material non linearity

[shearlag]

Dear all,

Can any of you help me to interpret the results of material non linearity analysis run on NASTRAN SOL 106.Material is AMS 4010 and properties are UTS:510 MPa, YEILD:450 MPa & ductility is 9%.As explained in nastran, i have input a stress-strain curve.My first point is (0,0) & second point is (450,0.006) & inbetween i have 6 more values and last value is (510,0.009).Since ductility is 9%, my last strain value 0.009 strain or 9000 micro strain (have i given the input in a right way considering ductility ?). No temperature effect is considered.Run was successful.Linear static had shown 560 Ma (Max Pri) at critical section of the component. So a non-linear was attempted.nonlinear showed 495 MPa at the same critical section but strain were 0.011 or 11000 micro strain.

has the component failed..? results were plotted from non-linear stress and strain tensor, Result strain should be compared against what allowable strain..? or non-linear elastic modulus...?

kindly help me out...

Thanks in adavance

with kindest regards

 

[CoryPad]

9 % ductility is not 0.009 strain, it is 0.09 strain. It appears that you created the wrong stress-strain curve.

The allowable strain is whatever has been decided - some components can have zero plastic strain, some can have any plastic strain that does not cause fracture.

 

[GregLocock]

Nice catch. The effect of that is that you have a very brittle structure, so that there is little margin for load relief into other paths as the critical section yields.

Your linear analysis should have caught that - all your deflections would be only 10% of what is reasonable.



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

yeah, but any ideas why a model would produce a strain of 0.011 when the stress/strain curve runs out at 0.009 ?

 

[CoryPad]

PEBKAC

 

[shearlag]

thanks for the responce and sorry for delay in replying.Dear corypad, 9% ductility is 0.09 percentage elongation at fracture or ductility is a measure of how much the material can deform before it fractures and strain is change in length by original length.
And as Mr.Greg mentions, material is more brittle considering the difference between Yeild and UTS
Yes rb1957, as i understand,NASTRAN extrapolates the last two stress-strain values if solution dose,nt converges within the given values.

 

[CoryPad]

9% ductility is 0.09 percentage elongation at fracture

No, 9 % elongation is 0.09 engineering strain.

Your last message suggests you are confused on what you are doing. I can tell you with certainty that a data point of (510,0.009) is nonsensical on either a percent or absolute scale for stress-strain.