Hello AnyBody

```
I use the STL surfaces to Define the Joint .
First ,adding FDK Features . Second,Using Surfaces to Define the Joint .Before adding some STL surfaces to the model and using them to calculate a contact force,the model runs successful,But when I add the STL surfaces to calculate a contact force ,there are always show:solver aborted after maximum number of line-search iteration.
Why?
Thanks for you help and time .
Best Regards
Yangyang
```

Hello Yangyang,

the definition of a joint using contact forces between STL surfaces using the FDK solver requires quite often a bit of trying out to find a good configuration, especially when you are not that experienced with this solver.

Basically this message tells you that the solver was not able to find a solution within the criteria you specified for the solver. This could have different reasons:

- The error tolerances you used are too low (in the study the parameter Study.InverseDynamics.ForceDepKin.ForceTol)
- The solver is allowed to do too big steps which could result in the problem where the STL surfaces penetrates through the other surface ( parameter Study.InverseDynamics.ForceDepKin.MaxNewtonStep) which could result in a state where the solver is not able to converge properly.
- The number of iteration is too low. In your case it does not look like this is the problem since the solver is reporting a line search problem. I just mention it for completeness in case you run into this problem later.
- The surfaces are too stiff, so the PressureModule has a too large value. This is a problem since very stiff surfaces produce very high forces with very small penetrations, i.e. small changes in the positions. This could be a reason for that the solver cannot solve the problem.

I would suggest that you start changing the PressureModule and review the results be checking if the position of the segments look right and checking that the contact forces are in a reasonable range (e.g. using Chart).

Best regards

Daniel