Material Characterisation at Elevated Temperatures Involving Digital Image Correlation (DIC)

Kolanu, Naresh Reddy (2016) Material Characterisation at Elevated Temperatures Involving Digital Image Correlation (DIC). Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

Materials used in high temperature environments like structural parts in aero engines, nuclear power plants and gas turbines have to withstand extreme thermal and mechanical loads. A proper understanding of their material behavior and knowing their material properties is important for designing and modelling aspects. The measurement of displacements and strains has always been an important consideration in the evaluation of material properties. Accurate method for characterizing the materials being used at ambient and high temperature environments is of utmost important, which is difficult and laborious using conventional methods. This work presents the applicability of the non-conventional digital image correlation (DIC) technique to measure whole-field surface deformations and in-plane strains at ambience and elevated temperature environments. Initially material characterisation of Al 2014-T6 alloy is carried out at room temperature using the DIC technique and conventional extensometery a detailed sensitivity analysis of the in uence of DIC parameters such as speckle size, subset size and step size on the displacement and strain measurements is also carried out and the optimal DIC parameters were found out. Further, a series of uni-axial tensile tests had been conducted on Al-2014 T6 alloy specimens at various elevated temperatures involving 2D-DIC and conventional extensometry. The tests are done as per ASTM E8 and ASTM E21 standards. The stress-strain response of Al-2014 T6 alloy is captured at each corresponding elevated temperature using the whole-field strain measurement obtained from 2D-DIC technique with the optimal parameter values. The investigated material properties are Young's modulus, Poisson's ratio, yield strength, ultimate tensile strength and % elongation at fracture. Parameters obtained from 2D-DIC technique are compared with the conventional extensometery results. The results obtained using 2D-DIC technique and conventional extensometry are found to be in good agreement. A similar comparative study on the same Al-2014 T6 alloy is also carried out using the natural speckle patterns generated on the specimen using emery paper. A quantitative comparison of the 2D-DIC strain values at different load values is done between artificial and natural speckle patterns and it is found that they are in good coherence.

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