Author Topic: Help. Frictional Contact Between Sliding Blocks in 2D  (Read 5719 times)

hackworth

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Help. Frictional Contact Between Sliding Blocks in 2D
« on: March 11, 2025, 01:59:42 PM »
Hello all,

This is my first time posting, so hope I don't miss anything or do anything wrong.
Attached is a simple contact solution I drafted as a temporary way generate solutions fast for frictional contact
and to easily check if the solution is generating anything accurate at all with analytical comparisons.

The simulation is set up for a rigid block (diamond properties) to indent, then slide on a surface of a deformable
sample block (tungsten properties). The simulation is locked to elastic deformation. The simulation is a simplified
version of a scratch simulation I hope to generate accurate solutions for, which uses a cylinder (due to plane strain)
to indent and slide on a tungsten block that permits plastic deformation.

The issue I'm running into is that, no matter the frictional coefficient or if the simulation is assumed to be frictionless,
the output returns virtually the same dataset for all cases. The only time I see any variation between different frictional
coefficients is during the indentation phase of the simulation, where the tangential force measured at the top of the
indenter decreases for increasing coefficients, but then increases when the coefficient equals 1. I'm not sure if this is
what's supposed to happen or if there's something missing in the input file that I need to specify, all I know is that I
ran a bunch of test cases, changing the PAIR definition, and no matter what I changed, I saw a consistent behavior
of near complete invariance across all test cases.

Sorry for the long winded post, attached is my script and any help/insight would be appreciated.

Prof. R.L. Taylor

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Re: Help. Frictional Contact Between Sliding Blocks in 2D
« Reply #1 on: March 12, 2025, 05:43:00 PM »
I do not find any attachment.  Can you attach the input file so we may check what is happening
Thank you.

Prof. R.L. Taylor

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Re: Help. Frictional Contact Between Sliding Blocks in 2D
« Reply #2 on: March 12, 2025, 05:43:39 PM »
Sorry I it appeared On second loading.

hackworth

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Re: Help. Frictional Contact Between Sliding Blocks in 2D
« Reply #3 on: March 13, 2025, 10:29:18 AM »
Ok cool, sorry for the late response. Was there any obvious issues with the input file?

Prof. R.L. Taylor

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Re: Help. Frictional Contact Between Sliding Blocks in 2D
« Reply #4 on: March 13, 2025, 12:05:17 PM »
Thank you for the careful check on the frictional contact.  Indeed there is a bug in "penarea.f" in./contact/nts2d when setting the friction force in the residual.  The routine should read:

!     Friction contribution

      if (iffric.eq.1) then
        d21   = ch2(p1(7))
        csibb = ch2(p1(17))
        d21o  = ch3(p3(1))
        ft= ch2(p1(53))
        call stifv1 (s21,c21,0.d0,0.d0,vn0,'N0')
        call stifv1 (s21,c21,csi,csi2,vts,'TS')

I have also made a couple of suggestions in the solution algorithm which helps the convergence significantly.  First is to use NEOHook for the models.  Second using CONTact CHECk to hold the contact search area for each iteration.  The latter is especially helpful for frictional problems.

Please let us know if this helps in solving your problems.

hackworth

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Re: Help. Frictional Contact Between Sliding Blocks in 2D
« Reply #5 on: March 13, 2025, 12:29:15 PM »
Thanks so much, yeah I'll let you know if it helps. Have a great day.