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					An Introduction to Finite Element
Analysis with Pro/MECHANICA

Stephen Seymour, P.E.
Seymour Engineering & Consulting Group, LLC
www.seymourecg.com
Presentation Outline

• Introduction to Pro/Mechanica
• Capabilities and differences
• Cantilever beam demo
• Materials, loads, and constraints
• Element types and meshing
• Idealizations, connections, and
 contact
• Analysis definition and convergence
• Reviewing results
What is Pro/Mechanica?

• Pro/Mechanica is general finite
  element analysis (FEA) software
  tool that is directly integrated into
  Pro/Engineer
• Pro/Mechanica (also referred to
  as Simulation) is generally
  classified as a structural and
  thermal Computer Aided
  Engineering (CAE) tool.
Pro/Mechanica Capabilities

• Static structural stress/strain/disp
• Modal, prestressed modal, and mechanical vibration
• Buckling
• Non-linear contact / large deformation
• Fatigue
• Hyperelastic materials
• Steady state thermal analysis
• Transient thermal analysis
How Does Pro/Mechanica Differ?

• Pro/Mechanica is a linear P-element
  finite element solver
• Most other commercial FEA packages
  are H-element codes

• The difference:
 convergence method
  – P: varies element
      shape functions
  –   H: mesh refinement
How Does Pro/Mechanica Differ?

• Pro/Mechanica by default is a
  linear finite element solver with
  some non-linear capabilities
• Automated convergence via
  element shape function
  adaptation
    – Multi-pass adaptive (MPA)
    – Single pass adaptive (SPA)
Analysis Methodology
Cantilever Beam Demonstration

                          • Goal: determine
                           the maximum
                           bending stresses
Solution Comparison
Analytical Solution
                      • Analytical model
                       based on classic
                       beam theory for
                       slender uniform
                       cross section beams
Solution Comparison
Pro/Mechanica FEA Solution
                        • Pro/Mechanica FEA
                          results indicate
                          maximum bending
                          stress is approximately
                          6000 psi
                        • Stress varies linearly
                          along length of beam
                          as expected
Applying Material Properties
Parts
• Pro/Mechanica provides a default library of materials
• Ability to create custom materials with descriptions
• Be careful of units!
Applying Material Properties
Assemblies
• Ability to assign different materials
  to different components
• Material assignment can be
  performed at either assembly or
  individual part level
• Material properties must be
  assigned before meshing
Degrees of Freedom (DOF)

• The primary 6 independent motions of any solid
  body. 3 translation and 3 rotation
• All static structural FEA problems required no rigid
  motion, therefore after constraints (and idealizations)
  there must be no motion
Displacement Constraints

• Constraints can be defined on surfaces,
  edges, or points
• Constraints can be free, fixed, or prescribed
  relative to the coordinate system selection
• Constraint coordinate systems can be
  Cartesian, cylindrical, or spherical.
Symmetry Constraints

• The symmetry constraint will
  simulate a symmetry type
  boundary condition by
  constraining motion normal
  (perpendicular) to the selected
  surface
• Should not be used with
  asymmetrical loading conditions
• Should not be used with modal
  analyses
Loads
Forces and Moments
• Most common of all load types
• Can be applied on surfaces, edges,
  and points
• Can reference user defined coordinate
  systems
• Moments must be specified with the
 advanced option Total Load at Point
Loads
Other
• Bearing loads
• Centrifugal loads
• Gravity loads
• Pressure loads
• Temperature loads
• Thermal simulation result loads
• Remember: gravity in the IPS unit
 system is 386.4 in/sec2
Element Types
Solid Elements
• Tetrahedral shape
• 3 translational DOFs at nodes
• Rotational constraints not required
• Shown in blue
• Ideal for solid bodies with large
  cross-sectional areas
• Not well suited for thin bodies
Element Types
Shell Elements
• 2D or 3D triangles and quadrilaterals
• 6 translational DOFs at nodes
• Shown in green
• Ideally suited for parts with thin
  cross-sections (i.e. tank walls, sheet
  metal components, etc.)
• Non-linear contact not possible for
  this element type
Element Types
Beam Elements
• 2D or 3D point-to-point or thru
  curve
• 6 translational DOFs at nodes
• Shown in light blue with cross-
  section (Shown here in red for
  clarity)
• Well suited to represent beams
  with a 10:1 slenderness ratio
Mesh

       • Meshing can be done either before
         or during analysis
       • The greater the # of elements…the
         longer the solution time
       • Mixed element meshes are
         possible
       • Convergence problems can
         typically be resolved by refinement
         in high gradient locations
Mesh Controls

• Control the density of
  elements within specific
  regions of the model
• Can be applied on volumes,
  surfaces, and edges
• Ability to specify regions of
  exclusion where
  singularities may exist
Idealizations
Masses
• Mass idealizations (also known as mass
  elements) are attached to a single point
  (either datum or vertex) within your model
• Mass idealizations by default are mass
  only with no inertia. However, an
  advanced mass element may also
  included mass moments of inertia (MMOI)
  to increase the accuracy of the solution
• Be careful of mass unit!
Idealizations
Springs
• Spring idealizations can simulate the
  behavior of real world springs in the model
  without having to solid model a spring
• Spring idealizations can range from very
  simple extension only springs that are
  defined point-to-point….to complex springs
  that can have varying linear and torsional
  spring constants in all 6 degrees of
  freedom
Connections

• There are four main connection types:
  – Interface
  – Weld
  – Rigid link
  – Weighted link
Connections
Interface
• Bonded
  – Merges coincident faces together
     for the analysis
• Free interface
   – Allows coincident faces to act
     independently of one another
• Contact
  –   Interpenetration not allowed.
      Can be frictionless or infinite friction
Connections
Welds
• Three main types of welds:
  – End weld
  – Perimeter weld
  – Spot weld
• End and perimeter welding extend the base shell
  geometry
• Spot welds are created using beams. May specify
  alternate material.
Connections
Rigid Link
• Can be created to points, edges,
  curves, and surfaces
• Couples the DOF
• Features with rigid links cannot have
  localized displacements or rotations
• Improper use of rigid links can
  adversely affect results
Connections
Weighted Link
• Developed primarily for distributing
  mass or loads
• Allow the attachment of mass
  idealizations without stiffening structure
• Source point must be a
  datum point, target entities
  can be points, edges,                or
  surfaces
Analysis Definition

• Once loads, constraints, and
  materials have been defined it
  is time to define the type of
  analysis to be performed
• Choose from the drop down list
  the analysis type or study you
  wish to perform
• Some analysis types may
  require additional licensing
Analysis Definition

                • Analysis name entered will be
                  subfolder name where files reside
                • Multiple load sets can be analyzed
                  independently or summed.
                • Select the convergence method
                • Choose output options
                • Enable/Disable the exclusions of
                  elements from the analysis
Convergence Options

• Multi-Pass Adaptive (MPA)
  – Polynomial order is repeatedly increased until
     specified convergence is obtained (default 10%)
• Single Pass Adaptive (SPA)
   – First pass using order of 3. Second pass order is
     increased to a max of 9 in high stress gradient areas.
• Quick check
  –   Mechanica performs a single pass at a uniform
      polynomial order of 3.
Convergence Options
Multi-Pass Adaptive (MPA)
• Percentage represents max
  allowable change from pass
  to pass
• A poorly converged model is
  equal to pretty picture
• Converged model doesn’t
  imply accurate solution
   – GIGO principle
   – Poor boundary conditions
Reviewing Results
Launch The Results Viewer
• There are three options for viewing
 the completed results:
  – Select the analysis and choose
    the results icon
  – Start the results viewer from
    Pro/Mechanica or Pro/Engineer
Reviewing Results
Results Selection
                    • Select from the drop down
                      the result you wish to plot
                    • Fringe is the default display
                      type, but vector and graph
                      plots are possible
                    • P-level is a plot of the
                      highest polynomial order
                      used for each element
                      throughout the domain
Reviewing Results
Results Display Location
• Gives the option to plot results
  on specific geometric entities
• For assemblies results may be
  plotted on certain components
  only or in exploded view
Reviewing Results
Results Display Options
• Control color display and
  animation effects
• Continuous tone creates smooth
  result plots, but requires more
  computing time and memory
• To see the true deformation set
  the scaling to a value of 1 and
  uncheck the % box
Results

• Dynamical query results
• Animate deformed shape
• Create section planes
• Customizable legend
Conclusion

• This completes the
  introduction to Finite
  Element Analysis (FEA)
  with Pro/Mechanica
• Many more features
  available
• Remember: always make
  sure your results make
  sense
• GIGO principle

				
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posted:11/2/2011
language:English
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