Evaluation of interfacial strength in microdroplet test using experiment and computational simulation

Interfacial strength is an important factor that dominates the mechanical properties of composites. This paper presents an evaluation method for fiber/matrix interfacial strength. In this study, we determine interfacial strength by comparing experimental data with FEM computational simulations of the microdroplet tests. We consider first the residual thermal stresses that result upon cooling from the cure temperature to room temperature. Cohesive elements are introduced on the interface of the FE model, and dilatational damage and shear damage, based on continuum damage mechanics, are introduced into the resin. Moreover, it is thought that compressive stress enhances interfacial shear strength. Coulomb's friction law is applied at the debonded interface. We discuss interfacial energy, which is a factor determining mechanical properties. Interfacial strength setting high energy value of traction-separation law might be inappropriate because the separation length becomes longer than the fiber radius, which is probably different from the actual behavior. This study attempts to simulate actual behavior with very low interfacial energy. As a result, it is revealed that the provided interfacial strength by numerical simulation is higher than IFSS (Interfacial Shear Strength).