“Stress Cracks”

by Don Friedman on July 21, 2011

Every profession has its own language – what lawyers call “terms of art,” in one of their terms of art – that can be confusing to outsiders. The reverse is also true: there are commonly-used words and phrases that grate on the nerves of people in one field or another because those words or phrases are too similar to some terms of art.

One example of a phrase that can be heard every day in contexts that include orthopedics, car-body repair, and glazing is “stress cracks.” To a structural engineer, this phrase is somewhere between redundant and meaningless. Structurally speaking, all cracks are stress cracks. Cracks are the result of some force creating tensile or shear stress within the material that exceeds the material’s strength. That force may be external loading, internal thermal changes, imposed movement, or something else entirely, but it’s always something that creates a stress. In short, without stress there are no cracks, so stating that something is cracked is stating that it was overstressed. The problem, usually, is to find out what caused the stress.

Will saying this here change popular usage? Of course not. But it’s still worth saying.

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