Introduction to Engineering...

Chapter Overview ■ 3

Chapter

1

Introduction to EngineeringAnalysis

This chapter introduces you to the Stress Analysis and Dynamic Simulation environments. Youlearn how digital prototyping can be used to simulate your designs before you build costly physicalprototypes.

Objectives

After completing this chapter, you will be able to:

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

evaluate motions in an assembly.

4 ■ Chapter 1: Introduction to Engineering Analysis

Lesson: Stress Analysis Overview

This lesson provides an overview of the Stress Analysis environment, interface, and tools. The lessonalso describes the processes you use to create simulations to evaluate the strength, deflection, andnatural frequencies of your designs. When you design products, you need to examine how your designs perform under real-worldconditions. When the product will be exposed to loads during normal use, it is important that youdesign the product to function properly so that it can withstand these loads. Proving the validity ofyour designs before you build saves time and money by eliminating costly reworking and alterationsafter the build process has begun. Simulation data serves as a valuable presentation tool forcustomers if you want assure them that you are providing a design that meets their requirements. The following image shows the stresses that result from an analysis on the arms of a front-end loader.

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.■ List the steps required to perform a stress analysis.■ Describe and identify the types of files that are created when you perform a stress analysis.■ Perform a basic stress analysis and review the results.

Lesson: Stress Analysis Overview ■ 5

About Stress Analysis

You use Stress Analysis to estimate the deformation, stress, and natural frequencies of your designs.Stress Analysis helps you to create better parts by indicating areas of your digital prototypes thatrequire further attention. You can reduce the number of design-test-redesign cycles by using StressAnalysis early in the design cycle to find and fix your models before you build the first prototype.

Stress Analysis does not completely eliminate physical testing; however, using analysis tools early inthe design process can significantly reduce the number of physical tests that are required. You oftenuse Stress Analysis to help design the test by identifying locations of high stress or deformation and todesign test jigs and fixtures. You use the test results to fine-tune your stress analysis so that you canpredict the stress on similar parts with greater confidence. The following image shows the stress and displacement plots for a wrench. In Stress Analysis, resultsare displayed graphically on the deformed model.

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. FEA is an approximation method that estimates the behavior of amodel.

If a model has simple geometry, it is straightforward to solve for stress and deflection manually byusing available equations. However, most models have complex geometry, and equations to predictthe stress, deflections, or mode shapes are not normally available. In FEA the model is subdivided intoa number of pieces called elements, each of which have simple shapes that have available solutions.The solutions for all of the elements are combined to get the behavior of the entire model.

The process of generating the elements in FEA is called meshing, and the resulting set of connectedelements is called the mesh. In the following illustration, the original and meshed models for a bracket are shown. The meshedmodel's shape is approximated using a large number of tetrahedral-shaped solid elements.


The size of each element in the mesh determines the resolution of the results. The smaller theelements, the more accurate the numerical results, but the longer the model takes 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.Learning how to set up an appropriate mesh and determining if it gives accurate results are key skillsin performing a stress analysis.

Example of Stress Analysis

The following image shows the stress on a bellcrank from the rear suspension in a small racecar. Thestress results were used to lighten the part in areas where the stress was low.


Potential Uses for Stress Analysis

You use Stress Analysis to identify the following:

■ Areas of your models that are highly stressed that 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 vibration,

stress, wear, or noise.

Stress Analysis Assumptions

You use Stress Analysis to solve linear static problems. Although many engineering components canbe analyzed using Stress Analysis, you might find situations in which the following assumptions do notapply:

■ 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 notconsidered in linear analysis.

■ Other nonlinear effects, such as buckling, are not considered. If you have a design for which these assumptions are not valid, you should pass the problem on to ananalyst with the appropriate knowledge and software to solve it.


Stress Analysis User Interface

The Stress Analysis environment uses the same major interface components that you use in thepart or assembly environments, including the graphics window, panel bar, and browser. The toolspresented on the panel bar, and the elements in the browser, are specific to the Stress Analysisenvironment. In the following illustration a part is shown in the Stress Analysis environment. Specific Stress Analysistools and features are shown in the panel, browser, and graphics window.

Stress Analysis tab.

Stress Analysis panels.

Stress Analysis browser. The browser contains reference to the part or assembly geometry, loads,constraints, contacts, other input data, and finally, the results.

Graphical display. Results are displayed graphically on models. The color bar displays the result rangefor each color.


Stress Analysis Panels

The Stress Analysis panels contain the tools for the Stress Analysis environment.

Manage The Manage panel contains tools that enable you to create a new simulation and toset up parameters for a parametric analysis.

Materials,Constraints,Loads, Contacts

The Materials, Constraints, Loads, and Contacts panels contain tools that you use toprepare your model for analysis.

Prepare The Prepare panel contains tools that you use to view and adjust the mesh and setup automatic convergence.

Solve The Solve panel contains the Solve tool, which you use to run an analysis.

Result, Display,Report

The Result, Display, and Report panels contain tools to view results.

Settings The Settings panel contains the Stress Analysis Settings tool, which you use to setdefault mesh and analysis settings. Most of the same settings can be changed fromwithin the various tools in the Stress Analysis environment.

Exit The Exit panel contains the tool to exit the Stress Analysis environment and returnto either the part or assembly environment.

Stress Analysis Browser

The Stress Analysis browser contains reference to the part or assembly geometry, loads, constraints,contacts, other input data, and finally, the results. You use the browser to exclude geometry, edit ordelete existing loads, constraints, contacts, and mesh settings, as well as to select the results that youwant to display.


An analysis can contain multiple simulations, all of which are listed in the browser. You use the browserto switch between simulations.

For a part, the features are displayed. For an assembly, the parts are displayed. You use the model treeto exclude features or parts from the analysis or to change the visibility of parts in an assembly.

The browser lists all of the constraints and loads and provides an interface to edit or delete existingitems.

The browser lists all of the contacts and provides an interface to edit or delete them. The icon next tocontacts indicates that the contacts are out of date and need to be updated.

The mesh settings node in the browser contains a list of any local mesh settings.

The Results folder contains all of the results for the analysis. You use the browser to select which resultsare displayed in the graphics window.


Performing a Stress Analysis

The process of performing a stress analysis involves several steps, some of which must be repeated asyou refine the model geometry based on the analysis results. When you perform a stress analysis, yourgoal is to simulate real-world conditions on your part by duplicating forces, loads, and constraints inthe 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. Identify the goals of the analysis:■ Are you concerned about the deflection?■ Is the stress a concern?■ Is the model subjected to vibrations, meaning that a modal analysis is required?

2.

Learn about the model and how it interacts with its environment:■ Determine where and how loads are applied.■ Determine the magnitude (or range of magnitudes) and direction of the loads.■ Determine how the model is constrained from motion by external constraints or by its interaction

with other parts. 3.

Prepare your model for analysis:■ If you plan to analyze an assembly, create a Level of Detail for each analysis if you want to eliminate

nonstructural parts and other parts that you do not need to analyze.■ For parts, identify features that do not contribute to the strength but may add significantly to the

number of elements. Typical features to exclude from the analysis include holes that are in lowstress areas, external rounds, cosmetic embossing, and so on.

4.

Enter the Stress Analysis environment.


5.

Create a new simulation. Specify the simulation type and default settings. Multiple simulations can be created in the same file,each with different settings. For example, a single assembly part file might contain simulations forstatic analysis of several different configurations of components and modal analyses of those sameconfigurations.

6.

Add loads to the model. You can add forces, moments, pressure, bearing, and body loads such as gravity and acceleration. 7.

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

8.

For assemblies, add contacts to represent the connection between components. Contacts can simulaterigidly bonded joints or allow sliding and separation under loading.

9.

Run the analysis. The model is meshed according to the settings and the results for the activesimulation are determined and displayed on the model.

10.

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. 11.

Determine if the model behaved as expected:■ Does the displacement make sense?■ Do the reaction forces at the constraints add up to the applied loads?■ Does the area of high stress make sense? If the model's behavior does not look correct, review the loads and constraints and adjust them asnecessary.

12.

Prove that results are accurate. Stress Analysis uses a mathematical technique that approximates the actual stress in a part. Stresssingularities and inadequate mesh size can lead to results that are not accurate. Before you accept anyresults, you must prove that the results are accurate by performing a convergence study. Stress Analysiscontains several tools that help you to adjust the mesh automatically in areas of concern while ignoringthe stress at singularities.

13.

Refine the model:■ If there are areas of concern, return to the part or assembly environment, make appropriate model

changes, and then update the stress analysis.■ Repeat this cycle until you are satisfied with the model's results.

14.

Document the results:■ Create a report that summarizes the input values and results, including images of the results.■ The report is in HTML format; therefore, you can share it with others on the design team and

include it in documentation.


Guidelines

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

■ Determine the smallest number of parts that you can analyze. You typically do not analyze an

entire assembly with all of its parts.Determine the load path and decide which componentsare critical.Can you analyze one part on its own? Can you isolate a small number of partsin theassembly? Can you perform several analyses, each with differentparts of interest?

■ For parts, suppress features that do not affect the results, especially if the features are small.Typical features to suppress include small cosmetic rounds or chamfers on outside corners, andsmall holes or other features in areas where the stress is low. These features do not contribute tothe stiffness of the model but can greatly increase the time to generate the mesh and solve for theresults.

■ For assemblies, exclude parts from the analysis that do not contribute to the strength or stiffness.Small parts, fasteners, bearings, cosmetic parts such as plastic or sheet metal covers do notcontribute to the strength but may take considerable time to mesh and solve. A Level of Detail isan efficient method to exclude parts from Stress Analysis.

Stress Analysis Files

When you add stress analysis information to a part or an assembly, and then save the file, foldersand files are created to hold the stress analysis results. You need to be aware of the folder names andlocations so that you can manage them along with the model files.

Example of Stress Analysis Files

The following image shows the files and folders that result from running an analysis on a single partfile (1). When the file is saved, a folder (2) with the same name as the part file is created. It containsmultiple subfolders and files that contain the results. If a report is generated and saved to the modelfolder, the report HTML file (3) and Images folder (3) are also created.


By default, OLE links are created to each of the analysis files so that other applications, such asAutodesk® Vault, are aware of the link to the files. The links are listed in the 3rd Party folder in theModel browser as shown in the following image. Because the results files are linked to the modelfile, if the results files cannot be found when the model file is opened, you must resolve the file linksbefore you can open the file.

If the Results folder is deleted, the results can be recreated by running the analysis again because thepart or assembly file contains the inputs and settings for the stress analysis. However, the analysismay take a while to run, especially if the model is complex and there are multiple analyses.


Exercise: Perform a Basic Stress Analysis In this exercise, you determine the stress and safetyfactor in a wrench. The analysis has been startedbut is not complete. You complete the analysis byexcluding some features from the analysis, reviewingthe current constraints, adding a load, and runningthe simulation.

The completed exercise

Completing the ExerciseTo complete the exercise, follow thesteps in this book or in the onscreenexercise. In the onscreen list ofchapters and exercises, click Chapter 1:Introduction to Engineering Analysis.Click Exercise: Perform a Basic StressAnalysis.

1.

Open Stress_Overview.ipt.

2.

Click Environments tab > Begin panel > StressAnalysis.

3.

In the browser, expand Stress_Overview.ipt. 4.

Select both Hole1 and Emboss1. Right-click andselect Exclude from Simulation.

5.

In the browser, expand the Constraints folder.Move the cursor over the fixed constraint andconfirm that two faces are fully constrained.

6.

On the Loads panel, click Force. Select thethree faces as shown.


7.

In the Force dialog box, click the DirectionSelection button. Select the edge of the face asshown. The forces align with the edge.

8.

In the Force dialog box, for Magnitude, enter500N. Click OK.

9.

On the Solve panel, click Simulate. Click Run. 10.

When the analysis is complete, the Von Misesstress is displayed on the displaced model.

11.

On the Prepare panel, click Mesh View. Themesh is displayed.

12.

Click Mesh View again to turn off the mesh. 13.

In the browser, in the Results folder, double-click Safety Factor. The minimum safety factor of less than one is acause for concern. Further analysis and modelchanges may be required.

14.

In the browser, in the Results folder, double-click Von Mises Stress.

15.

On the Result panel, click Animate. 16.

In the Animate Results dialog box, click Play.Watch the animation for a few cycles. Click OK.

17.

On the Exit panel, click Finish Stress Analysis. 18.

Save the file. 19.

In the browser, expand the 3rd Party folder. The files containing the stress results are listed.

20.

In Windows Explorer, navigate to thelocation of the part file. Confirm that a foldercontaining the results was created.

21.

Return to Autodesk® Inventor®. Close the file.

Lesson: Dynamic Simulation Overview ■ 17

Lesson: Dynamic Simulation Overview

This lesson describes the Dynamic Simulation environment, and its interface and tools. The lessonalso describes the processes you use to create simulations to evaluate motions in an assembly, sizeactuators, determine bearings, and compute stresses in parts. Proving the validity of your designsbefore you build saves time and money by eliminating costly reworking and alterations after the buildprocess has begun. Simulation data serves as avaluable presentation tool for customers because itassures them that youare providing a design that meets their requirements. The integration of Dynamic Simulation with Autodesk Inventor, and the Dynamic Simulation evaluationmechanisms, provide you with valuable tools to test, refine, and prove your designs. In the following image, a revolution joint is applied to a glass window lever mechanism so that asimulation 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.


About Dynamic Simulation

Dynamic Simulation is used to simulate and analyze dynamic characteristics of an assembly undervarious load conditions. You can also export load conditions at any motion state to the Stress Analysisenvironment to see how parts respond from a structural view to dynamic loads at any point in theassembly's range of motion. In addition, you have the option to transfer multiple load conditionsin the assembly’s range of motion to the Stress Analysis environment. This option enables you tovalidate and compare designs without the need to go back to Dynamic Simulation to transfer loadsagain. A wiper arm assembly in the Dynamic Simulation environment is shown.

Definition of Dynamic Simulation

Dynamic Simulation provides you with the tools to simulate the actual performance of your designbefore the product is built. By default, Dynamic Simulation automatically converts assemblyconstraints between components into mechanical joints. You also have the option to manually definemechanical joints between components. After the joints have been finalized, forces, accelerations,or velocities need to be applied to them where applicable if you want to reproduce real-worldconditions. 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 asgravity and friction on the mechanism. An assembly in the middle of a simulation is shown. In the Output Grapher the force data is displayed.This data is used to perform Stress Analysis on a component.

Starting Dynamic Simulation

You can access Dynamic Simulation from an assembly file.

On the Environments tab (1), Begin panel, click Dynamic Simulation (2).


Example of Dynamic Simulation

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

Running the Output Grapher provides the data required to calculate the torque.


The joint with the applied force.

The selected option to be displayed in the window.

The maximum force.

The maximum force on the graph.


The Dynamic Simulation Interface

The DynamicSimulationenvironment uses the same major interface components that you use inthe part or assembly environments, including the Autodesk Inventor window, the graphics window,the ribbon, the application frame, the browser, and the shortcut menus. The tools presented onthe ribbon, and the elements in the browser, are specific to the DynamicSimulationenvironment.Additionally, the Simulation Player window contains controls to runsimulations and set their timeparameters.

Dynamic Simulation tab

Dynamic Simulation panels

Dynamic Simulation tool

Dynamic Simulation browser

Simulation Player

Dynamic Simulation Panels

The Dynamic Simulation panels are divided into seven sections according to the types of operationsthat they perform.


Tools to create joints, convert constraints, and check the status of the mechanism.

Tools to apply force and torque.

Tools used to display results and traces.

Tools used to create animations.

Tools used to manage simulation settings and parameters.

Tool used to export data to FEA.

Tool used to exit Dynamic Simulation.

Dynamic Simulation Browser

The Dynamic Simulation browser provides elements that are unique to the Dynamic Simulationenvironment. Components areclassified as Groundedor Mobile. Joints are grouped by category, as areexternal loads and traces. In the browser you access the shortcut menus to open joint properties, editand delete joints, lock degrees of freedom, and control the display of joints. The elements in the Dynamic Simulation browser are shown.

Rigid components linked to ground on one end and all parts not yet used by the dynamic definition ofthe mechanism.

Subassemblies, weldments, and parts that are not grounded.

Joints created automatically or manually.

Loads such as gravity, individual forces, or individual torque.


Simulation Player

The Simulation Player is used to run or replay a simulation. With this tool, you control the simulationtime, how many time steps are calculated, and the speed at which the simulation runs. The SimulationPlayer is synchronized with the mechanism in the graphics window and the Output Grapher so thatyou can see the position of the mechanism and the resultant force in the Output Grapher at any timestep that you choose.

Return to the construction mode.

Deactivates the screen refresh.

Sets the time for the simulation to run.

Displays the number of images to save during the simulation.

Displays the number of frames to display.

Creating Dynamic Simulations

With Dynamic Simulation, the intent is to build a functional mechanism, and then add dynamic, real-world influences of various types of loads to create a true kinematicchain.You thenrun the simulationto see how the joints, loads, and component structures interact as a moving dynamic mechanism.


In this simulation, the maximum acceleration of a revolution joint (1) is displayed in the time stepspane (2) and the graphics window (3).

Process: Creating Dynamic Simulations

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

1.

Open an assembly file. 2.

Enter the Dynamic Simulation environment. 3.

Create standard joints by converting existing assembly constraints automatically or manually. 4.

If required, insert other types of joints such as contact, rolling/sliding, or spring. 5.

Define the physical environment in the joint properties and apply forces. 6.

Run the simulation to see how joints, loads, and component structures interact. 7.

Use the Output Grapher to analyze the results. 8.

Select the loads on a part and export to the Stress Analysis environment to study the effect of theloads.

9.

Analyze the results in the Stress Analysis environment.


Exercise: Review a Cam Valve Simulation In this exercise, you run a simulation of a cam valveassembly with and without friction to determine thetorque required to overcome the spring resistanceand the friction force.

The completed exercise

Completing the ExerciseTo complete the exercise, follow thesteps in this book or in the onscreenexercise. In the onscreen list ofchapters and exercises, click Chapter 1:Introduction to Engineering Analysis.Click Exercise: Review a Cam ValveSimulation.

1.

Open CamValve.iam.

2.

Click Environments tab > Begin panel. ClickDynamic Simulation.

3.

If required, click No to close the messagewindow.

4.

Review the cam valve assembly. The spring isa force joint and was inserted using DynamicSimulation.


5.

On the Simulation Player, click Run or Replaythe Simulation.

At the beginning of the simulation note thatthe valve is bouncing. You correct this and runthe simulation again.

6.

On the Simulation Player, click ConstructionMode (1).

7.

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

8.

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

9.

On the Simulation Player, click Run or Replaythe Simulation. The valve does not bounce.

10.

On the Results panel, click Output Grapher.Resize the Output Grapher and zoom and panin the CamValve assembly to view both.

11.

In the Output Grapher, double-click the dashedline at 0.25 (1). The timeline (2) is displayed,and the cam position (3) is updated to show itsposition at that point of the simulation.

12.

To cycle through the simulation, use the rightand left arrow keys on the keyboard to stepforward and backward in the simulation. Cyclethrough the simulation to 1.00 to show thecam at the end of the simulation.


13.

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

14.

On the Simulation Player, click ConstructionMode.

Add a Coefficient of Friction The following steps describe how to add a coefficientof friction to calculate the effect on the torque that isrequired to rotate the cam and overcome the springforce and friction force. 1.

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

2.

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

3.

On the Simulation Player, click Run or Replaythe Simulation. The Output Grapher is stillopen, so you see the graph being generated asthe simulation is running. In the next step, you change the color of thenewly generated curve. When you comparethe saved graph curve with this new one, youcan distinguish between the two of them.

4.

In the Output Grapher, right-click theU_imposed[1]/N mm column heading. ClickCurve Properties.

5.

In the Dynamic Simulation - Properties dialogbox, click the color box.

6.

In the Color dialog box, click the red colorswatch. Click OK.


7.

In the Dynamic Simulation - Properties dialogbox, click OK. The graph changes to red.

8.

On the Output Grapher toolbar, click ImportSimulation.

9.

In the Dynamic Simulation - Load file dialogbox, select CamValve.iaa. Click Open.

10.

Review the Dynamic Simulation browser. TheCamValve.iaa element is added to the OutputGrapher.

11.

In the Output Grapher, expand CamValve.iaa.Expand Revolution:2 (Support:1, Cam:1).Expand Driving Force and select theU_imposed [1] check box.

12.

The Output Grapher displays the graphs ofthe torque required to rotate the cam withoutfriction (blue) and with friction (red). Also, anew column is added in the time-steps panefor the numerical values.

13.

Close the file. Do not save changes.


Chapter Summary

In this chapter, you learned about the Stress Analysis and Dynamic Simulation environments. Youlearned how digital prototyping can be used to simulate your designs before you build costly physicalprototypes. Having completed this chapter, you can:

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

evaluate motions in an assembly.

Introduction to Engineering...

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