Meaning
Structural internal reactions induced when eccentric loads or perpendicular mechanical forces act along an elongated battery component generate rotational deformation across that component cross section. This internal force distribution, formally designated as bending moment, governs the mechanical stress profiles encountered by busbars, cell terminal pins, structural module side plates and module tie rods during pack assembly and dynamic vehicle operation. It measures the product of the applied mechanical force and the perpendicular distance from the rotational point of interest, expressed in newton meters.
Calculation of this value stops applying once pure axial tension, pure compression or uncoupled planar shear without rotational eccentricity becomes the sole active force mechanism within the joint.
Structural Distribution
Mechanical loads on high-voltage battery busbars during pack vibration create severe localized stresses near rigid terminal weld joints. The bending moment concentrates peak tensile stress along the outer radius of curved connector bends and peak compressive stress along the inner radius. Flexible laminated copper shunts minimize these internal couples by lowering the effective section modulus of the interconnect.
Stiff extruded aluminium bars experience substantial root stress concentrations under equivalent road vibration profiles.
Limit Validation
Dynamic shaker table testing according to standards such as UN 38.3 and ISO 16750-3 establishes whether terminal joints survive repetitive cyclic flexure. Finite element analysis correlates simulated moment distributions with physical strain gauge readings across terminal header assemblies. Excessive bending moment during pack drop testing shears laser-welded joint seams or fractures brittle ceramic cell feedthrough seals.
Qualification mandates that peak dynamic bending values remain below sixty percent of the yield strength calculated for the weakest interconnect alloy.
Fatigue Response
Repetitive cyclic bending drives low-cycle fatigue failure along terminal posts over extended operational lifetimes. Microscopic fatigue cracks initiate at weld root notches where geometric discontinuities amplify nominal stresses. Progressive crack growth reduces the net conductive cross section of the terminal, increasing electrical contact resistance and generating localized resistive heating under high charge currents.
Component rejection occurs whenever ultrasonic inspection reveals crack propagation following endurance vibration cycles.
