چكيده به لاتين
Calibration blocks play a vital role in nondestructive testing (NDT) of mechanical parts. Calibration blocks are parts with known specifications and characteristics which are used to verify testing equipment. Ultrasonic testing (UT) is one of the most common Nondestructive Testing methods were used for inspection and evaluation of metallic and composite parts. Manufacturing of calibration blocks for UT testing has a strong background in the past few decades, however, they haven’t experienced significant changes since then due to limitations in manufacturing processes.
Additive manufacturing (AM), also known as 3D Printing, open up a new way of fabricating parts layer-by-layer in oppose to conventional (subtractive) manufacturing processes. With the aid of AM-based processes, parts with any level of complexity in geometry could be built directly from CAD models. As a consequence, the calibration block industry could obtain benefits from this huge development and blocks with artificial embedded defects with known geometry and coordinates could be built in order to make better representatives of real flaws.
In this thesis, the possibility of manufacturing calibration blocks by means of AM processes were investigated in detail, along with the proposition of innovative designs and their superiorities for the future calibration blocks. To this goal, first, definitions and scientific background of AM processes and parameters, as well as ultrasonic testing were fully addressed. Then, an extensive review in the literature were carried out. In the next step, calibration block manufacturing procedure and specification standards were studied. Simultaneously, several factors were addressed and investigated to evaluate the habilitation of additive manufactured parts, especially selective laser melted (SLM) parts, to be replaced with conventional blocks. Finally, one of the proposed blocks with some embedded features, which are played as simulated internal defects, were fabricated by means of SLM process and evaluated via A-scan ultrasonic testing and radiography testing (RT), along with machining of mentioned part for light optical microscopy (LOM) observation as destructive testing. The result of each test discussed in detail and compared to the others.
With regard to anisotropic microstructure of SLM parts, several simulations were done to study ultrasound wave propagation in an anisotropic media to predict wave behavior and reflections in such cases, as well as to understand the mechanism of ultrasonic testing. Mechanical properties of fabricated SLM sample were determined via pulse-echo ultrasonic testing to feed into finite element software in order to obtain more reliable results. Simulations were carried out in two ways, 3D and 2D, for both normal and transverse wave propagation via ABAQUS/CAE software. Results for defective and healthy parts for isotropic and anisotropic structures were compared and justified. Throughout the simulations, concepts of infinite elements and phased array ultrasonic wave propagation and some MATLAB programming were used. In the final section, the results from numerical simulations were approved by test results.
