Linear BucklingI-DEAS Tutorials: Simulation Projects

This tutorial shows how to compute linear buckling loadfactors. You’ll analyze a part from an automobile jack forbuckling.

Learn how to:

• perform a buckling analysis• display buckling results

2

Before you begin...

Prerequisite tutorials:

• Introducing the I-DEAS InterfaceQuick Tips to Using I-DEAS–and–Creating Parts

• Extruding and Revolving Features• Introduction to Simulation• Free Meshing• Boundary Condition Sets• Boundary Condition Surface Loads• Boundary Condition Symmetry• Displaying Results

Recommended tutorials:

• Parameter Studies

3

Setup 1 of 5

If you didn’t start I-DEAS with a new (empty) model file,open a new one now and give it a unique name.

FileOpen

Open Model File form

Model File name: any unique name

OK

Make sure you’re in the following application and task:

Simulation

Master ModelerSet your units to mm.

OptionsUnits

mm (milli newton)

4

Setup 2 of 5

What: Create a part to the dimensions shown.

Hint

.

5

Setup 3 of 5

Save your model file. File

Save

Warning! If you are prompted by I-DEAS to save your model file,respond:

NoSave only when the tutorial instructions tell you to––notwhen I-DEAS prompts for a save.

Why:If you make a mistake at any time between saves andcan’t recover, you can reopen your model file to the lastsave and start over from that point.

Hint To reopen your model file to the previous save, pressControl-Z.

6

Setup 4 of 5

What: Delete three part faces to create an open channelsection.

Hint

Why: Thin-shell elements will be meshed on theremaining faces. Deleting the three faces makes themeshing process easier. The face delete operations arerecorded in the part history if you need to modify the partlater.

7

Setup 5 of 5

What: Name the part.

Hint

Name: Auto Jack

What: Create an FE model.

Hint

Boundary Conditions

Geometry Based Analysis Only

Recovery Point

FileSave

8

Introduction

As the car jack is loaded, this part will be incompression.

This analysis will predict the possibility that the part mayfail due to buckling.

1 2

9

Perform a buckling analysis 1 of 6

What: Restrain the edges shown.

How:

1

2 shift-pick

X Translation: constant

Y Translation: constant

Z Translation: constant

(all rotations: free)

OK

Continued on next page...

10

Perform a buckling analysis 2 of 6

3

4 shift-pick

3

4

X Translation: constant

all other rotations/translations: free)

OK

Why: Restraints used here are a simplification for thisanalysis. The X restraint at edges 3 and 4 simulates abolt and a bushing in the hole.

11

Perform a buckling analysis 3 of 6

What: Apply edge forces.

Hint

1

2 shift-pick

Total Force

In Plane Force: 4.3E6

12

Why: The load in the member is calculated as:

600 Kg x 9.8 / sin(20) / 2 = 8600 NApplied load per edge = 8600 N / 2 = 4.3E6 mN

600Kg

12

Perform a buckling analysis 4 of 6

What: Create a boundary condition set containing therestraints and loads.

Hint

Linear Buckling

Restraint Set

Load Set 1

OK

What: Create a thin shell physical property.

Hint

Meshing

Thicknesses: 1.2

13

Perform a buckling analysis 5 of 6

What: Mesh the surfaces.

Hint

All

Element Length: 3

Free Options...Curvature Based Length

None

Why: Curvature Based refinement is set to None to limitthe number of elements used on the curved surfaces.

OK

Modify Mesh Preview form

Keep Mesh

Recovery Point

FileSave

14

Perform a buckling analysis 6 of 6

What: Solve the model using linear buckling analysis.

Hint

Model Solution

Create...

Type of Solution: Linear Buckling

Options...

Solution Control...

OK

OK

Output Selection...

OK or Dismiss (all forms)

Things to notice The default is to compute the first three buckling shapes,and to store only the shape.

15

Display buckling results 1 of 2

What: Display the buckling shapes.

Hint

Create Display form

OK

Things to notice The buckling load factor is listed in the header of theplot. A value of 2.5 means that the structure wouldbuckle if the applied load was multiplied by (2.5).

Mode shapes are simply shapes. The relative sign ofthese shapes is arbitrary. The actual direction of bucklingis determined by whether the calculated buckling load isslightly above or below the actual load. Because therelative sign for a shape can vary, your buckling shapesmay be the negative of those shown here.

16

Display buckling results 2 of 2

What: Display the other buckling shapes.

Hint

Close (Visualizer)

Things to notice Buckling shapes are similar to dynamic mode shapes.This is the shape the structure would begin to buckle.Because this is a linear analysis, nothing can be statedabout what happens after the structure begins to buckle.

Recovery Point

FileSave

17

On your own... 1 of 6

Buckling load factors may be sensitive to thickness orpart dimensions which may vary due to manufacturingtolerances. Performing a parameter study is an effectiveway to examine buckling sensitivity to designparameters.

If you haven’t completed the tutorial “ParameterStudies,” you may want to review it before tryingthe following steps.

What: Perform a parameter study to show how thebuckling factors change as the thickness is decreased.

Hint

Optimization

Create...

Parameter Study

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On your own... 2 of 6

Create...

Type of Solution: Linear Buckling

Number of Positive Steps: 0

Create...

Design Parameter Type: Physical

Original Value: 1.2

Step Size: 0.2

Select Geometry

All

Surface

OK

Dismiss

19

On your own... 3 of 6

0.72

2.9

1.0

1.5

2.0

2.5

0.80 1.2 0.90 1.0 1.1

Things to notice The Y axis is the buckling load factor for values ofthickness on the X axis. A relatively small decrease inthickness can cause the buckling load factor to dropbelow 1. This may be a factor in defining the allowabletolerance on the sheet metal thickness.

20

On your own... 4 of 6

What: Perform a second parameter study to show howthe buckling factor changes as the vertical dimension isvaried in either direction.

Hint

Total Number of Steps: 5

Create...

Design Parameter Type: Geometry

Select Dimension

Show Dimensions

1

1

Step Size: 5.0

21

On your own... 5 of 6

Things to notice Buckling load factors decrease as the height isincreased from its initial value because there’s lessstiffening effect from the bend. Also, the way the problemis modeled, the center of the load moves down as theside wall dimension increases.

0.97

4.3

2.0

3.0

4.0

10.0 30.0 15.0 20.0 25.0

Things to notice When the dimension is decreased below a certain point,the lowest buckling load factor suddenly decreases. Thisis because the lowest buckling mode is then a differentshape, as shown on the next page.

22

On your own... 6 of 6

Things to notice Buckling is not always very intuitive. Performing aparameter study may uncover surprising results.

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Tutorial wrap-up

You have completed the Linear Buckling tutorial.

You can delete or put away the FE model and the part.This part is not used in any other tutorials.

Hint

What’s next?Other tutorials introduce different element types andsolution methods.