Force Distribution
Normal stress acting perpendicular to the plane of an adhesive bond tends to pull the joined layers apart at the edge of the overlap. This peel stress concentration at the initiation point of a crack drives the debonding process until the stress intensity falls below the material resistance.
Stress Calculation
Analytical models like the Volkersen or Goland-Reissner equations estimate the distribution of forces along the bonded joint. In most assemblies, peel stress reaches its maximum at the very end of the adhesive layer where the stiffness mismatch between the substrate and the bond is greatest. Tapering the edges of the adherends can redistribute this load.
Measurement Standard
Standardized tests such as the ninety degree or T-peel test measure the force required to separate a flexible member from a rigid or flexible base. The resulting peel stress value is sensitive to the thickness of the adhesive and the rate of displacement. High values indicate a ductile adhesive that can dissipate energy through deformation.
Design Impact
Structural configurations that place bonds in pure tension across the joint thickness are limited in favor of shear loading. Peel stress is minimized by ensuring the joint is loaded primarily in shear.
