FEAP User Forum

FEAP => Input File Issues => Topic started by: halleluja on June 21, 2018, 03:22:17 PM

Title: Contact of 6 nodes triangle
Post by: halleluja on June 21, 2018, 03:22:17 PM

Hi everyone,

i try to test a contact problem, all elements are 6 nodes triangle.
Following code, which i found somewhere, is just an example for 3 nodes triangle

Code: [Select]

CONTact ON
SURFace 1
POINts
FACEts
651  0  651
652  0  652
653  0  653
654  0  654
655  0  655

SURFace 2
LINE
FACEts
1 0 672 664
2 0 664 666
3 0 666 667
4 0 667 668
5 0 668 669

PAIR 1
NTOS 1 2
SOLM LAGM
END

So my first question is why in above code SURFace 2 is rigid?

For 6 nodes triangle problem, how should i define the surface? For example nodes 7, 8 and 9 are on the surface, node 9 is the midpoint of nodes 7 and 8. So shoud i use

Code: [Select]

SURFace 2
LINE
FACEts
1 0 7 8or

Code: [Select]

SURFace 2
LINE
FACEts
1 0 7 8 9?

Title: Re: Contact of 6 nodes triangle
Post by: Prof. R.L. Taylor on June 22, 2018, 05:11:27 AM

FEAP currently does not support contact for elements with higher order edges (3 or more) or faces (3 node triangle or 4 node quadrilateral).  This requires a surface treatment which is not coded.  Thus, to do the problem you describe you will need to develop a new contact module first.

Title: Re: Contact of 6 nodes triangle
Post by: halleluja on July 10, 2018, 01:10:46 AM

Quote from: Prof. R.L. Taylor on June 22, 2018, 05:11:27 AM

FEAP currently does not support contact for elements with higher order edges (3 or more) or faces (3 node triangle or 4 node quadrilateral).  This requires a surface treatment which is not coded.  Thus, to do the problem you describe you will need to develop a new contact module first.

Dear Prof. R.L. Taylor,

thanks for your answer.
What i want to simulation is a cutting process. I have following idea. The cutting tool is discretized using 3-nodes-triangles and the workpiece is discretized using 6-nodes-triangles. For this contact problem the node to surface (NTOS) algorithm is used. And nodes are from workpiece and surfaces are from cutting tool. Here even though the workpiece is discretized using higher oder elements, but i use the NTOS strategy and we don't need to consider the higher oder edges. So i think it may work.


Best

Title: Re: Contact of 6 nodes triangle
Post by: Prof. R.L. Taylor on July 10, 2018, 04:42:52 AM

while the program may solve the problem, the accuracy is likely to be very bad.  The difficulty is that forces on a 6-node triangle have very different distribution between vertices and mid-edge.

Title: Re: Contact of 6 nodes triangle
Post by: halleluja on July 14, 2018, 02:33:47 PM

Quote from: Prof. R.L. Taylor on July 10, 2018, 04:42:52 AM

while the program may solve the problem, the accuracy is likely to be very bad.  The difficulty is that forces on a 6-node triangle have very different distribution between vertices and mid-edge.

Dear Prof. R.L. Taylor,

does mid-edge mean the middle point of the edge?
may i ask you why the forces on a 6-node triangle have very different distribution between vertices and mid-edge?


Best

Title: Re: Contact of 6 nodes triangle
Post by: FEAP_Admin on July 14, 2018, 04:06:40 PM

Just try it:
   F_A = int{ p(x) N_A(x) dA }
and you will see the distribution for various variations in p(x)

Title: Re: Contact of 6 nodes triangle
Post by: halleluja on July 19, 2018, 07:20:32 AM

Quote from: FEAP_Admin on July 14, 2018, 04:06:40 PM

Just try it:
   F_A = int{ p(x) N_A(x) dA }
and you will see the distribution for various variations in p(x)

Dear Prof. R.L. Taylor,

thanks again for your reply :).
I do a simulation of the cutting process. The workpiece is discretized with 6-node triangle und cutting tool is discretized with 3-node triangle. And i use NTOS strategy. Im attachments you find the plot of time-step 31 and 32. In t32.png a strange split of the workpiece is observed. Is it because as you said the forces on a 6-node triangle have very different distribution between vertices and mid-edge?

And you have advised me to develop a new contact module because it requires a surface treatment. What did you mean surface treatment? Does it mean that i should use Surface-surface contact?


Best