Clamp-knife-base system of cutting instrument of a harvester is considered. This is typical multicomponent tribo-fatigue system loaded by both cutting force bending the knife and contact forces caused by bolted connection. Stress-strain state of all elements of clamp-knife-base system is obtained taking into consideration frictional contacts between clamp and knife and knife and base. The influence of bending force on contact interactions in the system are shown (tribo-fatigue back effect).