Notes¶
This document contains general notes that were taken during development of the procedures used to setup the FE model
Ligament Contact¶
Ligaments intersecting other bodies in the FE model can cause issues at the beginning of a FE simulation. These issues normally result in the intersecting parts of the ligament being ‘thrown’ out of the insersecting body. If the simulation does not fail due to large deformations, then often the spring elements that compose the ligament will become ‘tangled’. This behavior is caused by contact between the ligaments and the other bodies in the model. Through trial and error, it was noticed that having zero contact in the first step, then applying contact between the ligaments and other bodies in the second step yields a ‘well behaved’ simulation.
- Step 1) No contact between ligaments and other bodies
- Fixed femur and tibia
- Can be a short time (0.01 sec)
- Step 2) Define contact between ligaments and other bodies
- May have ‘tangling’ issues if the ligament is still slack
- These issues may be fixed by defining a fixed distraction displacement in the first step, then defining a subsequent third step to remove the fixed distraction displacement.
Also, defining a less strict contact definition appears to give more desireable behavior
*Surface Behavior, pressure-overclosure=TABULAR
0.0e3, -0.01
1.0e3, 1.0