Modeling contact in asymmetric-axisymmetric problems:
requires the use of contact elements (ISL or IRS);
requires independent contact elements on each circumferential plane; and
can be done only on certain circumferential planes.
CAXA or SAXA elements (see Axisymmetric solid elements with nonlinear, asymmetric deformation, Section 22.1.7, and Axisymmetric shell elements with nonlinear, asymmetric deformation, Section 23.6.10) are used to model problems where initially axisymmetric structures may undergo asymmetric deformations. These asymmetric deformations may include asymmetric contact conditions. The surface-based contact capability cannot be used to model such problems; contact elements (ISL or IRS) must be used.
Independent sets of two-dimensional contact elements must be created for each circumferential plane in the CAXA or SAXA elements. You must specify the angle, , of the circumferential plane with which each set of contact elements is associated and the number of Fourier modes, n, used with the underlying CAXA or SAXA elements.
If the circumferential planes in an asymmetric-axisymmetric problem rotate more than a few degrees, ABAQUS/Standard can model contact conditions correctly only on the =0 and 180 circumferential planes. The asymmetric-axisymmetric elements have internal degrees of freedom for the rotation and out-of-plane motion of the circumferential planes, but these degrees of freedom are not accounted for in the contact elements. Ignoring these degrees of freedom means that ABAQUS/Standard keeps the contact directions fixed in initial circumferential planes and the position of the nodes is projected back onto these initial planes for contact calculations. If the rotation and motion of the nodes from these initial planes are small, the errors caused by this approach are minimal. If they are large, the errors will become very large, making the results unrealistic.