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In This Chapter

24

Calculating Stress on 3D
Parts

Autodesk

®

Mechanical Desktop

®

6 Power Pack includes

a feature called 3D finite element analysis (FEA). FEA is

used to calculate deformation and stress conditions on

3D parts. The 3D FEA calculations feature is a reliable

tool that helps you meet the demands of today’s

sophisticated mechanical engineering.

In this tutorial, you calculate stress on a 3D part using

3D FEA. You create the mesh required to display the

results of the calculations, and then you define the loads

and make the calculations. When you finish, the

calculations are displayed in tables.

Run Mechanical Desktop with the power pack to

perform this tutorial.

■

New in this tutorial

■

Using 3D FEA calculations

■

Defining loads

■

Calculating and displaying the
result

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Key Terms

Term

Definition

distributed force

A force that is spread over an area.

FEA

Finite element analysis. A calculation routine, or method. Calculates stress and
deformation in a plane for plates with a given thickness, or in a cross section with
individual forces, stretching loads, and fixed and/or moveable supports. The FEA
routine uses its own layer group for input and output.

fixed support

A support that is fixed to a part and cannot be moved.

load

Forces and moments that act on a part.

mesh

Graphical representation of a mesh pattern on a model, required for FEA
calculation and display of the result.

result

Results of FEA calculations. Result is displayed in a table, and as surface isoareas on
a model.

stress

Force or pressure on a part. Stress is force per area.

surface isoarea

Graphic representation of a stress calculation result displayed on the surface of a
model.

Tutorial at a Glance

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Tutorial at a Glance

The 3D FEA calculations feature is a simple tool that eliminates the need for
the complex programs and calculations previously required to perform stress
and deformation calculations. In this tutorial, you learn to use 3D FEA for
calculations as you

■

Start a finite element analysis.

■

Define stress loads.

■

Generate a mesh.

■

Calculate and display the result.

Basic Concepts of 3D FEA

In Mechanical Desktop Power Pack, you use the FEA Calculation 3D dialog
box options to choose the

■

Material of your part

■

Revolution direction

■

Type and quantity of supports and loads

The FEA calculations are dependent upon the definitions you enter for loads
and boundary conditions.

You consider how to reproduce the reality in your model, and how to define
the boundary conditions to achieve the best result. The more precise your
model is, the more useful the results are.

The FEA procedure uses a separate layer group for input and output.

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Using 3D FEA Calculations

To begin calculating the stress conditions on your model, you open the FEA
Calculation 3D dialog box. You work in this dialog box to choose the types
and quantity of loads and supports, and to define the loads and boundary
conditions.

Before you perform the calculation, you create a mesh on your 3D part. This
mesh is required to display the results of the calculation. The calculation is
displayed on your model using isoareas that define the limits of the stresses
and deformations. Tables are automatically created to define the calculations
for each isoarea.

Performing Finite Element Analyses

In the following exercise, you work with a lever that is loaded with a mass
and bolted at two faces. You reproduce these two points on the model as two
face supports, and define the mass as a face load at the front rectangular face.

Open the file md_ex03.dwg in the desktop\tutorial folder.

NOTE

Back up the tutorial drawing files so you still have the original files if you

make a mistake. See “Backing up Tutorial Drawing Files” on page 40.

The drawing contains a 3D part, which is the basis for your calculations.

The first step is to open the FEA Calculations 3D dialog box.

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To start a finite element analysis

1

Use AMFEA3D to perform the FEA calculation.

Menu

Content 3D ➤ Calculations ➤ FEA

Respond to the prompt as follows:

Select 3D-Body:

Select the 3D part

The FEA Calculation 3D dialog box is displayed.

NOTE

If the FEA Calculation 3D dialog box hides your drawing, move the

dialog box to another position on the screen.

Defining Supports and Forces

Next, you define the supports and forces that act on your part. These defini-
tions are used for the FEA calculations.

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To define supports and forces on a part

1

In the FEA Calculation 3D dialog box, choose the Face Support icon and
respond to the prompts as follows:

Select a surface:

Click the edge (1) of the surface

Specify face [Accept/Next] <Accept>:

Press

N

to cycle to the surface you selected, then press

ENTER

NOTE

You may prefer to turn OSNAP off before you create and constrain the

work point. Click the OSNAP button at the bottom of your screen.

The Define Border for Load, Support dialog box is displayed.

1

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2

In the Define Border for Load, Support dialog box, choose Whole Face.

Respond to the prompts as follows:

Define insertion point for main symbol:
Specify point or [Dialog]:

Specify a point, other than an edge, on the selected face

NOTE

If the support does not act on the whole face, you can define an area

using the different options. See the Help for more information.

3

In the FEA Calculation dialog box, choose the Face Support icon again, and
respond to the prompts as follows:

Select a surface: Click the edge (2) of the surface
Specify face [Accept/Next] <Accept>:

Press

N

to cycle to the surface you selected, then press

ENTER

The Define Border for Load, Support dialog box is displayed.

2

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4

In the Define Border for Load, Support dialog box, choose Whole Face, and
respond to the prompts as follows:

Define insertion point for main symbol:
Specify point or [Dialog]:

Specify a point, other than an edge, on the selected face

5

In the FEA Calculation dialog box, choose the Face Force icon and respond
to the prompts as follows:

Select a surface:

Click the edge (3) of the surface

Specify face [Accept/Next] <Accept>:

Press

N

to cycle to the surface you selected, then press

ENTER

The Define Border for Load, Support dialog box is displayed.

6

In the Define Border for Load, Support dialog box, choose Whole Face, and
respond to the prompts as follows:

Define insertion point for main symbol:
Specify point or [Dialog]: Specify a point, other than edge, on the selected face

The Angle type dialog box is displayed. Choose Normal, and respond to the
prompt as follows:

Specify value of load <10 (N/mm^2)>:

Enter 2

3

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You have the defined the border conditions for two supports and one force.
Your drawing should look like this:

Calculating and Displaying the Result

Continue in the FEA Calculation 3D dialog box to perform the calculations
and display the results.

Before you can calculate and display the result, you need to generate a mesh.

To generate a mesh

1

In the FEA Calculation 3D dialog box, under Run Calculation, turn on Auto
Refining.

2

Choose the Run Calculation icon.

The Working dialog box is displayed during the automatic calculation of the
mesh. When the calculation is finished, a mesh is displayed on your model.

Next, define the placement of the mesh.

3

Respond to the prompt as follows:

Specify base point or displacement <in boundary>:

Press

ENTER

This completes the mesh.

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Continue in the FEA Calculation 3D dialog box to calculate surface isoareas
and deformation.

4

Under Results, choose the Isolines (Isoareas) icon.

5

In the Surface Isolines (Isoareas) dialog box, choose the Isoareas button, and
choose OK.

Your model with isoareas is displayed on the screen beside the model with
mesh.

Respond to the prompts as follows:

Specify base point or displacement <in boundary>:

Press

ENTER

Specify insertion point or [Paper space]:

Specify a location for the table to the left of the isoareas display

NOTE

If necessary, zoom to fit the entire display to your screen before you

place the second table.

6

In the Surface Isolines (Isoareas) dialog box, choose the Deformed Mesh icon.

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7

In the Deformed Mesh dialog box, turn on Automatic, and choose OK.

Respond to the prompts as follows:

Specify base point or displacement <in boundary>:

Enter 150,150

Specify second point of displacement:

Press

ENTER

Specify insertion point or [Paper space]:

Specify a suitable location for the table near the mesh display

8

Close the FEA Calculation 3D dialog box.

The calculations are finished, and the results are displayed.

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