Meaning
Mechanical force per unit area acting parallel to a surface arises from the relative movement of adjacent components during operation or thermal expansion. This shear stress affects the integrity of adhesive bonds and thermal interface materials within a battery module or pack.
Adhesive Integrity
Structural adhesives hold the cells securely to the cooling plate or module frame while providing a path for heat transfer. When the cells expand during charging or thermal cycles, they exert a parallel force on the adhesive layer, creating high internal tension. This mechanical loading can lead to cohesive or adhesive failure of the bond if the material limits are exceeded.
The resulting separation reduces thermal contact and can cause mechanical instability of the pack structure, potentially leading to electrical disconnects or catastrophic failures.
Mechanical Vibration
Road vibrations and vehicle acceleration exert continuous dynamic loads that create cyclical parallel forces on the cell joints. These cyclical loads can lead to fatigue failure of the adhesive or welding joints over time. The module design must distribute these forces evenly to prevent high stress concentrations in localized areas.
Sourcing specifications for adhesives must define the minimum lap shear strength required to survive these vibration profiles.
Material Evaluation
Laboratory testing of lap shear specimens determines the maximum force an adhesive can withstand before failure. Sourcing teams compare these test results from different suppliers to select materials that offer the best balance of strength and flexibility. Elastomeric adhesives offer higher flexibility to absorb these forces but may have lower absolute strength.
Analyzing this trade-off must be carefully evaluated to match the specific structural requirements of the battery pack.
