Analysis using poly-ethylene material!

[ksarita20]

hi ,


i have to do a analysis problem in which the material is poly-etylene, and i am pretty sure that pro/e cannot handle non-linear materials.


Can anyone suggest aprossible approximation for this problem.


thanks


sarita

 

[Luis Aguirre]

Hello Sarita,


All non linear problems are iterative and they require adjustment for each iteration. In the case of a polyethylene material you may have 2 to 4 different types of non linearities. The polyethylene has a non linear relationship between stress and strain but the model may also have large displacements and contact included in the nonlinearities. All this type of analysis will require so type of iterativescheme (i.e newton-rapson)to converge to a solution. Although this problems could possibly be done manually ( not recommended) they are better deal bywriting a computer algorithm to do the job. The bad news is that Mechanica cannot do material non linearities (at this point) the good newsis that PTC has put together a team to add material nonlinearity to their code. I hear this from a reliable source within PTC. If stable, the new functionality is to be released in WF 3.0.





Luis
Edited by: Luis Aguirre

 

[ksarita20]

Hi Luis,


thanks for the information. So u mean that it is not apt to use the polyethylene aslike any other common material asuuming it as a elastic.U have mentioned that it has 2or 4 different types of non-linearities. Can u explain this in detail.Can i knowthe limit until which the stress andstrain are proportional for this material.


please guide me,


thanks in advance.


Sari

 

[Luis Aguirre]

Sari,


I did not mean that the material had 4 different type of non linearities. What I ment is that the model or analysis could have all these nonlinearites.


There are actually only three general types of nonlinear analys.
<LI>Material nonlinearity </LI>


1) The materialhas no linear stress-strain (plastics, rubbers) (large strain theory)


2) The material yields and no longer satisfies the linear stress-strain relationship


3) creep and relaxation of materialsare another type of nonlinear analyses
<LI>Geometric nonlinearity </LI>


1) Linear theory refers to small deformation. If the deformations are large the element mesh must be updated to take into account the new position of the elements.
<LI>Nonlinear boundary conditions </LI>


1) usually this refer to contact analysis


Luis

 

[ksarita20]

ohhhhh,


thanks luis,


ok let me explain the problem in details, so that i will be more clear. i have a cup made pf polyethylene which is bounded by a steel ring in the top. I am applying an internal pressure in the insode of the cup in a small region. So do i need to apply contact regions between the ring and the cup interface. and can i see the material flow if i do non linear contact analysis.


another question which is not related to this topic , but related to this problem: since the ring is placevery tight onto the plate, do i need to perform a prestress analysis. If so how do i need to proceed.what idid is apply a load radially on the ring for the static analysis and used this results for the prestress analysis where i have applied the internal pressure in the cup. Do u think i am right.


do i need to select the radial loadagain when performing theprestress analysis also.


sooooooo many questions. please help me out.


thanks alot inadvance.


sari