© 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.
Any Questions?