A unified viscoelastic-viscoplastic constitutive framework for optically clear adhesives: Experiments, modeling, and...

Area of Science:

• Materials Science
• Mechanical Engineering
• Polymer Science

Background:

• Optically clear adhesives (OCAs) are critical bonding layers in modern display manufacturing, particularly for foldable devices.
• The time- and temperature-dependent deformation of OCAs during repeated bending necessitates accurate constitutive modeling for reliable stress prediction and design.
• Existing models often neglect the coupled viscoelastic-viscoplastic response, limiting their predictive accuracy for foldable display applications.

Purpose of the Study:

• To develop and validate a unified constitutive framework for characterizing the coupled viscoelastic-viscoplastic behavior of OCAs.
• To provide a reliable tool for stress analysis and design optimization of foldable displays incorporating OCAs.
• To enhance the long-term reliability assessment of flexible OLED devices through accurate material modeling.

Main Methods:

• A unified constitutive framework combining a generalized Maxwell model with the Qian-Liu viscoplastic formulation was developed.
• The proposed model was calibrated using stress-relaxation experimental data obtained at 30, 60, and 85°C.
• The framework was implemented into an ABAQUS UMAT for finite-element simulations and validated against experimental observations.

Main Results:

• The calibrated model successfully captured the coupled viscoelastic-viscoplastic behavior of OCAs under various temperature conditions.
• Finite-element simulations using the implemented UMAT corroborated the experimental findings, validating the model's predictive capabilities.
• The study demonstrated the framework's effectiveness in simulating the mechanical response of a simplified foldable display structure.

Conclusions:

• The developed unified constitutive framework effectively models the complex mechanical behavior of OCAs in foldable displays.
• This research fills a critical gap in OCA constitutive modeling, offering a validated tool for structural optimization.
• The validated framework is essential for improving the design and ensuring the long-term reliability of flexible OLED devices.