nonlinear2_7

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2.7-1

BASIC

ANALYSIS

Slide Line - Hertz Contact Stress

2.7


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Slide Line - Hertz Contact Stress2.7-2


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BASIC

ANALYSIS

2.7-3

Model Description:

The Hertz contact stress problem provides a good example for 3-D slide line contact. The completemodel data has been provided and the model is ready for analysis. However, the example will con-

centrate on looking in detail at the modeling requirements and slideline definition.

Before proceeding with the example, we will look at some general aspects of slide line modeling

and analysis, then review the procedure for setting up a slideline model referring to the entries

already defined in the Hertz contact stress model.

Overall Considerations

Slideline contact is always performed as a nonlinear analysis, either static or transient dynamic

methods can be used.

The slideline is always defined in the XY plane of the basic or local coordinate system that is

referenced by the element property definition.

The definition of the master and slave segments is for naming purposes only, except in the case

of unsymmetric penetration. In this case only slave nodes are checked for penetration into mas-

ter segments.

The slide line is aligned with the referenced coordinate system z-axis, by applying the right

hand rule when selecting master and slave nodes.

Initial penetration cannot be modeled with a slide line.

Symmetrical penetration is more accurate, but also more computationally intensive than unsym-

metrical penetration.

Enforced displacement may yield better convergence than applied loads (not applicable with

nonlinear transient analysis).

Error messages concerning initial penetration, even if not modeled, or displacements in a rigid

body mode, indicate improper ordering of master and slave nodes. Check that the right hand

rule law mentioned above has been observed.

The model comprises a sphere of radius of 6 mm, modeled as a 10-degree segment of a semi-sphere

using solid elements, with the appropriate boundary conditions applied. The material is assumed to

be an isotropic high strength steel with a Youngs Modulus of 210,000 N/mm 2, and a Poissons

Ratio of 0.3. The rigid plane is modeled using plot elements, the nodes of which are completely

constrained - the slide line elements are used to model the contact behavior in this case.


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Exercise Procedure:

1. Start MSC/NASTRAN for Windows 3.0.2 by double-clicking on the MSC/NASTRAN forWindows icon.

For this exercise, you will select the New Modeloption.

The bulk of the model data already exists in the form of a FEMAP neutral file. The file can be

imported into the database from the examples directory.

Your view screen should look similar to the following:

Open Model File: New Model

File/Import/FEMAP Neutral...

File name; hertz.neu

Open

OK

View/Select...

Model Style: Draw Model

Model Data...

Group: Select

Group: 5..sphere + plate

OK

OK

View/Rotate...

Dimetric

OK


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BASIC

ANALYSIS

2.7-5

2. Review the slide line definitions.

While we have all of the model data already defined, the initial step would be to create the basic FE

model without the slide line data. In this case the basic model data are the nodes, solid elements that

form the segment, and symmetry and boundary condition constraints.

The plane of contact of the slide line must be the XY plane of a coordinate system (basic or local),

this usually requires that one or more local coordinate systems have to be set up. In this case there

are two local coordinate systems, numbers 3 and 4, that have been defined such that their XY

planes correspond to the two planar sides of the segment.


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3. View the slide line properties.

The next items that should be defined are the slide line properties (Model | Property, set Elem/Prop-

erty Type).

To view the slide line properties that have been defined in this model do the following:

In this case unsymmetrical penetration has been selected, and the relevant local coordinate system

has been referenced in the Slide Line Plane box.

Once the properties have been defined, the slide line elements themselves can be defined (Model |

Element, set Type to Slide Line).

To view the slide line elements that have already been defined in this model (Element 447and

448), do the following:

Modify/Edit/Property...

ID: 4

OK

OK

Modify/Edit/Element...

ID: 447

OK


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BASIC

ANALYSIS

2.7-7

This dialog box is used to define the master and slave nodes that form the slide line, it also refer-

ences the slide line property definition. In this model the slide line elements have already been

defined, notice on both the Master Nodes and Slave Nodes buttons the word (On) appears. If you

click on either of these buttons you can see the nodes that have been defined as master and slave

nodes.

As mentioned before, the master and slave nodes have to be selected in a direction that corresponds

to the z-direction of the referenced local coordinate system by applying the right hand rule.

Master Nodes... (On)

OK

Slave Nodes... (On)

OK

Cancel


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To view the slide line elements do the following:

The following figure should appear on your view screen.

View/Select...

Model Data...

Group: Select

Group: 4..slide lines

OK

OK


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BASIC

ANALYSIS

2.7-9

4. Apply the load.

The loading is modeled as a single force acting on the central node of the sphere. This node is the

independent node of two rigid elements connecting all other nodes of the upper plane of the model

as dependent nodes with respect to the global z-displacement.

The load has already been defined as a single force of -50 N (in the z-direction), which corresponds

to an equivalent load of 1800 N for the whole sphere. The load is created using the Model | Load

menu.

The rigid elements (Element 445and 446) have also been defined. They are created using the

Model | Element menu, with Type set to Rigid.

They can be viewed in this model by doing the following:

5. Set the nonlinear solution parameters.

Modify/Edit/Element...

ID: 445

OK

OK

Model/Load/Nonlinear Analysis...

Solution Type: Static

Defaults...

Number of Increments: 5

Intermediate: 3..ALL


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Further changes in the nonlinear solution parameters are possible, like choosing different solution

strategy overrides, but are not necessary in most cases. For certain types of problems however, the

default settings may lead to solutions not converging.

6. Analyze the model.

OK

File/Analyze...

Analysis Type: 10..Nonlinear Static

Additional Info: Large Disp

Output Types: 2..Displacements and Stresses


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BASIC

ANALYSIS

2.7-11

When asked, "OK to Save Model Now?, select Yes.

Save the new file under a temporary (TEMP) directory.

When asked, OK to read direction cosines for solid element principal stresses?, select Yes.

When asked, OK to read solid element corner stresses?, select Yes.

When the MSC/NASTRAN manager is through running, MSC/NASTRAN will be restored on

your screen, and the Message Review form will appear. To read the message(s), you could select

Show Details. Since the analysis ran smoothly, we will not bother with the details this time.

7. Process the results.

OK

Yes

File name: Slide_Line.mod

Save

Yes

Yes

Continue

View/Select...


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Display the entire model back onto the view screen.

The resulting display will have an exaggerated displacement plot. Modify the fringe plot by doing

the following:

Model Style: Quick Hidden Line

Deformed Style: Deform

Contour Style: Contour

Deformed and Contour Data...

Output Set: 5..Case 5 Time 1.

Deformation: 1..Total Translation

Contour: 600031..Solid VonMises Stress

OK

OK

View/Select...

Model Data...

Group: Select

Group: 5..sphere + plate

OK

OK

View/Rotate...

ZX Front

OK

View/Options...

Category: PostProcessing

Options: Deformed Style

% of Model (Actual)


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BASIC

ANALYSIS

2.7-13

Your view screen should display the following figure.

8. Finally, exit the program when you are done.

When asked if you wish to save the model, select Yes.

OK

File/Exit

Yes


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