Total energy to catastrophic failure
Total energy to catastrophic failure
(OP)
Hello all,
I'm wondering if there is information on common metals for "total energy" to catastrophic failure. E.g. The area under the stress strain curve.
It seems to me this information would be really useful. Back when I was in school when I chose a material I'd just look at the bottom of the chart, the one with the highest yield strength number. That material always had some ridiculous hardness and high strength numbers. When I'd try to use it they'd say "you can't. it's too brittle, you need to use something softer". But they could never tell me what was too soft or too hard.
Example of two materials w/ same yield str.
Steering spindle.
1060 steel Q&T @1000F. Yield str 97ksi ultimate 140 17% elongation, 277 brinell
4140 steel Q&T @ 1200F. Yield str 95 ksi, ultimate 110. 22% elongation, 230 HB
Let's assume they cost the same and the machinist will hate me with either material and ignore all other "I wouldn't use this one becaue...".
A bent spindle is bad, and would require a refund of the customer's money. But a broken spindle is VERY bad (call the coroner). Even though the 1060 has a higher ultimate str, I wonder, in an impact situation, which one *really* has a higher factor of safety against death? There must be many more examples of materials w/ similar numbers, where one is considered "brittle" and another not.
I recently tried to cut a piece of carbide. The abrasive chopsaw wasn't having it, but a chisel and a hammer owned it. A high speed steel piece would certainly have bent and deformed, but not broken. I have to assume carbide is far superior in yield and ultimate strength numbers; however, its "total energy to catastrophic failure" is much less than an equivalent piece of steel.
Is their data for Total Energy to catastrophic failure written anywhere?
Jason
btw, I thought I just posted something like this last night, but it doesn't show up?
I'm wondering if there is information on common metals for "total energy" to catastrophic failure. E.g. The area under the stress strain curve.
It seems to me this information would be really useful. Back when I was in school when I chose a material I'd just look at the bottom of the chart, the one with the highest yield strength number. That material always had some ridiculous hardness and high strength numbers. When I'd try to use it they'd say "you can't. it's too brittle, you need to use something softer". But they could never tell me what was too soft or too hard.
Example of two materials w/ same yield str.
Steering spindle.
1060 steel Q&T @1000F. Yield str 97ksi ultimate 140 17% elongation, 277 brinell
4140 steel Q&T @ 1200F. Yield str 95 ksi, ultimate 110. 22% elongation, 230 HB
Let's assume they cost the same and the machinist will hate me with either material and ignore all other "I wouldn't use this one becaue...".
A bent spindle is bad, and would require a refund of the customer's money. But a broken spindle is VERY bad (call the coroner). Even though the 1060 has a higher ultimate str, I wonder, in an impact situation, which one *really* has a higher factor of safety against death? There must be many more examples of materials w/ similar numbers, where one is considered "brittle" and another not.
I recently tried to cut a piece of carbide. The abrasive chopsaw wasn't having it, but a chisel and a hammer owned it. A high speed steel piece would certainly have bent and deformed, but not broken. I have to assume carbide is far superior in yield and ultimate strength numbers; however, its "total energy to catastrophic failure" is much less than an equivalent piece of steel.
Is their data for Total Energy to catastrophic failure written anywhere?
Jason
btw, I thought I just posted something like this last night, but it doesn't show up?





RE: Total energy to catastrophic failure
CTOD
J-integral
R curve
Failure assessment diagram
You should get a first step onto the long and winding road!
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Total energy to catastrophic failure
For brittle fractures, fracture toughness is the appropriate measure. Fracture toughness is the resistance to crack propagation, and is related to strain energy release rate. This is a complex topic, and SJones has given you some good keywords.
Mixed in there is impact energy, usually determined by the Charpy impact test. This is a simple energy to fracture a notched (but not cracked) bar, and is commonly used to quantify the ductile to brittle transition temperature for steels.
Not an easy subject. Good luck with your education.
RE: Total energy to catastrophic failure
RE: Total energy to catastrophic failure
h
RE: Total energy to catastrophic failure
http://www.fatiguecalculator.com/
https://efatigue.com/
RE: Total energy to catastrophic failure
(The Charpy V-notch test has been a useful engineering tool for a hundred years, the databases are huge, and the test is easily performed. It has units of energy as does the area under the curve in a uniaxial tensile test. However CVN does have some limitations so for any quantitative predictions on fatigue life or catastrophic failure at less than yield stress, the science of fracture mechanics provides the answers. Any data you can find on 'plain strain fracture toughness' or KIc for the steel alloys and the carbides you mentioned would provide insight. For any design work, a few other factors to consider are service temperature, applied strain rate, chemical purity of the material, and sizes of the preexisting flaws on the part.)
RE: Total energy to catastrophic failure
Any suggestions where to find said huge databases?
JM
RE: Total energy to catastrophic failure
1) the deformation theory of plasticity must adequately describe the small strain monotonic loading of a real material and
2) For the material under consideration the regions in which finite strain effects are important and in which the relevant microscopic processes occur must each be contained well within the region of the small strain solution dominated by the singularity fields.
The first requirement will be satisfied if proportional loading exists everywhere ( i.e. stress components changing in fixed proportion to one another) while the second, analogous to the small scale yielding criterion in LEFM, requires a complete understanding of the conditions required for j-dominance for the given geometry and loading conditions. A good presentation of the J-integral technique can be accessed here:
http://
Maui
RE: Total energy to catastrophic failure
1. ASM Handbook, Vol 1, Properties & Selection..., pp. 431 – 447, and elsewhere therein.
2. Hertzberg – Deformation and Fracture mechanics ... has a good collection
3. journal papers
4. web searches on [Charpy + alloy number]
As noted previously, CVN tests are not the end-all and be-all of quantifying toughness, but are an easy lab test which accounts for the prevalence of data as opposed to the more desireable fracture toughness values K(or J)-Ic.
RE: Total energy to catastrophic failure
Super good question, deserved a star
very very impresive explanations from all
RE: Total energy to catastrophic failure