Autodesk Inventor Inventor Simulation - 2010 Getting Started
Autodesk Inventor Simulation 2010
Getting Started
January 2009Part No. 466B1-050000-PM01A
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Contents
Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 1 Get Started With Stress Analysis . . . . . . . . . . . . . . . . . . 3
About Autodesk Inventor Simulation . . . . . . . . . . . . . . . . . . . 3
Learn Autodesk Inventor Simulation . . . . . . . . . . . . . . . . . . . . 4
Use Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Use Stress Analysis Tools . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Understand the Value of Stress Analysis . . . . . . . . . . . . . . . . . . 6
Understand How Stress Analysis Works . . . . . . . . . . . . . . . . . . 7
Analysis Assumptions . . . . . . . . . . . . . . . . . . . . . . . . 7
Interpret Results of Stress Analysis . . . . . . . . . . . . . . . . . . . . . 9
Equivalent or Von Mises Stress . . . . . . . . . . . . . . . . . . . . 9
Maximum and Minimum Principal Stresses . . . . . . . . . . . . 10
Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Safety Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Frequency Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Chapter 2 Analyze Models . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Do a Static Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 13
Enter Environment and Create a Simulation . . . . . . . . . . . . 14
Exclude Components . . . . . . . . . . . . . . . . . . . . . . . . 15
Specify Material . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Add Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
iii
Add Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Add Contact Conditions . . . . . . . . . . . . . . . . . . . . . . 19
Generate a Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Run the Simulation . . . . . . . . . . . . . . . . . . . . . . . . . 20
Run Modal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Chapter 3 View Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Use Results Visualization . . . . . . . . . . . . . . . . . . . . . . . . . 23
Edit the Color Bar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Read Stress Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . 26
Interpret Results Contours . . . . . . . . . . . . . . . . . . . . . 26
Animate Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Set Results Display Options . . . . . . . . . . . . . . . . . . . . . 28
Chapter 4 Revise Models and Stress Analyses . . . . . . . . . . . . . . . . 31
Change Model Geometry . . . . . . . . . . . . . . . . . . . . . . . . . 31
Change Solution Conditions . . . . . . . . . . . . . . . . . . . . . . . 32
Update Results of Stress Analysis . . . . . . . . . . . . . . . . . . . . . 34
Chapter 5 Generate Reports . . . . . . . . . . . . . . . . . . . . . . . . . 35
Run Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Interpret Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Model Information . . . . . . . . . . . . . . . . . . . . . . . . . 36
Project Info . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Save and Distribute Reports . . . . . . . . . . . . . . . . . . . . . . . . 38
Saved Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Print Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Distribute Reports . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Chapter 6 Manage Stress Analysis Files . . . . . . . . . . . . . . . . . . . 39
Create and Use Analysis Files . . . . . . . . . . . . . . . . . . . . . . . 39
Understand File Relationships . . . . . . . . . . . . . . . . . . . 39
Resolve Missing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Dynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . 41
Chapter 7 Get Started with Simulation . . . . . . . . . . . . . . . . . . . 43
About Autodesk Inventor Simulation . . . . . . . . . . . . . . . . . . . 43
Learning Autodesk Inventor Simulation . . . . . . . . . . . . . . . . . 44
Use Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Understand Simulation Tools . . . . . . . . . . . . . . . . . . . . . . . 45
iv | Contents
Simulation Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 45
Interpret Simulation Results . . . . . . . . . . . . . . . . . . . . . . . 45
Relative Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 45
Coherent Masses and Inertia . . . . . . . . . . . . . . . . . . . . 46
Continuity of Laws . . . . . . . . . . . . . . . . . . . . . . . . . 46
Chapter 8 Simulate Motion . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Understand Degrees of Freedom . . . . . . . . . . . . . . . . . . . . . 47
Understand Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Convert Assembly Constraints . . . . . . . . . . . . . . . . . . . . . . 49
Run Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Chapter 9 Construct Moving Assemblies . . . . . . . . . . . . . . . . . . 55
Retain Degrees of Freedom . . . . . . . . . . . . . . . . . . . . . . . . 55
Add Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Impose Motion on Joints . . . . . . . . . . . . . . . . . . . . . . . . . 58
Run Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Chapter 10 Construct Operating Conditions . . . . . . . . . . . . . . . . . 61
Complete the Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Add Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Add a Sliding Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Contents | v
vi
Stress Analysis
Part 1 of this manual presents the getting started information for Stress Analysis in the Autodesk
Inventor® Simulation software. This add-on to the Autodesk Inventor assembly, part, and
sheet metal environments provides the capability to analyze the static stress and natural
frequency responses of mechanical designs.
1
2
Get Started With Stress Analysis
Autodesk Inventor® Simulation software provides a combination of industry-specific tools
that extend the capabilities of Autodesk Inventor® for completing complex machinery and
other product designs.
Stress Analysis in Autodesk Inventor Simulation is an add-on to the Autodesk Inventor
assembly, part, and sheet metal environments.
Static Analysis provides the means to simulate stress, strain, and deformation.
Modal Analysis provides means to find natural frequencies of vibration and mode shapes of
mechanical designs.
You can visualize the affects in 3D volume plots, create reports for any results, and perform
parametric studies to refine your design.
This chapter provides basic information about the stress analysis environment and the
workflow processes necessary to analyze loads and constraints placed on a part or assembly.
1
About Autodesk Inventor Simulation
Built on the Autodesk Inventor application, Autodesk Inventor Simulation
includes several different modules. The first module included in this manual is
Stress Analysis. It provides functionality for Structural Static and Modal analysis
of mechanical product designs.
This manual provides basic conceptual information to help get you started and
specific examples that introduce you to the capabilities of Stress and Modal
Analysis in Autodesk Inventor Simulation.
3
Learn Autodesk Inventor Simulation
We assume that you have a working knowledge of the Autodesk Inventor
Simulation interface and tools. If you do not, use Help for access to online
documentation and tutorials, and complete the exercises in the Autodesk
Inventor Simulation Getting Started manual.
At a minimum, we recommend that you understand how to:
■ Use the assembly, part modeling, and sketch environments and browsers.
■ Edit a component in place.
■ Create, constrain, and manipulate work points and work features.
■ Set color styles.
Be more productive with Autodesk® software. Get trained at an Autodesk
Authorized Training Center (ATC®) with hands-on, instructor-led classes to
help you get the most from your Autodesk products. Enhance your productivity
with proven training from over 1,400 ATC sites in more than 75 countries.
For more information about training centers, contact atc.program@autodesk.com
or visit the online ATC locator at www.autodesk.com/atc.
We also recommend that you have a working knowledge of Microsoft
Windows® XP or Windows Vista®. It is desirable, but not required, to have a
working knowledge of concepts for stress analysis of mechanical assembly
designs.
®
Use Help
As you work, you may need additional information about the task you are
performing. The Help system provides detailed concepts, procedures, and
reference information about every feature in the Autodesk Inventor Simulation
modules as well as the standard Autodesk Inventor Simulation features.
To access the Help system, use one of the following methods:
■ Click Help ➤ Help Topics, and then use the Table of Contents to navigate
to Stress Analysis topics.
■ Press F1 for Help with the active operation.
■ In any dialog box, click .
4 | Chapter 1 Get Started With Stress Analysis
■ In the graphics window, right-click, and then click How To. The How To
topic for the current tool is displayed.
Use Stress Analysis Tools
Autodesk Inventor Simulation Stress Analysis provides tools to determine
structural design performance directly on your Autodesk Inventor Simulation
model. Autodesk Inventor Simulation Stress Analysis includes tools to place
loads and constraints on a part or assembly and calculate the resulting stress,
deformation, safety factor, and resonant frequency modes.
Enter the stress analysis environment in Autodesk Inventor Simulation with
an active part or assembly.
Use Stress Analysis Tools | 5
With the stress analysis tools, you can:
■ Perform a structural static or modal analysis of a part or assembly.
■ Apply a force, pressure, bearing load, moment, or body load to vertices,
faces, or edges of the model, or import a motion load from dynamic
simulation.
■ Apply fixed or non-zero displacement constraints to the model.
■ Model various mechanical contact conditions between adjacent parts.
■ Evaluate the impact of multiple parametric design changes.
■ View the analysis results in terms of equivalent stress, minimum and
maximum principal stresses, deformation, safety factor, or modal frequency.
■ Add or suppress features such as gussets, fillets or ribs, re-evaluate the
design, and update the solution.
■ Animate the model through various stages of deformation, stress, safety
factor, and frequencies.
■ Generate a complete and automatic engineering design report in HTML
format.
Understand the Value of Stress Analysis
Performing an analysis of a mechanical part or assembly in the design phase
can help you bring a better product to market in less time. Autodesk Inventor
Simulation Stress Analysis helps you:
■ Determine if the part or assembly is strong enough to withstand expected
loads or vibrations without breaking or deforming inappropriately.
■ Gain valuable insight at an early stage when the cost of redesign is small.
■ Determine if the part can be redesigned in a more cost-effective manner
and still perform satisfactorily under expected use.
Stress analysis, for this discussion, is a tool to understand how a design
performs under certain conditions. It might take a highly trained specialist a
great deal of time performing what is often called a detailed analysis to obtain
an exact answer with regard to reality. What is often as useful to help predict
and improve a design is the trending and behavioral information obtained
6 | Chapter 1 Get Started With Stress Analysis
from a basic or fundamental analysis. Performing this basic analysis early in
the design phase can substantially improve the overall engineering process.
Here is an example of stress analysis use: When designing bracketry or single
piece weldments, the deformation of your part may greatly affect the alignment
of critical components causing forces that induce accelerated wear. When
evaluating vibration effects, geometry plays a critical role in the natural
frequency of a part or assembly. Avoiding, or in some cases targeting critical
frequencies, can be the difference between failure and expected performance.
For any analysis, detailed or fundamental, it is vital to keep in mind the nature
of approximations, study the results, and test the final design. Proper use of
stress analysis greatly reduces the number of physical tests required. You can
experiment on a wider variety of design options and improve the end product.
To learn more about the capabilities of Autodesk Inventor Simulation Stress
Analysis, view the online demonstrations and tutorials.
Understand How Stress Analysis Works
Stress analysis is done using a mathematical representation of a physical system
composed of:
■ A part or assembly (model).
■ Material properties.
■ Applicable boundary conditions (loads, supports), contact conditions, and
mesh, referred to as preprocessing.
■ The solution of that mathematical representation (solving).
To find a result, the part is divided into smaller elements. The solver adds
up the individual behaviors of each element to predict the behavior of the
entire physical system by resolving a set of simultaneous algebraic
equations.
■ The study of the results of that solution is referred to as post-processing.
Analysis Assumptions
Extremely important to your simulation is the accuracy with which you model
and specify the actual physical conditions (constraints, loads, materials, contact
conditions). The accuracy of these conditions directly influences the quality
of your results.
Understand How Stress Analysis Works | 7
The stress analysis provided by Autodesk Inventor Simulation is appropriate
only for linear material properties where the stress is directly proportional to
the strain in the material (meaning no permanent yielding of the material).
Linear behavior results when the slope of the material stress-strain curve in
the elastic region (measured as the Modulus of Elasticity) is constant.
The total deformation is assumed to be small in comparison to the part
thickness. For example, if studying the deflection of a beam, the calculated
displacement must be less than the minimum cross-section of the beam.
The results are temperature-independent. The temperature is assumed not to
affect the material properties.
The following is a block (model) with well-defined mechanical and modal
behaviors.
In this example of a simple part, the structural behavior would be difficult to
predict solving equations by hand.
Here, the same part is broken into small elements, each with well-defined
behaviors capable of being summed (solved) and easily interpreted
(post-processed).
8 | Chapter 1 Get Started With Stress Analysis
Interpret Results of Stress Analysis
The output of a mathematical solver is generally a substantial quantity of raw
data. This quantity of raw data would normally be difficult and tedious to
interpret without the data sorting and graphical representation traditionally
referred to as post-processing. Post-processing is used to create graphical
displays that show the distribution of stresses, deformations, and other aspects
of the model. Interpretation of these post-processed results is the key to
identifying:
■ Areas of potential concern as in weak areas in a model.
■ Areas of material waste as in areas of the model bearing little or no load.
■ Valuable information about other model performance characteristics, such
as vibration, that otherwise would not be known until a physical model
is built and tested (prototyped).
The results interpretation phase is where the most critical thinking must take
place. You compare the results (such as the numbers versus color contours,
movements) with what is expected. You determine if the results make sense,
and explain the results based on engineering principles. If the results are other
than expected, evaluate the analysis conditions and determine what is causing
the discrepancy.
Equivalent or Von Mises Stress
Three-dimensional stresses and strains build up in many directions. A common
way to express these multidirectional stresses is to summarize them into an
Equivalent stress, also known as the von-Mises stress. A three-dimensional
solid has six stress components. If material properties are found experimentally
Interpret Results of Stress Analysis | 9
by an uniaxial stress test, then the real stress system is related by combining
the six stress components to a single equivalent stress.
Maximum and Minimum Principal Stresses
According to elasticity theory, an infinitesimal volume of material at an
arbitrary point on or inside the solid body can be rotated such that only normal
stresses remain and all shear stresses are zero. When the normal vector of a
surface and the stress vector acting on that surface are collinear, the direction
of the normal vector is called principal stress direction. The magnitude of the
stress vector on the surface is called the principal stress value.
Deformation
Deformation is the amount of stretching that an object undergoes due to the
loading. Use the deformation results to determine where and how much a
part will bend, and how much force is required to make it bend a particular
distance.
Safety Factor
All objects have a stress limit depending on the material used, which are
presented as material yield or ultimate strengths. If steel has a yield limit of
40,000 psi, any stresses above this limit result in some form of permanent
deformation. If a design is not supposed to deform permanently by going
beyond yield (most cases), then the maximum allowable stress in this case is
40,000 psi.
A factor of safety can be calculated as the ratio of the maximum allowable
stress to the equivalent stress (von-Mises), when using Yield Strength, and
must be over 1 for the design to be acceptable. (Less than 1 means there is
some permanent deformation.) When using Ultimate Strength, Maximum
Principal stress is used to determine safety factor ratios.
Factor of safety results immediately points out areas of potential yield, where
equivalent stress results always show red in the highest area of stress, regardless
of how high or low the value. Since a factor of safety of 1 means the material
is essentially at yield, most designers strive for a safety factor of between 2 to
4 based on the highest expected load scenario. Unless the maximum expected
load is frequently repeated, the fact that some areas of the design go into yield
does not always mean the part will fail. Repeated high load may result in a
10 | Chapter 1 Get Started With Stress Analysis
fatigue failure, which is not simulated by Autodesk Inventor Simulation Stress
Analysis. Always, use engineering principles to evaluate the situation.
Frequency Modes
Use modal frequency analysis to test a model for its natural resonant
frequencies (for example, a rattling muffler during idle conditions, or other
failures).
Each of these incidences may act on the natural frequency of the model,
which, in turn, may cause resonance and subsequent failure. The mode shape
is the displacement shape that the model adopts when it is excited at a
resonant frequency. Autodesk Inventor Simulation calculates the natural
frequencies of vibration and the corresponding mode shapes. It presents the
mode shapes as results that you can view and animate. Dynamic response
analysis is not offered at this time.
Frequency Modes | 11
12
Analyze Models
2
After you define your model, you use the stress analysis environment to prepare the model
for analysis. You define the materials, loads, and constraints for the condition you want to
test, and establish contact conditions and mesh preferences. Then, you perform an analysis,
also called simulation, of the model.
This chapter explains how to define materials, loads, constraints, contacts, and meshing, and
then run your analysis.
Do a Static Stress Analysis
Use the stress analysis environment to analyze your assembly or part design
and evaluate different options quickly. You can analyze a model under different
conditions using various materials, loads and constraints (also called boundary
conditions), and then view the results. You have a choice of performing a static
analysis or a frequency (also called modal) analysis with associated mode shapes.
After you view and evaluate the results, you can change your model and rerun
the analysis to see the effect your changes produce.
Typical Stress Analysis workflow
1 Create Simulations and specify their properties.
2 Exclude components not required for simulation.
3 Assign materials. If you define a modal simulation, you can run it now.
There is enough information to see the natural frequencies.
4 Add Constraints.
5 Add Loads.
6 Specify contact conditions, an optional step.
7 Specify and preview the mesh, an optional step.
13
8 Run the simulation.
9 View and Interpret the Results
When you make modifications to the model or various inputs for the
simulation, it can be necessary to update the mesh or other analysis parameters.
A red lightning bolt icon next to the browser node indicates areas that need
an update. Right-click the node and click Update to make them current with
respect to the modifications. For the Results node, you must run the Simulate
command to update results.
Enter Environment and Create a Simulation
You enter the Stress Analysis environment from the assembly, part, or sheet
metal environments.
To enter the environment and create a new simulation:
1 Open the model you want to analyze. By default you are in the modeling
environment.
2 On the ribbon, click Environments tab ➤ Begin panel ➤ Stress Analysis.
The Stress Analysis tab displays.
3 On the ribbon, in the Manage panel ➤ Create Simulation.
You can create multiple simulations within the same document. Each
simulation can use different materials, constraints, and loads.
4 Specify the simulation properties. Specify a name, type of simulation,
and on the Model State tab, the model representation to use for the
simulation.
14 | Chapter 2 Analyze Models
5 Click OK. The new simulation populates the browser with analysis nodes.
Exclude Components
In assemblies, some components have no
bearing on the simulation.
You can exclude the components. Right-click
the component node and click Exclude from
simulation.
Exclusion in a simulation has no effect on the
assembly in the modeling environment.
In parts, you can exclude part features, such as
small fillets and cosmetic features that have no
bearing on the performance of the part.
Exclude Components | 15
Specify Material
The stress analysis environment provides the means to override materials for
any component. The default material provided in Inventor templates is not
completely defined for simulation purposes. When modeling your components,
use materials that are appropriate and completely defined, particularly if you
are going to use simulation.
1 Click Assign Materials. This step is optional based on the materials used
for the components. If all materials are completely defined materials, you
can forego material overrides.
2 In the dialog box, specify an override material for the components as
needed. The override material is listed in the third column. Use the
pulldown list to see what materials are available.
3 Make all necessary material overrides and failure criteria choices (Yield
or Ultimate Strength) used for Safety Factor calculations, then click OK.
Inventor materials are maintained through the Styles and Standards editor.
You can modify existing materials or define new ones according to your need.
You can access the editor from the Assign Materials dialog box or by clicking
Manage tab ➤ Styles and Standards panel ➤ Styles Editor.
Add Constraints
You add constraints to mimic environmental conditions. Constraint instances
are child nodes of the browser Constraints node. Double-click a constraint
node to edit the constraint.
NOTE Constraints are a crucial part of building a simulation model and can greatly
affect the end results of the simulation. Take time to consider them carefully and
accurately represent the physical conditions,
Fixed Constraint
Pin Constraint
16 | Chapter 2 Analyze Models
Constraint-Specific InformationConstraint
Apply a fixed constraint to a face, edge, or vertex in the part.
Apply a fixed constraint to establish zero or non-zero displacement on a part.
Apply a pin constraint on cylindrical faces. Apply pin constraints to prevent cylindrical faces from moving or deforming
in combinations of radial, axial, or tangential directions.
Constraint-Specific InformationConstraint
Frictionless
Constraint
Apply a frictionless constraint to a flat or cylindrical surface in
the part. Frictionless constraints prevent the surface from
moving or deforming in the normal direction relative to the
surface.
To add a constraint:
1 Click the constraint command corresponding with the type of constraint
you want to assign.
2 The select command is active and you can begin selecting the geometry
related to the constraint type. You can expand the dialog box to access
advanced settings.
If you right-click a constraint in the browser, you can: :
■ Edit the constraint. The appropriate dialog box displays so that you can
make changes.
■ View reaction forces. Values are zero until a simulation is run.
■ Suppress the constraint.
■ Copy and Paste between simulations within the same document.
■ Delete the constraint.
To rename an item in the browser, click it, pause, click it a second time, enter
a new name, and then press ENTER.
NOTE For some types of simulations you define, constraints are not required.
Add Constraints | 17
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