RESIDUAL STRESS MEASUREMENT NDT

Date 07-04-2008 10:02

RESIDUAL STRESS MEASUREMENT NDT

TECHNICAL DESCRIPTION

Preface:

For internal stresses are considered: 1) Strains to which the materials are submitted and calculated. 2) Residual stresses of material due to heat treatment or forging, welding, etc. The equipment measure all stress types than equilibrate themselves in the surface of the material, and in a relatively large volume sometimes the same order of entire structures, these stresses are within the elastic metal field and have a spatial orientation, triaxial.

Theory:

Oscillations elastic (also called vibration) in an elastic material, consist in alternately movement around the respective equilibrium positions of the elementary masses, cause of these movements generate a conversion of potential energy into kinetic energy. This phenomenon occurs due to reactions (elastic forces) that the elementary masses, above views, opposed to elastic movements, these reactions are proportional for the Hooke law to the displacement. The elastic waves produced, propagate themselves with a fixed speed, which depends on how quickly the masses elementary enter into oscillation. The elastic waves of this type are called 'permanent progressive, which spreads to a constant speed is absolutely independent of the speed by which the elementary masses move during their oscillation, and hence the respective accelerations. Is easily to verify that the oscillations of material point P. (on which suppose concentrated elementary mass m.) are harmonics. In any instant the elastic force, applies to P, is proportional to distance x from its position of equilibrium 0, the acceleration of P (for proportionality between the forces and the corresponding accelerations), this has occurred in harmonious motion. The impulse creates in a metal mass a harmonic oscillation (vibration), characterized by a specific frequency and displacement   (movement of its mass) acceleration and speed.
This wave is longitudinal, when the direction of vibration is the same motion of point P, or transversal,
in both cases the resulting values were identical, the only difference is a delay of 1 / 4 phase.

Elastic energy, as subordinate to a impulse energy, is:

Ei = Ek + Ed + Ep

Ei = Impulse energy    Ek = Kinetic energy

Ed = elastic deformation energy

Ep = plastic deformation energy

   Ed = ½ K dx² =   ½ m ω² dx² = Ed = ½ m X dx

   K = constant elastic material (stiffness)

   dx = displacement

   X = acceleration

   Behaviour elastic metals, due to new discovery:



Technique

The tester, through accelerometer mounted with magnetic base, gives the value of acceleration of the vibrations generated by the impact device with constant energy, on metal. The acceleration value combination with other parameters gives the exact value of residual stress or loads applied at the point tested. This value is displayed in the LCD directly in N/mm². For non-magnetic metal, will be using wax or gel to attach the accelerometer at the metal. The application of this non-destructive method, gives the opportunity to measure the residual stress in every surface point and more time. It is
very easy to use, efficient and allows for the measurement of residual stress in welded elements, and existing structures, for all types of metals with NDT method.

Quality of surface

The test method requires smooth surfaces free of oxides, paint, lubricants, oil. The indentation deep and the accurately of the test depend from the roughness of the surface. For the preparation of the surface, is necessary, must be careful not to alter the surface over certain values of heating or hardening. More practical results can be realized by using a high-speed grinder (> 12000 rpm).

Residual stress.

The residual stress in a metal doesn't depend on its hardness, but from the module of elasticity or Young module and from its chemical composition (density).
The hardness of a metal indicates its ability to absorb energy elastic, plastic or kinetic energy, but through it not possible to determine the value of residual stress. In a metal with the same hardness we will have different values of this stress. Therefore, the problem will be to measure the values that vary so exactly proportional to the residual stress values in a given metal.
The residual stresses tend to equilibrate themselves in the surface of the material.
The measurement made with all the major methods, X-ray, string gauge (destructive), optical etc. the residual stress is determined between the measuring the displacement of the equilibrium point the reticule crystalline.
The method discovered analyzes the value of acceleration vibratory generated by an impulse to constant energy with the subsequent reaction elastic (elastic field) from the metal. The equipment don't recognize the value of compression from that of tensile stress. It gives the value of the space resulting or volume but with the applying of a triaxial accelerometer we can have forces values axis x, y, z.

You will realize the convenience of this apparatus.
1) Portable and easy to use and very rapid.
2) NDT non-destructive test (strain gauges).
3) Repeatable in unlimited number of times.
4) Not complicate (X-ray).
5) All metals type a-magnetic (Barkhausen)
6) Don't expensive. Effective for welding, hardened treatments, vessels control, bridges, pipes line, aeronautics, NDT inspection for every metal types.

Ennio Curto

By G.S.Crisi (****)

Date 07-05-2008 18:11

Is this method the same, or similar to, measuring the residual stresses by X ray diffractometry?
Giovanni S. Crisi
Sao Paulo - Brazil

By ennio curto (*)

Date 07-08-2008 18:38

Yes Dr. G. S. Crisi
The accuracy is the same but more simple and practice.

Best regards.
Ennio Curto

By CWI555

Date 07-07-2008 11:41

Sounds more like Accoustic emissions meets UT.

How does this process handle Dendretic structures?

By ennio curto (*)

Date 07-08-2008 18:43

My be you wrong because this is not a processing and without the sound .

By CWI555

Date 07-08-2008 19:11 Edited 07-08-2008 20:21

"Oscillations elastic (also called vibration) in an elastic material, consist in alternately movement around the respective equilibrium positions of the elementary masses"

"The residual stress in a metal doesn't depend on its hardness, {but from the module of elasticity or Young module} and from its chemical composition {(density)}"

"The residual stresses tend to equilibrate themselves in the surface of the material."

"The method discovered analyzes the value of acceleration vibratory generated by an impulse to constant energy with the subsequent reaction elastic (elastic field) from the metal."

Maybe you don't know what the product is your advertising. Oscillations are oscillations.
wave front: A continuous surface drawn through all points in a wave disturbance which have the same phase.
wave length: The distance, measured along the line of propagation, between two wave surfaces in which the phase differs by one complete period. Numerically, the wavelength is equal to the velocity of propagation divided by the wave frequency.

No matter what the mechanism your using for initiation of the wave oscillation, the end result is the same. Propagation of a wavefront(s) through the material. That mechanism can be a hammer blow, a mechanical piston, or a piezoelectic transducer. Sonic, sub sonic, hyper sonic, ultrasonic.. all production a wave front, and with a P wave front it will find it'self in compression or rarefraction.
those wavefronts can take many forms of oscillation depending on the material, temperature etc.
There is longitudinal, transverse, rayleigh, lamb, love, stoneley, sezawa, etc.
V= square root of C ij / p
V is velocity(speed of sound), C = elastic constant, and p = material density ij = directionality of the elastic constants with respect to the wave type and direction of wave travel.

I understood completly what your after. This device your describing is a different twist on an old principle.
(graphic created by Dan Russel PHD Kettering University.)
Suggest you read more on the subject. http://www.kettering.edu/~drussell/Demos/wave-x-t/wave-x-t.html

By CWI555

Date 07-09-2008 12:01

I asked a simple question, and you responded with what I took to be a negative statement. I suggest you arm yourself first before trying to take shots in my direction and please do not send me another pm like the one below. If you have something negative to say, say it in the open.

"I don't believe you know very well residual stress, and the vibration is different of acoustic sound, reed more well the information an than we can discuss, I remember to you that is e discovery of applied mechanical a therefore no patentable. "I can not explain the completely theory."

With all due respect, I understand residual stress far more than you realize. I don't really care where you got your information from, or for whom you work.
I ask a question, and you responded with negative comments, if your going to tell someone they don't have clue, you better have your act together. The nature of your post above, the language used, punctuation, etc, is not the same as your initial post. You as much state so when you say "I can not explain the completely theory". The structure of that sentence is not the same structure as the initial post, therefore the conclusion it was two different persons writing them.

This device or method that your trying to drum up interest on may or may not work, I have severe reservations in that regards, but the theory of transmitting a vibration through a part and picking up the differences in how each area reacts to that vibration is basic UT theory, and basic Acoustic emissions, theory. Modeling stresses has been done already with both. Suggest you read further. Stating that you cannot explain the complete theory in the same paragraph as telling someone you don't think they have a clue is an oxymoron. Some books and information for you to aquire and comprehend before you start taking shots at someone:

http://www.weldstress.radaj.de/residual_stress.pdf
http://www.fra.dot.gov/downloads/Research/ord9906.pdf
http://www.ndt.net/news/2000/stress06.htm

If you need more, let me know.

By ennio curto (*)

Date 07-09-2008 12:55

come on , is 19 years I an studying this method, and you write about the acoustic propagation wave, I repeat to you I can not publish the theory because is an discovery then confirm experimental tests. (sorry for my English)

Best regards
Ennio Curto

By CWI555

Date 07-09-2008 13:42

Maybe you have. However; I did understand what you were saying the first time. I only asked how it handled
dendretic structures and stated that it sounded like acoustic emissions, and UT. Which both use the same principles
you initially posted. I can provide you more links, and after this weekend when I can get to my storage unit, I can provide you information on books and papers already written to the effect. No matter how you describe it, to use
a vibration a mode of testing, it all comes back to the same basic theory, transmitting a "vibration" through the material in question and monitoring the response to various areas to that vibration.
The only thing that has held this field back for years was computational speed and inherent programming issues.
Pass a wave front (vibration) through a material of known dimensions, and map the response from various zones of the same material.

Going back to what you have stated, you use the term vibration, and state the use of an impactor. No matter how you describe it, energy has to pass from point A to point B. Otherwise you have static test, just sitting there doing nothing.
I can hit a piece of steel with a hammer and it's going to set up a vibration in that steel to some degree or another.
If your principle is using youngs modulus, elastic co-efficients, and the rest that you describe, then there is a wave front moving through the material.
Quote: "The tester, through accelerometer mounted with magnetic base, gives the value of acceleration of the vibrations generated by the """"impact device"""" with constant energy, on metal"
If you were using electromagnetic energy, or anything other than mechanical energy "impact device" then you may have something different. Otherwise a wave is a wave is a wave which is bound by the same rules of physics as any other means of transmitting vibrations through any given material. "gives the value of acceleration of the vibrations" effectively you measuring changes in material velocity as you pass through various densities of material.

Then again maybe you didn't read what you posted
Another quote:
* "This wave is longitudinal, when the direction of vibration is the same motion of point P, or transversal"
Longitudinal waves are compressional waves, or Lwaves, a transverse wave is a shear wave, either is a vibration mode utilized in UT.

Your more recent post "you write about the acoustic propagation wave"
Well sir, thats exactly what you wrote about in your first post, and your questioning me for drawing simularities to acoustic wave fronts????

"For the preparation of the surface, is necessary, must be careful not to alter the surface over certain values of heating or hardening"

this impactor your speaking of, sounds more like a cross breed with a hardness impactor if localized surface hardening can have that effect on your test. Either way the end result is the same.

Finally; and it will be finally, I've personally performed the EMAT version, and have read extensively on it.
The Emat version in particular is not usually subject to concerns of localized surface hardening, and therefore a more accurate means of initiating the "vibration" than an impactor ever will be. For that matter, I know people developing an Eddy current version of this as well.
They all skin the same cat, but some are more efficient and accurate at it.

Good day sir.

By ennio curto (*)

Date 07-09-2008 16:05

Dear Sir.

The EMAT system don't give the residual stress value in N/mm², and you know that is very important for welding because same time the residual stress, near the welding, can be very high an worth near to yield point or broken point of metal. All this without flaw of metal. We need to stay in this question and what this new technique can do, all other is knowledge of material.

Best regards
Ennio Curto