fractography
/ frac-TOG-ra-fee /
When a detective arrives at a scene, the way things are broken and scattered tells the story of what happened. Fractography is exactly that for broken parts: reading the fracture surface itself to work out how, why, and where a component failed. The broken face is a recording of the whole event, if you know how to read it.
Different failure modes leave different fingerprints. Ductile failure leaves a dull, fibrous surface covered in tiny dimples. Brittle cleavage leaves flat, shiny facets with river patterns and chevron marks that point back to the origin. Fatigue leaves smooth beach marks (macroscopic bands, each a pause in loading) and, at high magnification, fine parallel striations, one for each load cycle. An investigator uses the naked eye and a hand lens for the big features, then a scanning electron microscope for the micro-scale dimples and striations, sometimes with energy-dispersive spectroscopy to find a corrosive contaminant at the origin.
Fractography is the heart of failure analysis: it answers whether a crash was caused by overload, a manufacturing flaw, fatigue, or corrosion — which decides who is liable and how to prevent the next one. A key skill is tracing features back to the initiation site, because that tiny spot (a pore, an inclusion, a machining scratch, a sharp corner) is usually the true root cause, not the final big tear.
After an aircraft engine disk burst, investigators found concentric beach marks on the fracture surface converging on a single sub-surface inclusion — proof the disk died slowly by fatigue from a hidden defect, not from a one-time overload.
Reading the surface: beach marks and striations point back to where and how a crack was born.
The last, largest region of a fracture surface is where it finished, not where it started. Beginners often blame the biggest tear; the real culprit is the small, quiet origin the features radiate from.