Meaning
Lowering mechanical clamping pressure across electrical interconnects increases interface resistance and causes localized thermal spiking in high-current battery packs. Mechanical relaxation phenomena trigger contact force degradation over thousands of thermal and vibration cycles. The metric governs joint integrity across busbar connections, cell terminal welds, and module compression frames.
It stops applying when physical contact completely breaks or when joint interface behavior transitions from elastoplastic mechanical clamping to permanent metallurgical fusion.
Relaxation Mechanism
Viscoelastic creep in polymer housings and micro-plastic deformation at metallic contact asperities continuously reduce interfacial clamping pressure during operation. When battery modules undergo repeated thermal expansion and contraction, differential thermal expansion between dissimilar metals accelerates bolt tension loss. The contact force degradation process reduces effective contact patch area, forcing electrical current through fewer microscopic contact spots.
Local electrical resistance increases sharply as clamping force decays below critical design limits, creating localized hotspots during high-rate charging.
Thermal Consequence
Elevated contact resistance generates localized Joule heating that further accelerates thermal degradation of adjacent seals and structural adhesives. Temperature rises around busbar joints alter material yield strengths, exacerbating force loss in a self-reinforcing feedback loop. Thermal imaging reveals distinct temperature gradients originating at compromised terminal interfaces during dynamic discharge cycles.
Severe clamping force loss can eventually trigger localized arcing or thermal runaway under sustained load conditions.
Measurement Boundary
Direct monitoring of joint clamping force relies on embedded load cells or ultrasonic bolt tension sensing during accelerated aging tests. Measuring interface pressure distribution requires specialized pressure-sensitive films inserted before mechanical torque application. Assessment procedures cease producing valid quantitative force loss data once severe corrosion or oxidation physically binds the joint elements together.
