Meaning
Stored mechanical stress remaining within a material matrix after manufacturing, heat treatment, or mechanical forming operations exists independently of external applied loads. Documented in quality assurance standards for battery foil slitting and cell casing drawing, residual internal stress causes springback, edge waving, and unexpected dimensional warping during electrode web processing. Non-uniform stress distributions across copper or aluminum current collector foils lead to misalignment during continuous roll-to-roll coating operations.
Stress relief annealing schedules reduce internal strain gradients before slitting and winding steps.
Formation Mechanism
Thermal gradients and non-uniform plastic deformation during rolling, stamping, or rapid cooling generate trapped stress fields. Differential thermal expansion between metal current collectors and active material coatings creates interfacial shear strain during drying operations. Subsequent calendering compresses active material particles, introducing lateral stress components into the thin metallic substrate.
Unbalanced stress distributions induce cell pouch cupping and module stacking errors.
Evaluation Method
X-ray diffraction and hole-drilling strain gauge methods quantify local residual strain levels across component surfaces. Non-destructive diffraction measurements record lattice parameter distortions to map residual internal stress variations across processed metal foils. Test profiles highlight localized strain concentrations near slitted electrode edges.
Process engineers adjust roll tension parameters based on measured stress maps.
Failure Threshold
Uncontrolled internal strain promotes micro-crack propagation under cyclic charge-discharge expansion. High residual internal stress levels cause catastrophic foil tearing during high-tension web handling and cell winding operations.
