Elements with incompatible displacement modes add additional degrees of freedom (DOF) to the element to improve the accuracy of the element. For example, an eight-node isoparametric brick element possesses 24 DOF (3 DOF/node) with linear accuracy. With incompatible displacement modes, three additional internal nodes are added to the element so the element possesses 33 DOF and has near quadratic accuracy. The internal nodes are condensed out of the element equations, so the final element matrices have 24 DOF but the element retains its near quadratic accuracy. The term incompatible displacement modes arises because the extra internal nodes added to each element are not shared between adjacent elements, thus the displacement fields of adjacent elements are not compatible. Elements with incompatible displacement modes are also referred to as non-conforming elements. To activate incompatible displacement modes, select the Not Enforced option in the Compatibility drop-down menu in the Element Definition dialog box.