Ultrasonic testing -1

So far we have protected the three subject matters in this path and all the three themes have been on surface entity methods so today i’m going to a brand new topic which will be on bulk entity and the subject that i’ve chosen for this will be on ultrasonic testing so it is a method which can be utilized for doing entity into the majority of the fabric if there’s any flaw or defect which might be so much beneath the skin ultrasonic process is one procedure which can be utilized for inspecting this style of defects which lie into the bulk of the material and this method will also be used for doing floor entity so it can be used for both that is why ultrasonic checking out is one of the most versatile entity approach and from at present onwards in following couple of lessons we will be able to be discussing about this distinctive technique so considering that this manner as the title suggests headquartered on ultrasonic waves so allow us to first see what ultrasonic waves are and what their houses are and then we are going to see how these waves are used for doing NDT okay so allow us to first gain knowledge of little bit about ultrasonic waves ultrasonic waves are nothing but sound waves which have frequency larger than 20 kilo Hertz okay so whatever under or 20 kilo watch can be within the audible variety whilst you go to a frequency past 20 kilo Hertz then the sound waves are within the ultrasonic variety ok so this is what all de sonic waves are and for those who see their nature and houses for instance for those who see the wavelength it’s within the variety of 1 to 10 millimeter frequency is zero.12 fifteen megahertz but frequently 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 trying out for doing NDT and this wavelength lambda is a factor of the velocity of these waves and the frequencies in this trend ok after which they travel at unique velocity in special medium and in lots of the metals the speed exchange with frequency is just not very tremendous so these are one of the average characteristics of ultrasonic waves k and now let us speak about what variety of ultrasonic waves you may have what are the specific forms of waves primarily so far as entity is concerned you’ve got two types of waves one is longitudinal and the other one is transverse ok allow us to see why it’s known as longitudinal and transverse and what is the change between them k so now in the event you talk about the longitudinal waves in this case when you see the propagation of the wave via a medium allow us to say the wave is moving on this direction so this is the wave propagation path and when sound moves via a medium it creates a nearby strain local sound strain that will push the atoms or the particles and create a lattice wave throughout the strong so it will create some elastic waves and with the help of those elastic waves the sound moves from one part to different one other section in a medium okay so there is a motion of the particles or the atoms inside the medium okay so on this case the path of particle action is parallel to the course of the action of the wave okay so on this case it is moving in this path so the particle action path additionally will be the identical so that is the path of particle action okay so that implies the motion of those particles will probably be coordinated in the sense that the primary atom can push the second one and the second can push the third one and many others due to the fact that they are relocating within the same direction because the where okay so in this case the motion of the particles are coordinated and they may be able to aid each and every other in moving when the sound wave is relocating through the medium k however if you look at the transverse waves on this case if this be the course of wave propagation the particles will transfer in a perpendicular course like this so on this case the movement will likely be like this ok that implies the particles are going up and down and the wave is relocating horizontally okay so on this case as you might have an understanding of at the same time the sound is propagating via the medium so as to create that elastic wave which helps in relocating the sound wave the particles need to pull each other okay after which create this movement within the path of the propagation of the wave and that is how these wave propagates on this case so here the movement will not be as coordinated or the movement of the particles is not as handy as in the case of longitudinal waves and because of this the pace of the longitudinal waves is perpetually bigger than that of transverse waves that is because of 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 path of wave propagation and particle movement are same and for that reason the particles can move with no trouble and in the case of transverse waves because the path of the particle action is perpendicular to the motion of the wave propagation here the concern degree for movement of the particles is more in comparison with the longitudinal waves and for this reason the speed of the longitudinal wave in a special medium shall be more than transverse waves so these are the two most important varieties of ultrasonic waves now while you talk about the velocity it is concerning the elastic constant of the fabric via which the sound waves are moving and the density of the medium on this fashion so C IJ is the elastic consistent of the fabric for example it would be the younger’s modulus or the shear modulus so shear modulus can be utilized for transverse waves and younger’s modulus can be used for the longitudinal waves sometime poisons ratio can be used and Rho is the density k so the properties of the fabric will make a decision what’s going to be the pace of sound through that distinct fabric now there are exact different varieties of ultrasonic waves also considering that we’re talking about exceptional forms of waves allow us to talk about these additionally for example in surfaces or interfaces you would have various varieties of particle movement and that would give upward thrust to different variety of ultrasonic waves for instance you could have elliptical or other intricate sort of paths within the action of the particles as the sound moves by way of the medium so this form of elliptical or other elaborate vibration which can be generated on the skin referred to as surface or Rayleigh waves which are generated in relatively thick samples you okay so let us say if the sound is relocating on this course so which you could have a particle motion path like this like in an elliptical direction as I mentioned so this will be the action of the particles and by way of this form of motion you are going to generate the motion for the waves within the horizontal direction a so this variety of waves which might be generated at surfaces or interfaces in thick substances they are often called floor or household ok and in skinny plates you could have any other variety of waves being generated that are referred to as plate waves and this may also be further divided into two classes one is referred to as Lam and the opposite one is known as love k so Lam is the component of the vibration which is perpendicular to the skin and love is parallel to the aircraft layer and perpendicular to the direction of the waves okay so these are two one-of-a-kind forms of plate waves that you will find on skinny plates one is lamb and one more is love okay and in in the lamb waves you could have a symmetric lamp like this symmetric lamb or these are often referred to as extensional waves and you would even have a symmetric like this and that is in bendy mode ok so these are one-of-a-kind forms of ultrasonic waves our fundamental difficulty for ultrasonic testing for NDT could be the longitudinal and the transverse waves so we can talk about extra about them most effective once we talk about ultrasonic trying out as a NDT system now let me inform you how this ultrasonic waves are used for doing something the basic precept behind this is really simple we all know about reflection of sound waves or the echo of sound like for instance if you speak loudly in an empty room the walls will mirror the sound and you will get an eco adequate so while doing ultrasonic testing what is done is that this ultrasonic waves are despatched into the pattern and when these waves are mirrored back they are collected by means of a transducer which is in the end will generate the signal if there is any defect k so this defect will even act as a reflector which is able to replicate the sound waves adequate but if that’s the case the reflection interface is much smaller compared to a wall so that suggests the vigor which is there in the mirrored waves must be ample for the transducer or the instrument to acquire this sign again adequate ok so the power in the transmitter the sound waves is determined by the sound pressure which is created by this a touring waves ok you might understand that sound waves travel via a medium by way of oscillatory action of the atoms or the particles and this motion is as a result of the neighborhood strain which is created by using sound so this strain is the surplus pressure above that Mascara pressure k so when sound waves are travel by means of a medium this local stress presents some action to the atoms and due to the bonding between the atoms it creates an oscillatory movement which in turn will create a wave ok so that’s how the sound waves are propagate by way of a exact medium okay so allow us to say this neighborhood strain which is created with the aid of the sound is P and let us say it presents a velocity to the particles or the atoms which is Q k considering that as I told this may increasingly furnish some action to the particles of the atom so let us say the speed of that action is Q so P can be proportional to Q larger the P bigger would be the motion between the atoms now in the event you introduce this proportionality steady then which you could write in in this trend and this parameter Z which is P by Q this is known as acoustic impedance so this is nothing but the total resistance to the action of sound waves by means of a distinctive medium ok and the vigour of the transmitted beam the vigor in the transmitted waves II is once more elegant on the strain P on this manner we’re in Rho is the density of the medium and V is the speed of sound waves through the medium k so you have got why you must have sufficient vigor initially within the transmitted sound waves which go to the sample after which when it’s reflected back that mirrored waves additionally should have sufficient vigour so that the instrument which is used for doing ultrasonic checking out must be able to seize it okay and if you want to get an expression for P and Q if the wave is represented by an equation like this so if this be the wave k 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 ok is known as wave quantity which is the same as 2 pi by way of lambda lambda is the wavelength ok 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 might be equal to this so that is the outcomes of sound waves when it travels through a medium it presents this speed cue and the resistance to the action of sound wave is supplied is given by means of that parameter acoustic impedance ok so centered upon this transmitted beam vigour it’ll enter a unique pattern or a targeted medium after which when it encounters an interface part of this sound beam might be mirrored again ok and the power of that mirrored beam as a way to depend on this certain parameter acoustic impedance as to what’s the exchange of impedance throughout that reflecting interface ok so that’s what we will be able to make a decision the vigour within the mirrored beam and as I stated if the energy is enough in this echo or on this reflected beam then you can use an instrument a transducer to seize that energy and convert that right into a sign which can also be shown within the show of the procedure and that is how you will get to find out about presence of defects if that reflecting interface be a defect okay so that is how the elemental precept is in the back of this precise procedure it’s a quite simple one is situated upon the reflection of sound waves from a discontinuity which presents a reflecting interface to the sound waves which might be propagating by means of the sample yeah so with that today i’m going to discontinue here and within the subsequent category we are going to see how these ultrasonic waves are used to do non-harmful testing and leisure of the matters additionally about this certain approach we are going to see within the subsequent courses so for at present i will stop right here thanks on your awareness

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