Introduction to FEA and Nastan Analysis Types

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Welcome to the Getting Started with Inventor Nastran module.

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In this first unit, we're going to be looking at an introduction to Finite Element Analysis as well as the Inventor Nastran analysis types.

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In the Digital Prototyping process, there are several stages.

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And a Finite Element Analysis tool like Inventor Nastran can be used in any one of them.

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You will often see it used in the Design & Engineering stage as a way to explore different geometries and materials,

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in order to optimize a product.

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However, you may also see it at the test and validation stage,

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alongside physical testing as a way to make sure products will perform as expected,

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while making physical prototypes less expensive.

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And lastly, it can be used in the Manufacturing & Production stage as a way to validate manufacturing processes,

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as well as explore failures and determine their root cause.

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FEA softwares allow users to take their three-dimensional model and subject it to forces, vibrations,

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thermal loads and other effects to see how it would respond before producing an actual physical prototype.

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With FEA, you'll take a three dimensional model and break it up into a series of nodes and elements.

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This mesh that's created can then be constrained and loaded in order to generate results.

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The results are typically your stresses and displacements,

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but you can also calculate other things like velocity and acceleration in a dynamic analysis.

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Once the actual solution has been generated, you can then determine how much the part is going to yield,

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how much it might displace or deform, and whether or not it's going to wear out under a series of cycles.

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Once that model has been imported, the first step in any Inventor Nastran analysis is going to be creating an idealization.

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An idealization contains two things, the material and the element type that will be used to represent the solid in the mesh.

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The three different element idealization types are Solids, Shells and Lines,

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and these can be used individually or combined in an assembly level analysis.

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After defining an Element type, the next step in the process will be defining a material for that idealization to use.

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Inventor Nastran has a very large library for its users to pull from, as well as several different ways to define materials for the FEA.

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One of the most common material types is going to be an Isotropic material.

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Isotropic materials behave with the same strength and stiffness characteristics in each direction.

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An example of this would be aluminum or steel.

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Orthotropic 2D and 3D materials behave with different strength and stiffness characteristics in each direction.

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An example of that would be a wood material where the strength with the grain versus against the grain might be slightly different.

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For a linear static analysis, you will be working with a linear material.

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However, if you would like to perform a nonlinear analysis, you can also input the nonlinear material data.

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This is going to be the stress and strain data beyond the yield strength of a material.

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Having these different ways to define a material,

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give the user the ability to appropriately model the characteristics of their actual design and get accurate results.

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After all the idealizations and materials have been defined, the next step in the process is going to be generating a finite element mesh.

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Inventor Nastran has several global Mesh Settings including Element Size,

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Element Order, and whether or not to use Continuous Meshing.

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Inventor Nastran also has the ability to apply local mesh controls to accurately control the size of elements in key regions.

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A default mesh size will be created automatically based off of a bounding box size of the model,

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but that can be refined further as the analysis progresses.

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Boundary Conditions is a term that FEA solvers use to represent constraints and loads that are added into an FEA problem.

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Constraints are going to represent your true supports or contacting geometry.

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Anything that is going to restrict the number of degrees of freedom available to a component.

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Loads are used to simulate a force, pressure, thermal load,

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or maybe even an acceleration that's going to be applied to the mesh that will generate a displacement or a stress.

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It's important to correctly define these boundary conditions,

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in order to accurately represent the physics that your model is going to undergo.

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Inventor Nastran is embedded into the Autodesk Inventor platform.

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It acts as a preprocessor that allows you to set up the FEA problem with your mesh, constraints, loads and materials,

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and then it will be exported to the Autodesk Nastran Solver to actually create a result.

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Once the solver is finished, it will take the results file and import it back into Inventor Nastran,

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where the actual contours and data points can be reviewed.

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The advantage of having an embedded FEA tool within the CAD platform is that you are able to make changes to the CAD model,

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and then update the mesh and resolve without having to start over every single time a change is made.

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FEA solvers allow users to predict many different physical effects.

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The most common result is going to be your Von Mises stress, as well as your displacement or your amount of deformation.

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However, other things can be analyzed as well.

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Some of these include vibration and acceleration, as well as fatigue and how well something will perform after a series of cycles.

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You can also look at more dynamic problems like motion and buckling as well as thermal analysis such as heat transfer.

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The reason that Inventor Nastran has so many different study types is so that a user can find the study,

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that most accurately represents the physics that their problem requires.

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This slide shows some of the basic analysis types that Inventor Nastran has for its users.

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The default analysis type for all studies is going to be your Linear Static analysis.

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You can also perform eigenvalue and eigenvector analysis or your Normal Modes analysis.

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Buckling is a great way to troubleshoot geometric instability and determine failure points,

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and then Prestress Static and Prestress Normal Modes are the same as your statics and normal modes,

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except you can apply a preload in a separate sub case.

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You'll also see Linear Steady State Heat Transfer and Thermal Stress available in this software as well.

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Some of the more advanced analysis types include your Nonlinear.

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This can be your Nonlinear Statics or your Nonlinear Transient Studies to look at things like Impact.

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An automated Impact Analysis tool is also included for Drop Testing.

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If a more dynamic analysis is required,

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you can perform a Direct and Modal Frequency Response to determine how something responds to a driven input frequency.

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Linear dynamics can also be performed, and that would be something like a Random Response or a Shock Response Spectrum.

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And Nonlinear Steady State Heat Transfer and Transient Heat Transfer can also be performed within an Inventor Nastran.

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When choosing a static analysis, it's important to understand the difference between Linear and Nonlinear.

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Linear static studies assume that the displacements and rotations are going to be fairly small.

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This means you will not see a significant amount of bending or rotation in the final result.

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It also assumes that your supports do not move or settle under load.

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That means you typically won't have constraints allowing sliding or geometric instability.

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The material itself should remain linear, meaning that you will be in the linear working range of the material.

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All stresses should be below the yield strength and stress is going to remain directly proportional to strain at all times.

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The last assumption is that loads in their orientation, magnitude and distribution are going to remain constant at all times.

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This means that if a part deforms, the load vector will remain the same.

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It will not follow that deformation and the distribution of the load will remain the same throughout as well.

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There are three effects that would make a user consider using a nonlinear study instead of a linear one.

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The first of these is called geometric nonlinearity.

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This is when you're seeing large amount of displacement or strain.

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The nonlinear solver is able to break up the load into increments and update the stiffness matrix,

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which will more accurately capture the effect of a large amount of bending.

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Material nonlinearity is when you go beyond the yield strength of a given material.

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This will create what's called permanent or plastic deformation,

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and a nonlinear stress/strain curve is required in order to accurately capture that data.

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The last nonlinear effect is boundary condition nonlinearity.

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This would be when a load or a constraint might be changing orientation or direction,

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as well as more complex contact interactions in things like impact analysis.

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Opening up a part here in Autodesk Inventor Professional 2024, you will see the Model Tree on the left hand side,

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as well as your typical 3D modeling tools along the top.

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One thing to note with this model is that if you look at the material properties, Mild, Steel has already been defined.

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If you define a material with an Inventor,

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it'll automatically be copied over to the idealization within Inventor Nastran So if I go to the Environments tab,

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once I've installed Inventor Nastran, it'll automatically be embedded into this panel.

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I can go ahead and open it up.

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And what you'll see right away is it brings in the model.

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And on the left hand side, you'll see the Analysis 1.

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It is a Linear Static analysis shown in parentheses there and then Solid 1 is the first idealization that's been created.

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And if I expand it, you'll notice that Mild, Steel is automatically added.

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So that's done when you first import a model.

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If you have not defined the material with an Inventor,

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this material will show up as generic and you'll want to make sure that you update that idealization.

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Another thing that you will notice right away is that beneath the analysis tree is the Model Tree.

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If you were to expand this, you will see that there's a separate set of settings and options below the analysis tree.

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One thing to keep in mind is that the analysis tree will contain all of the items that will go into the Solver.

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This includes your idealizations, materials, mesh, loads and constraints.

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The Model Tree is a backup or a library of all the resources you create during your studies.

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So if you have multiple analyses that you create over time, a backup of those resources will automatically be created in the Model Tree.

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However, nothing in the Model Tree will be given to the Nastran Solver when you click "Run".

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So let's say that we want to change the Analysis type.

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All you have to do is double click on "Analysis 1".

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This will open up this dialog box here where you can choose an analysis name as well as the type of study that you'd like to perform.

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Hitting this drop-down menu, you will see Linear Static, which is the default analysis type.

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But you can also perform a Normal Modes analysis to calculate natural frequencies, Linear Buckling to look at geometric instabilities,

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Preloaded Static and Preloaded Normal Modes, which require an additional sub case,

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and then your Nonlinear Statics and Nonlinear Buckling.

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Most of these analyses in this first chunk here are going to be your Statics or Buckling.

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The next section here contains your Dynamic Analyses.

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This would be your Transient Response, your Frequency Response Impact Analysis and then your Linear Dynamics,

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which would be Random Response and Shock Response Spectrum.

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Down further, you have your Fatigue Studies, Heat Transfer and then Explicit Dynamics or Quasi-Static.

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So they're grouped into these five categories.

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And once you change the analysis type and you select, "Okay", you will notice each analysis has different requirements.

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For instance, normal modes will require a Modal Setup in addition to Idealizations, Loads and Constraints.

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The analysis is saved with the Inventor part file or the Inventor assembly file,

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which means if you were to Finish the Autodesk Inventor Nastran environment,

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and go back to the 3D modeling environment and then you click "Save",

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the next time you open this part. When you open up Inventor Nastran, all of your changes will automatically be saved.

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So any analysis that you create will show up in there without having to create a separate file.