Hi Daniel,
You are right and adding a fillet would reduce the stress concentration. Please see the video below where the topic of artificially high stresses is discussed in detail.
Understanding and Dealing with Artificially High Stresses — Lesson 3 - ANSYS Innovation Courses
Regarding the contact with bonded behavior, as far as I know, no friction coefficient is needed because the parts are fully bonded and thus no sliding is allowed.
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