by the C3D20RI element is weaker than those implemented by a material law, since only the corner nodes are involved.