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Tutorial for Generative Structural Analysis in Catia V5

U.Bhat1

1Aerospace Department, Coventry University.

Abstract.

Structural analysis of a component is very important process for design and

development of any part. It enables a designer and engineer to check if the design

can take the required loads, if the material is good enough for the stresses, critical

sections within the design and lots more.

This report gives a brief introduction to Generative Structural Analysis module

available in CATIA V5. The report also includes a worked example of how to use

the module for carrying out a structural analysis.

1. Introduction

This report looks at the Generative Structural Analysis (GSA) module (work

bench) within CATIA V5 which is used for Finite Element Analysis of 3D parts.

GSA allows the user to quickly model a part’s mechanical behavior with very few

steps. This report will demonstrate how to perform first order mechanical analysis

for 3D parts.

Generative Structural Analysis module can be accessed from standard tools bar

menu in CATIA V5 window, Start >> Analysis & Simulation >> Generative

Structural Analysis.

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Figure 1.1 Generative Structural Analysis module in CATIA V5

GSA provides verity of tools and stress visualization options. Next section contains

some background of Finite Element and Analysis and how it can be used within

CATIA V5 followed by a simple worked example.

It is important to have some knowledge of at least Sketcher and Part Design

modules before GSA can be used.

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2 Background to Finite Element Analysis

Finite Element Analysis (FEA) is a numerical tool used for solving problems

defined by ordinary or partial differential equations. The most common Finite

Element technique is displacement-based technique. In this approach displacement

is assumed to be an unknown quantity.

The problem is solved by using Finite

Element Methods to find out

displacement. It uses a complex system

of points called nodes which make a grid

called a mesh. This mesh is programmed

to contain the material and structural

properties which define how the structure

will react to certain loading conditions.

Nodes are assigned at a certain density

throughout the material depending on the

anticipated stress levels of a particular

area. Regions which will receive large

amounts of stress usually have a higher

node density than those which

experience little or no stress. Points of

interest may consist of: fracture point of previously tested material, fillets, corners,

complex detail, and high stress areas. The mesh acts like a spider web in that from

each node, there extends a mesh element to each of the adjacent nodes. This web of

vectors is what carries the material properties to the object, creating many

elements.

Figure 2.1 Finite Element Analysis

process.

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Using CATIA V5 the overall process for FEA can be subdivided into smaller steps

shown in Figure 2.1. These steps are explained below.

2.1 Pre-Processing

This step involves preparing the part for Finite Element Analysis. This will involve

the complex physical structure to be converted into an equivalent Finite Element

model. This will be followed by applying the material properties to the model.

There are five structural properties associated to isotropic materials in CATIA V5.

These are Young’s Modulus, Poisson Ratio, Density, Thermal Expansion and

Yield Strength. Next step within pre-processing applying the boundary conditions

and restraining to the FE model. And finally conversion of actual loads to

equivalent FE Loads.

2.2 Computation

In computation step the standard FE solutions procedures uses data provided by

pre-processing step and then solves the FE model to find out the unknown

displacement values.

2.3 Post-Processing

Using the values of displacement computed in pervious step strain and stresses are

calculated for the whole structure. The deformation of the structure can be studied

by looking at the variation of strains and stresses throughout the structure.

2.4 Mesh Refinement Iteration

The first solution provides initial estimation of stress/strain values. In order to get a

more accurate solution, the mesh needs to be refined and the computation is to be

done. Because when the mesh is refined, the computation is always invalidated. A

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number of mesh refinement and computations iterations are performed till the

required solution accuracy is achieved.

2.5 Report Generation

Once the required accuracy level is achieved, various plots such as Displacement,

Principal stress, Von-Mises Stress can be obtained.

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3 Example of using GSA module

Below is a worked tutorial to show how Generative Structural Analysis module

within CATIA V5 can be used to do a Finite Element Analysis. The example

shows the FEA done on a rectangular beam. The example below is based on a

tutorial in “Advanced CATIA V5 Workbook” by Richard Cozzens.

Section A-G: Pre-processing

As mentioned in the previous section the first step required is to create a FE model

of the part that needs to be analyzed. Below are the steps of how to do it.

A. Creating the part.

A.1. Start CATIA V5 and select Start and Mechanical Design and Part

design commends for the standard Windows tool bar to create a new

CATPart document.

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A.2. Name the new part as Beam

A.3. Save the document as Beam.CATPart

A.4. Enter the Sketcher module using YZ plane.

A.5. Create the rectangular profile using Rectangle tool . Use

dimensions 70mm wide by 140mm tall, centered at the axis by creating

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constrains as shown in figure below

A.6. Select the Exit module tool.

A.7. In the Part Design module select Pad tools.

A.8. Type 1500mm in the Length field of Pad Definition.

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A.9. Select OK and save the document.

B. Apply Material and Apply View Properties

Before the Generative Structural Analysis module us used for the FEA of

Beam.CATPart, it must have material assigned to it. Each material in CATIA

V5 has mechanical properties for computing the analysis. These properties are

Young’s Modulus, Poisson Ratio, Density, Thermal Expansion and Yield

Strength. For this tutorial Steel will be applied to Beam.CATPart. Below are

the steps to apply the material.

B.1. Select Beam in the Specification Tree so that it is highlighted as

shown in the figure below

B.2. Select Apply Material tool.

B.3. Select Metal tab in the Library window.

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B.4. Select Steel and then select OK button.

B.5. Set the view mode by selecting View and Render Style and

Customize View.

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B.6. The Custom View Mode window will appear. Select Edges and

points, Shading and Material.

B.7. Select OK button and save the document.

C. Starting the Generative Structural Analysis Module

After the Material has been applied the part is ready to enter the Generative

Structural Analysis work bench. Follow the steps below to enter the GSA work

bench.

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C.1. Select Start from the menu bar then Analysis & Simulation and

finally Generative Structural Analysis.

C.2. A New Analysis Case window will appear in the document as shown

in figure below. Select Static Analysis.

C.3. Select the OK button and save the document as

BeamAnalysis.CATAnalysis.

The Static Analysis selection allows evaluation of the fixed boundary

environment for the BeamAnalysis.CATAnalysis document. The document

will generate a default Specification Tree with tow default branches called

Links Manager and Finite Element Model.

D. Links Manager

The Links Manager which appears in the Specification Tree, contains the link

to the Results and Computations files directory. It also contains link to the

Beam.CATPart document.

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The Links Manager allows saving the Results and Computations files in

whatever directory is specified. This and import feature incase the files are

moved to different directory or a different computer is used to do the analysis.

Steps to modify the files directory are given below.

D.1. Select the Storage Location tool.

D.2. This will bring up the Current Storage Location window with two

Modify buttons that allow to select the file path for storing the results and

computations files (BeamAnalysis.CATAnalysisResults and

BeamAnalysis.CATAnalysisComputations)

D.3. Select the appropriate director for each.

D.4. Select OK button

E. Finite Element Model

The second branch from the Specification Tree is the Finite Element Model. It

always contains Nodes and Elements, Properties.1, Materials.1 and either

Free Frequency Case, Frequency Case or in this example, a Static Case as

shown in the figure below

Node and Elements are used to turn the model into a discrete numerical

problem through the use of mesh data. The important features of a Mesh are

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Size, Sag and Order. If more precision is required the size and sag of mesh need

to be decreased.

F. Applying Advanced Restrains

An Advanced Restraint tool removes translation and rotational degrees of

freedom and blocks these points from the analysis. The Advanced Restraint

tools allow translation directions to be blocked from the analysis. The Clamp

tools is also a restraint, however it restrains all translations and rotations. The

following steps show how to apply and Advanced Restraint to fix one end of

the BeamAnalysis.CATAnalysis to simulate a cantilever beam.

F.1. Select the Advance Restraint tool as shown below.

F.2. Select the front surface of BeamAnalysis.CATAnalysis nearest the

screen. The Supports field text should now read 1 Face.

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F.3. Only the Restrain Translation 1, Restrain Translation 2 and

Restrain Translation 3 options should be selected as shown in the previous

figure.

F.4. Finally select the OK button and save the document.

G. Applying a Force

G.1. Select the Force tool. The Distributed Force window will appear

as shown below.

G.2. The Supports field should be highlighted in blue. The text will read

No Selection. Select the top surface. The Supports field text should now say

1 Face

G.3. Type “-10000N” in the Z Force Vector field. The negative sign

symbolizes that the force is applied downwards.

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G.4. Type “0N” in the X and Y Force Vector fields.

G.5. Select OK.

The force symbols appear as red arrows shown in the figure above. The

resultant force is applied to the centroid of the top surface. The Structural

Analysis work bench now has enough information to compute the analysis.

Section H: Computing

Steps below show the how the computing of displacements and stresses can be

done in GSA.

H. Compute Solution

The Static Case now has the minimum amount of restraints and loads to

Compute the Static Case Solution.1. The Steps Below Show how to Compute

the analysis

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H.1. Compute the analysis by selection the Compute tool. The

Compute window will appear.

H.2. Select the pull down arrow and select the All from the list of options.

H.3. Select the Preview option.

H.4. Select the OK button.

H.5. The Computation Resources Estimation window will appear. The

window appears because the Preview option was selected in the previous

step. If this is deselected the window would not appear and the computation

would begin after completing Step 8.4. This window is helpful because it

estimates the time and memory that the computation will take. This

machine dependent and s the numbers will be different.

H.6. Select Yes button.

Section I- J: Post-Processing

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I. Visualizing the Displacement

Upon successful computation, the image tools bar will be activated as shown in

the figure below. The Load arrows symbol will turn red to yellow. The restrains

symbol will turn from red to blue. If the computation was not successful a

singularity error most likely occurred. This is generally due to missing restraint.

Look at the displacement view by following the steps below

I.1. Select the Displacement tool.

I.2. To determine the maximum and minimum displacement of the beam, select

the Image Extrema .tool. The Extrema Creation window will appear as

shown below.

I.3. Select Global option.

I.4. Type “1” in the Minimum extrema at most and Maximum extrema at most

fields

I.5. Deselect the Local option.

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I.6. Select the OK button and save the document.

J. Visualizing the Vone Mises Stress

J.1. Select the Von Mises Stress tools to view the Von Mises Stress

distribution and the Von Mises Stress distribution color palette.

J.2. Optional: Move the cursor over any area of the part and the values for the

Von Mises Stress at each node will appear.

J.3. To determine the minimum and Maximum Von Mises Stress click on the

Image Extrema tool.

J.4. The Extrema Creation window will appear.

Section K: Mesh Refinement Iteration

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K. Changing Mesh size and Mesh Sage

K.1. Double click on OCTREE Teranhedron Mesh.1:Beam in the

Specification Tree. The OCTREE Teranhedron Mesh window will appear

K.2. Type 20mm in Size field

K.3. Type 3mm in the Absolute Sag field.

K.4. Select the OK button.

K.5. Compute the analysis another time by repeating Steps in H.1 through

H.6. If an effort occurs there is probably not enough memory; change the

mesh size to the default values.

K.6. Repeat Step I.1 through J4 to find the new maximum displacement

extrema. Thos time the there will be more displacement vectors.

Section L: Report Generation.

L. Report Generation

L.1. Select the Report Generation tool.

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L.2. The Report Generation window will appear. Select the location and

the title of the report and click OK.

L.3. A new document in HTML format will appear in the specified

directory. This document can be opened in any web browser and will give

the summary of the analysis.

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Results and Comparison with other packages

The worked example in the previous section only shows a Static analysis done on a

simple part. However CATIA V5 Generative Structural Analysis can easily be

used for analysis of complex part and assemblies. It also provides options for

Frequency Analysis along with many visualization options.

One of the most important things to remember is that the accuracy of the model

depends on size and sag of the mesh. Smaller the size of the mesh more accurate is

the results. However this also means that more processing power will be required.

There are other software packages available like Ansys that are dedicated for stress

and FEA analysis. However the GSA module provides a quick, simple and easy

way for such analysis for first time users who have never used any other software

for such analysis before.

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Reference

Cozzens, C. (2004) Advanced CATIA V5 Workbook: Schroff Development

Corporation

CATIA Companion: Dassault Systèmes