(540g) Inferring Effective Interphase Properties in Composites Reinforced with Randomly Distributed Spherical Particles

Composite materials consist of a matrix reinforced by one or more fillers each having unique material properties. Fillers or filler-coatings often induce an interphase region between a matrix and filler with distinct, but poorly known, physio-chemical properties. Determination of the physical properties of this region is important for the modeling and design of composite materials through advanced structure-property engineering. However, direct measurements of the interphase properties are challenging. Most experimental methods involve abrasive techniques that alter local mechanical properties or are impractical for particulate composites, where cutting across a filler particle is infeasible. In this study, a comprehensive framework is proposed to numerically model the interphase effects and infer the key mechanical properties of the interphase region from experimental measurements of the composite elastic modulus, a macroscale property which can be readily measured. This framework is demonstrated for a matrix reinforced by randomly distributed spherical particles using finite element (FE) analysis but is generalizable to any composite system. Representative volume elements are evaluated under periodic strains and the resulting stresses are used to determine the effective stiffness of the simulated composite. Gaussian process regression is used to generate computationally cheap, surrogate models that approximate the FE model output. The surrogate models are then explored through statistical inverse analysis to infer the interphase thickness and modulus that best match macroscale experimental data of six different composite systems. The paper presents the obtained results from calibrated FE analysis as an alternative for the mechanical characterization of interphase regions. The calibrated results show good agreement with the experimental measurements of the composite modulus and account for particle size-dependent elastic behavior. Furthermore, the relationship between filler particle size and the interphase thickness and modulus is explored.