Meaning
Mechanical tension generated within the threaded rods that clamp battery modules together. Tie rod stress maintains the required compression on cells and compression pads to prevent expansion during cycle life. The value must be managed to prevent structural failure of the rods or module endplates.
Force Accumulation
Thermal expansion and cell swelling during charge cycles increase the tensile load on the rods. This load must remain below the yield strength of the rod material to prevent permanent deformation or fracturing. Rods are made of high-strength steel or glass-fiber composites to withstand these cyclic forces.
Sourcing Evaluation
Procurement specifications for module structural components require detailed stress and fatigue analysis of the clamping assembly. Sourcing teams compare the yield margins and weight of different rod designs to optimize cost and structural margin. Choosing a lighter rod with sufficient strength is necessary for maximizing pack energy density.
Operational Lifetime
Long-term creep and thread relaxation can cause a gradual reduction in the tension, leading to lower cell compression. A loss of tension can result in electrode delamination and accelerated cell degradation. Sourcing contracts require suppliers to use anti-loosening thread designs or locknuts to preserve tension.
This requirement is verified through long-term vibration and thermal cycling tests on fully assembled modules.
