mar120_lecture_07.pptVIP

OVERVIEW Selecting and Using Finite Elements Element Topology Versus Element Property Dimensions of Structural Space versus Dimensions of Finite Element Connecting Elements of Different Topology Methods of Numerical Integration Plane Elements Plane Strain Plane Stress Axisymmetry Orientation of Beam Cross Sections in Space Thin Shells Versus Thick Shells ELEMENT TOPOLOGY STRUCTURAL ELEMENT TYPES IN MSC.MARC 0-D Point Masses 1D Bar Elements 2D Solid Continuum Elements 2D Shell Elements 3D Solid Continuum Elements 1D BAR ELEMENTS Beam Elements Standard, Euler-Bernoulli Truss Spar Elements Axisymmetric Shell Elements Springs Dashpots Use Springs Options These elements may have nonlinear properties Example : Snap-through of Bottom of a Soft-Drink Can Simulated with quadratic 3-node 1D Axisymmetric elements Aluminum can –plasticity included When pressure increases the bottom of the can “snaps” thus increasing the volume inside the can –relieving the pressure- and preventing the rupture and spilling of contents. Because of plasticity the bottom cannot return back to the original shape thus protecting the consumer from spoilage. BEAM SECTION ORIENTATION VECTOR 2D SOLID CONTINUUM ELEMENTS Plane Stress Elements 2 DOF @ nodes: Ux, Uy Planar structures, All out-of-plane stresses zero Typical: Flat panels subject to inplane loads Plane Strain Elements 2 DOF @ nodes: Ux, Uy Planar model, All out-of-plane strains constant or zero Typical: Slice of car’s door rubber seal Membrane Elements 3 DOF @ nodes: Ux, Uy, Uz Curved, very thin structures unable to sustain bending 2D SOLID CONTINUUM ELEMENTS CONT. Axisymmetric Elements 2 DOF @ nodes: Ux, Uy Axisymmetric structures with axisymmetric loadings 2D SHELL ELEMENTS  THIN SHELL: 5 DOF @ NODES In-plane/out-of-plane loadings in planar and curved surfaces Ignores out-of-plane normal stress Ignores out-of-plane transverse shear stresses Normals remain normals Thickness very small 5% co