# Flow Models in PNM Material Models using PolyUMod

Hi everyone,

I have done various fits of experimental data using the PNM in PolUMod along with MCalibration software. This has all worked successfully but now I am writing up my thesis and Im struggling to define the equations. I can se the differences between linear viscoelastic flow, power-law flow, BB flow and BBND flow but I dont know what the f[SUB]p[/SUB] , f[SUB]E[/SUB] and f[SUB]0[/SUB] actually mean. Everything else I can find a definition for but these values I cant.

Can anyone help?!?!

Thanks,

Al

Hi Al,

I am happy to help 🙂

f_theta : is a scalar factor that is only used if you define a temperature dependent elastic component (ET_Type) or a temperature dependent flow component (FT_Type)

f_p : is a scalar factor that is only used if you define a pressure dependence of the yield stress equation (FP_Type)

f_epsp : a scalar factor that is only used if you define a yield evolution factor (FYE_Type)

These variables are otherwise equal to 1.

-Jorgen

Hi Jorgen,

Thanks very much for this, you are a gentleman. It does however prompt a couple of extra questions. I see that the BBND flow model introduces a factor f_v, where:

f_v = 1+alpha E:E_e

does this E=ln[v] refer to true strain? and does E_e=ln[V_e] refer to engineering strain? If so what does the ratio actually mean??

I have also played around with the power-law flow with strain dependence. Does the f_v in this model equal the f_v in the BBND? Also I see that the E_p is the mises strain from F_p. I am presuming that this is a deformation gradient but cant figure out the relevance of the p superscript in the PolyUMod users manual.

Thank you so much for your help.

Al

E=ln[v] is the true strain

E_e=ln[V_e] is the true elastic strain

The factor f_v is not active in the FType=507 model.

The variable E_p is the true strain calculated from the viscoplastic deformation gradient (Fp).

Fp is obtained from: F = F_e F_p.

What type of material are you trying to model? The Parallel Network Model (PNM) features that you are investigating are typically only needed in specific cases, and there may be an easier way to get accurate results.

-Jorgen

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