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"Crack" versus "Fracture"

Andrew Bunger's picture

 It seems that within the field of fracture mechanics, some authors use "fracture" to refer to the mechanism of creating new surfaces within a body by breaking the material bonds and reserve the word "crack" for the sharp-tipped discontinuity that results from fracture of a brittle material. But it does not appear that this distinction is followed consistently throughout the literature, and perhaps different research areas within the fracture mechanics field use the two words in different ways.

 Interestingly, the Oxford dictionary gives some examples in which a crack is used to refer to a very tiny or incompletely separated fracture, which does not appear to be its typical use in the modern technical literature. At the same time, crack is implied as a synonym for fracture under the Oxford's definition for fracture. This usage, as a synonym, appears to be adopted by some in the technical literature, but really it takes a bit of detective work to figure out and there does not appear to be consistency.

So I am wondering how others distinguish between "fracture" and "crack" (if at all).

Additionally, can the distinction be traced to an original work, or has it evolved along with certain areas of research to the point that the two words may have different meanings or connotations to researchers who approach fracture mechanics from different angles (or perhaps at different scales or with different analysis tools or relevant to different types of materials)?


Mark E. Walter's picture

I think there is a third term that is more important. That term is "failure." I really dislike it when people talk about the "fracture strength" of a tensile specimen. To me "fracture strength" is reserved for bodies that have cracks. If a body does not have a crack when initially loaded, then the value at which it breaks should called the "failure strength". 

With regard to "fracture" versus "crack", I would never say something like "The body has a 2 mm fracture." I would say "The body has a 2 mm crack." The word "fracture" could be a noun, but I never use it that way. 


I think that you have already made a good distinction between "crack" and "fracture"  in that"crack" is the usually result of some "fracture"mechanisms or processes. However, sometimes, people use them interchangeablly, like in "crack formation" and "fracture initiation". 

We have got three terms 'crack', 'fracture' and 'failure' . I think we may consider them as-

as a fault or flaw or discontinuity, which we can see in an
object/solid from whether it is loaded or not it is increasing in size
or not; 

'fracture' as a process to take place over time to
create/increase the 'crack' ( we consider crack as a limit of ellispe,
I dont know if any geometric estimation is there like we have for
slenderness ratio to check a column for short or long).

'failure' as an extreme of fracture (hence, a process) when the body fails to resist the load/ serve the purpose. 

Also, as Mark mentioned, the difference is clear from '2 mm crack NOT 2 mm fracture'. 

Sandip Haldar

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