 Hello, I am Milka Jagle working as assistant professor in Department of Mechanical Engineering Walton Institute of Technology, Solaapur. Today, we are going to see non-destructive testing methods, let us see. Learning outcome. At the end of this session, students will be able to select various non-destructive testing methods and its significance. The content for today's session is testing of materials, non-destructive testing methods. So, these are the testing of material. So, why we need testing of those materials? So, these are the few points to assess the mechanical properties like toughness, hardness, tensile strength, ultimate strength and so on. To determine the data, to determine the surface and subsurface defects, to check chemical composition, to determine suitability of material. In this test, the actual components are subjected to test and the inspection is 100 percent. While in destructive testing, a test bar is subjected to the actual test and the result is valid for whole lot produced, that is, it is a sampling type of inspection. The results of the NDT are qualitative in nature and does not affect the quantity. So, these are the non-destructive testing methods. As the definition indicates, non-destructive testing is the testing of metal or testing of material to determine the defects, surface or subsurface defects without affecting the service life or without hampering the specimen and that specimen can be further used for which it was made. So, these are the non-destructive type of testing, that is, dipenetrant test, magnetic particle test, ultrasonic test, radiography, that is, X-ray and gamma ray test and eddy current test. So, as we have already discussed about non-destructive test, just have a look and NDT is examination of component in any manner which will not affects its future use. So, various tests are available for finding the soundness of the components without sectioning or without the destructive test. So, the ability to detect the invisible subsurface defects not only aids in maintaining high quality standards, but provides valuable help in development of manufacturing methods and not provide direct mechanical properties, but they are extremely useful in revealing the defects in components that improve the performance when put in service. So, non-destructive tests are more real and they are economical. So, let us see first is dipenetrant test. So, dipenetrant test, so, in this the dye is applied on the specimen, so, let us see what is this. So, invisible cracks, porosity and other defects can be easily detected by this technique. So, components may be of ferrous, non-ferrous, glass or plastic. Material used in dipenetrant test, first is cleaner that is cleans the surface, removes the irregularity, removes the corrosion and cleaner is used on the specimen. Second is penetrant that is dye penetrant penetrates into the discontinuity or irregularities present on the specimen by the capillary action. And the third is developer it is a tach or a chalk powder. So, if you see this figure first this is the crack which is present in the specimen. Firstly, we need to clean this defect or clean this specimen and then the penetrant or the dye is applied on this irregularity. So, due to the capillary action that the dye penetrates into this cavity and then the specimen the surface of the specimen is cleaned by a soft cloth. Then the developer is applied on the specimen. So, the defect or the dye is on the the defect whatever present on this is can be seen on this developer. So, if you see this after applying the developer so, if you let it set for some time the time may be from minutes to hours depending upon the type of the defect. The dye which is penetrated into this defect that can be easily seen on the developer. So, this is here you can also see the diagram which shows the procedure of dye penetrant test. So, advantages limitations of DPT so, that can be used for ferrous and nonferrous alloy components. So, there is no size limitation of the specimen or the cavity. So, this does not require skill for the to detect the defect. So, it is little time consuming because after applying the developer it needs to go set in the cavity and then after cleaning and then after applying the developer. So, it needs to just come out. So, it is cheaper, portable and cannot this test cannot detect cracks just below the surface. Now, next is magnetic particle testing. So, magnetic particle testing is used for the ferromagnetic components such as welding, casting, forging of steel and cast iron. So, the component to be inspected for flaw is magnetized and inspection medium is applied to the component. So, this test is exclusively made for ferromagnetic specimens and firstly before getting into the test the specimen is magnetized. So, there are two types of method that is dry method and wet method. In dry method ferromagnetic powder is spread on the specimen by hand shaker or some vibrator so that the powder is uniformly distributed over the specimen surface and in wet method liquid containing fine ferromagnetic materials are such as kerosene, petroleum oil is applied by spraying or by using brush or some dipping. So, these are the two methods of spreading the ferromagnetic material. So, next this is the principle. So, can you see the specimen is magnetized and this is the defect. So, the magnetic field is formed around this specimen and wherever the crack is present the ferromagnetic powder clings around the defect. So, easily the defect is found out. So, you see the particle cling to the defect like tags or a simple magnet. So, the next method of magnetization the longitudinal method if we magnetize longitudinally we can get the defect and second is circular method. So, magnetization of component is done by external magnetic yoke coil or passing an electric current. So, magnetic pole is formed at the crack of flaw which causes the magnetic powder to concentrate on the area and flaw easily gets detected. So, transverse crack can easily be detected. So, this is one form of magnetization in which the crack is formed over here this is the coil electric current and the magnetic field is generated. So, this is the circular magnetization whereas, this is longitudinal magnetization. So, in longitudinal magnetization circular crack is detected whereas, in circular magnetization longitudinal cracks are detected. So, advantages limitation and applications are they are fast and relatively easy to apply. So, they are used for only ferromagnetic materials under water inspection they might be carried out can be adopted for small de magnetization is necessary. It is used to detect the production of defects such as seams, laps, grinding, cracks etc. So, these are the references the book by material science and metallurgy doctor Kodgire and book introduction to engineering materials BK Agarwal. Thank you.