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interference fit simulation


Hello,
I would like to simulate and interference fit of a shaft inserted into a bore in
a non axisymmetric geometry, with a radial intereference of 0.012 mm. I tried to
build some simple examples first, with symmetry, but I cannot obtain results comparable
to theoric ones. For example, I built a shaft of 10 mm diameter in a hub of OD 20
mm with the same interference, using a delta T with coupled mesh and using a contact
region with 0.006 mm offset in each contact surface (as stated in the help), and
I obtain contact pressures and circumferential stresses much higher than the theorical
ones. Is anyone expert in this kind of analysis? Please give me any advice. Related
question: I built a cylindrical CSYS using it as output CSYS for all nodes, but
FEMAP doesn't give me out displacements in this CSYS... how can I obtain that?
Thanks
Marco
4 REPLIES

Re: interference fit simulation


Marco,
You state that you've used a delta T and a 0.006 mm offset on the contact surfaces.
While these are both means to model an interference fit, they typically should not
be used in the same model at the same time.
If the bore and the shaft are modeled to the same diameter, you either apply a thermal
load to expand the shaft (or shrink the bore), or you specify an offset on one or
both of the contact surfaces such that the total offset equals your radial interference.

The output CSYS controls how NX Nastran prints results to the .f06 or punch file.
FEMAP always displays results in the basic CS by default.
Use Model, Output, Transform to transform an output vector to a different coordinate
system.
Regards,
Jim

"Marco" wrote:
>
>Hello,
>
>I would like to simulate and interference fit of a shaft inserted into a bore
>in
>a non axisymmetric geometry, with a radial intereference of 0.012 mm. I tried
>to
>build some simple examples first, with symmetry, but I cannot obtain results
>comparable
>to theoric ones. For example, I built a shaft of 10 mm diameter in a hub of
>OD 20
>mm with the same interference, using a delta T with coupled mesh and using
>a contact
>region with 0.006 mm offset in each contact surface (as stated in the help),
>and
>I obtain contact pressures and circumferential stresses much higher than the
>theorical
>ones. Is anyone expert in this kind of analysis? Please give me any advice.
>Related
>question: I built a cylindrical CSYS using it as output CSYS for all nodes,
>but
>FEMAP doesn't give me out displacements in this CSYS... how can I obtain that?
>
>Thanks
>
>Marco

Re: interference fit simulation


Thanks Jim for your answer. I didn't explain myself, I didn't use thermal expansion
together with contact offset, but I tried with both methods separately. So contact
surfaces with offset are ok to simulate interference, but do I have to use linear
contact (not glued) with sol 101? Another question: if I setup the solid property
with material alignment csys cylindrical along the bore axis, I should obtain sigma
x as radial stress, sigma y as circumferential stress and sigma z as axial stress,
am I right? and sigma x should be equal to contact pressure (with opposite sign),
right?
Thanks
Marco
"Jim Bernard" wrote:
>
>Marco,
>
>You state that you've used a delta T and a 0.006 mm offset on the contact
>surfaces.
>While these are both means to model an interference fit, they typically should
>not
>be used in the same model at the same time.
>
>If the bore and the shaft are modeled to the same diameter, you either apply
>a thermal
>load to expand the shaft (or shrink the bore), or you specify an offset on
>one or
>both of the contact surfaces such that the total offset equals your radial
>interference.
>
>
>The output CSYS controls how NX Nastran prints results to the .f06 or punch
>file.
>FEMAP always displays results in the basic CS by default.
>Use Model, Output, Transform to transform an output vector to a different
>coordinate
>system.
>
>Regards,
>Jim
>
>
>"Marco" wrote:
>>
>>Hello,
>>
>>I would like to simulate and interference fit of a shaft inserted into a

>bore
>>in
>>a non axisymmetric geometry, with a radial intereference of 0.012 mm. I tried
>>to
>>build some simple examples first, with symmetry, but I cannot obtain results
>>comparable
>>to theoric ones. For example, I built a shaft of 10 mm diameter in a hub

>of
>>OD 20
>>mm with the same interference, using a delta T with coupled mesh and using
>>a contact
>>region with 0.006 mm offset in each contact surface (as stated in the help),
>>and
>>I obtain contact pressures and circumferential stresses much higher than

>the
>>theorical
>>ones. Is anyone expert in this kind of analysis? Please give me any advice.
>>Related
>>question: I built a cylindrical CSYS using it as output CSYS for all nodes,
>>but
>>FEMAP doesn't give me out displacements in this CSYS... how can I obtain

>that?
>>
>>Thanks
>>
>>Marco

>

Re: interference fit simulation


Marco,
Yes, you have to use linear contact. Glue adds stiffness at the interface without
doing any iterations to resolve the penetration condition. Contact is the only on
that will iterate to enforce the zero penetration condition.
You are correct with regard to the material system stress output.
wrote:
>
>Thanks Jim for your answer. I didn't explain myself, I didn't use thermal
>expansion
>together with contact offset, but I tried with both methods separately. So
>contact
>surfaces with offset are ok to simulate interference, but do I have to use
>linear
>contact (not glued) with sol 101? Another question: if I setup the solid property
>with material alignment csys cylindrical along the bore axis, I should obtain
>sigma
>x as radial stress, sigma y as circumferential stress and sigma z as axial
>stress,
>am I right? and sigma x should be equal to contact pressure (with opposite
>sign),
>right?
>
>Thanks
>
>Marco
>
>"Jim Bernard" wrote:
>>
>>Marco,
>>
>>You state that you've used a delta T and a 0.006 mm offset on the contact
>>surfaces.
>>While these are both means to model an interference fit, they typically should
>>not
>>be used in the same model at the same time.
>>
>>If the bore and the shaft are modeled to the same diameter, you either apply
>>a thermal
>>load to expand the shaft (or shrink the bore), or you specify an offset on
>>one or
>>both of the contact surfaces such that the total offset equals your radial
>>interference.
>>
>>
>>The output CSYS controls how NX Nastran prints results to the .f06 or punch
>>file.
>>FEMAP always displays results in the basic CS by default.
>>Use Model, Output, Transform to transform an output vector to a different
>>coordinate
>>system.
>>
>>Regards,
>>Jim
>>
>>
>>"Marco" wrote:
>>>
>>>Hello,
>>>
>>>I would like to simulate and interference fit of a shaft inserted into a

>>bore
>>>in
>>>a non axisymmetric geometry, with a radial intereference of 0.012 mm. I

>tried
>>>to
>>>build some simple examples first, with symmetry, but I cannot obtain results
>>>comparable
>>>to theoric ones. For example, I built a shaft of 10 mm diameter in a hub

>>of
>>>OD 20
>>>mm with the same interference, using a delta T with coupled mesh and using
>>>a contact
>>>region with 0.006 mm offset in each contact surface (as stated in the help),
>>>and
>>>I obtain contact pressures and circumferential stresses much higher than

>>the
>>>theorical
>>>ones. Is anyone expert in this kind of analysis? Please give me any advice.
>>>Related
>>>question: I built a cylindrical CSYS using it as output CSYS for all nodes,
>>>but
>>>FEMAP doesn't give me out displacements in this CSYS... how can I obtain

>>that?
>>>
>>>Thanks
>>>
>>>Marco

>>
>

Re: interference fit simulation


So, according to my understanding, I can model an interference fit with matching
mesh and a delta T, or unmatching mesh with contact surfaces and an offset equal
to radial interference. But at the interface I obtain positive radial displacement
on both parts in first method, while in the second one I get positive displacement
for hole nodes and negative for shaft nodes. Doesn't this bring to different results
and different radial stresses?
Marco
"Jim Bernard" wrote:
>
>Marco,
>
>Yes, you have to use linear contact. Glue adds stiffness at the interface
>without
>doing any iterations to resolve the penetration condition. Contact is the
>only on
>that will iterate to enforce the zero penetration condition.
>
>You are correct with regard to the material system stress output.
>
> wrote:
>>
>>Thanks Jim for your answer. I didn't explain myself, I didn't use thermal
>>expansion
>>together with contact offset, but I tried with both methods separately. So
>>contact
>>surfaces with offset are ok to simulate interference, but do I have to use
>>linear
>>contact (not glued) with sol 101? Another question: if I setup the solid

>property
>>with material alignment csys cylindrical along the bore axis, I should obtain
>>sigma
>>x as radial stress, sigma y as circumferential stress and sigma z as axial
>>stress,
>>am I right? and sigma x should be equal to contact pressure (with opposite
>>sign),
>>right?
>>
>>Thanks
>>
>>Marco
>>
>>"Jim Bernard" wrote:
>>>
>>>Marco,
>>>
>>>You state that you've used a delta T and a 0.006 mm offset on the contact
>>>surfaces.
>>>While these are both means to model an interference fit, they typically

>should
>>>not
>>>be used in the same model at the same time.
>>>
>>>If the bore and the shaft are modeled to the same diameter, you either apply
>>>a thermal
>>>load to expand the shaft (or shrink the bore), or you specify an offset

>on
>>>one or
>>>both of the contact surfaces such that the total offset equals your radial
>>>interference.
>>>
>>>
>>>The output CSYS controls how NX Nastran prints results to the .f06 or punch
>>>file.
>>>FEMAP always displays results in the basic CS by default.
>>>Use Model, Output, Transform to transform an output vector to a different
>>>coordinate
>>>system.
>>>
>>>Regards,
>>>Jim
>>>
>>>
>>>"Marco" wrote:
>>>>
>>>>Hello,
>>>>
>>>>I would like to simulate and interference fit of a shaft inserted into

>a
>>>bore
>>>>in
>>>>a non axisymmetric geometry, with a radial intereference of 0.012 mm. I

>>tried
>>>>to
>>>>build some simple examples first, with symmetry, but I cannot obtain results
>>>>comparable
>>>>to theoric ones. For example, I built a shaft of 10 mm diameter in a hub
>>>of
>>>>OD 20
>>>>mm with the same interference, using a delta T with coupled mesh and using
>>>>a contact
>>>>region with 0.006 mm offset in each contact surface (as stated in the help),
>>>>and
>>>>I obtain contact pressures and circumferential stresses much higher than
>>>the
>>>>theorical
>>>>ones. Is anyone expert in this kind of analysis? Please give me any advice.
>>>>Related
>>>>question: I built a cylindrical CSYS using it as output CSYS for all nodes,
>>>>but
>>>>FEMAP doesn't give me out displacements in this CSYS... how can I obtain
>>>that?
>>>>
>>>>Thanks
>>>>
>>>>Marco
>>>

>>
>