Do bending or twisting moment contribute to cohesive bond breakage ?

Hi,

The contact moments can have upper bounds (strength) but for the moment the upper bound can only take the form Mmax=a*Fn where "a" is user defined coefficient. Also rotational plasticity will not interfere (will not "break") in the calculation normal/shear terms, as you found out.
It is not very difficult to generalize the current code if someone has a precise idea in mind.

>when the contact is in tension, i.e. Fn < 0 , does the equation above actually reduce the value of maxFs ?

Yes indeed, if cohesion and friction are combined this is what happens.

Bruno

Hello Bruno,

Thanks for your response.

So in the current implementation, the bending moment and twisting moment act on the particle but do not contribute to the breakage of bonds in any way.

>when the contact is in tension, i.e. Fn < 0 , does the equation above actually reduce the value of maxFs ?
>>Yes indeed, if cohesion and friction are combined this is what happens

I am still confused about the second question.
I understand that when the two particles are slightly overlapping, i.e. in compression, maxFs = shearAdhesion + Maximum friction force. In other words, the shear force is carried by these two different components. However, when the contact is in tension, particles are not in touch and the friction shouldn't act. In that case, why should friction interfere in the value of maxFs ? Shouldn't maxFs simply be equal to shearAdhesion ?

Thanks
Varun

 >However, when the contact is in tension, particles are not in touch and
the friction shouldn't act

It really depends on which physical situation you have in mind, which
material properties, and so on. No general rule.
If you speak of granular materials with any sort of porous cement, though,
there is no reason to assume constant fs in traction. The current equation
makes sense.
If the cement is more a Von Mises material then fs should be independent of
fn in both traction and compression, this is also possible with current
code.
Bruno

On 29 June 2016 at 18:57, VG <email address hidden> wrote:

> Question #295745 on Yade changed:
> https://answers.launchpad.net/yade/+question/295745
>
> VG posted a new comment:
> Hello Bruno,
>
> Thanks for your response.
>
> So in the current implementation, the bending moment and twisting moment
> act on the particle but do not contribute to the breakage of bonds in
> any way.
>
> >when the contact is in tension, i.e. Fn < 0 , does the equation above
> actually reduce the value of maxFs ?
> >>Yes indeed, if cohesion and friction are combined this is what happens
>
> I am still confused about the second question.
> I understand that when the two particles are slightly overlapping, i.e. in
> compression, maxFs = shearAdhesion + Maximum friction force. In other
> words, the shear force is carried by these two different components.
> However, when the contact is in tension, particles are not in touch and the
> friction shouldn't act. In that case, why should friction interfere in the
> value of maxFs ? Shouldn't maxFs simply be equal to shearAdhesion ?
>
> Thanks
> Varun
>
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Once again, Thanks for your response Bruno!
I am sorry to bother you further on this question. I am just trying to have a better understanding of what I am using in Yade.

In your last post, I assume you meant maxFs.
So just to clarify, in traction, does it mean that if the magnitude of shearAdhesion = magnitude of (Fn*FrictionCoefficient), maxFs will be equal to zero ?

Thanks Bruno Chareyre, that solved my question.