Tech Briefs

Improved Contact Solutions and Traction Calculations

In the previous versions of ADINA, contact surfaces are identified by linear segments. For improved accuracy, in particular when quadratic elements are used, the actually-interpolated surfaces are employed in ADINA 8.3 to detect and calculate the contact conditions. Hence, in 3-D analysis, 10- and 11-node tet elements in contact use a 6-node contact segment, while 20- and 27-node brick elements use 8- and 9-node contact segments, respectively. This enhancement is also used for the 2-D and shell elements resulting frequently in a significant increase in accuracy for contact problems involving quadratic elements. A new, more accurate contact traction calculation algorithm is also used for all elements.

These improved contact analysis procedures are available for linear and large deformation nonlinear solutions and are different from the "gluing algorithm" presented in the previous News, see ADINA News, Sep 15, 2005. In the gluing algorithm, surfaces are glued together, that is, separation and sliding are not possible, whereas in the new contact algorithm, the conditions of contact, sliding with friction, and separation are all automatically solved for.

To demonstrate the accuracy of the improved ADINA 8.3 contact analysis procedure, the above shown 3-D patch test is solved using three different mesh combinations as shown in the figure below. In the first case, both bodies are meshed with 10-node tets. In the second case, both are meshed with 20-node bricks, and in the third case, the bottom body is meshed with 27-node bricks, while the top one with 11-node tets. Note that the top and bottom meshes are totally incompatible in each case, see also the last figure where the contact surfaces are separated and the top bodies have been rotated about the X axis by 180 degrees.

In all three cases, the error in the calculated tractions is within ±6%. Note also that the band plotting of contact tractions is a new feature in ADINA 8.3. The gluing algorithm, referred to above, satisfies the patch test exactly, but the contact algorithm has much more general capabilities.