When is the full shear strength of an MS20470D rivet attained?

The full shear strength of an MS20470D rivet is attained only after a period of age hardening. Age hardening is a heat treatment process that enhances certain types of materials, primarily aluminum alloys, by increasing their strength and hardness through a controlled aging process. When MS20470D rivets, which are made from heat-treatable aluminum alloys, are first installed, they do not reach their maximum strength immediately. Instead, they undergo a transformation over time, where the microstructure of the rivet stabilizes and strengthens after installation.

This gradual increase in strength is a critical consideration when evaluating the performance of riveted joints, especially in aviation applications where safety and reliability are paramount. Age hardening allows the rivets to reach their optimal load-bearing capability, ensuring that the joint can withstand the stresses and strains experienced during flight.

Initial torque application and the first flight of the aircraft do not result in the rivets achieving full shear strength since the rivets require time at a certain temperature to achieve the desired mechanical properties. Immediate shear strength upon installation does not account for the ongoing changes that occur within the material.