Optimal Design of Thickness and Young’s Modulus of Multi-Layered Foldable Structure Considering Bending Stress, Neutral Plane and Delamination under 2.5 mm Radius of Curvature

The present study included the finite element analysis and optimal design of a multi-layered foldable structure (foldable display) to satisfy stress, neutral plane, and delamination requirements under a 2.5 mm radius of curvature (i.e., 2.5R) due to static bending load. Two bending types (inner folding and outer folding) were considered to accommodate the repeated bending, and their maximum stress values were evaluated. In the approximate optimization for the thickness and Young’s modulus of multiple film layers, the objective was to minimize the folding stress subjected to constraints on the positioning of the largest stress value to a neutral plane and prevention of delamination. Through the simultaneous change in thickness and Young’s modulus, the study identified the new position of a neutral axis so that a 16% improvement in the stress magnitude was obtained. A simulation-based T-peel test was also performed to analyze the fracture behavior of the adhesive, and the relation between the fracture toughness G C and separation load L P could be expressed as L p = 12.687G c . The optimized objective function value of von Mises stress was improved by 18% compared to an initial design, and constraints of the delamination indicator and positioning of the neutral plane were satisfied.