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[Jan Stránský <question269724@xxxxxxxxxxxxxxxxxxxxx>]

Question #269724 on Yade changed:
https://answers.launchpad.net/yade/+question/269724

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hi Alexander,


> I'm so sorry about my lack of knowledge but i'm trying to understand what
> type of interactions are used in CpmMat:
>

you can read [1], chapter 3 "Concrete particle model"


>
> 1) Is CpmMat a bonded particle model (BPM) which is described for example
> in "A bonded-particle model for rock"
> D.O. Potyondya,  P.A. Cundall. (
> http://mech.spbstu.ru/images/b/bd/Potyondy_Cundall_2004_A_bonded-particle_model_for_rock.pdf).
> Generally, are all models in yade that support cohesion can be viewed like
> BMP?
>

After a short look to the article, it is similar approach, although CpmMat
has no bending nor torsion stiffness. I don't know other materials very
well, but in *my opinion* "bonded particle model" equals particle model,
that supports cohesion. Maybe you can ask another question concerning
cohesive models and also other poeple (not confused by CpmMat in question
title) would give their opinions :-)


>
> 2) If first is true, does CpmMat use contact bond model or beam bond mode,
> like here (http://i10.pixs.ru/storage/0/9/8/picPNG_2192511_18182098.png).
>

Cpm has only normal and shear behavior, no bending nor torsion


>
> 3) Do i understand correctly for CpmMat that:
> a) cohesive contact is created only at the beginning before simulation has
> been started?
> b) during simulation new cohesion contacts aren't created only old can be
> broken?
>

by default yes (if the script is written correctly :-)


>
> 3) Is it possible to use CpmMat for modeling damages (e.g. break on
> tension) for metallic and composite materials (not concrete and rock)? (I
> mean that concrete and metal have different behavior under tensile load
> because metal is streched fist and concrete breaks immediately) .
>

This is really a tricky question :-) The model is inspired by continuous
mechanics damage and plasticity and in tension it is designed to behave
elastically, then short plastic behavior and then exponential-like
softening. Furthermore damage has the effect of stiffness reduction, which
is not the case of metals (at least for the most part of stress-strain
diagram).

it also strongly depends on definition of "damages (e.g. break on tension)
for metallic and composite materials" and loading scenarios. For pure
tension only maybe it could work, but if it should describe tension and
compression failure at the same time, then definitely not, as the
compressive/tensile strength ratio is usually >8 in Cp,, wich is definitely
not the case of metals :-)

So a general answer is no, it is not possible, but there is some very
little chance it could work in very special circumstances.

cheers
Jan

[1] http://beta.arcig.cz/lide/eudoxos/smilauer2010-phd-thesis.pdf

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