Department of Mechanical Engineering

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The present study investigates a novel control strategy to create a sweeping oscillatory jet using fluidic actuation principle. A supersonic underexpanded primary jet issued into a suddenly expanding duct is oscillated by giving cyclic pulsed secondary jet blowing in the top and bottom step regions of the suddenly expanding duct. The current study employs the bistable nature of jet expansion seen in a suddenly expanding duct for the jet oscillation. The cyclic perturbations (pulsed secondary jet blowing) given in the streamwise direction switch the direction of the asymmetric jet expansion of the underexpanded primary supersonic jet to the top and bottom wall alternatively, thereby creating an oscillatory supersonic jet. It is found that the switching of the direction of the primary jet to any one wall is caused by the Coanda effect produced by the secondary jet issued in the corresponding wall side. The results show that the primary jet quickly responds to the secondary jet perturbations and that the supersonic primary jet oscillation frequency nearly matches secondary jet perturbation frequency. A parametric study to investigate the jet oscillation characteristics with various secondary jet oscillation frequencies and mass flow rate ratios are also being carried out in the present study. It is found that the jet oscillation frequency increases with increase in the secondary jet pulsation frequency. The jet deflection is found to increase with increase in the secondary jet to primary jet mass flow ratio (blowing ratio) up to a critical limit, after which the increment in jet deflection ceases due to the restrictions imposed by the duct geometry. © 2022, AIAA International. All rights reserved.

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AIAA Journal

Active Flow Control of Supersonic Jet Using Streamwise Pulsed Blowing

In supercritical thermal power plant units, a dissimilar joining of heat-resistant Cr-Mo steels such as P91 and P22 is commonly employed for components like boiler headers, piping, and steam turbine casing to increase the flexibility in design and application and also to reduce the material costs. However, a dissimilar joining of these two steels with matching filler has been subjected to several issues like mismatch in coefficient of thermal expansion, diffusion of elements, and unmixed zone formation. In the present investigation, microstructure and mechanical behavior study was conducted for the welded joint of different grade Cr-Mo steel, i.e., P22/P91 for the as-welded (AW) and post-weld heat treatment (PWHT) condition. The dissimilar welded joint (DWJ) was produced using the multi-pass gas tungsten arc welding (GTAW) process with Ni-based superalloy filler Inconel 82. Microstructure observation showed the absence of any type of possible cracking in the weldments obtained by Inconel 82 filler; however, an inhomogeneity in microstructure was found along the weldments. After the PWHT, carbon diffusion across the interface of P22 steel and Inconel 82 weld metal occurred, which resulted in the formation of soft zone (SZ) and hard zone (HZ). The welds produced using Inconel 82 filler displayed tensile strength and impact toughness of 608 ± 3.5 MPa and 83 ± 4 J, respectively. After PWHT, tensile strength and Charpy impact toughness were 507 ± 8 MPa and 75 ± 3 J, respectively. The fracture of tensile-tested specimen had occurred in the weak P22 base region for both AW and PWHT conditions, which ensured that welded joint was safe for supercritical power plant applications. The longitudinal residual stress of 380 MPa and transverse residual stress of 400 MPa were measured in top region of the weld metal, while in the root region, magnitude of 130 and 185 MPa was measured in longitudinal and transverse directions, respectively. © 2022, ASM International.

Journal of Materials Engineering and Performance

Characterization of Microstructure and Mechanical Properties of Cr-Mo Grade P22/P91 Steel Dissimilar Welds for Supercritical Power Plant Application

Friction stir welding (FSW) is a non-traditional welding procedure for joining identical and divergent substances that are comparatively hard to weld using fusion techniques. The FSW is more competent and eco-responsive when correlated with the traditional processes. The tensile characteristics of thermally susceptible alloys are minimized as a result of heat iterations. The roughening of the consolidated deposits in friction stir welding induces joint moderation. For non-heat-treatable alloys, intergranular and stress corrosion cracking are developed in grain boundaries during the FSW. Because of this, the overall performance and mechanical properties were reduced. Underwater friction stir welding (UWFSW) is preferred to prevail over the problems. UWFSW is appropriate for both heat-treatable and non-heat-treatable alloys that are receptive to thermal activity throughout the procedure. This research examines the effects of response surface methodology (RSM)-based grey relational methods on the optimization of UWFSW procedural characteristics such as the straight hexagonal tool profile (SH), tool rotational speed (TRS) of 1200 rpm, tool transverse velocity (TTV) of 20 mm/min, and water head (WH) of 10 mm in military-grade AA5083 alloy. The mechanical properties of the AA5083 UWFSW joint, such as its average ultimate tensile strength (UTS) and hardness, have been greatly improved. Grey Relation Analysis was used to determine welding specifics such as UTS and hardness. The ANOVA was used to assess the formulation's significance. The micro-structural behaviour and grain structure of different weld zones were investigated with the help of the scanning electron microscope (SEM). The image processing technique can be used to quantitatively assess the UWFSW process using the non-destructive testing (NDT) ultrasonic B-scan image and radiographic image. Confirmation tests at the optimal parameter level improved the performance of each response. © IMechE 2022.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Optimisation of underwater friction stir welding parameters of aluminum alloy AA5083 using RSM and GRA

A dissimilar laser beam welded joint of ferritic/martensitic P92 steel, and 304L austenitic stainless steel (ASS) has been examined in as-weld and post-weld heat treatment (PWHT) at 760 °C for 120 min for microstructure feature and mechanical aspects. The microstructure of the weld metal, interface, and heat-affected zone (HAZ) was characterized in detail, and it was observed that a great level of inhomogeneity exists in a dissimilar joint. In addition, the effect of the inhomogeneity in microstructure on mechanical properties, microhardness, and impact strength of the welded joint was discussed. The welded joint's mechanical properties met the USC boiler requirement for both as-weld and PWHT situations. The welded joint showed a decent combination of tensile strength and impact strength for both as-weld and PWHT conditions. The tensile results showed the failure from the 304L SS base metal, which ensured the acceptable strength of the weld metal for the laser welded joints. The part of the welded joint with relatively poor impact strength was the weld metal. Though, the Charpy impact toughness of the weld metal (89 J) was measured higher than the ASME standard value (>41 J) and EN 1599:1997 standard value (>47 J) in the as-weld situation. The impact strength of the weld fusion zone was 138 J in PWHT condition. © 2022 Elsevier Ltd

International Journal of Pressure Vessels and Piping

Study on microstructure and mechanical behavior relationship for laser-welded dissimilar joint of P92 martensitic and 304L austenitic steel

Integrated Assembly and Performance Evaluation

Uncertainty and Sensitivity Analysis

Journal of Materials NanoScience

Recent development in carbon nanotubes based gas sensors

We experimentally report evaporation characteristics from leaf-like surfaces having low open (exposed) area ratio. Even at much lower (1–10%) exposed areas, higher transpiration rates (60–70% compared to a bare water source) are sustained by a leaf. We mimic stomata, tiny openings present on the leaves using holes punched on silicon wafers (SW). The leaf-mimics have different opening diameters, ranging from (Formula presented.) to (Formula presented.) but nearly the same open area of (Formula presented.) The leaf-mimic with the smallest opening size was found to evaporate the most, while for the larger opening sizes it seems to decrease. In all the cases, evaporation ratio (ratio of the evaporation rate from the leaf-mimic to that of from a bare water surface at the same net incident radiation) increased with decreasing pore sizes; we compute this ratio based on three different definitions including one for the isothermal cases. In non-isothermal cases, we recognized that the variation in surface temperature led to nonlinear variation in the surface water vapor concentration. The effect of increased surface temperature, compared to a bare water surface in similar conditions, is missing in defining the evaporation ratios in previous approaches and thus we include it. © 2020 Taylor & Francis Group, LLC.

Drying Technology

Understanding the coupling between the moisture loss and surface temperature in an evaporating leaf-type surface

Stainless steel is one of the most widely used steels for structural applications. This paper quantifies the effect of heat treatment on the wear resistance behaviour of stainless steel 304 grades using pin on disc method. Ageing at different temperature ranges imparts hardness to the SS304 specimen which in turn affects the wear resistance characteristic. Different wear parameters have been calculated using Archard's equation and wear scar diameter method. Microstructure has been studied using optical microscopy. Scanning electron microscopy has been used to investigate the wear mechanism.

Lecture Notes in Mechanical Engineering

Effect of Heat Treatment on Wear Behaviour of Austenitic Stainless Steel

Dissimilar autogenous welding of ferritic/martensitic P92 steel and Inconel 617 alloy was conducted using the laser beam-welding process. The microstructure evolution such as element segregation, grain size, and precipitate morphology was investigated in different areas of the welded joint for as-welded (AW) and post-weld heat treatment (PWHT) condition by using optical microscopy (OM) and Field Emission Scanning Electron Microscopy (FE-SEM). The tensile strength at room temperature, microhardness variation, and Charpy V impact toughness was evaluated for the welded joint to study the effect of laser beam welding on mechanical properties. Finally, the fractured impact-tested specimen was characterized by FE-SEM. Microstructure observation showed the microstructure heterogeneity across the welded joint. A typical martensitic lath structure devoid of carbide precipitates was observed in P92 HAZ, while Inconel 617 HAZ exhibited the fine-equiaxed austenite grains of average size 24 ± 7 µm with Ti-enriched Ti(C, N) and Mo-enriched carbide precipitates. A columnar and cellular structure consisting of the alloying element segregation in the inter-dendritic areas was observed for the weld metal (WM) near the interface, while the interior WM showed the cellular and equiaxed dendrites along with particles of type NBC, TiC, and M23C6. Fairly good strength and ductility were obtained for the welded joint, and it qualified the ultra-supercritical (USC) boiler requirement. The WM was witnessed as the weakest part of the welded joint for impact strength. However, the impact strength of the WM (61 ± 2 J) was measured higher than the ASME standard value (&gt; 41 J) and EN ISO 3580:2017 standard value (&gt; 47 J) in the AW joint. After the PWHT, a drastic reduction in impact strength of WM (48 ± 3 J) was measured, and it was very close to EN ISO 3580:2017 recommended value of 47 J. The HAZ of P92 and Inconel 617 showed good impact strength for both AW and PWHT joints. The austenitic microstructure in WM exhibited the hardness of 150 ± 8 HV0.5, which was lower than the hardness of P92 and Inconel 617 base metal. The hardness in P92 HAZ was estimated higher than other regions of the weldments (WM and Inconel 617 HAZ). PWHT resulted in a drastic reduction in hardness of P92 HAZ, while WM (154 ± 7 HV0.5) and Inconel 617 HAZ showed a minute change in hardness value. The tensile strength of welded joints for the transverse tensile-tested specimen was also measured higher than the base metal, and fracture was observed in weaker parent metal, i.e., P92 steel for both AW and PWHT joint. © 2022, Wroclaw University of Science and Technology.