Effects of particle interaction and size variation on damage evolution in filled elastomers

A micromechanical analysis of damage evolution (interfacial debonding) in particle-filled elastomers addresses the effect of the interactions between particles and of variation in filler size. The composite is treated as an assembly of two constituents in a finite-element model. It is shown that the interaction between particles controls the damage evolution: (1) For high volume fraction, a relatively small change:in particle size has a surprisingly large effect on the local material response; (2) for large differences in particle sizes (e.g., bimodal distribution), damage occurs at interfaces between large particles and matrix, with limited damage occurring at small particles. While these effects of particle interaction and size variation are smoothed out in a large ensemble of particles, it is foreseeable that they are an important factor in a failure process such as macroscopic crack propagation, which spans scales considerably larger than the maximum particle size. Specifically, one thus expects that in the vicinity of a macroscopic crack the large particles become sites for small cracks which coalesce into larger ones and join up with the macro crack, while small particles operate primarily so as to locally stiffen the matrix without incurring significant damage in their vicinity.