Meaning
Number of loading cycles a component can withstand before failure occurs under cyclic stress is a fundamental limit for battery interconnects and cooling plates. The fatigue life of busbars is challenged by continuous vibration from the road and thermal expansion of the cells during charging. It is a vital parameter in determining the operating lifetime of electric vehicle battery packs.
Stress Concentration
Sharp corners and sudden changes in cross-section concentrate the stress and reduce the cyclic durability of the joint. Adding U-shaped bends or loops to the copper busbars allows them to flex without experiencing plastic deformation. These flexible geometries distribute the mechanical strain over a larger area.
Thermal Influence
Elevated temperatures accelerate the aging of metals and solder joints, reducing the number of cycles they can survive. In thermal cycling, the mismatch in thermal expansion coefficients between copper busbars and aluminum terminals creates continuous stress. Active cooling helps maintain the joints within safe temperature ranges to preserve the metal structure.
Accelerated Evaluation
Solder joints and interconnects undergo rapid shake and temperature testing to simulate a decade of field wear in a few weeks. These tests apply extreme vibration profiles while cycling the temperature from sub-zero to high limits. Recording the resistance of the joint during the test reveals when micro-cracks begin to form, giving engineers a clear view of the material limits and enabling them to select alloys that prevent premature field failures.
