Clamshell Marks

A series of nested curves, resembling tide marks on a beach, that indicate a fatigue crack progression through a metal component. The advancement of a fatigue crack in a stressed component is usually caused by changes in environment and load. Whenever there is an interruption in the propagation of a fatigue fracture, a unique visible mark or ridge feature, referred to as a clamshell mark, may be found. Clamshell marks are different than fatigue striations, although they are also frequently found on fracture surfaces. There may be many thousands of microscopic striations between each pair of macroscopic clamshell marks.

Also known as Beach Marks.