experimental stress analysis two marks with answers

23. What are the important properties of an ideal photoelastic material?  Data Acquisition for principal stress magnitude and direction  Coating material and process for damp concrete-problem from bond failure and unknown shrinkage stress effects in concrete  The difference between thermal coefficient in coating material and concrete leads to errors to field investigation  Too sensitive to the Young Modulus and Poisson’s ratio ( local effect from coating process) 24. With a suitable sketch explain the process of Fluorescent penetrant technique. The selection of a liquid penetrant system is not a straightforward task. There are a variety of penetrant systems and developer types that are available for use, and one set of penetrant materials will not work for all applications. Many factors must be considered when selecting the penetrant materials for a particular application. These factors include the sensitivity required, materials cost, number of parts, size of area requiring inspection, and portability. 25. Explain the brittle coating method in brief. Briefly explain the following which are used in the experimental analysis: a. Fibre – optic sensors A fiber optic sensor is a sensor that uses optical fiber either as the sensing element ("intrinsic sensors"), or as a means of relaying signals from a remote sensor to the electronics that process the signals ("extrinsic sensors"). Fibers have many uses in remote sensing. Depending on the application, fiber may be used because of its small size, or because no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflect meter.

b. Thermography Infrared thermography, thermal imaging, and thermal video are examples of infraredimaging science. Thermal imaging cameras detect radiation in the infrared range of the electromagnetic spectrum (roughly 9000–14,000 nanometers or 9–14 µm) and produce images of that radiation, called thermograms. c. C – Scan The test area is fully scanned with an ultrasonic transducer. A video camera tracking the transducer or an X-Y encoder is used to plot the movement of the transducer. The ultrasonic signals from the geometric features and any flaws that may occur are recorded with each movement of the transducer. Signal processing is used to convert this information into a coloured image similar to that shown below. The various colours of the image represent a range of thickness values resulting in a topographic map of the test item. The signals, processed image, calibration parameters and other relevant information are stored electronically and can be recalled whenever required.

26) Explain the Electrical resistance strain gauge. Automatic strain measurement is usually done with an electrical resistance strain gauge (or gage). It looks like this: A thin plastic base supports thin ribbons of metal, joined in a zig-zag to form one long electrically conductive strip. The entire device is typically 10 mm long, with 16 or more parallel metal bands. When the plastic is stretched the wires become longer, and thinner. The electrical resistance

therefore increases. The % increase is about twice the % extension, because if the wire is stretched to twice its original length the electrons have to struggle twice as far through a conductor of half the original cross section. 27) Explain Radiographic Testing 

Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation (high energy photons) to penetrate various materials.

28) Explain Magnetic Particle Inspection

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Magnetic particle inspection (MPI) is a non-destructive testing (NDT) process for detecting surface and subsurface discontinuities in ferrous materials.

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The process puts a magnetic field into the part. The piece can be magnetized by direct or indirect magnetization.