# Incremental/Total Slip Displacement and Distance in PFC3D

**URL:** <https://forum.itascainternational.com/t/incremental-total-slip-displacement-and-distance-in-pfc3d/823>\
**Category:** PFC\
**Created:** [November 13, 2022, 9:12pm UTC](https://forum.itascainternational.com/t/incremental-total-slip-displacement-and-distance-in-pfc3d/823 "2022-11-13T21:12:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![awbrandt](https://avatars.discourse-cdn.com/v4/letter/a/cdc98d/32.png) [@awbrandt](https://forum.itascainternational.com/u/awbrandt)\
**Post date:** [November 13, 2022, 9:12pm UTC](https://forum.itascainternational.com/t/incremental-total-slip-displacement-and-distance-in-pfc3d/823/1 "2022-11-13T21:12:32Z")

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Hi,

I am looking to access the total distance “slipped” by the clump in my model. My model includes a clump in contact with a wall, and the wall has an input velocity. I am using the linear contact model. Is there a way to implement this in PFC3D Version 7.00.154?

I know that I can access the slip state (as either being true or false) using contact.prop(cp,‘lin\_slip’), but I am looking to get the distance travelled during slipping by the clump itself (not just whether or not it is slipping).

Thank you.

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**Author:** ![dblanksma](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@dblanksma](https://forum.itascainternational.com/u/dblanksma)\
**Post date:** [November 17, 2022, 3:10pm UTC](https://forum.itascainternational.com/t/incremental-total-slip-displacement-and-distance-in-pfc3d/823/2 "2022-11-17T15:10:52Z")

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Hello @awbrandt,

This can be tricky for clumps, especially if the clump has more than one contact at a time, and some may (or may not) be slipping.

With that said, there is no record of the plastic (shear) displacement _at a contact_ for the liner model. One way to compute this value would be to use a set of FISH functions and back-calculate it from the slip energy. This would require:

1. activating energy tracking
2. have a FISH callback function registered with the “slip\_change” event: if slip has initiated put the contact in a list of contacts to track. If slip has ended then remove the contact from the list
3. Implement another FISH function registered as a callback after force-displacement law in the cycle sequence, to back-calculate the plastic shear displacement increment from the slip-energy increment at each timestep for each contact in the list (until the contacts are removed from the list)

It may be easier and faster to implement a custom contact model based on the linear contact model that would have this property actually recorded.

– Derrick