Meaning
Stress distribution in adhesive joints is highly non-uniform, concentrating heavily at the boundary edges of the bonded assembly. The Volkersen shear lag theory calculates this non-uniform shear stress along the length of a single-lap joint, assuming elastic behavior in both the adherends and the adhesive. This mathematical model helps battery pack designers calculate the required overlap length for cell-to-plate bonding to avoid joint failure.
Shear Distribution
Tensile loads applied to the bonded cells are not transferred evenly across the adhesive surface. Calculations using Volkersen shear lag show that the stress peaks sharply at the entry and exit points of the joint, while the center remains relatively unstressed. This shear concentration can initiate localized tearing that eventually propagates through the entire bonded interface, which is a major concern when designing the bottom plate of the pack.
Joint Geometry
Optimization of the adhesive layer thickness can mitigate these localized peak stresses. Sourcing engineering teams use these calculations to determine the minimum line width and thickness of the dispensed adhesive. Modifying these structural dimensions lowers the peak forces and extends the mechanical service life of the battery pack casing.
Sourcing Evaluation
Polymeric compounds with higher elasticity are selected to smooth the stress gradients predicted by this model. Flexible polyurethane adhesives deform slightly to redistribute the peak loads. This selection ensures that the structural bonds resist the dynamic impacts during vehicle crashes.
