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06-29-2007 09:42 AM

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

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07-02-2007 01:54 PM

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"

>

>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

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07-06-2007 03:41 AM

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"

>

>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"

>>

>>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

>

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07-06-2007 03:49 PM

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.

>

>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"

>>

>>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"

>>>

>>>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

>>

>

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07-09-2007 10:59 AM

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"

>

>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.

>

>

>>

>>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"

>>>

>>>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"

>>>>

>>>>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

>>>

>>

>

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