A brief history of fractography

Abstract

Fracture surfaces have, no doubt, been studied throughout the history of mankind, probably starting with observations on stone-age tools. In the 16th to 18th centuries, the macroscopic appearance of fracture surfaces was used to assess the quality of metallic materials, with studies by Reaumur in 1722 being the most notable. However, it was not until 1943 that fracture surfaces were first examined at high magnifications (using optical microscopy up to 1000 ×), and that the first attempts were made to examine replicas of fracture surfaces using transmission electron microscopy (TEM). Early replicas had poor fidelity and resolution, and it was not until 1956 that Crussard et al. pioneered high-resolution TEM fractography using shadowed, direct-carbon replicas. This technique (and its subsequent variations) revolutionized fractography and led to a plethora of studies in the 1960's and 70's. It therefore seems appropriate to commemorate the 50th anniversary of high-resolution electron fractography with a review of how it, and subsequent scanning electron microscopy (SEM) and other techniques, have led to a better understanding of fracture processes. Such understanding has been invaluable in failure analysis and in developing improved materials. Milestone observations for a number of important models of fracture in inert environments including cleavage, brittle intergranular fracture, dimpled overload fractures, and fatigue fractures, are described first, followed by examples of key observations for fractures produced in embrittling environments.