 Hello, I am Milka Jagle, working as assistant professor in Department of Mechanical Engineering, Vulture Institute of Technology, Solapur. Today, we are going to learn on non-destructive testing methods too, let's see. Learning outcome At the end of the session, students will be able to select various non-destructive material testing methods and its significance. So, the content for today's session is non-destructive testing methods. So, testing of materials. So, why testing of material is needed is because, so by testing of material, we can assess the mechanical properties like tensile strength, hardness, toughness, resilience and so on. So, that is why it is required to test the material. So, next to determine the data. So, it is very important to know the data of the material which are going to use for the purpose. Next one is to determine surface and subsurface defects. So, by using this material, by using, so the third point is to determine surface and subsurface defects. So, most of the material has defects, whether they might be subsurface or surface defects. To check the chemical composition of the material, the testing of material is must and to determine the suitability of material for a particular application. Non-destructive testing. So, non-destructive testing is nothing but it does not destroy the material which we are going to test. So, it is the name itself indicates it will not destroy the specimen. So, there are many non-destructive tests such as dipenetrant test, ultrasonic test, eddy current test and so on. So, let us see today we are going to learn about non-destructive tests. So, in this test actual components are subjected to the test and 100 person inspection is done. So, various in destructive test the specimen is no more used after the test is done because the specimen is destroyed whereas in non-destructive the specimen is not destroyed. So, just now we have discussed the ability to detect the invisible subsurface defects. It maintains the high quality standards but provides valuable help in manufacturing methods. So, before going further, so these are the tests for the testing of materials that is dipenetrant test, magnetic particle test, ultrasonic test, radiography test in which X-ray and gamma rays or X-ray and gamma rays are used. So, eddy current test, ultrasonic test. So, it involves the time required by the ultrasonic vibrations to strike or to penetrate into the material or the specimen and then reflect back from the defect or reflect back to its the point from where they were introduced. Time is calculated if the defect is present then this ultrasonic rays, ultrasonic waves will strike the specimen and reflect back, strike the defect in the specimen and then reflect back. If there is no defect present it will strike to the other end of the specimen and reflect back. So, the behavior of waves through such a cycle with respect to time is recorded on the CRO, cathode ray oscilloscope screen. So, by visual observation of the wave pattern, so on the screen the presence of defects and the location of defects can be detected. So, this method is very sensitive method and very fine defects and discontinues can be found out in this method. This is very fast method for testing defects because the time for travel of ultrasonic waves is the order of microseconds. So, there are two types of methods of ultrasonic that is first is pulse echo method and transmission method. So, this is the setup for pulse echo method. If you see here this is a coaxial cable to the instrument, this is the cot crystal which sends and pickups the ultrasonic waves. So, if you see here the defect is present over here in this specimen. So, when ultrasonic waves are inserted from this cot crystal that will if there is no defect present the wave will strike the other end of the specimen and reflect back. Whereas, if the specimen has the defect, if you see this is a defect. So, when the rays are inserted that will penetrate into the defect and then reflect the time difference to strike and come back is calculated. In this way we can find out the time and distance of the defect. This is the pulse echo setup to find out the defect. If you see this is the oscilloscope screen of ultrasonic tester, here waves are reflected from the opposite side. So, this is the total distance from the test surface to the opposite surface whereas, if the defect is present over here this is the total distance. This distance is less as compared to this distance because here the defect is present whereas, here there is no defect shown in this tester. Second is ultrasonic transmission setup. So, in this the transducer is there whereas, if flaw is present this is the pulse where the transmission is given. So, if there is no defect present over here there is no any disturbance. If the flaw is there here the rays are obstructed. So, this is how the defect is shown. So, advantages of ultrasonic testing. It is sensitive to small discontinuities both surface and subsurface. Depth of penetration for floor detection or measurement is superior as compared to the other methods. Highly accurate the minimum part preparation is required. Electronic improvement provides instantaneous results. Time is also very less as in microseconds. Then detail images can be produced with automated system and has the other uses such as thickness measurement etcetera. Radiography. This method is used to detect the flaws in the components manufactured by casting, welding, forging and etcetera. So, this method the components to be examined is exposed to the radiations of short wavelength. So, this is the schematic diagram of radiograph. This is the defect. This is the film. The radiograph is produced x-ray from x-ray tube or a radium capsule is there. It produces x-rays or gamma rays. So, this is the porosity or a hole or a defect. This is our specimen. So, a film is radiograph is produced. So, this is in this way the defect is shown in the radiograph. A photograph or a film is kept and then that will produce a radiograph which indicates the exact location of the defect. So, as we have seen these radiations penetrate through the components and they are absorbed by the material. The penetrating ability of these radiations depend upon the wavelength and the absorbing power of the material. Amount of radiations emerging from the opposite side of the material can be recorded and observed. The variations can be detected. So, the recording is usually done by placing a film sensitive to radiation in a cassette at the end of the object. So, as we have seen the film is present. After developing a film, it shows a picture of light and dark areas. Dark areas representing the regions of low density such as holes, porosity, cracks and etc. The film is called Xerograph. Eddy current testing. Alternating current is brought near a metallic specimen. Eddy currents are developed. Due to electromagnetic induction, the eddy currents are developed. So, eddy current depends upon the magnitude of eddy current depends upon frequency of alternating current flowing through the coil, magnetic permeability, shape of the specimen, the relative position of the coil and specimen, the amount and type of the defect in the specimen. So, variation in any one of the above factor would result in the variation of the induced current. So, the change in the eddy current will change the magnetic impedance of the specimen or a component which is converted to voltage and observed on a voltmeter. So, these are the types of coils, the absolute coils and differential coils. This in this the standard specimen is surrounded by one coil and the specimen under test is surrounded by the another. So, when the output of two coils is zero, the specimen under test is similar to standard specimen otherwise they are different. So, as we have seen the coil are flat or cylindrical, high frequency of AC current are used to detect the flaws on the surface just below the surface. These are the advantages, they are very fast, no direct electrical contact is needed that can be, they can be automated, low cost, no final cleanup is required, it is a portable equipment and applicable to both ferrous as well as non-ferrous alloys. So, these are the references the book by Kodgiri and the book by B.K. Agarwal. Thank you.