Meaning
Crack propagation driven by a combination of tensile and shear stresses represents a complex failure mechanism in structured materials. This mixed mode fracture occurs when the loading direction does not align perpendicularly to the crack plane, forcing the crack to experience both opening and sliding forces. In battery cells, the constrained swelling of layered components frequently creates these multi-directional stress fields.
Stress Distribution
The local stress field near the crack tip is described by a combination of stress intensity factors for different failure modes. Under these conditions, the crack often deviates from its original plane to align with the path of maximum strain energy release. Understanding this path deviation is essential for predicting the mechanical reliability of pouch cell seals and electrode interfaces.
Interface Failure
Multi-layered pouch laminates and coated electrodes are particularly susceptible to delamination under combined stresses. This separation occurs when the shear forces along the thin foil boundary exceed the adhesive strength of the polymer binder.
Adhesion Testing
Standardized peel tests at varying angles measure the resistance of cell layers to multi-directional splitting. These assessments provide the quantitative adhesion parameters needed to optimize binder chemistry and coating density during manufacturing. Accurate measurement of these parameters ensures that cell components can withstand the physical abuse encountered during high-rate charging and thermal expansion.
