Ultrasonic testing -1

So far we’ve protected the three topics in this course and all the three subject matters have been on surface entity methods so at present i’m going to begin a new topic to be able to be on bulk entity and the subject that i’ve chosen for this will be on ultrasonic testing so this can be a process which can be utilized for doing entity into the bulk of the material if there is any flaw or defect which can be so much below the outside ultrasonic process is one system which can be utilized for inspecting this type of defects which lie into the majority of the material and this process will also be used for doing floor entity so it may be used for both because of this ultrasonic checking out is one of the most versatile entity procedure and from at present onwards in following few lessons we will be discussing about this unique procedure so given that this manner as the title suggests based on ultrasonic waves so let us first see what ultrasonic waves are and what their residences are and then we’re going to see how these waves are used for doing NDT ok so allow us to first learn little bit about ultrasonic waves ultrasonic waves are nothing however sound waves which have frequency bigger than 20 kilo Hertz k so some thing under or 20 kilo watch could be in the audible range when you go to a frequency beyond 20 kilo Hertz then the sound waves are within the ultrasonic variety okay so this is what all de sonic waves are and if you happen to see their nature and houses for instance should you see the wavelength it’s in the range of 1 to 10 millimeter frequency is zero.12 fifteen megahertz but commonly for doing ultrasonic testing a frequency within ten megahertz is used so twenty twenty kilo arch and above up to ten mega Hajj is used for ultrasonic checking out for doing NDT and this wavelength lambda is a element of the speed of these waves and the frequencies on this trend k after which they travel at different pace in one of a kind medium and in lots of the metals the speed alternate with frequency isn’t very enormous so these are one of the most typical traits of ultrasonic waves okay and now let us speak about what form of ultrasonic waves you might have what are the specific forms of waves above all as far as entity is concerned you may have two forms of waves one is longitudinal and the other one is transverse k let us see why it is known as longitudinal and transverse and what is the change between them k so now in case you speak concerning the longitudinal waves in this case for those who see the propagation of the wave by way of a medium allow us to say the wave is moving on this path so this is the wave propagation course and when sound moves by means of a medium it creates a nearby stress neighborhood sound strain so they can push the atoms or the particles and create a lattice wave throughout the stable so it will create some elastic waves and with the aid of these elastic waves the sound moves from one phase to other an additional part in a medium ok so there is a motion of the particles or the atoms within the medium k so on this case the direction of particle movement is parallel to the course of the movement of the wave okay so in this case it’s relocating in this course so the particle motion direction also will be the identical so that is the direction of particle action ok so that suggests the motion of those particles might be coordinated in the sense that the first atom can push the second and the second can push the third one and so forth on the grounds that they’re moving within the equal path because the the place okay so in this case the motion of the particles are coordinated and they can help each different in relocating when the sound wave is moving through the medium okay on the other hand when you look on the transverse waves on this case if this be the path of wave propagation the particles will move in a perpendicular path like this so on this case the motion might be like this k that suggests the particles are going up and down and the wave is relocating horizontally okay so in this case as you would realize even as the sound is propagating by way of the medium with a purpose to create that elastic wave which helps in moving the sound wave the particles have got to pull each and every different okay and then create this movement within the direction of the propagation of the wave and that is how these wave propagates in this case so right here the action is not as coordinated or the motion of the particles is just not as handy as in the case of longitudinal waves and this is why the velocity of the longitudinal waves is at all times higher than that of transverse waves that is due to the change within the motion of particles with appreciate to the path of wave propagation ok so in a single case within the longitudinal case the path of wave propagation and particle action are identical and consequently the particles can move simply and in the case of transverse waves due to the fact the course of the particle motion is perpendicular to the action of the wave propagation here the predicament stage for action of the particles is extra in comparison with the longitudinal waves and because of this the speed of the longitudinal wave in a distinct medium shall be more than transverse waves so these are the 2 major varieties of ultrasonic waves now while you talk concerning the pace it is related to the elastic steady of the material through which the sound waves are relocating and the density of the medium in this fashion so C IJ is the elastic regular of the material for illustration it might be the younger’s modulus or the shear modulus so shear modulus can be utilized for transverse waves and young’s modulus can be utilized for the longitudinal waves someday poisons ratio is also used and Rho is the density ok so the houses of the fabric will come to a decision what’s going to be the velocity of sound through that distinctive material now there are precise other forms of ultrasonic waves also seeing that we’re speakme about exceptional varieties of waves allow us to speak about these additionally for illustration in surfaces or interfaces you could have quite a lot of varieties of particle movement and that might supply upward thrust to different style of ultrasonic waves for instance you might have elliptical or other complicated style of paths in the motion of the particles as the sound moves via the medium so this kind of elliptical or different problematic vibration which might be generated on the surface known as surface or Rayleigh waves that are generated in somewhat thick samples you okay so allow us to say if the sound is moving in this course so you could have a particle movement route like this like in an elliptical direction as I stated so this will be the action of the particles and by means of this sort of action you’re going to generate the motion for the waves within the horizontal direction a so this kind of waves which are generated at surfaces or interfaces in thick substances they are often called floor or family okay and in thin plates you could have another sort of waves being generated which can be referred to as plate waves and this can be extra divided into two classes one is often called Lam and the other one is known as love ok so Lam is the aspect of the vibration which is perpendicular to the skin and love is parallel to the airplane layer and perpendicular to the path of the waves k so these are two distinctive varieties of plate waves that you’ll discover on thin plates one is lamb and an extra is love okay and in within the lamb waves that you could have a symmetric lamp like this symmetric lamb or these are often referred to as extensional waves and also you would even have a symmetric like this and that is in flexible mode adequate so these are distinctive types of ultrasonic waves our important situation for ultrasonic checking out for NDT often is the longitudinal and the transverse waves so we will be able to speak about more about them only after we talk about ultrasonic testing as a NDT system now let me let you know how this ultrasonic waves are used for doing whatever the fundamental precept in the back of this is rather easy everyone knows about reflection of sound waves or the echo of sound like for illustration for those who talk loudly in an empty room the partitions will reflect the sound and you will get an eco adequate so even as doing ultrasonic trying out what is done is that this ultrasonic waves are sent into the sample and when these waves are mirrored again they are accumulated via a transducer which is ultimately will generate the signal if there may be any defect ok so this defect may also act as a reflector which will mirror the sound waves adequate but if that’s the case the reflection interface is far smaller in comparison with a wall so that means the energy which is there within the mirrored waves must be ample for the transducer or the instrument to collect this sign again adequate ok so the vigor in the transmitter the sound waves is dependent upon the sound strain which is created by this a travelling waves okay you would 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 as a result of the regional pressure which is created by using sound so this pressure is the excess strain above that Mascara strain ok so when sound waves are travel via a medium this neighborhood strain provides some movement to the atoms and due to the bonding between the atoms it creates an oscillatory motion which in flip will create a wave okay so that is how the sound waves are propagate via a particular medium ok so allow us to say this local stress which is created by way of the sound is P and allow us to say it supplies a velocity to the particles or the atoms which is Q okay seeing that as I told this may increasingly provide some movement to the particles of the atom so allow us to say the pace of that action is Q so P can be proportional to Q higher the P higher will be the action between the atoms now when you introduce this proportionality steady then that you can write in in this trend and this parameter Z which is P by Q that is referred to as acoustic impedance so that is nothing however the whole resistance to the action of sound waves by way of a particular medium okay and the vigour of the transmitted beam the power within the transmitted waves II is once more elegant on the strain P in this manner we’re in Rho is the density of the medium and V is the velocity of sound waves by means of the medium k so you could have why you will have to have enough vigor first of all within the transmitted sound waves which go to the sample and then when it is mirrored again that mirrored waves additionally should have adequate vigor so that the instrument which is used for doing ultrasonic checking out must be competent to capture it k and if you want to get an expression for P and Q if the wave is represented with the aid of an equation like this so if this be the wave ok so if this be the wave where why no longer is the amplitude T is time Omega is the angular frequency which is 2 pi F where F is the frequency and okay is often called wave number which is the same as 2 pi by using lambda lambda is the wavelength okay so if this be the wave then the velocity which is given to the particles or to the atoms Q is that this dy DT so Q will be equal to this so that is the effect of sound waves when it travels via a medium it supplies this pace cue and the resistance to the motion of sound wave is offered is given via that parameter acoustic impedance ok so established upon this transmitted beam power it is going to enter a distinctive pattern or a distinct medium and then when it encounters an interface a part of this sound beam will be reflected back ok and the energy of that reflected beam on the way to rely upon this distinctive parameter acoustic impedance as to what’s the trade of impedance across that reflecting interface okay so that’s what we will be able to decide the vigour within the reflected beam and as I said if the power is adequate on this echo or in this mirrored beam then you can use an instrument a transducer to capture that vigour and convert that right into a sign which may also be proven within the show of the system and that’s how you’re going to get to know about presence of defects if that reflecting interface be a defect ok so that’s how the fundamental principle is at the back of this certain method it is a particularly easy one is based upon the reflection of sound waves from a discontinuity which provides a reflecting interface to the sound waves which can be propagating via the pattern yeah so with that in these days i’m going to discontinue here and in the subsequent class we’re going to see how these ultrasonic waves are used to do non-harmful testing and leisure of the matters additionally about this special method we are going to see within the subsequent courses so for in these days i’ll discontinue right here thanks for your awareness

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