FEAP User Forum
FEAP => General questions => Topic started by: carlygao on January 30, 2023, 10:18:08 PM
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Hi,
I am using FEAP v85. There is "plastic drucker sig_t sig_c" option in the manual. However, I didn't find the description of Dracker Prager model in the theory manual. Does Drucker-Prager plasticity model work in FEAP85? In small deformation or finite deformation? Thanks.
Carly
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The model is available only in finite strain: It uses the module: ./elements/material/finite/plasfd.f
You should check if it works though as it is not often used by others. The problem will be for cases leading to stresses outside the vertex of the cone.
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Prof. Taylor,
Thanks. Is there any plasticity model in FEAP85 can capture the pressure-dependent yielding based on small deformation? My material has different strengths under compression and tension. I want to figure out which plasticity model is good to use in FEAP85.
If I have to implement Drucker-Prager model based on small deformation via user subroutines, is there any good reference book? The Feap manual provides very good reference materials for the J2 plasticity, but I didn't find a good reference for implementing Drucker-Prager model.
Thanks.
Carly
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The main references used for plasticity are:
author = {J.C. Simo and T.J.R. Hughes},
title = {Computational Inelasticity},
series = {Interdisciplinary Applied Mathematics},
volume = {7},
publisher = {Springer-Verlag},
address = {Berlin},
year = 1998 }
and
author = {J.C. Simo},
title = {Topics on the numerical analysis and simulation of plasticity},
booktitle = {Handbook of Numerical Analysis},
volume = {III},
editor = {P.G. Ciarlet and J.L. Lions},
publisher = {Elsevier Science Publisher B.V.},
year = {1999},
pages = {183--499} }
The vertex is a main point to consider, possibly by using multiple surfaces.
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Prof. Taylor,
I have a question about how to choose the plasticity model based on the small deformation or the finite deformation. I attached a picture in this message from Melro (Micromechanical analysis of polymer composites reinforced by unidirectional fibres: Part I – Constitutive modelling, 2013). It seems the plasticity model proposed in this paper (belongs to the Drucker-Prager family) is based on the small deformation assumption. However, the stain in the picture is very large, around 30%, and the numerical results match the testing data very well.
1. In FEAP, J2 plasticity is based on the small deformation. Can I use to simulate the large deformation for the steel components, like 30% strain?
2. The Drucker-Prager in FEAP is based on the finite deformation, but can I use it for a small deformation case? I thought the it is easier to implement the numerical model based on the small deformation than the one based on the large deformation. The Drucker-Prager in FEAP is based on the finite deformation, not based on the small deformation. Is there any special reason for this? Does this mean the Drucker-Prager model is more applicable to the large deformation in reality?
Thanks.
Carly
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1) FEAP will not limit the strains that you apply to a model. You just have to be careful as to if the results are meaningful. If there are finite rotations, in particular, you can run into trouble.
2) A finite strain model can always be run with small strain values. It will just be more expensive than running a small strain model.
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Prof. Taylor,
I attached a simple case to figure out how to use the Drucker-Prager plasticity model in finite deformation. the p value will be changed to be positive or negative for tension or compression load.
If the material block is set as follows, the plasfd.f for the Drucker-Prager model will be called. I want to know whether there is a simple way to verify whether the tension or compression stress is smaller than 350e6 (tension) or 420e6 (compression) specified in the input file. I can't verify this in "plot,stres,1". If I print out all stressed, it seems the sigma_11 value for the first step is very close to sigma_t or sigma_c specified in the input file. Thanks.
mate,1
solid
elastic isotropic 200e9 0.3
plastic drucker 350e6 420e6
plastic hardening 0.0 0.0
finite
The model is available only in finite strain: It uses the module: ./elements/material/finite/plasfd.f
You should check if it works though as it is not often used by others. The problem will be for cases leading to stresses outside the vertex of the cone.
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plot,pstr,5 will plot tr(sigma)/3 for you.
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You may want to plot max min principal stresses see PLOT PSTREss page in manual