yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 21 April 2010 16:18, chiara modenese <c.modenese@xxxxxxxxx> wrote:

>
>
> On 21 April 2010 15:25, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:
>
>>
>>
>>> Doesn't the problem with different plasticity condition come into play
>>> only if you store shear force instead of strain? That would break for
>>> non-linear elasticity...?
>>>
>>>
>>>
>> Not sure it makes a difference. How do you define the plastic strain in
>> your case? I guess it uses plastic = total - elastic, with elastic = some
>> sort of  ftmax/ks (remember... ;)).
>> Now, what if you cannot write elastic=ftmax/ks due to non linearity?
>>
>> Worth than that : unload the normal component with null shear velocity. It
>> will meet the plasticity criterion at some point (assuming purely frictional
>> law). Some elastic energy will be transfered to plasticity with total dUs=0.
>> I see this special case only now... I'll have to tackle this even for
>> FrictPhys_basic.
>>
>
> In FrictPhys we do not compute strains/stresses, so let's put everything in
> terms of energy. It should not be too difficult to get the plastic work
> (alias the energy dissipated). All we need, I think, is to know the shear
> displacement at current and previous time step, the shear force and the
> maximum shear displacement after that we slip. In formula the plastic work
> would read
>
> of course If us,max_t > us_t

> W_plastic = Fs*(us_t - us,max_t)
>
otherwise W_plastic = 0

>
> Then we can sum up the above one among all the contacts and over the
> simulation time.  To compute _us,max_ should I just read
>
> us,max_t = Fs_max/ks
>
> per each time step (as Fn could increase, decrease.. )?
>
> Chiara
>
>
>
>> Bruno
>>
>>
>>
>>
>>
>>  v
>>>
>>>
>>>
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>>>
>>
>>
>> --
>> _______________
>> Bruno Chareyre
>> Associate Professor
>> Grenoble INP
>> Lab. 3SR
>> BP 53 - 38041, Grenoble cedex 9 - France
>> Tél : 33 4 56 52 86 21
>> Fax : 33 4 76 82 70 43
>> ________________
>>
>>
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>
>