Thermal Contact Resistance (TCR) & Contact Conductance in FEA

1. Definition & Mathematical Engineering Foundations

In multi-body thermal and thermo-mechanical Finite Element Analysis (FEA), assuming perfect thermal continuity across bolted joints, heat sink interfaces, and electronic package lids produces severe underestimations of operating temperatures. In reality, all metallic engineering surfaces possess microscopic surface roughness ($R_a$, $R_z$). When two surfaces are pressed together, true physical solid contact occurs only at microscopic peak asperities (typically covering less than 2% of the apparent nominal area), leaving the remaining 98% filled with air or thermal grease. This bottleneck creates significant Thermal Contact Resistance (TCR), quantified in FEA via the Thermal Contact Conductance (TCC) coefficient ($h_c$).

2. Technical Architecture & Key Formulations

• CMY Areal Contact Conductance Model: The Cooper-Mikic-Yovanovich (CMY) model predicts solid asperity conductance:
  h_c = 1.25 · k_harm · (m / σ) · (P / H_c)^0.95
  where $k_{\text{harm}} = 2 k_1 k_2 / (k_1 + k_2)$ is harmonic mean thermal conductivity, $\sigma = \sqrt{\sigma_1^2 + \sigma_2^2}$ is combined RMS roughness, $P$ is contact pressure, and $H_c$ is microhardness.
• Contact Pressure Dependence: As bolt clamping torque increases, asperity peaks deform plastically, increasing real contact area and elevating TCC ($h_c$) proportionally.
• Interstitial Medium Gap Conduction ($h_g$): Heat also conducts across the gas/grease gap ($h_g = k_{\text{fluid}} / Y$ where $Y$ is mean gap thickness). Applying thermal interface material (TIM) with $k=5\,\text{W/m}\cdot\text{K}$ eliminates low-conductivity air ($0.026\,\text{W/m}\cdot\text{K}$).
• Coupled Thermo-Mechanical Solving: In heavy braking or rocket engine nozzles, mechanical contact pressure and temperature must be solved iteratively because thermal expansion changes contact pressure, which dynamically alters TCC.

3. Industry Failure Modes & Risk Mitigation

In power electronics IGBT module design, neglecting thermal contact resistance across the module copper baseplate and aluminum heat sink leads to thermal runaway; the actual chip operating temperature can be 25°C to 40°C hotter than a naive 'bonded' FEA model predicts.

4. Production Governance & Metrological Standards

Thermal analysts measure interface conductance using ASTM D5470 test standards and input pressure-dependent TCC tables into ANSYS Mechanical, Abaqus, or COMSOL contact pair definitions.

Cross-Disciplinary Resources

Enterprise Production Implementation & GstarCAD 2027 Workflow

• Database Serialization & Binary Fidelity: Ensure all entities and symbol table records associated with Thermal Contact Resistance (TCR) & Contact Conductance in FEA are authored on standardized ISO 13567 layers rather than Layer 0 or Defpoints, and verify lossless round-trip persistence in native DWG (AC1032) format.