Module Compression Pad Mechanics under Non Linear Swelling Force Profiles
Non-linear swelling forces mandate hyperelastic compression pads that hold module interfacial pressure between 0.02 MPa and 0.60 MPa over full cell life.
Module Tie Rod Strain
Meaning
Tensile deformation occurs along the length of structural rods that secure individual cells together into a rigid block assembly. Monitoring module tie rod strain provides a measure of the internal pressure generated by the swelling of pouch or prismatic cells during operation.
Force Transmission
As cells expand during charging, they exert a force against the endplates of the module. This outward force is transferred directly to the tie rods, creating a rise in module tie rod strain. If this strain exceeds the yield point of the rod material, the tie rod will deform permanently, resulting in a loss of compression force when the cells contract.
This loss of compression can cause delamination and increase the internal resistance of the cells.
Measurement Method
Electrical resistance strain gauges bonded to the tie rods track these mechanical changes in real time. These sensors convert the minute physical elongation of the metal rod into a measurable change in electrical resistance. This measurement must be calibrated to account for temperature changes that alter both the metal and the gauge.
Safety Management
Tracking these values during thermal testing provides warning of abnormal cell swelling that could indicate internal short circuits. Sourcing engineers use this data to select high-strength alloys for the tie rods that can withstand these long-term fatigue cycles. It ensures the mechanical integrity of the pack under all conditions.