107 - Understanding Contact Analyses.pdf

8/14/2019 107 - Understanding Contact Analyses.pdf

1/15

StructuralAnalysisIIUnderstandingContactAnalysesLecture

UnderstandingContactAnalyses.mp3

Understanding Contact Analyses

Contact Analysis enable you to study how Contact Interfaces behave

when subjected to Loads and Constraints.

Contact Analysis: Inputs

Loads/Constraints typical to Static Analysis No Prescribed Displacements in Cylindrical/Spherical coordinate systems Contact Interfaces Include Contacts option

Contact Analysis: Outputs

Stresses, Deformations, and so on typical to Static Analyses Measures

o Total Contact Areao Maximum Contact Pressureo Slippage


2/15

Model for Contact Analysis

LectureNotes

Contact Analysis

Use Contact Analysis and Contact Region interfaces to model surfaces or components

that may either separate from, or come into contact with each other.

In a contact analysis, the relation between the load applied to the model and theresulting deformations and stresses is not linear. The changes in contact area becomenonlinear as the load increases, because the contact area depends on the deformation

of the model.

Contact Analysis Input

There are several requirements for the Contact Analysis:

This type of analysis enables any type of loading and constraints that you wouldtypically define for a Static Analysis.

Prescribed displacements defined in Spherical and Cylindrical coordinatesystems are not supported.

Contact Interface(s) must be defined to indicate the curves or surfaces on whichMechanica considers the effect of load during a Contact Analysis. You must usea Contact Interface between components when:


3/15

o You want the components to have the freedom to remain separate fromeach other.

o You want the components to transfer forces when they come in contactwith each other.

A Static Analysis must be defined and the Nonlinearand Include Contactscheck boxes must be selected.

Contact Analysis Output

During a Contact Analysis, Mechanica calculates the total contact area of all contactsin your model and the maximum contact pressure over all the contacts. Also,Mechanica checks if slippage has occurred in the contact region. Besides all thesemeasures, Mechanica computes stresses, deformations, and other typical Static

Analysis measures.

A Contact Analysis takes longer to run than a typical Static Analysis because its ageometrical non-linear analysis. Mechanica calculates results in several iterative steps.

The numerical iterations stop when the analysis reaches the convergence orMechanica performs maximum number of iterations. The minimum number of

iterations is 1 and the maximum number of iterations is 200 by default.

Best Practices

Mechanica includes both frictionless contacts and contacts with infinite friction inthe Contact Analysis. This is important to understand because if there isfrictionless contact (that is, no friction force is developing), Mechanica needs tocounteract the sliding effect to avoid insufficiently constrained models. If youselect Single-Pass Adaptive for the convergence method, you can use theLocalized Mesh Refinement option to improve the accuracy of contact pressure

results. You should select this item only if accurate contact pressures are animportant objective for the analysis.

UnderstandingContactAnalysesDemonstrationUnderstandingContactAnalyses_demo.mp4

UnderstandingContactAnalysesProcedureProcedure: Creating Contact Analyses

ScenarioIn this procedure, you will define a Static Analysis including contacts in a Pro/ENGINEER

assembly model for which loads and constraints were already created and defined.


4/15

CreateContact contact.asm

Task 1.Open the Mechanica Application, investigate the model and existingMechanica Simulation Features, and define a Static Analysis that includes contacts.

1. Click Applications > Mechanica.

2. Explore and examine the model. From the top of the model tree, click Show >

Expand All.

Note the existing Mechanica simulation features including:

Material Assignments Loads and Constraints Two Contact Interfaces and their associated Measures (force and area

for each)

3. Click Mechanica Analyses/Studies from the main toolbar.

4. Click File > New Static....

5. In the Name field, type Contact_Bolt.

6. Verify that the TOP_SHELFconstraint is selected in the Constraints area of the

dialog box.

7. Verify that the PULLload is selected in the Loads area of the dialog box.

8. Select the Nonlinearcheck box, then select the Include Contactscheck box.

Note: If you choose not to include the Contact Regions for the Static

Analysis the components will act bonded, which is the default connection

between mated Pro/ENGINEER parts. In the case where the components are

physically offset from each other, and no Contact Regions are defined (or

even if defined but not included), then the model may fail as insufficiently

constrained. This is because the load cannot be transferred properly from

the application to the supports (constraints) in the model.

Contact Regions interfaces are not taken into account when running a Modal

Analysis.

9. Select the Convergencetab and verify that the Method drop-down list is set toSingle-Pass Adaptive.

10. Verify that the Localized Mesh Refinementcheck box is not selected.


5/15

Note: It is recommended to run the Contact Analysis first without this option

and then based on the information from the Mechanica solver, update and

rerun the analysis. The solver will present a warning and proper action is

needed as recommended in the notes of the analysis summary report.

11. Select the Outputtab and verify that the Stresses, Rotations, and Reactionscheck boxes are selected, and that Plotting Grid is set to 4.

12. Select the Load Intervalstab. Use the default settings.

Note: You can specify the load intervals at which Mechanica calculates

results, enabling you to see how measure values vary with the load. If

Mechanica permitted loads on design variables, this would be equivalent to

performing a Global Sensitivity Design Study with a design variable for the

load.

13. The dialog box should now appear as shown in the figure. Click OKto complete

the Static Analysis Definition and close the dialog box.


6/15

Task 2.Save the model and erase it from memory.

1. Return to the Standard Pro/ENGINEER mode by clicking Applications > Standard.

2. Click Save from the main toolbar and click OKto save the model.

3. Click File > Erase > Current > Select All > OKto erase the models frommemory.

This completes the procedure.

UnderstandingContactAnalysesExerciseExercise: Contact Analysis


7/15

Objectives

After successfully completing this exercise, you will be able to:

Set up and define Contact Regions. Evaluate Contact Pressure and Contact Area measures using the analysis summary

report and result window fringe plots.

ScenarioIn this exercise you will use Mechanica to evaluate the Contact Area and Contact Pressurevalues between two components that interact with each other along a contact location. Acharacteristic of the Contact Analysis is that the load is being transferred from one

structural component to another by contact instead of by the typical bonded connection.

ContactExer lever_contact.asm

Task 1.Open the Mechanica application, explore the existing Mechanica simulationfeatures, and define a contact region.

1. Click Applications > Mechanica.

2. Explore and examine the model. From the top of the model tree, click Show >

Expand All. Scroll to the bottom of the model tree and review the existingMechanica simulation features.

Examine the Pro/ENGINEER model and note that the transfer of load is

occurring at the interface between the clip and the support part. Also note

that one of the parts is composed of imported geometry, in this case a solidSTEP part file. You can perform Mechanica analysis on any solid (or surface

if you plan to use Shell idealizations) native to Pro/ENGINEER or imported

3D/2D data.


8/15

Examine the Mechanica simulation features defined in the model closely. The

models are connected together by a spoke-wheel pattern of Beam elements

simulating a hinge joint. Each of these Beams has large cross-section and

material properties (Youngs Modulus). The reason for this approach is to

ensure that the hinge is the only one being simulated and that the beams do

not develop any stresses or deformations. If desired, edit any of the Beam

elements and identify these properties. The load is applied such that the

STEEL clip is pushing towards BRONZE support plate while the entire bottom

surface of the support plate is fully constrained.


9/15

3. Click Interface and select Contactfrom the Type drop-down menu.

Note: Whenever possible, a best practice is to define contact regions

between surfaces instead of components. If you select components, you

may have extra contact regions which may not ever interact when subjectedto your loads and constraints. However, the solver will always have to take

these into account, even if the contact pressure is zero, and this can

considerably increase your analysis run time.

4. For the first reference, select the curved surface from the IMPORTED_STEP.PRT

component as shown in the figure.

5. For the second reference, select the top flat surface of the SUPPORT.PRT componentas shown in the figure.

6. The dialog box should now appear as shown in the figure. Click OKto complete the

Interface Definition and close the dialog box.

Note that Mechanica has automatically created measures, listed in the model

tree, to track the area and force in the contact interface.


10/15

Task 2.Define and run a Contact Analysis.

1. From the main toolbar, click Mechanica Analyses/Studies .

2. Click File > New Static....

3. In the Name field, type CONTACT_3D.

4. Verify that the HOLDconstraint is selected in the Constraints area of the dialogbox.

5. Verify that the PUSHload is selected in the Loads area of the dialog box.

6. Select the Nonlinearcheck box, then select the Include Contactscheck box.

7. The dialog box should now appear as shown in the figure.


11/15

8. Select the Convergencetab and select the Localized Mesh Refinementcheckbox as shown in the figure.

As a general rule, you should only select the Localized Mesh Refinement

option if accurate contact pressures are an important objective for the

analysis.


12/15

9. Select the Excluded Elementstab and select the Exclude Elementscheck box asshown in the figure.

You are making use of the Exclude Elements option due to the stress

singularities that the Point-Point Beam elements bring in the model. This

option assists you in avoiding a non-converged solution for this scenario.

10. Click OKto complete the Static Analysis Definition and close the dialog box.

11. Verify that CONTACT_3Dis still selected in the Analyses and Design Studies

dialog box and click Start Run > Yesto start the design study.

12. Click Display Study Status once the analysis is started.


13/15

Task 3.Review the results of the analysis, save the model, and erase it frommemory.

The analysis should complete in 5060 minutes. If you do not have time to

wait for this analysis to complete, use the results in the Completedirectory

for the remainder of the exercise.

1.1. When the analysis has completed, review the information in the Run Statusdialog box. In particular note the following results:

Note that localized mesh refinement has increased the total number of elements byapproximately 40%.

Mechanica reports the values of the measures specifically created for the contactarea: Interface1_area and Interface1_force.


14/15

Although it is a Contact Analysis, Mechanica also reports other measures

typical to a regular Static Analysis such as Von Mises stress, max

displacement, and so on.

2. Click Closeto close the Run Status window.

3. Click Closeto close the Diagnostics window.

4. Click Closeto close the Analyses and Design Studies dialog box.

5. Click Results from the main menu.

6. Click Result Window .

7. Double-click the Completedirectory to view its contents. Select the CONTACT_3Dresults and click Open.

If you have completed the analysis, you can use the CONTACT_3D results

directly in the ContactExer folder instead of the CONTACT_3D results in the

Complete folder.

8. Type CONTACT_3Din the Name field and Contact Pressure Resultsin the Titlefield.

9. Verify that the Display Type drop-down menu is set to Fringe.

10. From the first drop-down menu on the Quantity tab, select Contact Pressureandverify that the units field is set to MPa.

11. Select the Display Optionstab and select the Deformedcheck box.

12. Click OK and Showto finish the Results Window Definition and show the results.

Note that for a Contact Pressure fringe plot, Mechanica strips down the solid

geometry display and shows only a fringe plot of the surfaces in contact.

Additional mesh refinement is required for a smoother fringe plot display.

13. When you are finished reviewing the results, click File > Exit Results > Notoexit the Result Window without saving any results.


15/15

14. Return to the Standard Pro/ENGINEER mode by clicking Applications >Standard.

15. Click Save from the main toolbar and click OKto save the model.

16. Click File > Close Window.

17. Click File > Erase > Not Displayed > OKto erase the model from memory.

This completes the exercise.

Documents

107 - Understanding Contact Analyses.pdf