diff --git a/src/paveit/datamodels/__init__.py b/src/paveit/datamodels/__init__.py
index 7deaec4..8708168 100755
--- a/src/paveit/datamodels/__init__.py
+++ b/src/paveit/datamodels/__init__.py
@@ -3,6 +3,7 @@ from .citt import *
 from .components import *
 from .data import *
 from .enumeration import *
+from .labworks import *
 from .machines import *
 from .material import *
 from .messages import *
@@ -14,4 +15,4 @@ from .regression import *
 from .sheartest import *
 from .taskmanager import *
 from .usermanagement import *
-from .workpackage import *
+from .workpackage import *
\ No newline at end of file
diff --git a/src/paveit/datamodels/labworks.py b/src/paveit/datamodels/labworks.py
index 63917b6..4f2bc1f 100644
--- a/src/paveit/datamodels/labworks.py
+++ b/src/paveit/datamodels/labworks.py
@@ -1,6 +1,7 @@
-from .tasks import TaskManagerBase
 from mongoengine import *
 
+from .taskmanager import TaskManagerBase
+
 
 # Vorbereitungen Performance Untersuchungen
 class LabworksDrillRoad(TaskManagerBase):
diff --git a/src/paveit/datamodels/taskmanager.py b/src/paveit/datamodels/taskmanager.py
index e76940e..628ef71 100755
--- a/src/paveit/datamodels/taskmanager.py
+++ b/src/paveit/datamodels/taskmanager.py
@@ -34,8 +34,8 @@ class TaskManagerBase(Document):
     
     series = StringField(default='Serie 01')
     
-    step_before = ListField(LazyReferenceField('self'), required=False)
-    step_after = ListField(LazyReferenceField('self'), required=False)
+    step_before = LazyReferenceField('self', required=False)
+    step_after = LazyReferenceField('self', required=False)
     
     meta = {
         'allow_inheritance': True,
@@ -52,6 +52,10 @@ class TaskCITTStiffness(TaskManagerBase):
     
     material = LazyReferenceField(Material, required=True)
     
+class TaskCITTFatigue(TaskManagerBase):
+    
+    material = LazyReferenceField(Material, required=True)
+    
     
 class TaskDynShearStiffness(TaskManagerBase):
     
diff --git a/src/paveit/labtest/citt.py b/src/paveit/labtest/citt.py
index 07ca76b..63a545b 100755
--- a/src/paveit/labtest/citt.py
+++ b/src/paveit/labtest/citt.py
@@ -7,7 +7,7 @@ import pandas as pd
 from bson import ObjectId
 
 from paveit import calc_nu, fit_cos
-from paveit.datamodels import CITTSiffness, CITTSiffnessResults
+from paveit.datamodels.citt import CITTSiffnessResults
 from paveit.io import read_geosys
 from paveit.labtest import DataSineLoad
 from paveit.labtest.citt_fatigue import CittAnalyseFatigue
diff --git a/src/paveit/labtest/dsv.py b/src/paveit/labtest/dsv.py
index a5e654d..e7e35a5 100644
--- a/src/paveit/labtest/dsv.py
+++ b/src/paveit/labtest/dsv.py
@@ -7,7 +7,6 @@ import pandas as pd
 from bson import ObjectId
 
 from paveit import calc_nu, fit_cos
-from paveit.datamodels import CITTSiffness, CITTSiffnessResults
 from paveit.io import read_geosys
 from paveit.labtest import DataSineLoad