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Residual strain after unloading the structure

Hi All,

 

I am quite new with nonlinear analysis so need help in test task.

Let me explain, I have simple bracket as shown below:

mdoel.png

 

I am trying to get results of residual strain that remained in the structure after exceeding yield point and then unloading the structure.

I am not sure whether my approach is correct. I did SOL 106, stress exceeded 235 MPa (Normal Strength Rolled Steel - taken from NX Mat Library).

In results I can see the Total Residual Force, but I am pretty sure that this is not what I am looking for, so could you advice where I can get this and whether the SOL 106 (and Basic Bundle of Advanced Simulation) supports this?

 

Just for information, this is what I get under Tolal Residual Force: what those results exactly mean? :

model1_fem1.png

 

Thanks for help Smiley Happy

4 REPLIES

Re: Residual strain after unloading the structure

Siemens Phenom Siemens Phenom
Siemens Phenom

In SOL 106, you need at least two subcases to do this. In the first subcase, apply the loads that cause portions of the model to exceed yield. In the second subcase, remove the loads. The strain results in the second subcase are the residual strains in the structure.

 

Re: Residual strain after unloading the structure

Pioneer
Pioneer

Hello,

 

first of all thanks for showing that NX has predefined nonlinear (PLASTIC) material in the library, and with nonlinear I mean stress-strain definotions not temerature dependent definitions. I didn't know that! Is there any other nonlinear material, for expample one for NLELAST? Smiley Happy

 

 

I had a similar case, the beam from the other example, and did the following:

 

Solution 106,

subcase 1 load 1000N

subcase 2 load 2000N

subcase 3 load 10N

subcase 4 no load

 

2000N_load.PNG

2000N load

 

 

0N_load.PNG

no load

 

 

 

After that, there where deformation left over (PLASIC). Looking at the "Nonlinear Stress - Elemental" there where leftovers as well. Maybe that is what you mean?

 

JonkMcCool

 

Re: Residual strain after unloading the structure

Pioneer
Pioneer

Hello,

 

JimB answered faster and he can do it much more briefly than I can and still telling everthing important. Great! Smiley Happy

 

Things I told you referred to stress but it works for strain as well. I did another simulation with 5000N maximum load and in the result you can see large remaining strain. The deformation is with scale 1!

 

0N_load_after5000N.PNG

 

JonkMcCool

Re: Residual strain after unloading the structure

Hi Guys, thanks for help,

 

I have just few questions for clarification so I know what exactly happens there.

please see below results:

1-  total load applied (subcase 1, last step) - non linear stress elemental

2 - total load applied (subcase 1, last step) - non linear strain elemental

3 - total load applied (subcase 1, last step) - equivalent plastic strain elemental

4 - no load applied in subcase (subcase 2, first step) - non linear strain elemental

5 - no load applied in subcase (subcase 2, first step) - plot of total reaction force (arrows)

6 - no load applied in subcase (subcase 2, last step) - non linear strain elemental

bracket_plastic.png

And now, let me ask:

a) what is the differenece between plot 2 & 3 ? is it the difference based on "true" and "engineering' strain in material ? I assume that 2 is the true strain right ?

b) why there are 29 steps in subcase 2 (subcase 2 does not contain any loads)?

c) why there are reactions applied to the nodes on plot 5 ? since this is subcase with no loads, the reactions (as well as applied nodal forces shall be equal to zero right ?) shouldn't be zero? Then if they are not zero we can not say that the strain from plot 4 (which corresponds to plot 5 reactions) are residual strain in the structure. right or not?

d) if plot 5 (based on explanation in (c)) is not residual strain, this shall be then the last step in subcase 2 (right ?) but if I plot mentioned last step on 6, it is equal to "0"... why ?

 

And now ... which plot gives me the residual strain in the structure after unloading ?

I stucked... Smiley Very Happy

 

just for info:

navigator.png

 

and results:

results.png

 

#refresh, any ideas ? Smiley Happy