Ultrasonic testing -1

So far we have now included the three topics in this direction and the entire three subject matters were on floor entity approaches so at present i’m going to begin a brand new subject so that it will be on bulk entity and the topic that i’ve chosen for this will likely be on ultrasonic checking out so it is a method which can be utilized for doing entity into the majority of the material if there’s any flaw or defect which can be so much below the outside ultrasonic process is one approach which can be utilized for inspecting this form of defects which lie into the majority of the fabric and this manner can also be used for doing surface entity so it can be used for both for this reason ultrasonic checking out is likely one of the most versatile entity system and from in these days onwards in next few lessons we will be discussing about this unique technique so on the grounds that this procedure because the title suggests centered on ultrasonic waves so allow us to first see what ultrasonic waves are and what their properties are after which we’re going to see how these waves are used for doing NDT ok so let us first gain knowledge of little bit about ultrasonic waves ultrasonic waves are nothing however sound waves which have frequency greater than 20 kilo Hertz okay so whatever beneath or 20 kilo watch could be within the audible range whilst you go to a frequency beyond 20 kilo Hertz then the sound waves are in the ultrasonic range ok so this is what all de sonic waves are and if you happen to see their nature and properties for illustration when you see the wavelength it’s in the variety of 1 to 10 millimeter frequency is zero.12 fifteen megahertz however commonly for doing ultrasonic checking out a frequency inside ten megahertz is used so twenty twenty kilo arch and above as much as ten mega Hajj is used for ultrasonic checking out for doing NDT and this wavelength lambda is a component of the pace of those waves and the frequencies in this trend k after which they journey at one-of-a-kind velocity in unique medium and in lots of the metals the pace trade with frequency just isn’t very massive so these are one of the crucial average traits of ultrasonic waves okay and now allow us to speak about what variety of ultrasonic waves you’ve got what are the one of a kind types of waves primarily so far as entity is concerned you’ve two varieties of waves one is longitudinal and the opposite one is transverse ok allow us to see why it’s known as longitudinal and transverse and what’s the change between them okay so now for those who talk concerning the longitudinal waves on this case for those who see the propagation of the wave by means of a medium let us say the wave is moving on this course so this is the wave propagation direction and when sound moves by means of a medium it creates a neighborhood stress nearby sound strain so that they can push the atoms or the particles and create a lattice wave within the strong so it will create some elastic waves and with the support of these elastic waves the sound moves from one section to other another part in a medium k so there’s a movement of the particles or the atoms within the medium ok so in this case the direction of particle action is parallel to the course of the motion of the wave k so in this case it is moving in this direction so the particle motion path additionally will be the same so that is the direction of particle movement ok so that means the motion of those particles will likely be coordinated in the feel that the first atom can push the second and the second can push the 0.33 one and so forth given that they are moving in the identical course as the the place ok so in this case the motion of the particles are coordinated and they may be able to help each different in relocating when the sound wave is moving by way of the medium k however should you seem at the transverse waves in this case if this be the course of wave propagation the particles will move in a perpendicular direction like this so on this case the action will probably be like this okay that means the particles are going up and down and the wave is relocating horizontally ok so on this case as you might comprehend even as the sound is propagating through the medium with a view to create that elastic wave which helps in moving the sound wave the particles must pull each different ok and then create this motion in the path of the propagation of the wave and that is how these wave propagates on this case so right here the movement is just not as coordinated or the motion of the particles will not be as effortless as in the case of longitudinal waves and because of this the pace of the longitudinal waves is consistently larger than that of transverse waves this is due to the difference within the action of particles with admire to the course of wave propagation k so in one case within the longitudinal case the direction of wave propagation and particle action are identical and therefore the particles can transfer with ease and in the case of transverse waves considering the fact that the direction of the particle action is perpendicular to the movement of the wave propagation right here the concern degree for movement of the particles is more in comparison with the longitudinal waves and this is the reason the speed of the longitudinal wave in a special medium will be more than transverse waves so these are the two most important forms of ultrasonic waves now while you talk in regards to the speed it’s related to the elastic constant of the fabric through which the sound waves are moving and the density of the medium in this trend so C IJ is the elastic regular of the material for instance it would be the younger’s modulus or the shear modulus so shear modulus can be used for transverse waves and young’s modulus can be used for the longitudinal waves someday poisons ratio can be used and Rho is the density ok so the properties of the material will decide what will be the velocity of sound by way of that particular fabric now there are targeted different types of ultrasonic waves additionally due to the fact we are speaking about specific forms of waves allow us to talk about these additionally for example in surfaces or interfaces you could have various varieties of particle action and that will supply rise to different variety of ultrasonic waves for example you would have elliptical or other tricky sort of paths within the action of the particles as the sound moves via the medium so this variety of elliptical or other elaborate vibration which can be generated on the skin known as floor or Rayleigh waves which might be generated in fairly thick samples you ok so let us say if the sound is relocating in this course so you can have a particle action path like this like in an elliptical direction as I stated so this will be the action of the particles and by way of this sort of action you’ll generate the movement for the waves within the horizontal course a so this type of waves that are generated at surfaces or interfaces in thick materials they’re known as floor or loved ones k and in thin plates you could have some other variety of waves being generated which are often called plate waves and this may also be further divided into two categories one is often called Lam and the other one is often called love ok so Lam is the aspect of the vibration which is perpendicular to the surface and love is parallel to the aircraft layer and perpendicular to the course of the waves ok so these are two exceptional forms of plate waves that you’ll find on thin plates one is lamb and a further is love k and in in the lamb waves which you could have a symmetric lamp like this symmetric lamb or these are sometimes called extensional waves and also you could also have a symmetric like this and that is in flexible mode adequate so these are special varieties of ultrasonic waves our primary quandary for ultrasonic checking out for NDT would be the longitudinal and the transverse waves so we will be able to talk about extra about them most effective after we speak about ultrasonic testing as a NDT method now let me tell you how this ultrasonic waves are used for doing whatever the basic principle behind that is really simple everyone knows about reflection of sound waves or the echo of sound like for illustration should you talk loudly in an empty room the walls will mirror the sound and you’re going to get an eco adequate so whilst doing ultrasonic trying out what is finished is that this ultrasonic waves are despatched into the pattern and when these waves are reflected again they’re gathered through a transducer which is subsequently will generate the sign if there’s any defect okay so this defect can even act as a reflector which will replicate the sound waves ok however in that case the reflection interface is far smaller compared to a wall so that suggests the vigor which is there in the mirrored waves must be sufficient for the transducer or the instrument to acquire this signal back good enough k so the energy in the transmitter the sound waves depends on the sound pressure which is created by using this a traveling waves k you might be aware of that sound waves journey by way of a medium by oscillatory action of the atoms or the particles and this action is due to the local strain which is created via sound so this stress is the surplus strain above that Mascara pressure k so when sound waves are journey through a medium this local pressure supplies some movement to the atoms and due to the bonding between the atoms it creates an oscillatory movement which in flip will create a wave ok so that’s how the sound waves are propagate by means of a specified medium ok so allow us to say this neighborhood stress which is created by the sound is P and let us say it supplies a speed to the particles or the atoms which is Q k considering that as I informed this may increasingly provide some motion to the particles of the atom so let us say the velocity of that movement is Q so P might be proportional to Q larger the P bigger would be the action between the atoms now should you introduce this proportionality consistent then you can write in on this trend and this parameter Z which is P through Q that is known as acoustic impedance so that is nothing but the complete resistance to the movement of sound waves by means of a specific medium okay and the power of the transmitted beam the power within the transmitted waves II is again stylish on the strain P in this manner we’re in Rho is the density of the medium and V is the pace of sound waves by means of the medium ok so you’ve why you should have adequate vigor to begin with within the transmitted sound waves which go to the pattern after which when it’s mirrored again that reflected waves also should have enough vigor in order that the instrument which is used for doing ultrasonic testing must be competent to seize it k and if you want to get an expression for P and Q if the wave is represented through an equation like this so if this be the wave ok so if this be the wave the place why not is the amplitude T is time Omega is the angular frequency which is 2 pi F the place F is the frequency and okay is known as wave quantity which is the same as 2 pi through lambda lambda is the wavelength k so if this be the wave then the speed which is given to the particles or to the atoms Q is this dy DT so Q will be equal to this so that is the effect of sound waves when it travels by way of a medium it supplies this pace cue and the resistance to the action of sound wave is furnished is given by way of that parameter acoustic impedance k so founded upon this transmitted beam power it’s going to enter a certain pattern or a exact medium and then when it encounters an interface a part of this sound beam will probably be reflected again k and the energy of that reflected beam on the way to rely on this targeted parameter acoustic impedance as to what’s the exchange of impedance throughout that reflecting interface ok so that is what we can make a decision the vigor in the mirrored beam and as I stated if the power is sufficient on this echo or on this reflected beam then you need to use an instrument a transducer to capture that energy and convert that into a signal which may also be proven in the display of the method and that’s how you are going to get to know about presence of defects if that reflecting interface be a defect okay so that’s how the fundamental principle is in the back of this detailed process it’s a particularly simple one is established upon the reflection of sound waves from a discontinuity which supplies a reflecting interface to the sound waves which can be propagating by way of the pattern yeah so with that at present i am going to stop here and in the next category we’re going to see how these ultrasonic waves are used to do non-damaging trying out and relaxation of the matters also about this targeted approach we’re going to see in the subsequent lessons so for in these days i’ll discontinue right here thank you on your concentration

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