"Residual Stress" vs "Microstrain" 5

[DWORT]

What is the difference between the terms "residual stress" and "microstrain" or "microstress"?

 

[Carburize]

I am not sure what you mean but...
When measurements are made using stain gages the output is frequently quoted in microstrain.
If you are talking about measurements of residual stress using stain gages and hole drilling or similar techniques the results of the residual stress measurements could well be listed as microstrain numbers.

 

[TVP]

Residual stress refers to the stress state in a part or material (sheet, bar, etc.) after some type of fabrication. The residual stress can be tensile or compressive, and may be specifically defined with respect to direction (longitudinal, transverse, radial).

The term microstrain usually is used when discussing results from strain gauges. Strain is the change in length divided by the original length of the specimen, and so microstrain just means YY.YY x 10[sup]-6[/sup] m/m (same as [µ]m/m). Microstress would be the avlue obtained when multiplying microstrain by the Young's modulus of the material in question.

 

[DWORT]

Thank You!

What are some common ways to characterize residual stress?

Are the micro properties of stress and strain substantially different than at bulk scale?

 

[TVP]

DWORT,

Check out the following links for more information on residual stresses, shot peening, x-ray diffraction, etc.:


Check out the following references:

http://www.protoxrd.com/residualstressinfo.htm

check out the various applications, publications, etc.

http://www.lambdatechs.com/html/resources/dn27.pdf

a great deal of information available including publications

http://www.shotpeener.com/library/pdf/1984034.pdf

many other items in this library on the subject

http://www.lanl.gov/contour/

http://www.ncnr.nist.gov/AnnualReport/FY1999/residual.pdf

http://www.metalimprovement.com/shot_peening.php

http://www.shotpeening.org/ICSP/confrns.htm

click on any of the conferences from 1 to 7 to freely download papers

 

[Carburize]

"Are the micro properties of stress and strain substantially different than at bulk scale? "

Depends on the cause of the residual stress. If it is due to highly localized changes such as a butt weld then yes the residual stress pattern will tend to show a peak close to the weld center-line and be balanced by opposite stresses of slightly longer range in the base material / heat affected zones on either side of the weld.
If the residual stress is caused by a more general effect such as bulk metallurgical transformation then they might be more uniform.

 

[EdStainless]

Even in generaly uniform products you can have significant variations is residual stress. You can see it in bar or heavy wall tube when you start non-symetrical machining.
You see it in sheet when you slit. If you have a slitter with a looping pit you will see how much longer one strand is than the one next to it, and they were attached.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[FrenchCAD]

Very interesting topic gents

Cyril Guichard
Mechanical Engineer Consultant
France

 

[NickE]

"You see it in sheet when you slit. If you have a slitter with a looping pit you will see how much longer one strand is than the one next to it, and they were attached."

Ed you get a star for this! Thank you! Thank you!


My first job out of masters school was on a service center floor, The first machine I was on was the slitter. (I only got to set 3 heads, too bad that was the interesting part.) I asked everyone there why some strands were longer than others, no one knew.

(I also learned why the overarm might be one of the most important parts of the machine, and what happens when .100" HRPO slips out from under it, slaps over, and knicks your knee. If I was 2" closer I wouldnt have a kneecap.)



Nick
I love materials science!