Abstract

It is apparent from the literature that the matrix-fiber mechanical interaction, as a result of adhesive bonds at interface, has a significant contribution to the constitutive modeling of hyperelastic fiber-reinforced materials. The present study represents an initial attempt to model matrix-fiber interface debonding in the context of pseudo-elasticity and, moreover, to characterize and computationally evaluate it. For this, inelastic phenomena such as discontinuous Mullins-type softening and permanent set as a result of the matrix damage, the fiber rupture, and the matrix-fiber interface debonding are modeled. The pseudo-elastic model is based on hyperelastic strain energy functions with two damage variables for each of the matrix, the fibers, and the matrix-fiber mechanical interactions. Each of the material and damage parameters are characterized independently through performing a comprehensive set of monotonic loading and cyclic tensile tests, respectively. The results of the cyclic tensile tests on the pure matrix, fibers, and composites imply that the underlying mechanism producing the Mullins-type softening and permanent deformations can be attributed to the matrix-fiber interface debonding neither matrix nor fibers. It is supported by the matrix-fiber interface debonding observed using the micrographs captured during in situ tensile tests and is reflected in the residual deformations recorded through the stretch maps via digital image correlation after unloading. The in situ optical micrographs are indicative of two different microstructural evolutions: A continuous matrix-fiber debonding along the fibers, which is barely visible after unloading; and a discontinuous, pointwise matrix-fiber debonding, starting from the top vicinity of the fibers and continued to the matrix. Furthermore, an FE-implementation using a user-defined subroutine is presented and compared against experimental data. The results show that the model is capable of reproducing the inelastic behaviors as a result of the matrix-fiber debonding for composites showing significant degradation in their mechanical properties. This work bridges the degradation of the mechanical properties to the microscopically visible matrix-fiber interface debonding for composites undergoing cyclic deformations.