Crack initiation and propagation under cyclic loading, S-N curves and the endurance limit, the surface finish and stress-concentration factors that dominate real-world fatigue life, and the beach-mark fracture surface that identifies a fatigue failure on sight.
Fatigue is what makes a part that passes every static strength check fail anyway — progressive damage that accumulates under cyclic stress well below yield strength, with no visible deformation to warn anyone beforehand. This module works through the three stages every fatigue failure passes through (initiation at a stress concentration, incremental propagation, sudden final overload), the S-N curve and why steel has a true endurance limit while aluminum does not, and the specific factors — surface finish, notches, residual stress, corrosive environment — that determine whether a real part gets anywhere near its textbook fatigue life.
By the end of this module you should be able to read a fatigue fracture surface — locate the origin point behind its beach marks and explain why that origin almost always sits at a surface stress concentration. Module 12's fracture mechanics content picks up directly where this module's crack-propagation stage leaves off.