Ultrasonic testing -1

To this point now we have included the three themes in this path and all the three themes were on surface entity approaches so today i am going to a brand new subject so that it will be on bulk entity and the subject that i’ve chosen for this can be on ultrasonic checking out so this can be a process which can be used for doing entity into the majority of the fabric if there’s any flaw or defect that are so much beneath the outside ultrasonic technique is one method which can be utilized for inspecting this form of defects which lie into the majority of the fabric and this technique can be used for doing floor entity so it can be used for each because of this ultrasonic trying out is among the most versatile entity approach and from at present onwards in next few courses we will be able to be discussing about this particular system so given that this process as the identify suggests established on ultrasonic waves so let us first see what ultrasonic waves are and what their properties are and then we are going to see how these waves are used for doing NDT ok so allow us to first be taught little bit about ultrasonic waves ultrasonic waves are nothing but sound waves which have frequency larger than 20 kilo Hertz ok so some thing beneath or 20 kilo watch would be within the audible range whilst you go to a frequency past 20 kilo Hertz then the sound waves are within the ultrasonic range okay so this is what all de sonic waves are and for those who see their nature and residences for instance if you happen to see the wavelength it’s in the range of 1 to 10 millimeter frequency is zero.12 fifteen megahertz however by and large for doing ultrasonic checking out a frequency within ten megahertz is used so twenty twenty kilo arch and above up to ten mega Hajj is used for ultrasonic testing for doing NDT and this wavelength lambda is a factor of the pace of these waves and the frequencies on this fashion ok after which they travel at special speed in distinctive medium and in many of the metals the pace trade with frequency just isn’t very massive so these are probably the most typical characteristics of ultrasonic waves k and now let us talk about what variety of ultrasonic waves you might have what are the extraordinary types of waves in particular as far as entity is worried you might have two types of waves one is longitudinal and the other one is transverse k allow us to see why it’s known as longitudinal and transverse and what is the change between them ok so now in the event you speak concerning the longitudinal waves on this case in case you see the propagation of the wave by way of a medium let us say the wave is moving in this direction so this is the wave propagation course and when sound moves via a medium it creates a local stress nearby sound strain so as to push the atoms or the particles and create a lattice wave within the strong so it’s going to create some elastic waves and with the aid of those elastic waves the sound strikes from one phase to different a further part in a medium k so there’s a motion of the particles or the atoms throughout the medium ok so on this case the course of particle movement is parallel to the path of the movement of the wave ok so in this case it is moving in this course so the particle movement direction additionally would be the same so that is the course of particle action okay so that suggests the action of those particles will likely be coordinated in the sense that the first atom can push the second one and the second can push the 1/3 one etc considering they’re relocating in the same course as the where ok so on this case the movement of the particles are coordinated and they may be able to aid each and every other in moving when the sound wave is moving by means of the medium k alternatively if you seem on the transverse waves on this case if this be the course of wave propagation the particles will move in a perpendicular path like this so on this case the action will likely be like this ok that means the particles are going up and down and the wave is moving horizontally okay so on this case as you could appreciate even as the sound is propagating by way of the medium as a way to create that elastic wave which helps in relocating the sound wave the particles ought 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 on this case so here the motion is just not as coordinated or the motion of the particles shouldn’t be as effortless as in the case of longitudinal waves and that is why the pace of the longitudinal waves is always greater than that of transverse waves this is due to the difference within the action of particles with respect to the course of wave propagation ok so in one case in the longitudinal case the direction of wave propagation and particle movement are same and hence the particles can transfer effectively and in the case of transverse waves due to the fact the direction of the particle motion is perpendicular to the movement of the wave propagation here the quandary stage for action of the particles is extra compared to the longitudinal waves and this is why the velocity of the longitudinal wave in a particular medium shall be more than transverse waves so these are the 2 fundamental forms of ultrasonic waves now when you talk in regards to the speed it is concerning the elastic consistent of the fabric through which the sound waves are relocating and the density of the medium on this fashion so C IJ is the elastic constant of the fabric for example it could 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 sometime poisons ratio is also used and Rho is the density okay so the homes of the material will decide what will be the pace of sound by means of that specific fabric now there are distinct other varieties of ultrasonic waves additionally seeing that we’re speakme about distinctive forms of waves allow us to talk about those also for example in surfaces or interfaces you might have quite a lot of types of particle movement and that would supply rise to other kind of ultrasonic waves for illustration you could have elliptical or different complicated kind of paths within the motion of the particles as the sound moves via the medium so this form of elliptical or different problematic vibration which can be generated on the skin referred to as floor or Rayleigh waves which are generated in slightly thick samples you k so allow us to say if the sound is relocating in this direction so you could have a particle movement course like this like in an elliptical direction as I said so this will be the movement of the particles and by means of this form of motion you’re going to generate the motion for the waves within the horizontal direction a so this sort of waves that are generated at surfaces or interfaces in thick materials they are often called surface or household okay and in thin plates you might have any other form of waves being generated that are known as plate waves and this may also be further divided into two classes one is often called Lam and the other one is referred to as love ok so Lam is the element 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 okay so these are two distinct varieties of plate waves that you will see on skinny plates one is lamb and one other is love k and in within the lamb waves you could have a symmetric lamp like this symmetric lamb or these are sometimes called extensional waves and also you could actually have a symmetric like this and this is in bendy mode good enough so these are different varieties of ultrasonic waves our major main issue for ultrasonic checking out for NDT would be the longitudinal and the transverse waves so we will speak about extra about them simplest after we speak about ultrasonic testing as a NDT process now let me let you know how this ultrasonic waves are used for doing anything the elemental precept at the back of that is fairly simple everyone knows about reflection of sound waves or the echo of sound like for illustration if you talk loudly in an empty room the walls will replicate the sound and you will get an eco good enough so while doing ultrasonic testing what is finished is this ultrasonic waves are sent into the pattern and when these waves are mirrored again they’re amassed with the aid of a transducer which is in the end will generate the signal if there is any defect k so this defect will also act as a reflector which can reflect the sound waves adequate however if so the reflection interface is far smaller in comparison with a wall so that means the energy which is there within the mirrored waves should be ample for the transducer or the instrument to collect this signal back ok k so the power within the transmitter the sound waves depends on the sound pressure which is created with the aid of this a traveling waves okay you could be aware of that sound waves journey by means of a medium through oscillatory motion of the atoms or the particles and this motion is due to the regional stress which is created by way of sound so this strain is the surplus stress above that Mascara strain ok so when sound waves are journey by means of a medium this neighborhood stress supplies some action to the atoms and as a result of the bonding between the atoms it creates an oscillatory movement which in turn will create a wave k so that’s how the sound waves are propagate through a distinctive medium ok so allow us to say this nearby strain which is created with the aid of the sound is P and let us say it supplies a pace to the particles or the atoms which is Q okay because as I instructed this will provide some motion to the particles of the atom so let us say the velocity of that action is Q so P can be proportional to Q greater the P better will be the action between the atoms now should you introduce this proportionality consistent then you could write in on this fashion and this parameter Z which is P by way of Q this is known as acoustic impedance so this is nothing but the total resistance to the action of sound waves by way of a distinctive medium ok and the power of the transmitted beam the vigour in the transmitted waves II is again elegant on the stress P on this method we’re in Rho is the density of the medium and V is the pace of sound waves through the medium ok so you might have why you will have to have adequate vigour initially within the transmitted sound waves which go to the sample and then when it’s reflected back that reflected waves additionally must have sufficient vigour so that the instrument which is used for doing ultrasonic trying out must be in a position to capture it ok and if you wish to get an expression for P and Q if the wave is represented by an equation like this so if this be the wave okay 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 number which is the same as 2 pi by lambda lambda is the wavelength k so if this be the wave then the pace 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 outcome of sound waves when it travels by means of a medium it supplies this speed cue and the resistance to the action of sound wave is provided is given by using that parameter acoustic impedance k so based upon this transmitted beam power it is going to enter a particular pattern or a precise medium after which when it encounters an interface part of this sound beam will likely be reflected back k and the vigour of that mirrored beam that will depend on this specified parameter acoustic impedance as to what is the change of impedance across that reflecting interface k so that’s what we will make a decision the power within the reflected beam and as I stated if the vigour is sufficient on this echo or in this mirrored beam then you need to use an instrument a transducer to capture that power and convert that right into a signal which can also be proven in the display of the procedure and that is how you are going to get to learn about presence of defects if that reflecting interface be a defect ok so that’s how the elemental principle is at the back of this distinct manner it’s a rather simple one is founded upon the reflection of sound waves from a discontinuity which supplies a reflecting interface to the sound waves which can be propagating via the pattern yeah so with that today i’m going to stop right here and within the next class we’re going to see how these ultrasonic waves are used to do non-damaging testing and relaxation of the things also about this detailed process we are going to see within the subsequent classes so for at present i will stop here thanks for your attention

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