Ultrasound vs. X-ray diffraction.

[ResidualStressMan]

Hi,

While I'm familiar with residual stress measurements by x-ray diffraction, I'm not so familiar with measurements done by ultrasound.
What advantages/disadvantages does ultrasound offer in comparison to x-ray diffraction?
I would assume you would be able to get a much deeper depth of penetration. Would the depth of penetration be adjustable (ie. be able to measure the first 0.1mm, or the first 1mm)?

Thanks

[Robert]

Yes ultrasound can penetrate deeper. The velocity of sound in the material is dependent on the residual stress state. However, it is also dependant on a lot of other material factors (grain size, composition etc). So I believe the main difficulty in getting ultrasound to work is decoupling all these effects. It may work qualitatively or if the part is always very similar (calibrated using coupons etc) but the variation in material properties from one sample to another causes a greater change than the residual stresses.

[sreeja]

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person. X-ray diffraction finds the geometry or shape of a molecule using x-rays. X-ray diffraction techniques are based on the elastic scattering of x-rays from structures that have long range order.

[jeffhardy]

The velocity of sound in the material is dependent on the residual stress state.
However, it is also dependant on a lot of other material factors
(grain size, composition etc). So I believe the main difficulty in getting
ultrasound to work is decoupling all these effects.

Good Luck!!!!!!!!!

[sirhomer251]

In addition to the aforementioned difficulties, one must also worry about spatial resolution, which is related to a number of factors, including probe size. I suspect this is particularly responsible for the method's inability to accurately resolve fields of high stress gradients, such as in welds. We are consistently seeing blunting of peaks over regions smaller than the probe diameter.

[Yuri]

Ultrasound work fine for RS measurement particularly in welded elements and structures and above mentioned difficulties could be resolved if one have/know:

1. Solid theory that relates RS and UW velosities.

2. Methodology (how to apply theory for certain application).

3. Special precise (not standard) instrumentation/equipment.

4. Right protocol of RS measurement

[Robert]

Yuri how is it possible to decouple all of the material affects in the welds? I would agree it may be possible to determine stress in a material with ultrasound on very controlled samples. In order to get accurate residual stress values the grain size, and material must be quite homogeneous and isotropic froim sample to sample. I would think that welds would represent the worst case senario in trying to determine RS with Ultrasound. A common problem with techniques such as ultrasound is that they are trying to measure residual stress through a second order effect which is highly depended on other material conditions and not just the stress.

[Yuri]

Dear All,

In our approach we take into account the factors mentioned above with the help of specially developed theory and methodology.

I am in business of development and application of ultrasonic technique UltraMARS for residual stress measurement in welded elements and structures since 1977. I would like to use this opportunity to provide you more info on ultrasonic technique and equipment for residual stress measurement.

This technique is non-destructive. So, one can measure the residual stresses in the same points many times studying the level of residual stresses depending on the parameters of technological process, the changes of residual stresses under the action of stress-relieving techniques and service loading.

The Ultrasonic Computerized Complex (UCC) includes a measurement unit with transducers and basic supporting software and a laptop (optional item) with an advanced database and an Expert System for analysis of the influence of residual stresses on the service life of welded elements.

The basic package for residual stress measurement includes the measurement unit with basic software and transducers, which is enough to perform measurement and computation of residual stresses.

Optional software UltraMARS contains an advanced database for residual stress measurement and analysis and an Expert System for calculation of the influence of residual stresses on the fatigue life of welded elements. For convenience these two programs are installed on a laptop that is connected to ultrasonic measurement unit.

We can perform the residual stress measurement as a service by ourselves or to provide the ultrasonic equipment for this purpose.

Do not hesitate to contact me if you have any other questions on ultrasonic residual stress measurement.

Best regards,

Yuri

E-mail:info@sintec.ca

Visit us at http://sintec.ca