ISRO Propulsion Complex

Friction stir welding (FSW) of dissimilar aluminium alloys provides significant advantages in aerospace applications. However, the microstructural variation and its influence on mechanical properties in dissimilar AA2219–AA2014 welds have not been sufficiently investigated. In this study, the tensile properties of dissimilar AA2219–AA2014 friction stir welded joints are examined across room temperature and cryogenic temperatures (77 K and 20 K). A miniature tensile test was conducted to study the local tensile behaviour of the stir zone in similar and dissimilar FSW welds. To corroborate the tensile behaviour, hardness evaluation was done across the weld regions. A detailed microstructural analysis was conducted at various regions of the dissimilar weld using optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) techniques. The results brought out a logical correlation between the tensile properties and microstructural data, including grain evolution, particle redistribution, and dislocation density. The dissimilar weld joint exhibited a UTS of 348 MPa and a YS of 195 MPa at RT, yielding a joint efficiency of 73%. It was evident that the weaker base material, AA2219 alloy, largely determined the tensile properties at RT, 77 K and 20 K.

This paper investigates the effect of injector panel temperature on the flame transfer function (FTF) for different fuel/air mixtures, including methane/air, propane/air, and hydrogen/air, by combining numerical simulations with system identification (SI) techniques. Under steady conditions, increasing the injector panel temperature leads to a reduction in the flame stand-off distance. A small amplitude Gaussian impulse is introduced to perturb the oncoming flow velocity, and once the flame returns to steady behavior, the FTF is extracted over a range of frequencies using system identification. The resulting FTFs are validated against those obtained using the conventional sinusoidal forcing method. The results show that increasing wall temperature enhances the peak gain of the FTF and shifts the peak frequency to higher values. In addition, variations in flame stand-off distance influence the phase characteristics of the FTF. Extra flame oscillations give rise to sub-peaks in the FTF spectrum, and the magnitude of these oscillations is modulated by the stand-off distance. • CFD/SI method was used to obtain the flame transfer function. • Flame stand-off distance change significantly due to injector temperature. • The FTF phase lag decreases with flame stand-off distance. • Flame stand-off distance influence FTF peak frequency. • Flame root oscillation may result in FTF sub-peaks.