introduction to engineering analysis - digital...

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Chapter

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Introduction toEngineering AnalysisChapter 1:

This chapter introduces you to the Dynamic Simulation and Stress Analysis environments. You learn how to use dynamic simulation and stress analysis to analyze designs and identify their successes and flaws before you build costly physical prototypes.

Objectives

After completing this chapter, you will be able to:

■ Describe the Dynamic Simulation environment and the processes you use to create simulations to evaluate motions in an assembly.

■ Describe the Stress Analysis environment and the processes you use to create and analyze designs.

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2 ■ Chapter 1: Introduction to Engineering Analysis

Lesson: Dynamic Simulation Overview

Overview

This lesson describes the Dynamic Simulation environment, and its interface and tools. The lesson also describes the processes you use to create simulations to evaluate motions in an assembly, to size actuators, to determine bearings, and to compute stresses in parts. Proving the validity of your designs before you build saves time and money by eliminating costly reworking and alterations after the build process has begun. Simulation data serves as a valuable presentation tool for customers to assure them that you are providing a design that meets their requirements.

The integration of Dynamic Simulation with Autodesk® Inventor®, and the Dynamic Simulation evaluation mechanisms, provide you with valuable tools to test, refine, and prove your designs.

In the following illustration, joints are being applied to a glass lever assembly so that a simulation can be performed.

Objectives

After completing this lesson, you will be able to:

■ Describe the Dynamic Simulation environment.■ Identify the Dynamic Simulation interface, its tools, and its unique browser nodes.■ Describe the basic process for creating a dynamic simulation.

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Lesson: Dynamic Simulation Overview ■ 3

About Dynamic Simulation

Dynamic Simulation is an environment included in Autodesk® Inventor® Professional. Dynamic Simulation is used to simulate and analyze dynamic characteristics of an assembly under various load conditions. You can also export load conditions at any motion state to the Stress Analysis environment to see how parts respond from a structural view to dynamic loads at any point in the assembly’s range of motion. In addition, you have the option to transfer multiple load conditions simultaneously in the assembly’s range of motion to the Stress Analysis environment. This option enables you to validate and compare designs without the need to go back to Dynamic Simulation to transfer loads again.

In the following illustration, an assembly is shown in the Dynamic Simulation environment.

Definition of Dynamic Simulation

A dynamic simulation simulates the dynamic motion in an assembly. The Dynamic Simulation environment automatically converts assembly constraints between components into mechanical joints. You also have the option to define mechanical joints between components manually. After the joints have been finalized, forces, accelerations, or velocities need to be applied to them where applicable to reproduce real-world conditions. You can use the results of the simulation to determine the integrity of a design, calculate the amount of force required to produce a desired motion, or view the effect of natural forces such as gravity and friction on the mechanism.

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In the following illustration, an assembly is in the middle of a simulation with the Output Grapher displaying force data used to perform stress analysis on a component.

Starting Dynamic Simulation

Within Autodesk Inventor Professional, you can access Dynamic Simulation only from an assembly file. You must click the Applications menu and then click Dynamic Simulation.

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Example of Dynamic Simulation

You have designed a windshield wiper assembly that is ready to be manufactured. Before the design is complete, you must determine the amount of driving torque required to rotate the drive arm at a velocity of 180 degrees per second. In Dynamic Simulation, you define the mechanism and impose the velocity on the drive arm. Using the Output Grapher, you can graph the torque curve for the drive arm. You can then extract the maximum drive torque on the drive arm, which you use to select the proper motor for the assembly.

In the following illustration, the drive arm for the wiper assembly is shown to the left of the Output Grapher.

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The Dynamic Simulation Interface

The Dynamic Simulation environment uses the same major interface components that you use in the part or assembly environments, including the graphics window, panel bar, and browser. The tools presented on the panel bar, and the elements in the browser, are specific to the Dynamic Simulation environment. Additionally, the Dynamic Simulation panel bar contains controls to run simulations and set their time parameters.

Graphics window

Dynamic Simulation panel bar

Dynamic Simulation browser

Simulation Panel

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Dynamic Simulation Panel Bar

The Dynamic Simulation panel bar is divided into four sections according to the types of operations that they perform.

Dynamic Simulation Browser

The Dynamic Simulation browser provides a set of groups and nodes that are unique to the Dynamic Simulation environment. Components are classified as Grounded or Mobile. Joints are grouped by category, as are external loads and traces. In the browser you access the shortcut menus to open joint properties, edit and delete joints, lock degrees of freedom, and control the display of joints.

Tools to create joints and the forces applied to them

Tools to simulate or to use the simulation output

Tool to set the simulation environment settings

Parameters tool to access assembly parametersSample Chapter



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The unique nodes in the Dynamic Simulation browser are shown in the following illustration.

Simulation Panel

The Simulation Panel is used to run a simulation. With this tool, you control the simulation time, how many time steps are calculated, and the speed at which the simulation runs. The Simulation Panel is synchronized with the mechanism in the graphics window and the Output Grapher, so that you can see the position of the mechanism and the resultant force in the Output Grapher at any time step that you choose. In the UI, the Simulation Panel is located below the Dynamic Simulation browser.

In the following illustration, the Simulation Panel is shown with the slider at 50%, halfway through the simulation.

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Creating Dynamic Simulations

With dynamic simulation, the intent is to build a functional mechanism, and then add dynamic, real-world influences of various kinds of loads to create a true kinematic chain. You then run the simulation to see how the joints, loads, and component structures interact as a moving dynamic mechanism.

In the following illustration, the Input Grapher is open to adjust properties of a joint.

Process: Creating Dynamic Simulations

The following steps provide an overview of the process of creating dynamic simulations of your assembly designs.

1. Open an assembly file in Autodesk Inventor Professional.

2. Click Applications menu > Dynamic Simulation.

3. Create standard joints by converting existing assembly constraints automatically and/or manually in order to create degrees of freedom.

4. Create other types of joints like contacts, rolling/sliding, or spring, to further constrain your mechanism.

5. Define the physical environment in the joint properties and apply forces by using the Input Grapher.

6. Run the dynamic simulation to see how joints, loads, and component structures interact.

7. Use the Input Grapher to apply joint forces and external forces.

8. Use the Output Grapher to analyze and export results.

9. Transfer loads on a part to be analyzed by Stress Analysis to study the effect of the loads on the part.

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Exercise: Review a Cam Valve Simulation

In this exercise, you run a simulation of a cam valve assembly with and without friction to determine the torque required to overcome the spring resistance and the friction force.

The completed exercise

Completing the Exercise

To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 1: Introduction to Engineering Analysis. Click Exercise: Review a Cam Valve Simulation.

1. Open CamValve.iam.

2. Click Applications menu > Dynamic Simulation.

3. On the Simulation Panel, click Run or Replay Simulation, and view the simulation.

At the beginning of the simulation you notice that the valve is bouncing. You will correct this and run the simulation again.

4. On the Simulation Panel, click Activate Construction Mode.

5. In the Dynamic Simulation browser, expand the Contacts Joints node. Right-click 2D Contact:4 (Cam:1, Valve:1). Click Properties.

6. In the 2D Contact:4 (Cam:1, Valve:1) dialog box, for Restitution, enter 0. Click OK.

7. On the Simulation Panel, click Run and view the simulation. The valve does not bounce.

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8. On the Dynamic Simulation panel bar, click Output Grapher. Resize the Output Grapher and zoom and pan in the CamValve assembly to view both, as shown.

9. In the Output Grapher, double-click the dashed line at 0.25 (1). The timeline (2) is displayed, and the cam (3) position updates to show its position at that point of the simulation.

10. To cycle through the simulation, use the right and left arrow keys on the keyboard to step forward and backward in the simulation. Cycle through the simulation to 1.00 to show the cam at the end of the simulation.

11. In the Output Grapher, click Save. Save the file as CamValve.iaa.

12. On the Simulation Panel, click Activate Construction Mode.

In the next two steps you add a coefficient of friction to calculate the effect on the torque required to rotate the cam and overcome the spring force and friction force.

13. In the Dynamic Simulation browser, for Contacts, right-click 2D Contact:4 (Cam:1, Valve:1). Click Properties.

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14. In the 2D Contact:4 (Cam:1, Valve:1) dialog box, for Friction, enter 0.15. Click OK.

15. On the Simulation Panel, click Run or Replay Simulation, and view the simulation. The Output Grapher is still open, so you see the graph being generating as the simulation is running.

In the next step, you change the color of the newly generated curve. When you compare the saved graph curve with this new one, you can distinguish between the two of them.

16. In the Output Grapher, right-click the U_imposed[1]/N mm column heading. Click Curve Properties.

17. In the Dynamic Simulation - Properties dialog box, click the color box.

18. In the Color dialog box, click the red color swatch and click OK.

19. In the Dynamic Simulation - Properties dialog box, click OK. Your graph in the Output Grapher changes to red.

20. On the Output Grapher toolbar, click Import Simulation.

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21. In the Dynamic Simulation - Load file dialog box, select CamValve.iaa and click Open. The CamValve.iaa node is added to the Output Grapher tree, as shown.

22. In the Output Grapher tree, expand the CamValve.iaa node. Expand Revolution:2 (Support:1, Cam:1). Expand Driving Force and select U_imposed [1].

23. The Output Grapher now shows the graphs of the driving force without friction (blue) and with friction (red), to compare the difference in force required for each situation. A new column also appears to display the numerical values.

24. Close the file. Do not save changes.

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Lesson: Stress Analysis Overview

Overview

This lesson introduces you to the concept and overall process for performing a stress analysis in Autodesk Inventor Professional.

In a typical product design cycle, you may need to examine how your design will perform under certain real-world conditions. When the product will be exposed to forces, loads, and constraints during normal use, it is important that you design the product to function properly to withstand these forces, loads, and constraints.

In the following illustration, the results of a stress analysis indicate how the part would be deformed under specific load and constraint conditions.

Objectives

After completing this lesson, you will be able to:

■ Describe stress analysis and how you can use it to validate your designs.■ Describe how the Stress Analysis environment is integrated into the Autodesk Inventor

user interface.■ Explain how to perform basic stress analysis.■ Perform a basic stress analysis and review the results.

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Lesson: Stress Analysis Overview ■ 15

About Stress Analysis

Stress Analysis enables you to estimate the deformation, stress, and natural frequencies of your parts as they are placed under certain load and constraint conditions. The process helps you to create better parts by indicating areas of your models that require further attention. You can reduce the number of design-test-redesign cycles by using Stress Analysis early in the design cycle to find and fix your models before you build the first prototype.

For most components, you can consider a physical test of the final part to ensure that it meets the performance criteria. You can even use Stress Analysis to help design the test by identifying locations of high stress or deformation. You use the test results to fine-tune your stress analysis so that you can predict the stress on similar parts with greater accuracy. Testing also builds confidence in your stress analysis methods and results.

Definition of Stress Analysis

Stress Analysis uses a technique called finite element analysis (FEA) to calculate the deformation, stress, and mode shapes of a model. Finite element analysis is an approximation method that estimates the behavior of a model.

If a model has simple geometry, it is straightforward to solve for stress and deflection manually by using available equations. However, most models have complex geometry, and equations to predict the stress, deflections, or mode shapes are typically unavailable. In finite element analysis, the model is subdivided into a number of pieces called elements, which have simple shapes that have available solutions. The solutions for each element are combined to obtain the behavior of the entire model.

The process of generating the elements in finite element analysis is called meshing, and the resulting set of connected elements is called the mesh.

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In the following illustration, the original and meshed models for a bracket are shown.

The size of each element in the mesh determines the resolution of the results. The smaller the elements, the more accurate the numerical results, but the model takes longer to process. In areas of the model where the stress is fairly constant, large elements are adequate; however, where the stress changes rapidly, such as near a stress concentration, smaller elements are required.

Example of Stress Analysis

In the following illustration, deformation results are shown for a stress analysis on a metal bracket.

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Potential Uses for Stress Analysis

You use Stress Analysis to identify:

■ Portions of your models that are highly stressed and may lead to part failure during the prototype or production phase.

■ Areas that carry little load, which may warrant a change in geometry to save weight or material.■ Components that deform beyond an allowable limit and that may need to be stiffened through

model or material changes.■ Parts with modal frequencies near the operating frequency that may result in excess wear or noise.

Stress Analysis Assumptions

You use Stress Analysis to solve linear static problems. Although many engineering components can be analyzed using Stress Analysis, there may be situations where linear static analysis assumptions do not apply.

Linear static stress analysis assumptions include the following:

■ The deflection and stress are linearly proportional to the load. If you double the load, the deflection and stress double.

■ Material properties are linear. The stress-strain curve is a straight line, with the stress remaining proportional to the strain. There is no yielding of the material.

■ The loading is static and is applied slowly. Dynamic loading effects such as sudden load application or impact are not considered.

■ Temperature has no effect on the part geometry or material properties.■ The deformation of the part is small when compared to the dimensions of the part. Large

deflection requires a nonlinear analysis to account for changing part and load geometry and is not considered in linear analysis.

■ Other nonlinear effects such as buckling are not considered.

If you have a problem for which these assumptions are not valid, you should either upgrade to a full analysis package such as ANSYS DesignSpace®, or pass the problem on to an analyst with the appropriate knowledge and software to manage it.

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Stress Analysis User Interface

The Stress Analysis environment uses all of the interface elements you are familiar with in the assembly and part modeling environments.

In the following illustration a part is shown in the Stress Analysis environment. Specific stress analysis tools and features are shown in the panel bar, browser, and graphics window.

Activating the Stress Analysis Application

Before you can access stress analysis tools, you must activate the Stress Analysis application. You do this with the Applications menu.

Access

Stress Analysis

Menu: Applications > Stress Analysis

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Stress Analysis Panel Bar

The Stress Analysis panel bar is displayed automatically when the Stress Analysis application is activated. The Stress Analysis panel bar provides the tool set for the Stress Analysis environment. You use the Applications menu to switch between the Stress Analysis and part environments.

Stress Analysis Browser

The Stress Analysis browser lists the loads, constraints, and results of an analysis. You use the browser to edit or delete existing loads and constraints, and to select the results you want to display.

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Stress Analysis Display Tools

In the Stress Analysis environment, you use tools on the Standard toolbar to control the display of input and results.

Stress Analysis Options in the Part Environment

After you perform a stress analysis, you may need to modify geometry in identified areas of concern. While you are working in the part environment, the Standard toolbar contains tools that enable you to update the stress analysis and display the last stress result item. Using these tools, you can identify areas of the model that require edits to address problems identified by the stress analysis. After making the changes, you can update the analysis to see the effects of your changes.

Select the desired contour setting.

Use these options to toggle the display of Elements, Boundary Conditions, Maximum Stress/Displacement Point, and Minimum Stress/Displacement Point.

Select a deformation scale in the list to exaggerate the visual results.

Click to update the stress analysis to incorporate changes in the part model.

Click to display the results of the last stress analysis result item.

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Performing a Stress Analysis

The process of performing a stress analysis involves several steps, some of which must be repeated as you refine the model geometry based on the analysis results. When you perform a stress analysis, your goal is to simulate real-world conditions on your part by duplicating forces, loads, and constraints in the design environment.

In the following illustration, Equivalent Stress results are shown on a simple part model.

Process: Performing a Stress Analysis

The following steps describe the process of performing a stress analysis.

1. Click Applications menu > Stress Analysis.

2. Add loads to your model that represent the actual loading conditions that will occur.

■ You can add forces, moments, pressure, bearing, and body loads such as gravity and acceleration.

■ Specify the load directions using geometry on the part or on other parts in the assembly.

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3. Add constraints that represent the physical connection of the part to other parts in the design. For example, use a constraint where the part is bolted or welded, or where it contacts other components.

4. Set the analysis options. In the Stress Analysis dialog box, select the type of analysis and the mesh size.

5. Analyze the model:

■ When you finish applying loads and constraints, click the Stress Analysis Update tool to analyze the model.

■ The Solution Status dialog box shows the analysis progress.

6. View the results.

■ When the analysis is complete, the results are displayed graphically on the model.

■ You can view contours for stress, deformation, factor of safety, or the different mode shapes.

■ You can also display or hide the mesh, loads, or constraints; change the display range for contours; and display or hide minimum and maximum markers.

7. Refine the model:

■ If there are areas of concern, return to the part environment, display the results of the analysis on the model to guide your changes, make appropriate model changes, and then update the stress analysis.

■ Repeat this cycle until you are satisfied with the model’s results.

8. Document the results:

■ Create a report that summarizes the input values and results, including images of the results.

■ The report is in HTML format, so you can share it with others on the design team and include it in documentation.

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Guidelines

Keep the following guidelines in mind when performing a stress analysis.

■ If your part is a component of an assembly, either edit the part in place or open the part separately.■ To analyze a series of rigidly connected components in an assembly, create a derived part and then

analyze the derived part.■ Suppress features that do not affect the results, especially if the features are small. ■ Typical features that you want to suppress include small cosmetic rounds, chamfers on outside

corners, and small holes or other features in areas where the stress will be low and which do not contribute to the stiffness of the model.

■ Small features increase the number of elements and can significantly increase solution time. If you are interested in converging the stress results, make sure that inside corners in the area of interest have fillets. Sharp inside corners result in infinite stress, and the stress results will not converge.

■ The processing time depends on the size of the model and of the mesh.■ You typically analyze several times at decreasing mesh sizes to prove that the results are

converged.■ When you are confident that the model performs correctly, select Result Convergence to

automatically converge on a result.

Using Autodesk Inventor

Although you must have Autodesk Inventor Professional software to perform a stress analysis and view analysis results, you can open and edit a part that contains Stress Analysis results with the Autodesk Inventor application. If you modify the part in an Autodesk Inventor application and then open it in Autodesk Inventor Professional software, the stress results must be updated so that they reflect the changes. You may need to edit loads and constraints if the geometry to which they were attached was modified.Sa

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Exercise: Perform a Basic Stress Analysis

In this exercise, you determine the stress and deformation of a plate with an end load. You apply loads and constraints, run an analysis, and view the results. You add a hole to the plate and determine the hole’s effects on the results. You perform a convergence study to determine whether the mesh size is adequate.

NOTE: The first part of this problem is a simple example with a known solution. Whenever you run a new analysis type, run a simple test case to familiarize yourself with the input values and other program settings.

The completed exercise

Completing the Exercise

To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 1: Introduction to Engineering Analysis. Click Exercise: Perform a Basic Stress Analysis.

1. Open Stress_SteppedPlate.ipt.

2. Click Applications menu > Stress Analysis.

■ Because no material was set for the model, the Choose Material dialog box is displayed.

■ From the Material list, select Steel, Mild. Click OK.

3. On the panel bar, click Force.

■ Move the cursor over edges, vertices, and faces on the plate to display the allowed selections.

■ Click the right end face of the plate.

The force is applied with its default direction perpendicular to and toward the selected face.

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4. In the Force dialog box:

■ Click the Flip Force button to make the force arrow point away from the face.

■ For Magnitude, enter 5000 N.■ Click OK.

5. Confirm the appearance of the force element in the browser.

6. Add a constraint to the part:

■ On the panel bar, click the Fixed Constraint tool.

■ Select the face at the left end of the plate. Click OK.

7. Confirm the appearance of the constraint in the browser.

8. To adjust the Stress Analysis Settings:

■ On the panel bar, click the Stress Analysis Settings tool.

■ In the Stress Analysis Settings dialog box, make sure that Stress Analysis is selected in the Analysis Type list.

■ Click Preview Mesh to view the finite element mesh.

■ Click OK.

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9. On the Standard toolbar, click the Stress Analysis Update tool.

When the analysis is complete, the equivalent stress is displayed on the deformed model.

As expected, the stress is highest at the fillets. The result is close to the theoretical stress of about 56 MPa (using a stress concentration factor of 1.6).

NOTE: In this analysis, the analysis result matched the theoretical result on the first run because the model loading and geometry are simple. Never consider an analysis complete after just one run. You must always perform a convergence study to confirm that the results of several runs are converged.

10. In the browser, right-click Fixed Constraint 1. Click Reaction Forces. In the Reaction Forces dialog box:

■ Confirm that the reaction force in the X direction is -5000 N.

■ Click OK to close the dialog box.

11. On the Standard toolbar, in the Deformation Scale list, select 2:1 Automatic.

The deformed shape changes. Remember that the deformation is exaggerated.

12. On the Standard toolbar, in the Deformation Scale list, select Actual.

Notice that the actual deformation is very small.

13. Return the deformation style to the default value of 1:1 Automatic.

14. On the Standard toolbar, turn the display tools on and off and notice the effects.

15. In the browser, double-click Deformation.

The deformation contours are displayed on the model.

The contours are parallel because the plate is loaded uniformly across the end. The contours are farther apart in the wider area of the plate and closer together in the narrower area because the plate deforms more per unit length in the narrower area. The result matches the theoretical estimate of 0.011 mm.

16. In the browser, double-click Safety Factor.

The safety factor contours are displayed on the model.

The lowest safety factor is 3.7214, which is equal to the yield strength of the material (207 MPa) divided by the maximum stress (55.6243 MPa).

17. To change the force magnitude:

■ In the browser, right-click Force 1. Click Edit.

■ In the Edit Force dialog box, for Magnitude, enter 6000 N.

■ Click OK.

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18. In the browser, notice that the icons in front of the results have lightning bolts, indicating that the results need to be updated.

19. Click the Stress Analysis Update tool.

20. View the stress, deformation, and safety factor. The stress and deflection values should be approximately twenty percent greater than the previous values.

21. In the browser, expand Features. Right-click Hole1. Click Unsuppress Features. Notice that the results need updating.

22. On the Standard toolbar, click the Stress Analysis Update tool to rerun the analysis. View the results.

The maximum stress is now 141.44 MPa and is located near the hole. The maximum deformation is 0.0159 mm.

23. Click the Stress Analysis Settings tool.

■ In the Stress Analysis Settings dialog box, change the Mesh Relevance slider to 100.

■ Click Preview the Mesh.■ In the warning dialog box, click OK.■ In the Stress Analysis Settings dialog box,

click OK.

24. Click the Stress Analysis Update tool to rerun the analysis.

The stress has decreased slightly, and the deformation is unchanged at 0.0159 mm. Because the percentage of change in stress is very small between the runs, the mesh size is probably adequate to predict the stress in the model.

You now try automatic convergence. The analysis may take several minutes.

25. To use Results Convergence:

■ Click the Stress Analysis Settings tool.■ In the Stress Analysis Settings dialog box,

under Mesh Control, select the Results Convergence check box.

■ Click OK.

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26. Click the Stress Analysis Update tool to rerun the analysis. The stress has decreased slightly again.

■ On the Standard toolbar make sure the Element Visibility button is selected. This causes the mesh to be displayed.

■ Notice that the mesh is much finer near the hole.

27. Close the file. Do not save changes.

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Chapter Summary ■ 29

Chapter Summary

This chapter introduced you to the Dynamic Simulation and Stress Analysis environments. You learned how to use dynamic simulation and stress analysis to analyze designs and identify their successes and flaws before you build costly physical prototypes.

Having completed this chapter, you can:

■ Describe the Dynamic Simulation environment and the processes you use to create simulations to evaluate motions in an assembly.

■ Describe the Stress Analysis environment and the processes you use to create and analyze designs.

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