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Residual stress measurement

GOPALAERO2000's picture

Hi Everyone,

 I would like to measure the residual stress imposed pattern through thickness of the plate by forming process (bending). Is it possible?

 I came to know that residual stress measurement through HOLE DRILLING METHOD offers only on the surface. That too, applicable only when residual stress imposed is uniform through thickness (like shot blasting process). If any one came across the experience of residual stress measurement, please throw some light in this regard.

 Thanks in advance

 M Gopalakrishnan

Comments

What is the thickness of the sample?? If the sample thickness is not a big concern, then, u can try X-ray diffraction technique to measure the residual stresses in the deformed sample. U have to plot a curve, d Vs Sin2 Ψ where d is the lattice spacing and Ψ is the various tilt angles. U need this provision in ur XRD to do it. After plotting ur curve, take the slope. Usually deformed patterns roughly show a near straight line trend for  d Vs Sin2 Ψ. So the slope calculation is relatively straight forward.

Karthic

GOPALAERO2000's picture

Hi karthik,

Thank you very much for the answer. The material is structural steel and thickness would be around 10-12 mm. Let me understand the X RAY diffraction method first. Then, I shall come to you.

 

Thanks

 

M Gopalakrishnan

Mike Prime's picture

There are many ways to measure residual stresses. The optimal choice will depend on the details of your application including the material and the thickness. Since you are interested in through-thickness stresses, the near-surface techniques like x-ray and hole drilling are probably not what you want. Depending on material and thickness, neutron diffraction might work if you are willing to go to a neutron facility. It is relatively simple to do it yourself with the incremental slitting method (crack compliance). Here is an example of through-thickness stresses on a bent beam:

http://www.lanl.gov/residual/bentbeam.shtml

The deep hole method could also work: http://www.veqter.co.uk/expertise/measurements or the contour method: http://www.lanl.gov/contour/ . Both give more information than slitting but are more difficult. And simple layer removal is also possible.

Best of luck,

Michael B. Prime, Los Alamos, New Mexico
http://public.lanl.gov/prime/

(Please do not reply by email, only on the blog)

GOPALAERO2000's picture

Hello Mike Prime,

 Thank you very much for knowledge sharing for the subject query.

The material is structural steel and thickness would be around 10-12 mm. And will you please tell me that what would be the approximate cost for measuring the residual stress through neutron diffraction method at one specific location on the component.

Whatever the details provided from your end are very interesting and useful. Let me go through and understand the details.Then, I shall get back to you with the queries striking in my mind.

Thanks

M Gopalakrishnan

 

Mike Prime's picture

Many neutron facilities are "user" facilities. Neutron diffraction can be free if the results will be published, but you have to go do the measurements yourself. I am only familiar with ones here in the US. You should be able to find one closer to you. There is one in Grenoble: http://www.esrf.eu/ . 10 mm thick steel is OK.

This would probably be an easy measurement for incremental slitting. This would be faster than neutron and not cost very much (but I do not know exact amounts). Here are 2 labs that do this commercially:

http://www.hill-engineering.com/    (US)

http://www.mat-tec.ch/          (Switzerland)

 

Michael B. Prime, Los Alamos, New Mexico
http://public.lanl.gov/prime/

HI gopal

As per mike's suggestion of using neutron diffraction is pretty expensive, since it requires a nuclear reactor to generate neutrons for shooting at the sample, so  it is obvious that it is going to be expensive. In india  i think u ll find it in center of nuclear energy or some nuclear research center. I suggest u to try using XRD first and see the pattern of ur variations in lattice strains, then u can go for neutron diffraction. Since ur sample thickness is around 10-12 mm, i feel u need to cut down ur sample thickness to less than 3mm for mounting purpose. Since ur sample is 10-12,  u can cut the sample into 3 segments to measure the variation in strain patterns and if there is something serious about that finding, u try Neutron diffraction.

I have already warned u and i wash my hands with innocence Cool

 

ennio curto's picture

 NEW TECHNIQUE  FOR RESIDUAL STRESS MEASUREMENT NDT                                                          p.i. Ennio Curto Key words:NDE Residual stress.  New technique NDT Residual stress.  Non destructive testing.    ABSTRACT  This type of non-destructive method NDT provides the possibility to measure residual stress and the effect of the service load with an impact device and a vibration measurement sensor.Internal stresses are to be considered as the following: 1) Operational strains referring to loads that the material is subject and calculated  2) Residual stresses in the material caused by heat treatments or stresses caused by welding, forging, casting, etc. The new technique is able to measure the applied load and residual stress that are balanced on the surface of the material, and in a relatively large volume, at times even the same size as the entire structures. This stress is part of the metal’s elasticity field and has a three axis spatial orientation. The system works through the accelerometer mounted with a magnetic base to generate the acceleration value of the vibrations created by the device impacting on the metal surface. The acceleration value, in combination with other parameters, permits obtaining the exact value of the residual stress or load applied in the desired point. This value will appear on the display directly in N / mm ². For non-magnetic metals, wax or gel will be used to mount the accelerometer.This new system, for buildings, bridges steel inspection is very simple for to use , portable ,measure exact values of residual stress due to welding and the applied loads. After many years of research and tests, and between e discover about elastics behavior in field of metal steel now is very practice inspection point to point building and bridge constructions. This new system, for buildings, bridges steel inspection is very simple for to use , portable ,measure exact values of residual stress due to welding and the applied loads.   Introduction Internal stresses are to be considered as the following: 1) Operational strains referring to loads that the material is subject and calculated  2) Residual stresses in the material caused by heat treatments or stresses caused by welding, forging, casting, etc. The new technique is able to measure the applied load and residual stress that are balanced on the surface of the material, and in a relatively large volume, at times even the same size as the entire structures. This stress is part of the metal’s elasticity field and has a three axis spatial orientation.    Description  Elastic oscillations (also called vibrations) of an elastic material consisting of elementary masses alternately moving around their respective balance positions; these movements cause a transformation of the potential energy into kinetic energy. This phenomenon takes place due to reactions (elastic forces) that the aforementioned masses produce in opposition to elastic movements; these reactions are proportional according to Hooke’s Law to the same movements. The elastic waves that are produced propagate according to a fixed speed that depends on how rapidly the elemental masses begin to oscillate.
Elastic waves of this type are called “permanently progressive”, and they propagate at a constant speed which is absolutely independent of the speed with which the elemental masses move during the oscillating motion, and therefore also their respective oscillations.  It is easy to verify that the elastic oscillations, from a material point P (in which the elemental mass m is supposedly concentrated) are harmonic. In reality, due to the fact that in any moment the elastic force that is applied to P is proportional to the distance x of the point from its position of  balance 0, P acceleration (caused by the proportionality between the forces and the corresponding accelerations) is also proportional to x; this is demonstrated in the harmonic movement. The impulse creates in the metallic mass  a harmonic oscillation (vibration) which is characterized by a specific frequency ù² and by a width equal to dx (movement of the relative mass).  If a constant impulse is produced in the metallic material, the elastic oscillation generated in the P point will also produce a sinusoidal wave with specific width, acceleration, speed and period values. This wave is longitudinal when the direction of the vibration is equal to the P point movement, or is transversal, and in both cases the values of the results are identical; the only difference is the ¼ delay of the phase.
    Analyze impact energies Impact with the metallic surface results an elastic deformation energy.  Ed  = Ei – ( Ek +  Ep )
      
 Ei = Impact energy     Ek = Kinetic energy      
       
 Ed = elastic deformation energy          Ep = plastic deformation energy + lost energy
 Ed = ½ K dx² =   ½ m ω² dx²       K = constant elastic material (stiffness) 
     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).
      Conclusion Application of this type of non-destructive method NDT provides the possibility to measure residual stress and the effect of the service load in a very rapid and simple way on any point of the metallic surface. The testing method requires smooth surfaces free of oxides, paint, lubricants and oil. Precision depends on the roughness of the surface.This technology has demonstrated its validity over years of mechanical experimentation and has confirmed its theoretical basis.       About residual stresses
The residual stress in a metal doesn’t depend on its hardness, but from the elasticity module  or Young module and from its chemical composition. The hardness of a metal indicates its ability to absorb elastic or plastic 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. 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 frequency and vibratory acceleration generated by an impulse with the subsequent reaction elastic (elastic field) from the metal.
  You will realize the convenience of this technique. 1) Portable system easy to use and very swift.
 2) NDT non-destructive test.
 3) Repeatable in unlimited number of points. 4) All metals type (a-magnetic) 5) Don’t expensive. Effective for welding, hardened treatments, vessels control, bridges, pipes line, aeronautics, NDT inspection for every metal types. Test example   p.i Ennio Curto.    ennio curto

sir,

i want to know cost to measure residual stresses by XRD method....

is that euipment is avaiable in Hyderabadh,Andhra pradhesh,India .

sahil464's picture

i have recieved the report but didnt get the desired results.   the gave me intensity chart vs 2 theta.

sahil464's picture

in contour method how do we apply boundary conditions and what are they.

and these results can the be calculated in solid works software or not

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