Because composite layers are usually very thin (in the order of hundreds of microns), real composites part are usually made of dozens of or even hundreds of layers. It is difficult to provide a layer by layer modeling of composite parts due to the large number of layers. Even if one uses the lamination theory which can provide a layer by layer modeling with a relatively efficient computing speed, it is difficult to capture the deformation along the thickness direction, which is essentially needed for many analyses related with composites, particularly predicting the distortion of composite parts due to manufacturing processes. Instead, we try to replace a stack of laminate as an anisotropic solid which not only reducing the computing time needed for analysis but also capturing the possible thickness deformation. Some formulas have been proposed for estimating 3D properties of a composite laminate and the most recent publication is a journal paper by AG Gibson in 2012. However, various in-consistent assumptions are used to derive these formulas and the resulting material properties only feature orthotropic which is not sufficient for general laminate. Furthermore, the effective coefficients of thermal expansion (CTEs) critically needed for composites manufacturing simulation are missing.

Based on an exact micromechanics solution for a composite laminate made of homogeneous layers previously developed by the senior author, we can conclude that the in-plane strains remain constant as the average strain and the transverse stresses remain constant as the average stresses. This observation enables us to develop a hybrid rule of mixture with the simplicity as the commonly known rules of mixture according to Voigt or Reuss assumptions. The analytical expressions are given for effective elastic properties and CTEs in terms of lamina constants. Various examples are used to compare the results with the results available in the literature and those implemented in commercial code such as ABAQUS. The exact solution can also be obtained by the recently discovered mechanics of structure genome (MSG). MSG has been implemented using the finite element method in a state-of-the-art micromechanics code called SwiftComp, which is available in the cloud through cdmHUB.org. The results predicted by SwiftComp are also used to verify the results obtained by the hybrid rule of mixture based on exact micromechanics solution.

The formulas presented in this work provide the best 3D properties for a composite laminate which is often a routine practice industry. This is essential equivalent to model the composite laminate as a black aluminum. The black aluminum is a homogenous material with possibly general anisotropy.