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Stress Cracks

9 REPLIES 9
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Message 1 of 10
rajeshkumarpv
1632 Views, 9 Replies

Stress Cracks

Hello,

 

Greetings!

 

We have a rectangular Door Part (600X400 mm) which is of Unfilled ABS. After molding the part cracks near the hinge region. This crack appears after some days (10-15 days) and not immediately after molding. Chances are there that they could be Stress Cracks. Is there any option to predict Stress Crack using Moldflow and suitable remedies.

 

Thanks in advance. 

 

Regards,

Rajesh P V

9 REPLIES 9
Message 2 of 10
sadashiv
in reply to: rajeshkumarpv

hallo Rajesh

 

U can check the in cavity residual stress result . But according to moldflow help

Note: The in-cavity residual stress is calculated by the Pack analysis and represents the stresses in the part before it is ejected. It does not necessarily reflect the stresses that a part experiences after ejection. This result is best used as an input to a Warp or Stress analyses, such as Warp or Abaqus, rather than by itself.

 

Best regards.

Sadashiv

 

 

Message 3 of 10
jean.uemura
in reply to: sadashiv

I usually check this result.

The yield stress (check material data sheet) is the limit for the in-cavity residual stress result.

Message 4 of 10

Hello,

Thanks for the reply.

In Cavity Residual Stress gives a very high range of values from + to - ve range.

In few cases the mesh  doesnot have the negative values but in Contour plot values are shown

 

Any changes needed to be done like single data/normalized thickness at SPecified location to infer results?

 

Kindly share if you have come across such values.

 

Regards,

Rajesh Kumar P V 

 

 

Message 5 of 10

G'day Rajesh,

 

If I understand correctly what you are saying, you need to go the plot properties tabs and the options tab (I think, the last one) turn off nodal averaging and it will display a constant value for each element and you will find the location of the max. and min's.  This same thing applies for any elemental property as the nodal averaging is turned on by default.

 

Bob Sherman,

RTP Company

Message 6 of 10

Dear Bob,

 

Thanks for the info. But when the Contour Plot have a very huge range of values for example +ve 30 MPa to -264 MPa, negative values are not able to be seen in part with averaging and without averaging.

 

Even wen values are changed and uncheck the extend option still we face the same problem of locating the areas where extreme -ve value appears.

 

In real the part has Stress cracks visible but whereas in moldflow the values are within the Modulus limit. This is for info.

 

 

Regards,

Rajesh Kumar P V

Message 7 of 10

hello,

you can also check the FROZEN PRESSURE prediction (it's not a default result, so you need to add it) as this shows if you have any residual pressure applied on the part that may later become a stress area (i.e. bosses, ribs) which under certain assembly conditions may create cracking issues.

 

Also verify the shear rate for any potential embrittlement issues...

 

best regards,

 

Hugo Herrera

Visteon

Message 8 of 10

Thanks for the Input. Let me check the results for any deviation in the results.

Message 9 of 10
Ncu-me
in reply to: rajeshkumarpv

Hi Rajesh P V,

 

Interested Topic.

 

May I know failure percentage of your case? Can I say if it is due to high residual stress and all parts will be affected?

 

Regards,

Ncu.

 

Message 10 of 10
changing
in reply to: Ncu-me

Anything update?

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