Header Weld Root Fatigue Life Prediction under Combined Thermal and Breathing Cycles
Root notch geometry and coupled breathing-thermal strain dictate header weld fatigue life, requiring non-linear strain-life prediction over far-field stress models.
Weld Root Notch
Meaning
Geometric irregularities at the base of a welded joint create a site for stress concentration. A weld root notch often occurs due to incomplete penetration or the natural profile of the weld bead where it meets the parent metal. This feature acts as a starting point for cracks in the busbars or casing of a battery pack.
Reliability in high vibration environments depends on minimizing these sharp transitions.
Fracture Initiation
Sharp corners at the root multiply the local stress far beyond the nominal load. Because the weld root notch is often hidden from the surface, it can lead to unexpected failures during operation. Cyclic thermal loading causes these microcracks to propagate through the joint.
Electrical resistance increases as the effective cross section of the conductor shrinks.
Visual Verification
Non destructive testing methods like ultrasonic or x ray imaging are used to detect internal flaws. Standards for battery assembly define the maximum depth and sharpness allowed for a weld root notch. If the defect exceeds the specified limit, the part must be reworked or scrapped.
Consistent laser welding parameters help maintain a smooth profile.
Design Fix
Changing the joint type to a double sided weld can eliminate the exposed root.