Dear all, Iam trying to figure out how to reduce or simplified the flexural rigidity (D) of composite orthotropic laminates consists of many plies into a single layer isotropic model. I know that for an isotropic case, D = Et^3/12(1-v^2). However, for the case of, say, 3 plies orthotropic laminates: Ply1 has D1x and D1y Ply2 has D2x and D2y Ply3 has D3x and D3y My question is that how to reduce or transform the above D1x, D1y, D2x, D2y, D3x and D3y into a single D that behave as an isotropic model. In another word, I wanted to treat the orthotropic laminates into an isotropic case by using 'smear' method. Any help is very much appreciated.