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Unformatted text preview: 1/30/2009 1 Shells, Composites & Anisotropy Shells, Composites & Anisotropy January 28 2009 January 28 2009 January 28, 2009 January 28, 2009 Todayâ€™s Agenda Â¡ Shells â€¢ Read Ch. 12 in Logan. Â¡ Brief review of isotropic materials Â¡ Anisotropic materials E. Chan â€“ SJSU ME297 Spring 2009 2 Â¡ Composites â€¢ laminate layups â€¢ laminate stiffness matrices (A, B, D) Shell Elements  Motivations Â¡ Why use shell elements when we have solid elements? Â¡ Performance!!!! For thin models, shells can be used to get very good results at a fraction of the computational cost. E. Chan â€“ SJSU ME297 Spring 2009 3 Â¡ Some structures are more naturally modeled with shells (vs thin solids). E.g. auto body, aircraft. 8160 solids or 108 shells Modeling Example Â¡ How would you model this mechanical part? E. Chan â€“ SJSU ME297 Spring 2009 4 Shell Elements  Motivations 3D Solid 3D Shell 163 solids E. Chan â€“ SJSU ME297 Spring 2009 5 2D Plane Stress ~49000 equations 124 secs elapsed 32 2D plates ~2040 equations 2.88 secs elapsed 29 shells ~5750 equations 7.8 secs elapsed Why use shells instead of plane stress? Shell Elements Â¡ Shells are fully 3D elements which are thin in one dimension (its depth). Â¡ Plates are a special case of shells ÃŽ flat shells Â¡ Shells deform: E. Chan â€“ SJSU ME297 Spring 2009 6 â€¢ Axially (membrane stretching) â€¢ Transverse shear â€¢ Bending Â¡ Which element do you know that has the same modes of deformation? 1/30/2009 2 Î¸ Side View w Degrees of Freedom for Shells Â¡ A shell has 6 dofs per function: â€¢ 3 translational dofs â€¢ 3 rotational dofs E. Chan â€“ SJSU ME297 Spring 2009 7 Â¡ Compare these with other elements such as beam and solid elements? Local Normal To surface w, Î¸ z v, Î¸ y u, Î¸ x Limitations of Shells Â¡ Shells are recommended for very thin sections. Thin direction should be < 1/10 th of other two dimensions....
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 Arabhi,Sundararajan
 Finite Element Method, SJSU ME297 Spring, E. Chan

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