In-Plane Strain in Thin Film Peeling: A Numerical Study and a Unified Criterion for Stage Transition

Releasing a thin film adhered to a rigid substrate by peeling is a fundamental issue in interfacial mechanics and is of practical significance in many fields including flexible electronics, heterogeneous integration, and advanced packaging. While classical peeling theories have established the relationship between peeling force and interfacial adhesion, the in-plane strain evolution that governs film deformation and possible damage remains underexplored. This paper presents a numerical investigation of the in-plane strain in thin film peeling using an energy-variational framework. The results show that the strain response cannot be inferred solely from the peeling force response. Moreover, the dependence of the global maximum strain on film thickness h, Young’s modulus E, interfacial adhesion energy γ, peeling angle θF, and the characteristic length l of the cohesive zone is systematically examined. To distinguish between two-stage and three-stage strain responses, a unified classification criterion is established based on these parameters. A closed-form polynomial decision boundary is obtained, which enables direct identification of the applicable regime and facilitates appropriate strain estimation in peeling processes.