Panel Buckling

MSC.Nastran 2007 r1 Implicit Nonlinear (SOL 600) User’s Guide510

Panel Buckling

Problem StatementThis problem illustrates the nonlinear post-buckling analysis of a curved panel. This simulationhighlights several SOL 600 capabilities including large displacement, material plasticity, and contactbetween multiple deformable bodies.

The Structure and its ApplicationPanels constructed from thin sheets reinforced with stiffeners are commonly used in many industries.In order to keep these panels light, the thin sheet (skin) is often designed to be thin and allowed tobuckle elastically at relatively low levels of compressive loading. Once the skin buckles, thecompressive load distribution changes in the panel, and any additional load is carried mostly by thestiffeners. The final failure load is reached when the overall panel fails due to a combination of materialyielding and instability.

MSC.Nastran SOL 600 provides the capabilities required to simulate this panel post-buckling behavior.

Model DescriptionThe model consists of a stiffened panel approximately 14” by 22”. The skin is constructed fromaluminum and has a slight curvature. A longitudinal Z stiffener is attached to the skin by a single row ofrivets. The stiffener has a joggle in it, and a doubler is used to fill the gap between the stiffener and theskin. Two additional longitudinal doublers are attached to the outside edges of the skin.

This model was originally constructed in metric units and was converted to English units. As a result ofthe conversion, some of the dimensions are rounded off.

Main IndexMain Index

511CHAPTER 13SOL 600 Example Problems

Geometry and Contact RegionsThe skin, stiffener, and doublers are all modeled as shell elements located at the mid-surface of thesecomponents. The gap between two components is equal to half the thickness of one component plus halfthe thickness of another component. These components are allowed to contact each other.

Finite Element and Contact ModelThe skin, stiffener, and doublers are modeled using CQUAD4 elements. The element properties aredefined using PSHELL entries.

The rivets are modeled using CBAR elements. The element property is defined using the PBAR entry.

The three doublers are modeled as three deformable contact bodies. The stiffener lower flange is definedas a deformable contact body. The skin is in contact with several components. Each contact area withinthe skin is defined as a deformable contact body.

An RBE2 rigid body element is used to connect all the nodes on one end of the panel to a single node.This node is used to apply the panel loading.

MaterialThe skin and doublers are made of aluminum alloy 2024 which is modeled as an elastic-plastic materialusing MAT1 and MATEP entries. The stiffener is made of aluminum alloy 7349 and is also modeled asan elastic-plastic material using MAT1 and MATEP entries. The plastic stress-strain relationships aredefined by pairs of stress-strain values using TABLES1 entries.

Loading and Boundary ConditionsAll the nodes on one end of the panel are fixed in all six degrees of freedom. At the other end of the panel,an RBE2 rigid body element connects the nodes to a single node, and an enforced displacement of 0.28”in the longitudinal direction is applied to this node.

The longitudinal edges of the panel are fixed in the lateral directions but are free to slide in thelongitudinal direction.

Solution Procedure and ControlsA nonlinear static analysis is performed to determine the capability of the panel to support a compressiveload. PARAM,LGDISP,1 is specified to activate the large displacement capability.

The NLPARM and NLSTRAT entries are used to specify the nonlinear analysis iteration strategy. 40fixed time increments are specified for this problem. Output requests are made for stress and strain usingthe MARCOUT entry. These results are included in the t16 output file.



Solving the ProblemThe panel post-buckling problem is designed to be constructed and setup using MSC.Patran and analyzedusing MSC.Nastran SOL 600. A MSC.Patran database is provided which contains the complete finiteelement model. A MSC.Nastan Bulk Data file (bdf) is exported and then run with MSC.Nastran. Analysisresults can be accessed in text format or viewed from inside MSC.Patran.

Input Files Required• stiffened_panel.db - MSC.Patran database containing the panel finite element model.

Recreating the Problem using MSC.PatranStep-by-step instructions for creating and running the analysis on the panel buckling model can beaccessed by linking to the Panel Buckling Modeling Instructions file below. Once you are done creatingthe model and running the SOL 600 analysis, proceed by accessing the results file to generate visualdisplays of the analysis results.

Click here for Panel Buckling Modeling Instructions


513CHAPTER 13SOL 600 Example Problems

Highlighted Sections of the MSC.Nastran Bulk Data File

Plasticity

Contact

Large Displacement



Inspecting the Results

Results PlotsThe plot below shows the final deformation of the panel.

The plot below shows a graph of the total longitudinal reaction force vs. time increments.


The 2005 New Template

Panel Buckling Modeling InstructionsDemonstrated:� Set up the Model Database 16� Examine the Model and Loading Conditions 18� Set up the Analysis 27� Review the Results 35

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Set up the Model DatabaseIn this example you will open an existing MSC.Patran database that contains the panel model, boundary conditions, and loading definitions.

To open a new MSC.Patran database:Step 1: On the File menu, click Open.

Step 2: Navigate to the directory containing the Stiffened_Panel.db file.

Step 3: Click once on Stiffened_Panel.db and click OK.

17CHAPTERPanel Buckling Modeling Instructions

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Examine the Model and Loading ConditionsTo review Loads and Boundary Conditions:

Use the following instruction to review the imported model:• Click and hold down the scroll wheel button on the mouse to rotate the model.• Click any of the view buttons to review the model in different views.

Things to consider about the model***• This model contains shell elements and bar elements.• Boundary Conditions have been applied as shown.• The compressive load is applied as an enforced displacement of 0.28 inch applied to an

RBE2 that spans the free end of the panel.


To examine the model:Step 1: On the Group menu, click Post...

Step 2: In the Select Groups to Post list, click once mat_2024T3, and click Apply to post.

Step 3: To review all the model, select different groups in the Select Groups to Postmenu, and click Apply to post the different groups.

Note: By posting the different groups, understand how the panel is assembled.

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To examine the Stress-Strain Curves:Step 1: On the MSC.Patran Main toolbar, click the

Fields button.

Step 2: From the Fields menu, select the following options:• Action: Select Show.• Select Field to Show: Select 7349_marc.• Click Specify Range...

Step 3: From the Specify Range menu, select the following options:• Use Existing Points: Select Check box.• Minimum: Enter 0.0.• Maximum: Enter 0.1.• No. of Points: Enter 15.• Click OK.

Step 4: On the Fields menu, click Apply.


Examine the Stress-Strain Curve.

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Step 5: Repeat Steps 1 through 4, except in Step 2, in the Select Field to Show list, click once 2024_marc.

Note: The 2024 curve has an additional data point at a strain of 0.997 which is not shown on this plot.


To examine the Contact Bodies:

Step 1: On the MSC.Patran Main toolbar, click the Loads/BCs button.

Step 2: From the Loads/BCs menu, select the following options:• Action: Select Plot Markers.• Assigned Load/BCs Sets: Select

Conta_db1a.• Select Groups: Select default_group.• Click Apply.

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Step 3: Examine the Contact Bodies. Circles will be drawn showing the contact.


Step 4: Repeat Steps 1 through 4, except in Step 2, select the remaining contact bodies for the Assigned Load/BCs Sets list.

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Set up the AnalysisTo set up the Analysis:

Step 1: On the MSC.Patran Main toolbar, click the Analysis button.

Step 2: From the Analysis menu, select the following options:• Action: Select Analyze.• Object: Select Entire Model.• Method: Select Full Run.• Available Jobs: Select SOL600-

Stiffened_Plate.• Click Solution Type...

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Step 3: From the Solution Type menu, note that the Solution Type is set to Implicit Nonlinear.

• Click OK.

Step 4: On the Analysis menu, click Subcases...


Step 5: From the Subcase menu, select the following options:• Action: Select Create.• Available Subcases: Select Default.• Analysis Type: Select Static.• Click Subcases Parameters...

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Step 6: From the Static Solution Parameters menu, select the following options:.• Linearity: Select NonLinear.• Nonlinear Geometric Effects:

Select Large Displacement/Large Strains.

• Follower Forces: Uncheck the Check box.

• Follower Loads: Select No Follower Loads.

• Click Load Increment Params...

Step 7: From the Load Increment Parameters menu, select the following options:• Increment Type: Select Fixed.• For the [Number of

Increments:]: Enter 40.• [Total Time:]: Enter 1.0.• Automatic Cutback: Check the

Check box.• Number of Cutbacks: Enter 10.

• Click OK.

Note: If you are not sure about what to use, the default “Adaptive” setting is a good place to start.


Step 8: On the Static Solution Parametersmenu, click Contact Table... and select Global Contact Detection:Default(by body #).

• Click OK.

Note: By default, all bodies are allowed to touch each other.

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Step 9: On the Static Solution Parameters menu, click OK.

Step 10: On the Subcases menu, click Output Requests...

Step 11: On the Output Request menu, click SelectNodal Results...

Step 12: From the Select Nodal Results menu, select the following options:• Available Result Types: Select

CONTACT NORMAL STRESS.• Click OK.

Step 13: On the Output Request menu, click Select Element Results...


Step 14: From the Select Element Results menu, select the following options:• Available Result Types: Select

STRESS COMPONENTS.• Click OK.

Step 15: On the Output Results menu, click OK.

Step 16: On the Subcases menu, click Apply.

Step 17: On the Message menu, click Yes to overwrite the existing subcase.

Step 18: On the Subcases menu, click Cancel.

Step 19: On the Analysis menu, DO NOT click Apply. Since the job takes about 30 minutes to run, the completed analysis results are included and ready to be attached.

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Review the ResultsTo attach the results:

Step 1: From the Analysis menu, select the following options:• Action: Select Access Results.• Object: Select Attach T16/T19.• Method: Select Results Entities.• Click Select Results File...

Step 2: Navigate to the directory containing the Stiffened_Panel.db file and select it.• Click OK.

Step 3: On the Analysis menu, click Apply.

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To review the results:Step 1: On the MSC.Patran Main toolbar, click the

Results button.

Step 2: From the Results menu, select the following options:• Action: Select Create.• Object: Select Quick Plot.• Select Result Cases: Select

A1:Incr=1,Time=0.02500.• Select Fringe Result: Select

Displacement, Translation.• Select Deformation Result: Select

Displacement, Translation.• Click Apply.


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Step 3: Repeat Steps 1 through 4, except in Step 2, select the remaining increments one by one for the Assigned Load/BCs Sets list to review the results.


Step 4: From the Results menu, select the following options:• Action: Select Create.• Object: Select Fringe.• Select Result Case(s): Select

A1:Incr=40,Time=1.00000.• Select Fringe Result: Select Stress,.• Click Apply.

Step 5: Repeat Step 4, except change layer by clicking Position...((NON-LAYERED)).

Step 6: On the Select... menu, click At Layer 1 and click Close.

Step 7: On the Results menu, click Apply.

Note: By going through Steps 4 through 6, you can plot the von Mises stress at different layers.

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Step 8: Repeat Steps 4 through 6, except in Step 6, click Layer 5 from the list.


Step 9: To examine panel longitudinal compressive stresses, from the Results menu, select the following options:• Action: Select Create.• Object: Select Fringe.• Select Result Case(s): Select

A1:Incr=1,Time=0.02500.• Select Fringe Result: Select Stress,.• Click Position...((NON-LAYERED)).• Quantity: Select Y Component.• Click Apply.

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Step 10: Repeat Step 9, except select the remaining increments one by one for the Select Result Case(s) list to understand how the compressive load is redistributed after the initial skin buckling.


Step 11: To examine panel longitudinal compressive stresses, from the Results menu, select the following options:• Action: Select Create.• Object: Select Graph.• Method: Select Y vs X.• Select Result Case(s): Select all the

increments (A1:Incr=0,Time=0.00000 through A1:Incr=40,Time=1.00000).

• Select Y Result: Select Force, Nodal Reaction.

• Click Position...((NON-LAYERED)).• Quantity: Select Z Component.• X: Select Global Variable.• Variable: Select Time.• Click the Target Entities Icon.

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Step 12: From the Results menu, select the following options: • Target Entities: Select Nodes.• In the Select Result Case(s) box, click on

node where the enforced displacement is applied (Node 3277).

• Click Apply.


Step 13: On the MSC.Patran Main toolbar, click the XY Plot button to adjust the scales and grid lines.

Note: This plot shows the panel loading history. The panel ultimate strength is obtained from this graph.

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Panel Buckling