Plastic product development - fem analysis

[fembig]

Hello,

For a glass filled nylon part, we have to do fem analysis using abaqus(probably). I have material datas like all modulus, possion ratio, stress-strain curve(tensile) etc.,

Design objective would be under high load, created stress should be in the elastic range. Anything beyond is not acceptable.

But, with the initial design if stresses go beyond yield limit(in linear static analysis), how to proceed with the analysis to deal with nonlinearity.

1. Plasticity - Plastic model (in abaqus) - Is it the right material model for plastic materials to define stress-strain curve.

2. Could you explain about viscoelasticity with respect to my project - should i consider this model for my analysis or how important is this in a general plactic product fem analysis. (material model looks complicated with unknown constants)

I have limited knowledge about fem. if anything wrong in my post, pls correct me.

Anyhelp would be nice.

fembig

 

[feaplastic]

Hello,

i am not an expert. But, it may help you.

1. run a static analysis. Look for displacement and stress values. Beyond yield, then results may not be reliable. You must analyze with stress strain curve(for ductile) and if needed with geometric nonlinearity also. For brittle plastic material, mostly material nonlinearity is not possible. You must reconsider your material selection.

About abaqus, I am very new. But, I could say Plasticity - Plastic material model may be right. You must define in terms of plastic strain. (go thru manuals to convert from engineering strain).

About viscoelasticity, sorry. Hope, someone would answer in this forum.

Thanks,

fea

 

[EdR]

If anything outside of the elastic range is unacceptable why would you do either an inelastic or viscoelastic analysis???

Ed.R.

 

[GBor]

Ed.R. deserves an answer. If your requirements are for stresses to stay in the elastic range, then you have either an elastic material, or, at most difficult, an orthotropic material model. You do not need plasticity or even a stress strain curve as the modulus will full define the material WITHIN THE ALLOWABLE RANGE. If your modulus is different depending on which way you pull on it, then you may need to consider orthotropic inputs.

ANY non-linearity would need to be a geometric non-linearity (large deflections), not material non-linearity. You can still use an elastic material, but would need large deflection formulations (Total or Updated LeGrangian).

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
Magnitude The Finite Element Analysis Magazine for the Engineering Community

 

[xerf]

Some remarks:
1. You should use the constitutive response which is most suitable to the experimental data you have.

2. Classical plasticity is most appropriate for metals whereas you seem to have a different material.

3. Viscoelasticity should be considered if the "viscosity" is important and if you have load-dependent material properties or if you are interested in creep/ stress relaxation phenomena. Viscoelasticity is a complex topic and cannot be explained in a post. Reading the theory manual of ABAQUS, the chapter on materials might help.

4. If you are not sure what constitutive model to use for your material you should check the literature (i.e. journals) to see what other people have used for similar materials.

5. It is a bad idea to use a computational constitutive model without knowing it.

 

[fembig]

Hello,

Thanks everybody.

EDR, I want to do inelastic analysis to know the real stress-strain values. I think static test is not sufficient to if stresses or displacements are exceeding.

Xerf,

I will check for material model. But, can you explain me what is the model preferred for plastic material for eg. PP, PE and so on.. (in abaqus)

fembig

 

[xerf]

PP, PE = ???

 

[cbrn]

PolyPropilene, Polyethilene

 

[xerf]

Then, I cannot explain.