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05-13-2016 06:05 PM

Hello everybody! i am having this problem from long time ago so today i got the courage to ask you guys . (if my question is too stupid please know that i'm a beginner)

I applied a Temperature load (on nodes) of 700 degrees CELSIUS on a 1000x1000mm plate, 8mm thick , the body load was 30 degrees CELSIUS . The plate was constrained at the top and the bottom (fixed constrains).I did a static analysis then showed elemental contour late top vonmises stress. the material is the stock one that we find in FEMAP , AISI 4340 Steel . after i select the views i get the legend on the right side of the screen . can you help me telling what the results are in ? are they n/mm2( way too big tensions)? what are they?

3 REPLIES

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05-14-2016 06:52 AM

Dear Mike,

CAUTION!!, you have the worst problem of FEMAP, **mixing units!!.**

I realized of this because the material name AISI 4340 STEEL only exist in the MATERIAL.ESP file, that is the default material library, but values are in INCHES & POUNDS!!.

This means that you have a serious problem of configuration, go to **FILE > PREFERENCES** and set as minimum two changes: geometry & material library (see my website in the following address: http://www.iberisa.com/soporte/femap/femap_tips_tricks_preferencias.htm):

• **GEOMETRY**: this option affect when you import any CAD model (Step, Parasolid, IGES, etc..) in FEMAP, choose "**2..Millimeters**" to get the length of geometry scaled to millimeters.

• **LIBRARY/Startup**: for **MATERIAL** choose the file "**mat_eng_mm-N-tonne-degC-Watts.esp**", units there are consistent to have the geometry length in millimeters.

Regarding the units of the stress results of your problem if you choose from the new library a steel material say "**AISI Carbon Steel 1006 Cold drawn**" please understand the following:

• Young module value, EX = 199948 MPa.

• Coef. Themal Expansion, AlphaX = 1.512e-5 /ºC

• Temperature Reference, Tref = 21.1 ºC

**Tref =21.1ºC **is an important value, it means that at 21º.1ºC we have a zero strain state. The thermal strain is proportional to the temperature change x linear coef. of themal expansion, **EpsilonX = AlphaX * DeltaT**. Then if you apply a nodal temperature of 700ºC and your Tref=21.1ºC then DeltaT=700-21.1 = 678.9ºC, OK?.

The next plot shows the thermal stress results, of course, units are MPa (ie, N/mm2). Of course, in real life the material never will reach that stress value, the material yields, but is important to understand the consequences of fully constraining structures, when thermal loads are present then inclusion of thermal joints to account for free dilation is critical!!.

Best regards,

Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

IBERISA • 48004 BILBAO (SPAIN)

WEB: http://www.iberisa.com

Blog Femap-NX Nastran: http://iberisa.wordpress.com/

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05-15-2016 11:11 AM

Thank you so much for helping me !

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05-16-2016 01:04 AM

The endurasim pdf covers the topic quite extensively for both heat transfer and mech.

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