A network-based visco-hyperelastic constitutive model for optically clear adhesives

Abstract

Optically clear adhesives (OCAs) are widely used as bonding materials in display industries. Accurate characterizations on the mechanical behaviors of OCAs are fundamental inputs in bending stress analysis of foldable displays for the optimal design purpose. Yet only a few works have studied the mechanical behaviors of OCAs. No network-based visco-hyperelastic constitutive model has ever been developed or applied to OCAs. In this work, we propose a visco-hyperelastic constitutive model based on the microscopic structure of polymer networks to characterize the mechanical behaviors of OCAs under different loading conditions. The model considers that the OCA consists of crosslinked networks and free chains, both of which are under topological constraints induced by entanglements. The hyperelastic response comes from the crosslinked networks, while the viscoelastic response originates from the free chains. We test the OCAs produced by 3M by loading them to large deformations with different loading rates. Results show that our model can well capture the visco-hyperelastic mechanical behaviors under these conditions. In addition, we program our constitutive model into ABAQUS UMAT and use two case studies to show the application of our model in finite element simulations.