S12-3 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation LIMITATION OF SHELL ANALYSIS n The vast majority of analyses use shell elements u Plane stress conditions are assumed (Szz = 0) u Out-of-plane shear stresses are sometimes derived by equilibrium methods l Assumption of independent force balances n Detailed out-of plane stress recovery sometimes required u Where thickness is of the order of radius of curvature u Thickness is varying rapidly due to ply drop-off u Transient thermal loading through thickness u Significant out-of-plane loading n If great detail is required a fine 2D analysis is most appropriate u T-junctions and joints n Otherwise, 3D solid element analysis is appropriate u Thermal analysis of thick sections
S12-4 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation SANDWITCH PANEL DESIGN n In order to increase bending and shear stiffness, panels are often constructed using face-skins bonded onto honeycomb or foam core. u Face-skins provide most strength and stiffness u Core gives sufficient strength and stiffness to hold face-skins apart u Core is usually very thick in comparison with face-skins n Does a sandwich panel obey the assumptions for classical laminate theory? u How thick is the sandwich relative to the smallest dimension of the panel? u Is shear deflection important?
S12-5 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation MODELING CORE AS PLY IN LAYUP n This is the simplest way to model a sandwich n Shear behavior is not accurately defined n Design may be insensitive to core properties n In MSC.Nastran stress and strain results are only given mid-ply u If stresses at top and bottom of core are needed, put in a thin ply of core material on each side of the main core ply Core Ply Core plies(thin) for stress recovery
S12-6 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation MODELING CORE WITH SOLID ELEMENTS n Gives better shear prediction n Gives better modelling of corners u Outside face skin has more material than inside face skin n Doubles the number of nodes in model n Use a 3D orthotropic material for core if it has different shear stiffness in 2 directions Core: solid element Shell elements for face skins
S12-7 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation CREATING SOLID ELEMENTS FROM LAYUP n Create/Solid Elements/LM_Layup n A single layer of solid elements is created by extruding shell elements through the appropriate thickness, and with as offset if needed n The element type must be selected to have properties created
S12-8 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation SOLID ELEMENT ANALYSIS n MSC.Nastran 2001 does not have a laminated solid element u Approximate anisotropic material properties are created (MAT9) l Do not use with unbalanced laminates l Equivalent properties are smeared l No ply stress data recovery is possible u Coordinate systems are generated perpendicular to the surface n MSC.Marc 2003 supports a laminated solid element u Uses same orientation rules as shell elements
S12-9 PAT325, Section 12, February 2004 Copyright 2004 MSC.Software Corporation n Perform Workshop 7 Modeling Honeycomb Using MSC.Laminate Modeler, and Workshop 7B Modeling Honeycomb With Solid and Shell Elements in your exercise workbook n Be sure to ask for help on anything you dont understand EXERCISES