Stress Amplification Factor 2

[eltooon]

Hi, anyone can advise what is Stress Amplification Factor (SAF) and its difference between Stress Concentration Factor (SCF)?
Thank in advance.

 

[rb1957]

can you put that in a sentence ? ie, i've not particularly heard of the SAF, where did you hear of it ??

 

[Cockroach]

Sounds like some electrical got his wires crossed. The proper terminology is "stress concentration factor", not "amplification". A simple parouse through the literature at the freshman level should of proved this.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[redpicker]

Sounds like some electrical got his wires crossed.

Could also just be a error in translation from another language.

rp

 

[hacksaw]

SIF: Stress Intensification Factors is commonly used in piping

 

[flash3780]

Could it be something to do with vibrations? An amplification or magnification factor makes me think of vibratory responses. Can you give some additional info about the context?

 

[eltooon]

Hi all, I first came across this term in a FEA report. After digging through more related reports, I manage to find a definition of SAF:

- Quote -
The change in local peak stress divided by the change in the stress at the reference point (SAF) was calculated for each increment using a threee point cnetral difference formula.
- Unquote -

The FEA study was on an assembly of 2 threaded steel pipes. SAF was calculated for various points on the thread under different load conditions, like bending, tension, etc.

It's quite straightforward that a point with higher SAF is more critical. What else can we tell from SAF?

Any comment?

 

[cloa]

I think he means Stress Intensification Factor which is a function of crack tip geomentry and crack relevant geometry conditions (is it thin enough to considered plane strain conditions) A higher SIF will make a crack of a given nominal length be more likely to grow it makes the stress at the crack tip higher. Stress concentration factor is purely a function of general geometry of a structure and loading conditions. SCF affects both the general stress that a crack faces and other stress failure mechanisations (general yielding, fatigue).

 

[corus]

It's not the stress intensity factor related to crack growth as that has strange units of N/mm^2/3, or something similar. This SAF, which has no units, is related to the stress concentration factor of the change in peak stress to the change in nominal stress. What the SAF will indicate is where fatigue damage is more likely to occur. If the stresses are linear though, then the SAF is simply the stress concentration factor of the peak stress divided by the nominal stress as stresses for each load case are proportionate to each other if the loads act in the same direction. If the calculated stresses are non-linear and have exceeded yield then the SAF will be zero as the change in peak stress (with each maximum at yield) will be zero, and that tells you absolutely nothing.

Tara

http://tinyurl.com/4ydjg7m

 

[flash3780]

I think that the answer is in the above post.

However, just to make sure that I understand correctly:

If the calculated stresses are non-linear and have exceeded yield then the SAF will be zero as the change in peak stress (with each maximum at yield) will be zero, and that tells you absolutely nothing.

The above statement (regarding zero SAF for plastic flow) is based on a perfectly plastic assumption, correct?

It sounds like, for all intents and purposes, the SAF is equal to the stress concentration factor for linear-elastic problems.