Analysis of Fiber Clustering in Composite Materials Using High-Fidelity Multiscale Micromechanics

A new multiscale micromechanical approach is developed for the prediction of the behavior of fiber reinforced composites in presence of fiber clustering. The developed method is based on a coupled twoscale implementation of the High-Fidelity Generalized Method of Cells theory, wherein both the local and global scales are represented using this micromechanical method. Concentration tensors and effective constitutive equations are established on both scales and linked to establish the required coupling, thus providing the local fields throughout the composite as well as the global properties and effective nonlinear response. Two nondimensional parameters, in conjunction with actual composite micrographs, are used to characterize the clustering of fibers in the composite. Based on the predicted local fields, initial yield and damage envelopes are generated for various clustering parameters for a polymer matrix composite with both carbon and glass fibers. Nonlinear epoxy matrix behavior is also considered, with results in the form of effective nonlinear response curves, with varying fiber clustering and for two sets of nonlinear matrix parameters. Introduction Clustering in composite materials refers to the aggregation of the constituents such that the composite does not exhibit uniform microstructural distribution. Composite microstructures are sensitive to the specific manufacturing processes utilized, and because the processing cannot be perfectly controlled, some degree of clustering will always be present. Clustering is more prevalent in composites with low fiber or inclusion volume fractions as there is more volume available in which one constituent may be segregated. In fact, in nanocomposites, whose volume fractions are typically very low, clustering is a dominant phenomenon, which strongly influences the properties and performance of the composite material (c.f., Shaffer and Windle (1999), Vigolo et al. (2000), Shi et al. (2004)). Several investigators have presented methods to characterize the degree of clustering in composite materials (c.f., Guild and Summerscales (1993), Pyrz (1994), Scanlon et. al. (2003), Al-Ostaz et al. (2007), Vaughan and McCarthy (2010), Wilding and Fulwood (2011), Zangenberg et al. (2013)). In terms of modeling the effects of fiber clustering in composites, most investigations have been finite element based, as this approach can explicitly account for the composite microstructure. Examples include