Nondestructive Testing - Science topic

Thank you Depivers

The green echoes are just a display mode called envelope. This mode holds the signal on the screen. To turn it off i believe it is in Display > Overlay > A-scan > Envelope.

I am not 100% sure on your setup or what your damage mechanism is, but the through transmission method (2 probes, one on either side of the specimen) will only indicate discontinuities through a lack of response.

The dimensions of the thin plate, the configuration of shaker or input device, support and/or constraint of the specimen during testing, the location or distribution of area being measured for signal to test for Ao & So, as well as what transducer(s) or optical technique(s) is/are being used for those measurements, and what circuits and software are being used to condition and process the signal after acquisition.

The are many reasons that may be causing attenuation or lack of effective detection or isolation of the desired or expected signals, including that they actually may not be there at sufficient energy level for effective detection. Are you sure your estimated values for So of the increased-thickness sandwich plate are reasonable and don't actually predict the lower So values? Are you measuring 'lamb' waves on one skin of the sandwich only or of the entire plate (i.e. do you have transducers on both surfaces of the plate with careful and accurate reproduction of phase in both cases, and relative to one and other? Do you isolate or effectively filter frequency or wavelength anywhere in the process of your data collection, conditioning and/or post-acquisition processing? Are the 'lamb' waves on the skin or in the overall plate, what is the ratio of characteristic wavelength to plate thickness and how did this change by your structural alteration?).

Without knowing more of your setup, you experiment and your instrumentation, it is difficult or impossible to offer meaningful guidance.

In terms of a general vibration measurement problem, what signal are you expecting and why? Does the measured value represent something that seems impossible or not, it the result within or nearly within the expected range, and if not, is there something in the method or instrumentation or conditioning/processing that might explain any observed discrepancy? Hope this helps.... -TH

Temperature measurement, surface temperature, intelligent pyrometer

The non-contact thermometer ensures precise ... Show details · Navigation: Applications · Industries Search by measurement · Acceleration & ...

You have a wave packet due to the the impact on the plate. We do not know where is the environment of the plate. The trailing packets can be excited by a far reflection from the boundary the enclosure of the plate.

I proposed this hypnosis because as you see the second wave packet is attenuated relative to the first wave packet. So, i assume trailing pulses are echos of the first pulse. They may come from a far boundary to the plate.

Best wishes

The infrared spectra for a natural gas flame has a peak at 4.2 to 4.7 μm due to emissions from CO₂. There is also a peak between 2.4 to 3 μm due to emissions from H₂O and CO₂. Then there is a broad band peak between 0.4 and 3.5 μm (dependent on the flame temperature). Cameras in the range 0.8 to 1.1 μm are typically used for higher temperatures typically above 600^oC. Therefore any infrared camera that operates in ranges below 5 μm should work, provided it is not restricted to the 3.9 μm band, should see flames.

I don't know your problem exactly, but i can guide you how to implement this in Matlab or some other software. Follow the steps in software coding:

1. First what is i,j. Fix it. What is u and v?

2. Find t(x,y) value using the given formula.

3. Second step evaluate u and v.

4. Third step find rij.

5. Its not simple. You should interrupt like this

rij(t(x,y)) =

6. Then find E(x,y)

Thanks to everyone who contributed and showed interest in this work. The final article is found here, with 50 days free access from today 21/09/2019: https://authors.elsevier.com/a/1ZmZs7tcTWXHTP. Enjoy the paper and thanks for your interest. #additivemanufacturing #microCT

Рами Карми прав! Акустическая эмиссия лучший известный метод. Но можно и методом с использованием эффекта Горбунова . Без дополнительных механических усилий.

Сканирующая контактная потенциометрия требует приложения (накладывания) специальных поверхностных контактов. Метод с эффектом Горбунова не требует этих операций. Обладает чувствительностью на порядок выше чем сканирующая контактная потенциопетрия.

Dear Zhang

I hope that these articles will be useful to you.

Thank you Mr. Leicht. I will try to contact Dr. Holger Friedrich from the link you provided.

Best Regards,

Prasad

Dear All,

I finally found the solution: the quasi-static mechanical analyser QMA-X from Mecanum. It uses a non-destructive method for determining elastic modulus and Poisson ratio of very weak, highly porous, materials. The very low frequency that it is used allows doing this kind of measurement for highly attenuating materials. Moreover, it complies with the ISO 18437-5 standard.

Have a look at the flyer, here attached.

Alain

Hi, try to use the ultrasonic waves inspection. Use the reflecting pulse method to calculate the depth of the defect from the specimen surface. The transmission pulse method can detect the presence of the defect only. Good luck.

Aside from Oleg's answer the other possible advantages of laser based generation are due to the mechanism in which lasers produce ultrasound. As the material under test acts as the 'transducer' all wave modes supported by the material are generated, as opposed to a piezoelectric transducer which relies on mechanical energy to induce ultrasonic waves in the sample, and thus relies on angled incidences to generate the various wave modes. Lasers also produce surface (Rayleigh) waves very efficiently when compared to piezoelectric probes.

Not sure this is the case in your application, but some types of damage give rise to significant non-linear behavior, causing higher harmonics in the received signal. Thus the presence of higher harmonics (particularly at twice the excitation frequency) is sometimes used as an indicator for damage. If your measurement is based on this effect it makes sense to choose the receiving probe to have twice the frequency of the transmitter.

I would approach the problem with a circumferential lamb wave.  This can be easily monitored continuously with a pair of EMATs which could measure the build up over time as a change in both attenuation and transit time.  The measurement would be easy and robust.  Calibration of thickness would require some measure of the physical properties of the scale, density, stiffness(modulus), or simply some experience or equivalent calibration specimens.  The EMAT could operate at high temperatures and will not degrade in time like a piezo with adhesive.  I have done similar measurements in Inconel (Ni alloy).  Contact me for more information. ralers@rosen-group.com

So far I can think of no method not yet cited.

You definitely must have a closer look to thermal imaging, but in your case with vibroacoustic stimulation (by a sonotrode). I would not be so sure that pulse thermography will not give results, but you will have to choose carefully the source.

Ultrasonic methods by transmission methods may (or may not!) work. It is worth a try with rather low frequencies transducers.

Marcelino I figured you would know the docs, I have only seen linatrons in the paperwork but had a colleague who repaired then for Varian at a govt munitions factory. I could understand the addition of the steel plate to harden the beam since it would rid the beam of a lot of the low energy and make imaging a whole lot easier. In fact on one of the data sheets Varian show a beam flattening filter which of course would not only improve the beam shape but also harden the beam. I know in the medical world the Varian flattening filter free linacs still have a insert in the beam line to "rid the beam of low energy". Cheers

Lindsay

It could mean two facts: how strong the fracture (atomic breakage) is, i.e. the source strength, and how close the fracture is located to your AE sensor, i.e. the geometric attenuation. The former is the characteristic of your material while the latter is of the relative location between the source and the sensor. The AE in the form of bulk elastic wave decays at the rate of 1/distance of propagation. Hope this helps. 

Hello! Firstly, although it has been a very long time, thank you for your response! I got caught up with the research and , afterwards, my studies, and completely forgot to answer. Unfortunately it was decided that due to the boundaries of the project no crack  is going to be introduced. We only introduced inclusions.

NDT methods can be roughly classified in two groups: surface techniques, which are used to identify surface and near surface defects such as cracks and surface porosity, and sub-surface techniques, that can be used to detect defects that lie under the material’s surface. In the first group, the most commonly used techniques are visual and optical testing, magnetic particle testing, liquid penetrant testing and electromagnetic testing. On the other hand, sub-surface techniques include radiography and ultrasonic testing among the most used.

Aside from the aforementioned techniques, which account for well over 90 per cent of the industrial NDT, there is a number of alternative methods each at different levels of technology readiness, such as thermography testing, process compensated resonance testing (PCRT), holography, shearography, alternating current field measurement (ACFM), and laser ultrasound.

A comprehensive description of the principles and applications of at least the classical NDT methods can be found in this reference: S. Ness, C. N. Sherlock, P. O. Moore, and P. McIntire. Nondestructive testing overview. American Society for Nondestructive Testing, 1996.

Hi Ehsan,

Thanks for the link to the comsol blog on the use of symmetry which I read with interest. This actually confirms what I thought might be happening. From what is described in the blog, the multi-turn coil feature in comsol appears to use what is usually called the 'current sheet' approximation. This replaces the current flowing through the multi-turn coil with a uniform current sheet that flows around the coil perimeter. This is an approximation which, once in place, permits the use of symmetry as a means to reduce the model size.

However, this approximation is only good for tightly wound coils and only for estimating the coil's inductance. The reason is that the inductance is primarily determined by the magnetic flux external to the coil (giving rise to the external inductance) which depends on the total current flowing in the wire. Therefore, using a uniform current sheet doesn't alter the result for the inductance too much from that obtained using the actual coil geometry.

However, the internal inductance (that due to the magnetic flux inside the wire) and - most importantly for what you are looking at - the coil's resistance will not be accurately determined by the current sheet approximation.

To get an accurate simulation of the resistance, the spatial distribution of current in the actual wire geometry must be detemined. In an isolated single turn of circular wire, this distribution of current will be cylindrically symmetric and follow the same kind of distibution as the electric field, that is, it will be concentrated near the surface of the wire and decay exponentially into the wire - the familiar 'skin effect'.

When additional turns of wire are added and brought close together (as in a tightly wound coil) the current distribution in the wire will be altered due to the 'proximity effect' which results from the Lorentz Force on the electrons in the wire due to the magnetic field in neighbouring parts of the coil. The net result is that the current gets concentrated in the parts of the wire cross section that are nearest to the other turns. The current is then no longer cylindrically symmetric within each turn of wire. This proximity effect therefore increases the resistance over and above that due to the skin effect since the current now flows in a reduced cross sectional area.

The proximity effect isn't modelled by the current sheet approximation. Therefore, one cannot utilise symmetry in the comsol multi-turn coil model for calculating resistance (or internal inductance).  A real multi-turn coil doesn't have symmetry with regard to the actual current distribution in the wire.

Regards,

Ray

Actually, it is possible but using broadband signals makes it harder to detect the BN; but it is possible!

J. Appl. Phys. 73 (lo), 15 May 1993

Ground penetrating radar (GPR) is a nondestructive geophysical method that produces a continuous cross-sectional profile or record of subsurface features, without drilling, probing, or digging. The GPR cross-section shows the ground surface at the top of the profile, and the reflections of subsurface geologic units and objects to a certain depth at the bottom.

Ground penetrating radar operates by transmitting pulses of ultra high frequency radio waves (microwave electromagnetic energy) down into the ground through a transducer (also called an antenna).

Ground penetrating radar (GPR) can be used in scanning of primarily concrete specimens to locate rebar, pipes, post tension bars, conduits in concrete structures and even cracks/anomaly in the concrete specimen . The scanning can also detect voids within concrete slabs and under concrete slabs. I hope the same can be used in your case.

I have been working with GPR on concrete and it has given be satisfactory and desired results. I think you can try using this device with ceramics as well. Hope this answer helps. 

It depends on what you are looking for:

There are different non-destructive tests that gives different properties of thin films.

1. Profilometer for film thickness. 

2. AFM or SPM (scanning probe microscopy) for surface topography.

3. Four point probe Sheet Resistivity or non contact mode sheet resistance measurement setup for electrical properties.

4. XRD crystal structure and for stress measurement in thin films.  

5. SEM, TEM .

6. XRF for elemental/chemical analysis.

7. UV-VIS spectroscopy for optical properties like transmission and for semi-conducting properties like band gap determination.

There are plenty of more techniques which are available in literature, but it would depend on what kind of property you are looking for.

There are several destructive techniques as well.

1. Like scratch test for adhesion measurement.

2. Nano Indentation for hardness and elasticity.

etc.

The standard and easier methodology for obtaining the frequency response of an ultrasound transducer is to drive it with a very short-time electrical pulse (spike), typically with a duration minor that -a quarter of the wavelength al the nominal tranducer frequency-, and then to see its echo-response (from a parallel reflector) in a oscilloscope. Finally, to make the FFT transform of the echo pulse properly windowed. 

Jitendra, 

I have read your papers. It is a huge part of my PhD thesis, the concept of NLU and your work is the main inspiration. One of the first papers I read. 

Thank you for your reply. It looks interesting, indeed. I sent you a request for a full text version, I would like to learn more about your topic. Thanks again.

I think that fibre optic sensors have a potential to be used on industial scale in construction engineering. They allow for continuous, real-time monitoring of structural beahviour which finds application in responsible structures, such as bridges. Because of their shape and reltively small dimensions optical fibres can be easily introduced into linear structural elements such as strands and cables. This is happening right now. In future fibre optics are considered to be a major component of the so-called smart structures - structural elements which serve both structural and monitoring functions. Fibre optics glued or woven into the fibrous structure of such a smart element will allow for colection of data about behavior of the structural element (deformations and strains).

Variable selection procedures such as genetic algorithms or interval partial least squares procedures are useful when developing your models. Once you have a model you should test the predictive ability with independent test sets and inspect the selectivity ratios of the selected variables. An alternative to selectivity ratios are variable importance to projection scores (VIP). You should be able to do this in Unscrambler (but it's been a very long time since I used this). Matlab and PLS toolbox are my recommendations.

We have Ultrasonic method with conventional devices and phased array devices.

In case we use a conventional device:

the most common technique (estimation method) is Pulse Echo technique.

This technique enables the inspector to have a detail depiction of the metalic structure with one probe. If we look weldings then we need definetely probes of 45 angle, 60 angle and 70 angle. We also need a zero( or 90) angle probe to inspect the metal base.

In all other cases we use only a zero( or 90) probe. We have to be

careful with the metal because each metal has a different velocity in longitudinal and transverse wave. For instance the aluminum has approximately 3.130 m/sec velocity in transverse wave but 6.230 m/sec velocity in longitudinal wave, when the steel has 3.250 m/sec velocity in transverse wave but 5.920 m/sec velocity in longitudinal wave.

If we are able to inspect only from one side of the sample, then we choose dual probes.

An other technique is named TOFD and we need two probes which are placed in a distance between them, but with this technique we can not have an estimation about the characteristics of a possible discontinuity.

Sincerely

N. Poulakis

Tech. Educ. Inst. of W. Macedonia, Kozani, Greece.

Normally I use digital FIR filter for guided waves in general. In my case I work with Burst excitation and it is necessary to filter the signal. Also it is possible to use average process to decrece noise

@Imran Shafi - It is not that I didn't like it. Actually I haven't read it, It is just that I think one should not advertise his/her own research this way. Publish it, go to conferences and present it and let readers and listeners decide :-)