Variation in dynamic contact resistance with the change in welding process parameters such as wel... more Variation in dynamic contact resistance with the change in welding process parameters such as weld current , weld time and electrode force were taken into account for establishing the range of adequate nugget formation parameters. Influence of the welding process parameters on the shear – tensile strength, nugget diameter and the observed failure mode was analysed. The adequate resistance spot welding process parameters for galvannealed high strength interstitial free steel sheets of 1.6 mm thickness were estimated as 8 kA weld current, 250 ms weld time and 3.5 kN electrode force. Increase in the mean dynamic contact resistance led to a significant reduction in nugget diameter. A critical nugget diameter distinguishing between the IF and PF mode was experimentally determined by failure mode analysis. Different numerical models for estimation of critical nugget diameter were evaluated.
AA5083 friction stir welds were produced using systematic experimental design, the process forces... more AA5083 friction stir welds were produced using systematic experimental design, the process forces and heat input with varying parameters were studied. Helpful empirical models were developed in designing friction stir welding (FSW) tools and FSW welders. These models may be further helpful for making process parameter choice for this sort of alloy, defining welding program and control of process parameters by using computer numerical control friction stir welding welders. The results show that tool rotational speed, welding speed and tool shoulder diameter are most significant parameters affecting axial force and heat input, while longitudinal force is significantly affected by welding speed and probe diameter.
Other than the brittle failure, the ductile behavior of the aged nuclear reactor pressure vessel ... more Other than the brittle failure, the ductile behavior of the aged nuclear reactor pressure vessel (RPV) steels is also of interest for the integrity assessment and evaluation of the irradiation response. The fracture toughness of high toughness materials like RPV steels can be characterized by a J-R curve. Since the RPV steel material available for testing purposes, like surveillance specimens, is limited, the single specimen method is used for the J-R curve determination. In this study, J-R curves were measured on Charpy size SE(B) and 1T-C(T) specimens of different RPV steels in the unirradiated and irradiated conditions. It was observed that despite the available sophisticated instrumentation and strict implementation of the recommended test procedures, the J-initiation value for all the different material specimens tested could not be ascertained according to the test standards ASTM E1820 and ISO 12 135. For Charpy size SE(B) specimens, it was found that though valid J IC /J 0.2BL values could be obtained in irradiated conditions, in un-irradiated conditions, especially for high toughness RPV steels, it was not possible. The evaluation showed that the a oq fit of the ASTM standard compensates uncertainties in the initial J-Da value resulting in reliable and more number of qualified test results. But these uncertainties strongly influence the A parameters of the ISO fit and the J 0.2BL(B) value. Additionally, in the ISO evaluation the lower offset of the first exclusion line and a higher slope results in lower J 0.2BL values compared to the ASTM analysis. Furthermore, for the two specimen geometries the course of J-R curves up to the J Q value was similar even for high toughness materials, but the lower specimen size was disqualified due to the lower prescribed J limit. Similarly, the J-R curves for un-irradiated and irradiated condition had a similar course up to the J 0.2BL value, even for extremely high irradiation induced embrittlement.
Variation in dynamic contact resistance with the change in welding process parameters such as wel... more Variation in dynamic contact resistance with the change in welding process parameters such as weld current , weld time and electrode force were taken into account for establishing the range of adequate nugget formation parameters. Influence of the welding process parameters on the shear – tensile strength, nugget diameter and the observed failure mode was analysed. The adequate resistance spot welding process parameters for galvannealed high strength interstitial free steel sheets of 1.6 mm thickness were estimated as 8 kA weld current, 250 ms weld time and 3.5 kN electrode force. Increase in the mean dynamic contact resistance led to a significant reduction in nugget diameter. A critical nugget diameter distinguishing between the IF and PF mode was experimentally determined by failure mode analysis. Different numerical models for estimation of critical nugget diameter were evaluated.
AA5083 friction stir welds were produced using systematic experimental design, the process forces... more AA5083 friction stir welds were produced using systematic experimental design, the process forces and heat input with varying parameters were studied. Helpful empirical models were developed in designing friction stir welding (FSW) tools and FSW welders. These models may be further helpful for making process parameter choice for this sort of alloy, defining welding program and control of process parameters by using computer numerical control friction stir welding welders. The results show that tool rotational speed, welding speed and tool shoulder diameter are most significant parameters affecting axial force and heat input, while longitudinal force is significantly affected by welding speed and probe diameter.
Other than the brittle failure, the ductile behavior of the aged nuclear reactor pressure vessel ... more Other than the brittle failure, the ductile behavior of the aged nuclear reactor pressure vessel (RPV) steels is also of interest for the integrity assessment and evaluation of the irradiation response. The fracture toughness of high toughness materials like RPV steels can be characterized by a J-R curve. Since the RPV steel material available for testing purposes, like surveillance specimens, is limited, the single specimen method is used for the J-R curve determination. In this study, J-R curves were measured on Charpy size SE(B) and 1T-C(T) specimens of different RPV steels in the unirradiated and irradiated conditions. It was observed that despite the available sophisticated instrumentation and strict implementation of the recommended test procedures, the J-initiation value for all the different material specimens tested could not be ascertained according to the test standards ASTM E1820 and ISO 12 135. For Charpy size SE(B) specimens, it was found that though valid J IC /J 0.2BL values could be obtained in irradiated conditions, in un-irradiated conditions, especially for high toughness RPV steels, it was not possible. The evaluation showed that the a oq fit of the ASTM standard compensates uncertainties in the initial J-Da value resulting in reliable and more number of qualified test results. But these uncertainties strongly influence the A parameters of the ISO fit and the J 0.2BL(B) value. Additionally, in the ISO evaluation the lower offset of the first exclusion line and a higher slope results in lower J 0.2BL values compared to the ASTM analysis. Furthermore, for the two specimen geometries the course of J-R curves up to the J Q value was similar even for high toughness materials, but the lower specimen size was disqualified due to the lower prescribed J limit. Similarly, the J-R curves for un-irradiated and irradiated condition had a similar course up to the J 0.2BL value, even for extremely high irradiation induced embrittlement.
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