© 2015 ESRD, Inc. All Rights Reserved. StressCheck® is a registered trademark of ESRD, Inc.

Interference Fit Bushing + SIFs

Eric Buettmann

ESRD, Inc.

2015

StressCheck Example Outline

Generate model for bearing-loaded interference

bushing with thru-thickness crack

• Create parametric solid geometry for the plate and

bushing

• Construct a parametric surface to represent a thru

crack face

• Create contact zones for the bushing and plate

• Generate an Automesh for the plate and bushing

• Assign load and constraint attributes

Bearing load on bushing

Apply built-in and spring constraints

• Solve linear by p-extension

• Post-process

Extract SIFs

Compare SIF distributions between three

different levels of interference between the

bushing and plate.

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Problem Definition

We want to extract

stress intensity

factors (SIF’s) from a

thru-thickness crack

that has formed at the

edge of a hole with an

interference fit

bushing that bears a

10 kip bearing load.

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Parameters and Geometry

Start StressCheck

SC Model Info

• Create parameters: a = 0.125, Bh = 1, Bid = .75,

Dh = 1, F = 10,000, PLw = 8, PLh = 4, PLd = 1, RadInt = .001, Bod = .875 > Accept

SC Input > Geometry tab

• Create > Box > Locate > Solid depressed > Check Input Box > Complete fields as shown in the image.

• Create > Cylinder > Locate > Solid depressed > Check Input Box > Complete fields as shown in the image.

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Parameters and Geometry

SC Input > Geometry tab

• Create > Body > Bool-Subtract >

Select the box then the cylinder >

Accept. This body will represent our plate with

a hole.

• Create > Cylinder > Locate > Solid

depressed > Check Input Box >

Complete fields as shown in the

image with Radius = Bod/2 + RadInt. Repeat with Radius = Bid/2 > Accept

• Create > Body > Bool-Subtract >

Select the larger cylinder, then the

smaller cylinder > Accept This new body will represent our bushing.

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Parameters and Geometry

SC Input > Geometry tab

• Create > Plane > Locate, X=0, Y=Dh/2+a/2,

Z=PLd/2, Width=PLd, Height=a, Rot-X=0,

Rot-Y=90, Rot-Z=0, P1-P2 min/max

unchecked > Accept.

This plane will be used to represent our

crack face

• Create > Body > Bool-Union> Select the

plate, then the plane > Accept

SC Input > Mesh tab

• Create two contact zones by selecting:

Create > Contact Zone > Surface

Click on the cylindrical surface of

the hole, then Accept.

Click on the outermost cylindrical

surface of the bushing, then

Accept.

Wireframe view

shown for clarity

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Automatic Meshing (Automesh)

SC Input > Mesh tab

• Global Mesh for Bushing and Plate:

Create > Mesh > Auto, select bushing and

plate, Accept (use defaults).

Turn on the wireframe view to access the

rectangular crack face and create the local

mesh record:

Create > Mesh > Crack Face. Select the

rectangular surface representing the crack, then

Accept.

• While still in wireframe view mode, turn off

the display of surfaces and then

Create > Mesh > Bndry.Layer, Ratio: 0.063,

Layers: 2, To: 0.05*a, T-Total: 0.25*a. Click on

the crack front curve, then Accept.

• Click on the Automesh button. Ignore any

warnings.

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Crack Face

Wireframe

Crack Front

Surface View Toggle

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SC Input > Material tab

• Define > Linear > Selection, Browse to the

StressCheck Material Library and Select 2014-T6

Extrusion > Accept.

Repeat process for TI-6AL-4V Plate (RT)

• Switch to Assign Tab > Select > Mesh Region >

Selection > Select the Aluminum record, change

the color to Aluminum and Select the plate body >

Accept.

• Repeat by selecting the Titanium record, change

the color to Titanium and select the bushing

body> Accept.

SC Input > Load Tab

• Select > Any Surface > Bearing

ID: Load, Direction: Mag./Dir., System:

SYS1, Magnitude: F, Angle = Zo = 0 >

Accept.

• Toggle on loads to confirm the load has been

applied correctly (surface changes green, arrows

appear).

Material and Loading

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Constraints

SC Input > Constraint tab

• Select > Any Surface > Built-In, ID:

Const, Select side of plate opposite the

direction of the bearing load > Accept

• Select > Any Surface > Symmetry, ID:

Const, Select one of the end surfaces of

the bushing > Accept.

• Select > Any Surface > Spring-Coeff.,

ID: Const, Direction: Norm./Tan.,

Tangent: 1e2, Normal should be

unchecked, select the opposite end

surface of the bushing > Accept.

Prevents rigid body rotation

• Select > Contact Zone > Contact ID:

Const, Direction: Norm./Tan., Normal:

1e6, Select both contact zones >

Constraint will automatically generate.

When all is done there should be four

constraint records (Built-In, Symmetry,

Spring and Contact)

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Mesh and Solve

Check the functionality of the model by changing parameters.

• Update parameters: a = 0.1, Bod = 1.0 > Accept

The model should update and re-mesh automatically

Ignore any warnings.

The model is now set-up for a condition of 0.002” of interference on the diameter, defined by the parameter, RadInt.

The interference is accounted for in the StressCheck contact algorithm.

• Oversize bushing is compressed

SC Input > Define > Name > Selection, Solution ID: SOL001, CONST, LOAD > Accept.

SC Solver > Linear > p-level 2 to 4 > SOLVE!

Quality Check and SIF Extraction

Results StressCheck

• Plot the deformed shape to

ensure the model behaves as

expected, Plot tab Select > All

Elements > Selection >

SOL001 > Run 3 > Shape:

Deform > Plot.

• Extract SIF’s, Display only

curves, Points tab > SOL001 >

Run 1 to 3 > Func: K1, Rad:

.15*a, # of pts.: 20, > Select

the crack front curve > Accept.

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SIF Convergence

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Note the converging value of

K1 as the p-level (Run #)

increases from 2 to 4.

• Can be improved with

increased p-level and/or

mesh density

Optional: Repeat solution

twice more with different

amounts of interference by

changing the parameter

RadInt, to 0.0015” and

0.002”, resulting in 0.003”

and 0.004” of interference on

the diameter respectively.

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SIF Comparison

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Summary and Tips

Performing contact + fracture mechanics in StressCheck is relatively simple• No special elements needed

• Contact zones specified on surfaces

• Hand-mesh may be in contact with automesh

For simple geometries, hand-meshing is best• Waste of DOF to automesh a cylinder, for example

• Simply increase p-level of hand-meshed elements to the maximum of 8

Make sure to limit rigid body motions!• Otherwise, “LAPACK” errors will occur in solver

Using a dense automesh around the crack typically means the p-level of the automesh elements can be lower (e.g. < 5)

Use a contour integral radius between the first and second layer of elements

Important to ascertain the effect of propping on SIF’s

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© 2015 ESRD, Inc. All Rights Reserved. StressCheck® is a registered trademark of ESRD, Inc.

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