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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 Todays Agenda Shells Read Ch. 12 in Logan. Brief review of isotropic materials Anisotropic materials E. Chan SJSU ME297 Spring 2009 2 Composites laminate layups laminate stiffness matrices (A, B, D) Shell Elements - Motivations Why use shell elements when we have solid elements? Performance!!!! For thin models, shells can be used to get very good results at a fraction of the computational cost. E. Chan SJSU ME297 Spring 2009 3 Some structures are more naturally modeled with shells (vs thin solids). E.g. auto body, aircraft. 8160 solids or 108 shells Modeling Example How would you model this mechanical part? E. Chan SJSU ME297 Spring 2009 4 Shell Elements - Motivations 3D Solid 3D Shell 163 solids E. Chan 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 Shells are fully 3-D elements which are thin in one dimension (its depth). Plates are a special case of shells flat shells Shells deform: E. Chan SJSU ME297 Spring 2009 6 Axially (membrane stretching) Transverse shear Bending Which element do you know that has the same modes of deformation? 1/30/2009 2 Side View w Degrees of Freedom for Shells A shell has 6 dofs per function: 3 translational dofs 3 rotational dofs E. Chan SJSU ME297 Spring 2009 7 Compare these with other elements such as beam and solid elements? Local Normal To surface w, z v, y u, x Limitations of Shells Shells are recommended for very thin sections. Thin direction should be < 1/10 th of other two dimensions....
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