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Specifying Yield stress at different temperatures in ANSYS
 
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Martin Liddle
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Joined: 15 Aug 2008
Posts: 1274
Location: Chesterfield, UK

PostPosted: Sat Apr 05, 2014 1:34 am  Reply with quote

On 05/04/2014 08:29, tanumay.bhattacharya wrote:
Quote:
I have the data for yield stress vs temperature for a material. How to give this material property in ANSYS as input? Kindly suggest any idea.

You don't give much information about whether this is Workbench
Mechanical or Mechanical APDL nor about what proposed material model.
Assuming the intent is to do a non linear analysis in Mechanical APDL
then a bi-linear kinematic material model would be a simple starting
point and the APDL would be something like:

MatNum=1
Numtemps=3
TB,BKIN,MatNum,NumTemps
TBTEMP,20 !Yield at 20 C
TBDATA,,YieldStressAt20,TangentModulusAt20

TBTEMP,250 !Yield at 250C
TBDATA,,YieldStressAt250,TangentModulsAt250

TBTEMP,500 !Yield at 500C
TBDATA,,YieldStressAt500,TangentModulsAt500

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Martin Liddle, Tynemouth Computer Services,
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Martin Liddle
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Location: Chesterfield, UK

PostPosted: Sun Apr 06, 2014 2:25 am  Reply with quote

On 06/04/2014 07:31, tanumay.bhattacharya wrote:
Quote:
I am using ANSYS APDL to model material non-linearity. Use of BKIN requires defining tangent modulus a those temperatures. However, if I mention Young's Modulus seperately, then an error is popping up saying the slope of stress-strain curve is different at certain temperature. Kindly help.

Firstly your signature is missing. Please ensure that it is present on
posts in future showing your full name and company.

Can you post the material property data part of your analysis as
otherwise we will just be playing guessing games?


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Martin Liddle, Tynemouth Computer Services,
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www.tynecomp.co.uk
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Martin Liddle
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Posts: 1274
Location: Chesterfield, UK

PostPosted: Sun Apr 06, 2014 7:05 am  Reply with quote

On 06/04/2014 14:18, tanumay.bhattacharya wrote:

Quote:
MPDATA,1,220E6,190E6,175E6,125E6,60E6,50E6
MPDATA,7,30E6,25E6,20E6,10E6,5E6

Fairly obviously that isn't going to work as you haven't specified a
material property label. You said in a previous post you wanted to do a
non linear analysis and non linear properties are specified with the
TABLE command as I stated in my previous post. You want something like:

TB,BKIN,1,11
TBTEMP,25
TBDATA,,220E6,TangentModulasAt20

TBTEMP,100
TBDATA,,190E6,TangentModulsAt100

and so for the other temperatures.

Note that for the Bilinear Kinematic model you need to specify a tangent
modulus; this can be zero for elastic perfectly plastic behaviour but
even if I am trying to model an elastic perfectly plastic situation I
prefer to give the tangent modulus a small positive value as it makes
convergence much easier.
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Martin Liddle, Tynemouth Computer Services,
Chesterfield, Derbyshire, UK.
www.tynecomp.co.uk
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ayo.brimmo
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Joined: 01 Jul 2013
Posts: 38
Location: Masdar City, Abu Dhabi

PostPosted: Sun Apr 06, 2014 7:45 am  Reply with quote

Tanumay,

A glance at your code tells me that you don't have a lab for the MPDATA you are trying to use to input Yield Stress. Don't think there's a way ANSYS would know that yield stress is what you are trying to input that way.

The way I see it the "EX" in "MPDATA,EX,1,200E9,195E9,190E9,180E9,170E9,125E9" tells ANSYS to store the data in a table allocated to the expansion modulus (in the x direction). Skipping that step doesn't tell it where the data should be stored.

Anyways, MPDATA doesn't have a documented lab for yield stress so your best bet is the BKIN or MKIN commands. See below an example of how to use the BKIN command:

MPTEMP,1,0,500 ! Define temperatures for Young's modulus
MP,EX,1,1E6,2 E6 ! Young's modulus at T1 and T2
TB,BKIN,1,2 ! Activate a data table
TBTEMP,0.0 ! Temperature = 0.0
TBDATA,1,3E3,4E3 ! Yield = 3000; Tangent modulus = 4E3
TBTEMP,500 ! Temperature = 500
TBDATA,1,5E3,6E3 ! Yield = 5000; Tangent modulus = 6000

Check documentation for definition of tangent modulus if you don't know what it means.

Best,
Ayo Brimmo
Research Engineer
Masdar Institute, UAE

-----Original Message-----
From: Xansys [mailto:xansys-bounces@xansys.org] On Behalf Of tanumay.bhattacharya
Sent: Sunday, April 06, 2014 5:19 PM
To: xansys@xansys.org
Subject: Re: [Xansys] Specifying Yield stress at different temperatures in ANSYS

I have the variation of Young's Modulus with temperature as,

MPTEMP,1,25,100,200,300,420,540
MPTEMP,7,640,780,800,900,1000

MPDATA,EX,1,200E9,195E9,190E9,180E9,170E9,125E9
MPDATA,EX,7,45E9,25E9,20E9,10E9,5E9

Also, I have the yield stress variation with temperature as,

MPTEMP,1,25,100,200,300,420,540
MPTEMP,7,640,780,800,900,1000

MPDATA,1,220E6,190E6,175E6,125E6,60E6,50E6
MPDATA,7,30E6,25E6,20E6,10E6,5E6

Kindly help how can I give this yield stress as input to ANSYS APDL.

T Bhattacharya
NFC, India






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Ayo Brimmo
Research Engineer
Masdar Institute of Science and Technology
UAE.
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