Thermal expansion behavior of composites based on non-axisymmetric ellipsoidal particles

A new model for calculating the coefficients of thermal expansion, CTE, in all three coordinate directions is developed for composites containing non-axisymmetric, ellipsoidal particles, i.e., three-dimensional ellipsoids (a1 ≠ a2 ≠ a3) characterized by two aspect ratios, ρα=a1/a3 and ρβ=a1/a2. The model makes use of Eshelby's equivalent tensor for the particles and utilizes the methodology from recent papers by Lee et al. The effects of the primary, ρα, and secondary, ρβ, aspect ratios and filler volume fraction (0-6%) on the various CTE for nanocomposites containing aligned inclusions are demonstrated by calculations for a matrix of nylon 6 and a filler of montmorillonite single platelets. The CTE in the longitudinal direction, α11, decreases, as both aspect ratios increase. The CTE in the transverse direction, α22, decreases as ρα increases but increases as ρβ increases. The CTE in the normal direction, α33, is greater than that of the matrix and increases as ρα increases but decreases as ρβ increases.