# Design Analysis: Thermal Bonded Contact

### Design Analysis:

nTop Platform features built-in steady-state structural and thermal analysis using a range of boundary conditions.  When performing Design Analysis a user may want to assign material properties to a mesh based specific CAD or Implicit bodies.  This article will focus on the use of "Structural and Thermal Bonded Contact" Blocks in nTop Platform.

### Block Name and Descriptions:Thermal Bonded Contact:

This block creates a bonded contact between two FE boundaries which allows for heat flow between two components.  Contact resistance between the two boundaries can be defined to account for a thin membrane material at the boundary (ie thermal paste).

In the figure below, a user would like to tie a copper slug into an aluminum frame.  The cad model on the left represents the geometry of the two materials and the subsequent mesh of the two regions is on the right.  Since the FEA meshes of two regions do not necessarily share common nodes and element faces it is necessary to "tie" these two regions together mathematically.  As such, this approach allows the user to mathematically “bond” two different objects (of different materials) together and couple them thermally.

To tie these two materials together the user would use the "Thermal Bonded Contact" block.  This block creates a bonded contact between two FE boundaries which allows for heat flux between the two components.

Contact resistance can be defined to account for thin membrane material at the boundary such as thermal paste.  The contact resistance between two materials is often calculated from experimental tests of contact conductance.  A table of values is provided below with some common materials.

Table 1: Thermal contact conductance of some metal surfaces (from various sources)

 Material Surface Condition Roughnessµm Temperature°C PressureMPa hc*W/m2· °C Identical Metal Pairs 416 Stainless steel Ground 2.54 90–200 0.3–2.5 3800 304 Stainless steel Ground 1.14 20 4–7 1900 Aluminum Ground 2.54 150 1.2–2.5 11,400 Copper Ground 1.27 20 1.2–20 143,000 Copper Milled 3.81 20 1–5 55,500 Copper (vacuum) Milled 0.25 30 0.7–7 11,400 Dissimilar Metal Pairs Stainless steel-Aluminum - 20–30 20 1020 29003600 Stainless steel-Aluminum - 1.0–2.0 20 1020 16,40020,800 Steel Ct-30-Aluminum Ground 1.4–2.0 20 1015–35 50,00059,000 Steel Ct-30-Aluminum Milled 4.5–7.2 20 1030 4800 8300 Aluminum-Copper Ground 1.3–1.4 20 515 42,000 56,000 Aluminum-Copper Milled 4.4–4.5 20 1020–35 12,00022,000

*Divide the given values by 5.678 to convert to Btu/h · ft2 · °F.

It should be noted that the Thermal Bonded Contact Block requires Thermal Contact Resistance and the table above provides conductance values.  It is required to perform some math operations to get conductance values properly input into the block.

With the contact resistance properly computed it is necessary to tie the two meshes together as shown in the image below.

To properly include Bonded Contact in your FEA analysis you must use include the thermal bonded contact block in the "Connectors" input of your FE Model as shown in the image below.

Once your thermal boundary conditions are input you can now run your thermal analysis using bonded contact!

# Keywords:

Finite FEA Thermal Bonded Contact Design Analysis Tie