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Determining the correct value of "unp" needed to achieve a specific CohFrictMat tensile strength

Asked by Christopher Stanbridge

Hi all,

This question follows on from my previous request, https://answers.launchpad.net/yade/+question/256364. Answer #1 in this thread notes that "You can change [the tensile strengths] by updating i.phys.unp after creation". How would I determine the value of i.phys.unp that corresponds to a SINGLE, SPECIFIC tensile strength? For example, if I wanted all normalCohesion values in the simulation to equal 1e6 pascals (after creating the initial network), what value or values would I set unp to?

Cheers,
Christopher Stanbridge

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Bruno Chareyre
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Bruno Chareyre (bruno-chareyre) said : 		#1

Hi,
There are misunderstandings. Sorry if I was not clear previously.
To quote answer #1 more completely:
"they will have very large tensile forces. You can change this by updating i.phys.unp after creation ( i.phys.unp = i.phys.penetrationDepth)"

It says you can change the forces by changing unp, not the strength (and the suggested update is to get null forces initially).
Strength can be assigned directly: i.phys.normalAdhesion = ... It has the dimension of a force, not a stress.

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Christopher Stanbridge (cws105) said : 		#2

I think I made a mistake too -- it is actually the forces I intend to change, not the strengths! I want to use your process (i.e. set normalCohesion to 1e20 for a single timestep) to generate the initial network, THEN I want to set the tensile strength back to 1e6 without having the bonds break instantly. Would there be a way to do this? What would I do with unp?

Cheers,
CS

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Best Bruno Chareyre (bruno-chareyre) said : 		#3

>Would there be a way to do this? What would I do with unp?

Again:
"i.phys.unp = i.phys.penetrationDepth [...]
to get null forces initially"

If the forces are null the interactions will not break.

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Bruno Chareyre (bruno-chareyre) said : 		#4

The elastic force is kn*(penetration-unp), that's why.

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Christopher Stanbridge (cws105) said : 		#5

Does "null" mean "balanced" (i.e. zero in all directions)?

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Bruno Chareyre (bruno-chareyre) said : 		#6

Null means equal to zero. We are speaking of the normal force, why "in all directions"??

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Christopher Stanbridge (cws105) said : 		#7

OK, I've set unp = penetrationDepth and have gotten no further errors. Thanks for the guidance.

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Christopher Stanbridge (cws105) said : 		#8

Thanks Bruno Chareyre, that solved my question.