In order for loads to be transferred between elements, normally, the nodes must be connected together. For example, if two bodies begin an analysis separated, no interaction will occur during the analysis. The bodies will pass through each other. In linear analyses, surface contact is achieved by connecting nodes on adjacent parts with 1D contact elements. In nonlinear analyses, general surface-to-surface contact is defined between parts or surfaces. The solver keeps track of the motion of the contact surfaces and produces resistive forces when the surfaces move together. Complex algorithms determine the contact stiffness and attempt to minimize contact chatter and surface penetration.
You can define surface-to-surface contact in Mechanical Event Simulation and other nonlinear stress analyses (but not natural frequency with nonlinear materials). Create surface-to-surface contact pairs when surfaces might come into contact with each other during the analysis or when they are initially in contact (but not necessarily bonded). The processor will determine the distance between the nodes on these surfaces at each time step of the analysis. When the nodes are sufficiently close to each other to indicate surface interaction, a force is applied to prevent penetration.
Before the user starts a contact analysis, he or she must clearly identify where the contact interaction might occur during the analysis. (Although possible, it would be very inefficient to define every surface of every part as contacting every surface of every other part.) Not only can multiple target surfaces interact with one master surface, but self-contact is also possible in a large deformation problems. A part can deform enough that it contacts itself (such as the folds of rubber bellows when they are closed during axial compression of the bellows). In such cases, the user must define multiple contact pairs that cover all potential contact interaction.
The contact pairs can consist of any two arbitrary surfaces. Surface-to-surface contact will produce interaction between the nodes on one surface and the faces of the other surface (and optionally, vice versa). However, to speed up the contact search, the user should only specify the contact pairs that will definitely interact within the given event duration. The analysis will converge more rapidly if the number of contact elements is minimized, especially in problems that involve small areas of sliding contact.
To define where contact can occur for hand-built models, put the surfaces to come into contact on a unique surface number. The lines along the contact face should have the highest surface number of any of the lines comprising the elements that come into contact. When an element face is bounded by lines of different surface numbers, a voting rule is used to determine which surface number applies to the face. To determine which of the six possible faces of a brick element are in contact, the solver checks the surface number of each line comprising an element. Each face that has a majority of these lines on the highest surface number (3 of 4 sides, or 2 of 3 sides) can participate in contact. Faces whose lines are not on the highest surface number on the element cannot participate in contact.
For CAD-based solid meshes, all interior mesh lines are on surface 0 (zero). Therefore, the outer (contact) surfaces are always on higher surface numbers than the other element faces, except perhaps at exterior corners, where two or more sides of a brick can be on the exterior surfaces.
For cases where it is difficult for the user to predict the relative motion of contact pairs, the processor provides an automatic updating scheme to help the user set up the contact pairs efficiently with only a few contact surfaces covering the entire contact area. However, this may require a large amount of memory in a 3D analysis. If the necessary memory is not available, the user must split the large contact surface into several smaller contact surfaces.
Apply Surface-to-Surface Contact
Since it may not be possible to calculate the contact between some element types and others, the Element Type and Element Definition headings of the tree view should be completed before applying surface-to-surface contact.
Surface-surface contact pairs can be defined using any of these methods.
- Select two parts or two surfaces in the display area and right-click. Select Contact
Surface Contact. The details of the contact can be set by selecting the contact pair just created in the tree view, right-click, and choosing Settings. The settings are described in the Surface-to-Surface Contact Options section. Note that the first part or surface selected becomes the primary surface, and the second selection becomes the secondary surface. This may be important when defining the Contact type as Point to Surface. (See the page Surface-to-Surface Contact Options for details on the Contact Type.) - Right-click the Contact (Default:) heading in the tree view and select the General Surface-to-Surface Contact command.
- With nothing selected, right-click in the display area and select the General Surface-to-Surface Contact command.