An Introduction to Finite Element Analysis with ProMECHANICA

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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

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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

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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.

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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

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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

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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)

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Analysis Methodology
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Cantilever Beam Demonstration

• Goal determine the maximum bending stresses

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Solution Comparison
Analytical Solution

• Analytical model based on classic beam theory for
  slender uniform cross section beams

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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

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Applying Material Properties
Parts

• Pro/Mechanica provides a default library of
  materials
• Ability to create custom materials with
  descriptions
• Be careful of units!

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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

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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

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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.

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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

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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

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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

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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

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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

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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 101
  slenderness ratio

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Mesh

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

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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

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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!

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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

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Connections

• There are four main connection types
• Interface
• Weld
• Rigid link
• Weighted link

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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

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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.

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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

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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

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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

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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

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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.

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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 doesnt imply accurate solution
• GIGO principle
• Poor boundary conditions

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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

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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

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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

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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

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Results

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

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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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