ENT604 Revision Lecture 2024 PDF

REVISION LECTURE Professor Rossi Setchi [email protected], S/2.41  Measurement Systems ✓ Characteristics - Accuracy, precision, hysteresis, linearity, resolution, response, dynamic characteristics and sources of errors ✓ Transducers – types and characteristics ✓ Nanometrology ✓...

REVISION LECTURE Professor Rossi Setchi [email protected], S/2.41  Measurement Systems ✓ Characteristics - Accuracy, precision, hysteresis, linearity, resolution, response, dynamic characteristics and sources of errors ✓ Transducers – types and characteristics ✓ Nanometrology ✓ Non-destructive testing  Accuracy ✓ Accuracy is the degree of agreement of the measured dimension with its true value. ✓ Accuracy can also be defined as the maximum amount by which the result differs from true value or as the nearness of the measured values to its true value often expressed as a %. ✓ True value may be defined as the mean of the infinite number of measured values when the average deviation due to the various contributing factors tends to zero.  Precision ✓ Precision is the degree of repetitiveness of the measuring process. ✓ It is the degree of agreement of the repeated measurements of a quantity made by using the same method, under similar conditions. a) Precise but not (b) Accurate but not (c) Precise and d) Not Precise and not Accurate Precise Accurate Accurate Accuracy and Precision.  Hysteresis in Measurement Systems ✓ When the value of the measured quantity remains the same irrespective of whether the measurements have been obtained in an ascending or a descending order, a system is said to be free from hysteresis. ✓ Many instruments do not reproduce the same reading due to the presence of hysteresis. This affects the repeatability of the system. ✓ Slack motion in bearings and gears, storage of strain energy in the system, bearing friction, residual charge in electrical components, etc., are some of the reasons for the occurrence of hysteresis.  Linearity in Measurement Systems ✓ Linearity is defined as the maximum deviation of the output of the measuring system from a specified straight line applied to a plot of data points on a curve of measured (output) values versus the measurand (input) values. ✓ measurand = an object or quantity being measured. Resolution of Measuring Instruments ✓ Resolution is the smallest change in a physical property that an instrument can sense. Resolution of an instrument can also be defined as the minimum incremental value of the input signal that is required to cause a detectable change in the output. ✓ The numerical value of the input to cause a change in the output is called the threshold value of the instrument. ✓ Drift can be defined as the variation caused in the output of an instrument, which is not caused by any change in the input. © Oxford University Press 2013. All rights reserved.  Response of Measuring Instruments The following are the dynamic characteristics of a measurement system: ✓ Speed of response is the speed with which the measuring instrument responds to the changes in the measured quantity. ✓ Measuring lag is the time when an instrument begins to respond to a change in the measured quantity. ✓ Fidelity is defined as the degree to which a measurement system indicates the changes in the measured quantity without any dynamic error. ✓ Dynamic error is the difference between the true value of a physical quantity under consideration that changes with time and the value indicated by the measuring system if no static error is assumed.  Revision Question What are the desirable characteristics of a transducer that will be used in hazardous conditions? Elements of Measurement Systems ✓ Three main functional elements: ✓ Primary detector – transducer stage ✓ Intermediate modifying stage ✓ Output or terminating stage © Oxford University Press 2013. All rights reserved.  Classification of Transducers Transducers are devices that are used to transform the information sensed (signals) between two different physical domains. They may comprise two important components: Sensing or detecting element responds to a physical phenomenon or a change in the physical phenomenon. It is termed a primary transducer. Transduction element transforms the output obtained by the sensing element to an analogous electrical output. Hence it is termed a secondary transducer. In addition to these, the primary stage also consists of auxiliary sources of energy, power amplifiers, and calibration sources.  Revision Question Using your knowledge of the structure of a generalised measurement system, discuss the main functional elements of a medical ultrasound imaging system used to examine pregnant women. …. Vision system to detect imperfections in precious coins … EEG system for early detection of traumatic brain injury  NDT Methods Most widely used Visual inspection Liquid penetrant inspection Magnetic particle inspection Pulsed thermography Radiography Eddy current testing Ultrasound imaging As well as Digital radiography Replication Laser interferometry Microwave Tap testing Thermography Ultrasound inspection Active thermography  Liquid Penetrant Inspection A liquid with high surface wetting characteristics is applied to the surface of the part and allowed time to seep into surface breaking defects. The excess liquid is removed from the surface of the part. A developer (powder) is applied to pull the trapped penetrant out the defect and spread it on the surface where it can be seen. The penetrant is often loaded with a fluorescent dye and the inspection is done under UV light to increase test sensitivity.  Magnetic Particle Inspection This technique consists of placing fine ferromagnetic particles on the surface of the part. When the part is magnetised with a magnetic field, a discontinuity (defect) on the surface causes the particles to gather visibly around the defect. The iron particles may be coated with a dye pigment for better visibility on metal surfaces. The defect then becomes a magnet, due to flux leakages where the magnetic field lines are interrupted by the defect. This creates a small-scale N-S pole at either side of the defect as field lines exit the surfaces. The particles take the shape and size of the defect. Subsurface defects can be detected too.  Magnetic Particle Inspection http://www.youtube.com/watch?v=qpgcD5k1494 Cracks that are in a direction parallel to the magnetic field (such as discontinuity A) would not be detected, whereas the others shown would. Discontinuities F, G, and H are the easiest to detect. Source: ASM International.  (b) same as (a) but the workpiece is rotated along a vertical axis and moved vertically. The monitor displays the data as a 2D image of the workpiece. (a) The source of radiation is a x-ray tube, and a visible, (c) Is similar to (b). The permanent image is made translation and rotation on a film or radiographic provide several angles from paper. which to precisely view the object. The monitor produces x-ray images of thin cross sections of the workpiece. Three methods of radiographic inspection: (a) conventional radiography; (b) digital radiography; and (c) computed tomography. Source: Reprinted with permission of ASM International. All rights reserved. www.asminternational.org. Eddy Current Testing Coil's Coil magnetic field Eddy current's magnetic field Eddy currents Conductive material Ultrasonic Inspection (Pulse-Echo) High frequency sound waves are introduced into a material and they are reflected back from surfaces or flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features that reflect sound. f initial pulse back surface echo crack echo crack 0 2 4 6 8 10 plate Oscilloscope, or flaw detector screen  Revision Question Provide examples of NDT methods used in the aerospace industry. … in rail industry … in the energy sector … oil and gas Role of robotics and AI in NDT? Examples?  Comparison Consideration Liquid penetrant Magnetic Radiography Eddy current Ultrasound particles Effect Capillary action Magnetisation. Electromagnetic radiation Electro-magnetic Propagation caused by the Any discontinuity (X-rays or Gamma-rays) induction of ultrasonic waves in intermolecular in the material with short wavelength the material tested forces between the allows liquid and the solid the magnetic surfaces flux to leak. Materials All materials Ferromagnetic A large variety of materials Conductive (e.g. Normally metals but materials (e.g. (metal, concrete, ceramics, copper, aluminum, gold, also concrete, wood iron, nickel, etc.) silver) and composites cobalt) Cost Low to medium Medium High Medium Medium to high Availability of Short delay Short delay Delayed Short delay Immediate result Geometry Not important Not important Important (solid, flat Not important Important material or hollow cylindrical or spherical object) Type of defect Surface defects External External & internal Surface and subsurface Internal defects Formal Record Not usual Not usual Standard Not usual Expensive Operator skill Low Low High Low High Ability to Fair Fair Good Fair Good automate  Revision Question Compare two NDT methods used in wire rope inspection in terms of effect, cost, type of defect and operator skill. Power plant inspection Storage tank inspection Jet engine inspection Pressure vessel inspection Rail inspection Pipeline inspection Bridge inspection …. Other criteria: materials, geometry, formal record/documentation, ability to automate… Lasers Laser is a coherent, convergent, and monochromatic beam of electromagnetic radiation with wavelength ranging from ultraviolet to infrared. Spatial coherence allows a laser to be focused to a tight spot. Spatial coherence also allows a laser beam to stay narrow over long distances (collimation). Lasers can also have high temporal coherence which allows them to have a very narrow spectrum, i.e., they only emit a single colour of light. Temporal coherence can be used to produce pulses of light—as short as a femtosecond (10 −15 s).  Applications of Nanotechnology Thanks to their large surface-to-volume ratio, nanoparticles are used as potential transporters of antibodies, drugs, or chemicals for use in diagnostic tests, targeted drug therapy, or for catalysing chemical reactions. Skin care products that use nanoparticles to deliver vitamins deeper into the skin. Silver nanoparticles in fabric that kill bacteria making clothing odour-resistant. Lithium ion batteries that use nanoparticle-based electrodes powering plug-in electric cars. Increasing the strength of tennis racquets by adding nanotubes to the frames which increases control and power when you hit the ball. Filling any imperfections in golf club shaft Nano is used in textiles mainly to provide stain-resistance or anti-bacterial materials with nanoparticles; this improves the properties. Example: Lotus Effect uniformity of the material that makes up the shaft and thereby improving your swing. Iron nanoparticles can be effective in cleaning up organic solvents that are polluting groundwater. Epoxy containing carbon nanotubes is being used to make windmill blades. The resulting blades are stronger and lighter.  Revision Question Why is nanometrology needed? Provide examples of applications of nanotechnology where the use of nanometrology is required. [Use information from the previous slide, the two detailed case studies or other examples you are familiar with]  Light vs Electron Microscopes Fluorescent screen (if Both light microscopes and TEM) Human eye electron microscopes use radiation Electron detector (if (light or electron beams) to form SEM) larger and more detailed images of Eyepiece (projector objects (e.g. biological specimens, Electromagnet (Magnetic lenses) materials, crystal structures, etc.) projector) than the human eye can produce unaided. In this region there is a real In this region there is a real Intermediate Image Intermediate Image Objective lens Magnetic Objective Specimen Electrically Specimen controlled coils Condenser Lens Magnetic Condenser Light source Electron gun (source of electrons)  Revision Question How different is the electron microscope from a classic light microscope? What is the principle of operation of a light/electron microscope? Transmission Electron Microscope In a transmission electron microscope (TEM), electrons penetrate a Fluorescent screen (if thin specimen and form transmission electron diffraction patterns. TEM) The selective absorption of electrons by the specimen is the effect Electron detector (if SEM) used to form images (parts of the specimen absorb electrons and appear dark on the micrograph, while other areas allow electrons to pass through - causing those areas to appear bright). Electromagnet (Magnetic projector) Unless the specimen is made very thin, electrons are strongly scattered within the specimen, or even absorbed rather than In this region there is a real transmitted. Intermediate Image Magnetic Objective Specimen Magnetic Condenser Electron gun (source of electrons) https://www.youtube.com/watch?v=KeirehoOAQ0 Scanning Electron Microscope Electron microscopes do not naturally produce colour images, as an SEM produces a single value per pixel. This value corresponds to the number of electrons received by the detector during a small period of time of the scanning when the beam is targeted to the (x, y) pixel position. This single number is usually represented, for each pixel, by a grey level, forming a "black-and- white" image. Several ways have been used to get colour electron microscopy images. For example, secondary electron and backscattered electron detectors are superimposed and a colour is assigned to each of the images captured by each detector (see next slide). Scanning Electron Microscope Signals generated in an SEM When an electron beam strikes a specimen, a variety Used to capture of electrons, photons, the topography phonons, and other signals of the specimen are generated. They are used to form images or diffraction patterns, or analysed to provide spectroscopic information. It is rare for a single machine to have detectors for all other possible signals. Scanning Tunneling Microscope ✓ When an atomically sharpened tip under a small voltage is brought close to the surface of a sample, so that the separation is of the order of a nanometer, there is a small change in current in the circuit. This effect is called the quantum tunneling effect. ✓ The induced tunneling current increases as the gap between the tip and the sample decreases. ✓ The change in tunneling current can be calibrated with respect to the change in gap. In other words, if we scan the tip over the sample surface while keeping the tunneling current constant, the tip movement depicts the surface topography, because the separation between the tip apex and the sample surface is always constant. https://www.youtube.com/watch?v=wNEqRq6NyUw (1:40 – 2:45 min)  Atomic Force Microscope ✓ An AFM is rather different from other microscopes, because it does not form an image by focusing light or electrons onto a surface, like an optical or electron microscope. ✓ It physically ‘feels’ the sample’s surface with a sharp probe, building up a map of the height or topography of the surface as it goes along. A piezoelectric element oscillates the cantilever. The photodiode registers the deflection of the cantilever. ✓ AFMs can be used to measure the forces between the probe and the sample. ✓ The reaction of the probe to the forces that the sample imposes on it can be used to form an image of the three-dimensional shape (topography) of a sample surface at a high resolution. https://www.youtube.com/watch?v=Ha53tFTsmW8 X Ray Diffraction System (XRD) Bragg law describes the relationship between the diffraction pattern and the material structure. If the incident X-rays hit the crystal planes with an incident angle θ and reflection angle θ as shown below, the diffraction peak is observed when the Bragg condition is satisfied That is, nλ = 2d.sin θ where λ is the wavelength, d is the distance between each adjacent crystal planes, θ is the Bragg angle at which one observes a diffraction peak, and n is an integer number, called the order of reflection. X Ray Diffraction System X-ra Diffraction System (XRD) (XRD) ✓ X-ray diffraction is ideal for examining samples of metals, polymers, ceramics, semiconductors, thin films and coatings. ✓ It can also be employed for forensic and archeological analysis. ✓ A two-dimensional diffraction pattern provides abundant information about the atomic arrangement, microstructure, and defects of a solid or liquid material. https://www.youtube.com/watch?v=lwV5WCBh9a0 (only the first 2 min)  Light vs Electron Microscopes Parameter Light microscope Electron microscope Radiation type visible light Electron beams Approx. wavelength of 400-700 nm effective wavelength < 1 nm radiation Radiation focussed by… Lenses Electromagnets Image formed by … Light (colour images) TEM: selective absorption of electrons by the specimen Image formed on... Human eye Projecting a focused image of the specimen onto a fluorescent screen Typical resolution 200 nm 0.5 nm (=0.5 x 10-9m) Typical useful magnification 1000x – 1500x ~ 100,000x in SEM ~ 250,000x in TEM Living cells/tissues Yes Not possible due to vacuum inside Thickness of specimen Thin Very thin sections only in TEM, surfaces only in SEM Depth: 2D or 3D? 2D 2D (seems like 3D in SEM) Specimen preparation Simple Takes a lot of time in TEM Size Small and light Big and heavy Cost Less expensive Very expensive  Revision Question What is the difference between Scanning Electron Microscope and Transmission Electron Microscope? With the help of a diagram, explain the working principle of TEM/SEM/XRD/AFM/STM, etc.