Meaning
Peak deformation occurring at the sharp internal corner or root of a welded joint under external load represents a critical failure predictor for battery casings. Analysis of root notch strain helps engineers identify the regions where the weld is most likely to initiate a tear during mechanical testing or pressure cycles. This parameter is highly dependent on the geometry of the weld root and the presence of any incomplete penetration.
It concentrates the nominal strain of the casing into a highly localized zone.
Structural Hazard
High localized strain at the weld root can trigger a sudden brittle or ductile failure of the hermetic seal. When the cell casing expands due to internal gas pressure or electrochemical swelling, the resulting forces bend the joint and concentrate at the notch. This root notch strain can exceed the uniform elongation limit of the metal even when the nominal pressure remains low.
If a microcrack initiates at this point, it can propagate rapidly through the remaining weld throat.
Stress Concentration
Geometry of the weld joint determines the magnitude of this local strain. Sharp transition angles and incomplete root penetration create a severe notch effect that multiplies the applied stress. Smooth, fully penetrated welds reduce this effect by distributing the forces more evenly across the joint.
Optimization Method
Utilizing laser power modulation during welding creates a smoother root profile to minimize the strain concentration.
