====== COUL2D ======
===== Description =====
Constitutive law for unilateral contact \\
Available for [[elements:cntcp|CNTCP]] \\
See coupled law [[laws:couc|COU2DC/COU3DC]]

==== The model ====
This law is only  used for mechanical analysis of problems involving unilateral contact between two bodies. COULOMB dry friction law  is used.  The contact condition in enforced via a penalty method.
==== Files ====
Prepro: LCOUL2D.F \\
Lagamine: COUL2D.F
===== Availability =====
|Plane stress state| NO |
|Plane strain state| YES |
|Axisymmetric state| YES |
|3D state| NO |
|Generalized plane state| YES |
===== Input file =====
==== Parameters defining the type of constitutive law ====
^ Line 1 (2I5, 60A1)^^
|IL|Law number|
|ITYPE| 94 |
|COMMENT| Any comment (up to 60 characters) that will be reproduced on the output listing|
==== Integer parameters ====
^ Line 1 (1I5) ^^
|IBOUE|Index to take into account residual pressure|
|:::|0 no effect taken into account|
==== Real parameters ====
^ Line 1 (4G10.0 ) ^^
|AKP| penalty coefficient on the contact pressure ($=K_P$) |
|AKTAU| penalty coefficient on the contact pressure ($=K_\tau$) |
|PHI| COULOMB’s friction coefficient, ($=\tan\phi$) |
|PBOUE| Residual pressure|

===== Stresses =====
==== Number of stresses ====
= 4 
==== Meaning ====
|SIG(1)| the normal pressure at contact |
|SIG(2)| no meaning |
|SIG(3)| the tangent stress at contact|
|SIG(4)| no meaning |

===== State variables =====
==== Number of state variables ====
2
==== List of state variables ====
|Q(1)| = 0 if the current state is elastic (no sliding) |
|:::| = 1 if the current state is elasto‑plastic (i.e. sliding has occurred at contact).|
|:::| = IELD |
|Q(2)| = 0 if there is a contact |
|:::| = 1 if there is no contact |
|:::| = NOCON |