Modeling Component Assembly of a Bearing Using Abaqus - SIMULIA

Modeling Component Assembly of a Bearing
Using Abaqus
By: Mike Guillot, Ph.D., P.E.
Bisen Lin, Ph.D., P.E.
May 16, 2012

2
Problem
A bearing leaked cooling fluid into a process
causing a major disruption at a chemical plant.
An investigation indicated a seal weld had failed
due to fatigue. The same bearing is on
numerous units and has been in service many
years with no issues. The client wanted to
evaluate the stresses in the seal weld due to the
variability in the manufacturing process as well
as operational variations. Abaqus was used to
conduct a sensitivity analysis on this complex
bearing assembly.

3
Overview
• Abaqus modeling techniques used in present work.
Model change for removal / reactivation of elements and contact pair.
Contact interference fit, shrink fit.
• FEA model descriptions:
Model geometry and mesh.
Temperature-dependent material properties.
Constraints and interactions
Loads and boundary conditions
• Model assemble and analysis procedure.
• Analysis results.
• Sensitivity study on the initial interference.
• Comments and closure.

4
Modeling Technique (1/2)
• Model Change: Removal / reactivation of elements and contact pairs with strain-free
condition.
• Abaqus input usage:
Parts (elements) removal:
*Model Change, Type=Element, Removal
Element_Set_Name
Parts (elements) reactivation w/ strain-free:
*Model Change, Type=Element, Add
Element_Set_Name
Contact pair removal:
*Model Change, Type=Contact Pair, Removal
Slave_Surface_Name, Master_Surface_Name
Contact pair reactivation:
*Model Change, Type=Contact Pair, Add
Slave_Surface_Name, Master_Surface_Name

5
Modeling Technique (2/2)
• Contact Interference Fit: to similate the sequential assemble of the three-layer
bearing.
• Abaqus input usage:
Automatic shrink fit in the first analysis step:
*Contact Interference, Shrink
Slave_Surface_Name, Master_Surface_Name
Interference fit in the subsequent steps for resolving initial interference:
*Contact Interference
Slave_Surface_Name, Master_Surface_Name, v
– v: reference allowable interference. This value is applied instantaneously at the start
of the step and ramped down to zero linearly over the step by default. It is
recommended that you specify the allowable interference v in a separate step that
there are no other loads applied. Additional loads and/or boundary conditions may
adversely affect the resolution of the interference fit and the response to the loading
with partially resolved interferences may be non-physical [1].

6
Abaqus FEA model
• An axisymmetric model of the bearing assembly
is used.
• Abaqus CAE version 6.10-1 is used.
• Linear elastic material and linear geometry are
considered.
• The four-step assembly process of the bearing is
performed followed by the coupled temperaturedisplacement
steady-state analysis.

7
Middle Layer
(Cooling
Sleeve)
Axis of
Rotation
Inner Layer
(Bearing
Sleeve)
Model Geometry and Mesh
Weld
Weld
Outer Layer
(Bearing
Housing)
The entire assembly was
modeled as CAX4T, a 4-node
axisymmetric thermally coupled
quadrilateral element, bilinear in
displacement and temperature.

8
Material Properties (1/3)
• Bearing housing is made of AISI 4140 low alloy
steel.
• Other parts, i.e. cooling sleeve and bearing
sleeve, and welds are made of 1026 low carbon
steel.
• Temperature-dependent mechanical and
thermal properties including Young’s modulus,
coefficient of thermal expansion, and thermal
conductivity are shown in the next slide.
Poisson’s ratio of 0.3 is used.

9
Young's Modulus (psi)
3.00E+07
2.90E+07
2.80E+07
2.70E+07
2.60E+07
2.50E+07
Material Properties (2/3)
0 100 200 300 400 500 600 700
Temperature (F)
1026 Steel
4140 Steel

10
Material Properties (3/3)
Thermal Conductivity (BTU/hr-ft-F)
Coefficient of Thermal Expansion (1/F)
40
35
30
25
20
15
10
5
0
8.0E-06
7.6E-06
7.2E-06
6.8E-06
6.4E-06
6.0E-06
Same for both materials
0 100 200 300 400 500 600 700
Temperature (F)
0 100 200 300 400 500 600 700
Temperature (F)
1026 Steel
4140 Steel

11
Int-3
Contact Interactions
Int-1
Int-2
Int-1: Upper contact between cooling sleeve
and bearing housing
Int-2: Lower contact between cooling sleeve
and bearing housing
Int-3: Contact between bearing sleeve and
cooling sleeve

12
Loads and Boundary Conditions
Pressure = 8000 psi
Temperature = 488 F
Insulated 380 F
Insulated
441 F
U2=0
Pressure = 75 psi
Temperature = 437 F
Linear thermal gradient
(380F to 441F)

13
Model Assemble and Analysis Procedure
Step-1. Shrink fit of outer layer (bearing housing)
and middle layer (cooling sleeve)
Step-2. Activation of the welds at two-end
grooves between cooling sleeve and bearing
housing in strain-free state.
Step-3. Activation of the inner layer (bearing
sleeve) in strain-free state.
Step-4. Interference fit of bearing sleeve and the
assembly of cooling sleeve and bearing housing.
Step-5. Applications of loads and thermal
boundary conditions for further stress analysis.

14
Consideration of Different Initial Interferences
Case No.
Int-1
(Bearing Housing
and Cooling Sleeve,
Upper)
Initial Diametral Interference (inch)
Int-2
(Bearing Housing
and Cooling Sleeve,
Lower)
Int-3
(Cooling Sleeve
and Bearing
Sleeve)
C-1 0.005 0.005 0.002
C-2 0.005 0 0.002
C-3 0.005 0.005 0.005
C-4 0.005 0 0.005

15
Analysis Results of Case C-1 (1/3)
• Step-1. Shrink fit cooling sleeve and bearing housing with initial
diametral interference equal to 0.005 inch for both Int-1 and Int-2.
This induces von Mises stress at a level of ~10ksi in cooling sleeve.
• Step-2. Activate groove welds with strain-free condition. Stresses in
the welds were verified to be zero.
• Step-3. Activate bearing sleeve with strain-free condition. Stresses
in the bearing sleeve were verified to be zero.
• Step-4. Interference fit bearing sleeve and the assembly of cooling
sleeve and bearing housing with initial diametral interference equal
to 0.002 inch for Int-3, and 0.002 inch for Int-3. This induces von
Mises stress at a level of ~11ksi in bearing sleeve. Meanwhile, the
stress in cooling sleeve is reduced from ~10ksi to ~8ksi and the
stress in bearing housing is increased to ~3ksi to ~8ksi.
• Step-5. Application of Loads. This introduces high stresses at tip
of the lower weld as well as at the discrete contacts between
bearing housing (outer layer) and cooling sleeve (middle layer).

16
Analysis Results of Case C-1 (2/3)
[ psi ]
von Mises Equivalent Stress Contour
Step-1 Step-2 Step-3 Step-4

17
Analysis Results of Case C-1 (3/3)
Temperature and von Mises Equivalent Stress Contours
[ ºF ] [ psi ]
Step- Application of Thermal and Mechanical Loads

18
Results of Sensitivity Study (1/4)
• Overall, the assembly in C-2 has the best stress distribution; while
the assembly in C-3 has the highest stress regions.
• As can be seen in the next slide for C-1 and C-2, decreasing the
interference at Int-2 (i.e. at lower interface between bearing housing
and cooling sleeve) tends to distribute the stress better and also
reduces stresses in bearing housing and sleeve. This is also
demonstrated by comparing C-3 to C-1.
• As can be seen in the next slide for C-1 and C-3, increasing the
interference at Int-3 (i.e. at interface between cooling sleeve and
bearing sleeve) tends to increase stresses, especially in bearing
housing and cooling sleeve. This can also be observed by
comparing C-4 to C-2.
• Therefore, reducing the initial interferences at Int-2 and Int-3 will
lower the stresses in the assembly including the welds.
• These stress results can then be used in the further structural
integrity and component fatigue life assessments.

19
Results of Sensitivity Study (2/4)
[ psi ] [ psi ] [ psi ] [ psi ]
C-1
Int-1=0.005in
Int-2=0.005in
Int-3=0.002in
C-2
Int-1=0.005in
Int-2=0 in
Int-3=0.002in
C-3
Int-1=0.005in
Int-2=0.005in
Int-3=0.005in
C-4
Int-1=0.005in
Int-2=0 in
Int-3=0.005in

20
Results of Sensitivity Study (3/4)
[ psi ] [ psi ] [ psi ] [ psi ]
C-1
Int-1=0.005in
Int-2=0.005in
Int-3=0.002in
von Mises equivalent stress at low weld
C-2
Int-1=0.005in
Int-2=0 in
Int-3=0.002in
C-3
Int-1=0.005in
Int-2=0.005in
Int-3=0.005in
C-4
Int-1=0.005in
Int-2=0 in
Int-3=0.005in

21
Results of Sensitivity Study (4/4)
[ psi ] [ psi ] [ psi ] [ psi ]
C-1
Int-1=0.005in
Int-2=0.005in
Int-3=0.002in
Max principal stress at low weld
C-2
Int-1=0.005in
Int-2=0 in
Int-3=0.002in
C-3
Int-1=0.005in
Int-2=0.005in
Int-3=0.005in
C-4
Int-1=0.005in
Int-2=0 in
Int-3=0.005in

22
Comments and Closure
• Modeling of a bearing assembly procedure was
considered in this paper using the special techniques in
Abaqus, i.e.
Model change.
Contact interference fit.
• The example demonstrates the high-quality capability of
Abaqus to simulate real world designs.
• Multiple cases in which design parameters, i.e. initial
overclosure values were varied allowed their sensitivity
to be understood.
• The results were then used in the structural integrity and
component fatigue life evaluations of the existing
equipment to aid in an improved fatigue resistant design.

23
Contact Information
Mike Guillot, Mike.Guillot@stress.com
Bisen Lin, Bisen.Lin@stress.com
Stress Engineering Services
13800 Westfair East Drive
Houston, Texas 77041
Phone: (281) 955-2900
Fax: (281) 955-2638
www.stress.com