The bolted joint is a force-locking joint type, and this is why we like it so much, it is releasable, reusable within its lifespan, robust, and easy to use. Unfortunately, it is also the force- locking itself, which causes the most challenges. In the case of force-locking binding the friction force ensures the self-locking. The friction, however, can cause some problems in practice. From engineering point of view the most problematic characteristic of friction is its non-permanent value (coefficient of friction). In addition to this, in engineering we can calculate mostly with the Coulomb friction model, which means that we cannot define the exact range of the slip, when the sliding appears at the interface. We can only estimate the range of this slip. Moreover, the size of this range depends on the coefficient of the friction. The higher the friction coefficient, the wider the range is, and the higher extremes we have to consider. Of course we have the same problem when realizing the tightening of the bolts during bolt mounting. In the calculations the different bolt tightening tools are considered with different parameters standing for the uncertainties of the special tools and methods (wrench, manual torque wrench, pneumatic torque wrench, tightening for angle, etc…) If the coefficient of friction is high it can be problematic, because it means a significant torque will appear in the bolt limiting the applicable pretension force. See the diagram below. Defining the impact of the friction using the finite element method is not obvious at all (here you can find the relevant blog post).