What is the difference between failure and fracture?

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Fracture and failure are distinct concepts in material science, as defined by the stress-strain curve. Failure signifies a complete loss of load-carrying capacity due to stiffness degradation, while fracture refers to the separation of material into pieces without necessarily resulting in failure. In some instances, materials can exhibit fractures without compromising their functionality, as seen in cases of metal fatigue. Additionally, certain components are designed to fracture intentionally, such as rupture disks and shear pins, to prevent more significant failures. Understanding these differences is crucial for material selection and application in engineering contexts.
Keval Patil
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How we can differentiate failure and fracture using Stress Strain Curve

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Welcome to the PF. :smile:
Keval Patil said:
How we can differentiate failure and fracture using Stress Strain Curve
Well, a fracture is certainly a failure, but what other part of the Stress-Strain curve would denote a permanent bad change in the material? :wink:
 
Material failure is defined as complete loss of load carrying capacity caused by stiffness degradation.

Fracture is more specific term. It refers to the separation of material into several pieces (crack/discontinuity).
 
Welcome, Keval Patil :cool:
It is common in cases of metal fatigue, to have one or more lines of fracture in a part that still does not fail.

Please, see:
https://en.wikipedia.org/wiki/Fatigue_(material)

Fig299_4.jpg
 
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Here's a photo of a fracture that is not a failure:
P4070009.jpg

It's in the elevator of a Cessna 172. The holes at each end are stop drills for the purpose of preventing the crack from spreading. It's an old crack, at least several years old. If the crack was to spread too far, then it would be necessary to replace the panel. As it is, neither I nor the A&P-IA is concerned about it. But we are keeping an eye on it.

Here's a photo of several fractures that are spreading:
P4070010.jpg

It's from the wing skin from a different Cessna 172. This wing skin was removed and replaced because three of the cracks spread beyond the stop drills. The A&P who replaced it is not the one that signed off on it a year ago. This mechanic would probably have replaced it before it got this bad.

None of this comes from the stress-strain curve. The stress-strain curve is useful for describing the properties of a material in order to select a material for a particular application.

There are also cases where fracture is not a failure because the part is supposed to fracture. Search rupture disk and shear pin for examples.
 
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