Contact Guidelines and Examples
Before assigning contact to your Mechanical–Thermal design, be aware of the following important guidelines:
- You can assign contact only to the following entities:
- Faces of solid objects
- Faces of shell objects (that is, sheets objects with the Shell Element option selected)
- Shell Objects (equivalent to assigning contact to all faces of a multifaced shell)
- If the same conductance or resistance value is applicable to multiple contact faces or multiple shell contact objects, you can assign contact for all of the entities in a single operation. It is not necessary to assign each contact area separately, except when the conductance or resistance values differ.
- Thermal contact is applicable to the following types of object interfaces:
- A flat face of a solid body and a coplanar face of an adjacent solid body
- A curved face of a solid body and a concentric curved face of another solid body (for example, a solid rod inserted into a hole in another object).
- A face of a solid body (flat or curved) and a coplanar or concentric shell (face or object)
- A shell object sandwiched between two solid objects, where all three faces are coplanar or concentric
- Though contact involves two or three faces, you only select one face or shell object for each contact area. The assignment face or shell object of the contact pair is the "Contact face," and the coplanar or concentric face of each adjacent object it touches is the "Target face."
- One Contact face can have multiple Target faces.
- When you select multiple faces for a contact assignment and specify a total Conductance or Resistance value, that total value is applied to the combined area of all selected faces; it is not treated as a per-face value.
- Contact can occur along an entire face or only a portion of a face. Also, a contact face may correspond to target faces on multiple objects, with each target involving either a full face or a portion of a face. Review the examples in the subtopics referenced under Contact Examples below.
- For a contact definition to be valid, at least a portion of the selected face or faces must be in physical contact with one or more faces (or a portion of one or more faces) belonging to a different body.
- If two solid bodies or a solid body and shell object touch, zero resistance (or perfect conductance) is assumed between the two objects unless overridden by a thermal contact assignment. You do not need to assign contact to support heat flow between objects unless you want to introduce thermal contact resistance.
Thermal contact can exist between a shell object and one or more adjacent solid objects.
Thermal contact between two shell objects is not currently supported:
In order for heat to conduct from one shell object to another, they must intersect at a common edge. The default contact in this case is bonded (without any resistance to the flow of heat). If two shell objects share only some overlapping face area but do not have at least one common edge, no heat flow will occur between the two objects. That is, the default bonding (with zero thermal resistance) that occurs between two solid objects, or between a solid and shell object, does not occur between two shell objects.
For thermal solutions, you must always select only the Contact faces, and not the Target faces. The solver automatically determines the target faces when you run the analysis.
For example, a single semiconductor substrate might have many separate dies in contact with it. Selecting the Contact face of the substrate is sufficient to define contact for all of the dies touching it (assuming that the same thermal resistance properties are suitable for every contact face). This method differs from many finite element analysis (FEA) applications that require selection of both entities in a contact pair, but it can be a great convenience when one object's face is in contact with multiple adjacent objects. For a fuller understanding, review the examples in the subtopics referenced under Contact Examples below.
Examples and guidelines are divided into the following two subtopics: