Impact and fracture toughness & impact and fracture strength

[liu xing]

hello,everyone
I am so confused about Impact and fracture toughness & impact and fracture strength.it's hard for me to understand fully of difference and relationship. Maybe they are not in One category.
hope for your point view and thank you so much~

 

[EdStainless]

Impact strength is the force that it takes to break a sample in sudden loading, think Charpy Impact.
Fracture toughness is usually related to crack propagation, so things like K1c (and the other modes).
At least in my mind that is how I separate them.

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P.E. Metallurgy, Plymouth Tube

 

[liu xing]

@EdStainless
thank you so much~
you just explained impact strength and fracture toughness. but is there impact toughness and fracture strength ?

 

[IFRs]

I don't know if it helps you visualize it but toughness is the area under the stress-strain curve and fracture strength is the final recorded point of the stress-strain curve (where the sample breaks).

 

[liu xing]

@IFRs (Petroleum)
your view is very ｖalue. I can got your point.
thank you so much~ you are so smart.

 

[rb1957]

I'd add the Ed's post (he did a good job of two of your terms) ...
fracture strength (more commonly called residual strength) is the strength in the presence of a crack ... thus variable depending on the crack geometry.
I don't know if I'd use a term like "impact toughness" ... the closest I can get to this would be the dynamic material stress/strain curve. "fracture toughness" is a separate material property, relating "fracture strength" to the crack geometry.

another day in paradise, or is paradise one day closer ?

 

[EdStainless]

One of the key terms is 'impact', that infers high strain rates (100-100,000 time higher than tensile testing).
In some applications very high strain rates (in the millions or higher).
Under impact conditions you can measure various parameters, though total absorbed energy is the most common. You cannot really distinguish between toughness and strength.
Once you get into fracture mechanics they are many different characteristics. This covers fatigue (which mode, what load, what frequency) and what you measure (crack growth rate, energy to propagate) and if you start with precracked samples or not.
This is a very large field of study.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

There is no such material engineering term as impact strength or impact toughness because Charpy impact is measured in values of ft-lbs energy. It is a qualitative test to compare fracture behavior between materials or for a range of temperature.