Zone Wise Local Characterization of Welds Using Digital Image Correlation: Uniform Stress and Virtual Fields Method

K M, Saranath (2014) Zone Wise Local Characterization of Welds Using Digital Image Correlation: Uniform Stress and Virtual Fields Method. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

The process of welding is associated with high and varying thermal gradients across the weld, resulting in inhomogeneous material properties surrounding the weldment. A proper understanding of the varying mechanical properties of the weld and surrounding materials is important in designing and modelling of components with weld. In the initial study the characterisation of dierent zones such as fusion zone, heat aected zones and unaected base material of a deposited weld is carried out using uniform stress method (USM) involving digital image correlation (DIC) technique. A methodology using the micrographic observation and image processing is proposed for accurate identication of various weld zones. The response of welded samples in the elastic and plastic region is compared with the virgin sample. Full range stress-strain curves are obtained for each zone using the whole eld strain measurement involving DIC. The parameters investigated are Young's modulus, Poisson's ratio, yield stress, strain hardening exponent and strength coecient. A study regarding the variation of properties with respect to varying weld currents of 100 A, 130 A and 150 A is carried out. The Vickers micro hardness measurement is also conducted to obtain the variation in hardness across weldment. Fusion zone of all the welded samples have reported lower Young's modulus and higher yield strength compared to virgin samples. The Vicker's hardness values obtained for fusion and heat aected zones are in line with the yield stress variation obtained zone wise.

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