From 076b0bb98f51536fc2e93cc5afe38232358f9905 Mon Sep 17 00:00:00 2001
From: FEA-eng <59876896+FEA-eng@users.noreply.github.com>
Date: Sat, 30 Aug 2025 21:24:22 +0200
Subject: [PATCH] FEM: Add tied contact with CalculiX (#23327)

* FEM: Update FemConstraintContact.cpp

* FEM: Update FemConstraintContact.h

* FEM: Update write_constraint_contact.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
---
 src/Mod/Fem/App/FemConstraintContact.cpp             | 11 +++++++----
 src/Mod/Fem/App/FemConstraintContact.h               |  2 +-
 .../femsolver/calculix/write_constraint_contact.py   | 12 +++++++++---
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/src/Mod/Fem/App/FemConstraintContact.cpp b/src/Mod/Fem/App/FemConstraintContact.cpp
index 3975c4339f..95f50e3c6c 100644
--- a/src/Mod/Fem/App/FemConstraintContact.cpp
+++ b/src/Mod/Fem/App/FemConstraintContact.cpp
@@ -30,6 +30,8 @@ using namespace Fem;
 
 PROPERTY_SOURCE(Fem::ConstraintContact, Fem::Constraint)
 
+static const char* SurfaceBehaviors[] = {"Hard", "Linear", "Tied", nullptr};
+
 ConstraintContact::ConstraintContact()
 {
     /*Note: Initialise parameters here*/
@@ -68,11 +70,12 @@ ConstraintContact::ConstraintContact()
                       "ConstraintContact",
                       App::PropertyType(App::Prop_None),
                       "Thermal contact conductance");
-    ADD_PROPERTY_TYPE(HardContact,
-                      (false),
+    ADD_PROPERTY_TYPE(SurfaceBehavior,
+                      (1),
                       "ConstraintContact",
-                      App::PropertyType(App::Prop_None),
-                      "Enable hard contact");
+                      App::Prop_None,
+                      "Surface behavior type");
+    SurfaceBehavior.setEnums(SurfaceBehaviors);
 }
 
 App::DocumentObjectExecReturn* ConstraintContact::execute()
diff --git a/src/Mod/Fem/App/FemConstraintContact.h b/src/Mod/Fem/App/FemConstraintContact.h
index 416c105954..f6a93cbdf3 100644
--- a/src/Mod/Fem/App/FemConstraintContact.h
+++ b/src/Mod/Fem/App/FemConstraintContact.h
@@ -53,7 +53,7 @@ public:
     App::PropertyStiffnessDensity StickSlope;
     App::PropertyBool EnableThermalContact;
     App::PropertyStringList ThermalContactConductance;
-    App::PropertyBool HardContact;
+    App::PropertyEnumeration SurfaceBehavior;
 
     // etc
     /* */
diff --git a/src/Mod/Fem/femsolver/calculix/write_constraint_contact.py b/src/Mod/Fem/femsolver/calculix/write_constraint_contact.py
index c46873c351..e8d02d1e6d 100644
--- a/src/Mod/Fem/femsolver/calculix/write_constraint_contact.py
+++ b/src/Mod/Fem/femsolver/calculix/write_constraint_contact.py
@@ -92,12 +92,18 @@ def write_constraint(f, femobj, contact_obj, ccxwriter):
     dep_surf = "DEP" + contact_obj.Name
     f.write(f"{dep_surf}, {ind_surf}\n")
     f.write(f"*SURFACE INTERACTION, NAME=INT{contact_obj.Name}\n")
-    if contact_obj.HardContact:
-        f.write("*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=HARD\n")
-    else:
+    if contact_obj.SurfaceBehavior == "Linear":
         f.write("*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=LINEAR\n")
         slope = contact_obj.Slope.getValueAs("MPa/mm").Value
         f.write(f"{slope:.13G}\n")
+    elif contact_obj.SurfaceBehavior == "Hard":
+        f.write("*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=HARD\n")
+    elif contact_obj.SurfaceBehavior == "Tied":
+        f.write("*SURFACE BEHAVIOR, PRESSURE-OVERCLOSURE=TIED\n")
+        slope = contact_obj.Slope.getValueAs("MPa/mm").Value
+        f.write(f"{slope:.13G}\n")
+    else:
+        return
     if contact_obj.Friction:
         f.write("*FRICTION\n")
         friction = contact_obj.FrictionCoefficient