Meaning
Repetitive physical loading arises from the breathing action of pouch and prismatic cells during successive charge and discharge events. Designers analyze cyclic mechanical stress to ensure that module brackets and battery pack frames resist fatigue over thousands of operating periods. This periodic load causes structural micro-damage in the surrounding restraining hardware.
Structural Fatigue
Metallic and plastic brackets suffer gradual loss of strength when subjected to continuous variation in load. This process can lead to the formation of micro-cracks at high stress concentration points, such as welded joints or sharp corners. Structural simulation software models this behavior using stress-life curves to predict when a component is likely to rupture.
Cell Degradation
Internal components of the battery also experience stress because the active material particles expand and contract on each cycle. This action can lead to electrical disconnects, particle cracking, and accelerated capacity loss. Managing the external pressure helps to stabilize the electrode structure and maintain uniform lithium distribution across the separator.
Design Margin
Safety factors in structural design account for the accumulation of material damage by ensuring that stress levels remain below the fatigue limit. Engineers select materials with high yield strengths and apply pre-tensioning strategies to distribute the loads evenly across the entire pack. By utilizing robust structural members, the system absorbs these repeating expansion cycles without experiencing catastrophic frame failure, preserving the mechanical integrity of the entire energy storage system under both normal usage and transport vibrations.
