Search

In the present study, functionally graded material (FGM) of Austenitic Stainless Steel-SS 316L and Nickel-based superalloy-Inconel 625 (IN625) was manufactured via Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM). WAAM processed FGM was well-formed without any defects and solidification cracking was not observed at the bi-metallic interface (IF) region. Microstructural features show a sharp transition at the IF with a discontinued dendritic structure. Energy-dispersive X-ray spectroscopy (EDS) examination confirmed the fine dissolution of elements at the IF and no major difference in the composition was observed. Electron Backscatter Diffraction (EBSD) maps confirmed that the grains are dominantly columnar while the IF revealed the smooth crystallographic growth along with large elongated dendrites in the< 001 >direction. The microstructure was mainly austenitic in the SS 316L layers with a lower fraction of ferrite while precipitates were noticed in the IN625 layers within the austenitic matrix. Yield strength (YS) and tensile strength (UTS) of SS 316L and IN625 were comparable with wrought ones. All the IF samples at 90° failed in the SS 316L region because of the lower UTS in comparison to IN625 and the mode of fracture was ductile. Microhardness measurements depicted the gradual change of hardness along the building direction. The present work highlights the potential of WAAM to fabricate FGM with required properties and is a viable manufacturing alternative to the traditional manufacturing techniques for producingFGM's. © 2022 CIRP

In the present study, functionally graded material (FGM) of Austenitic Stainless Steel-SS 316L and Nickel-based superalloy-Inconel 625 (IN625) was manufactured via Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM). WAAM processed FGM was well-formed without any defects and solidification cracking was not observed at the bi-metallic interface (IF) region. Microstructural features show a sharp transition at the IF with a discontinued dendritic structure. Energy-dispersive X-ray spectroscopy (EDS) examination confirmed the fine dissolution of elements at the IF and no major difference in the composition was observed. Electron Backscatter Diffraction (EBSD) maps confirmed that the grains are dominantly columnar while the IF revealed the smooth crystallographic growth along with large elongated dendrites in the< 001 >direction. The microstructure was mainly austenitic in the SS 316L layers with a lower fraction of ferrite while precipitates were noticed in the IN625 layers within the austenitic matrix. Yield strength (YS) and tensile strength (UTS) of SS 316L and IN625 were comparable with wrought ones. All the IF samples at 90° failed in the SS 316L region because of the lower UTS in comparison to IN625 and the mode of fracture was ductile. Microhardness measurements depicted the gradual change of hardness along the building direction. The present work highlights the potential of WAAM to fabricate FGM with required properties and is a viable manufacturing alternative to the traditional manufacturing techniques for producingFGM's. © 2022 CIRP

In the present study, functionally graded material (FGM) of Austenitic Stainless Steel-SS 316L and Nickel-based superalloy-Inconel 625 (IN625) was manufactured via Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM). WAAM processed FGM was well-formed without any defects and solidification cracking was not observed at the bi-metallic interface (IF) region. Microstructural features show a sharp transition at the IF with a discontinued dendritic structure. Energy-dispersive X-ray spectroscopy (EDS) examination confirmed the fine dissolution of elements at the IF and no major difference in the composition was observed. Electron Backscatter Diffraction (EBSD) maps confirmed that the grains are dominantly columnar while the IF revealed the smooth crystallographic growth along with large elongated dendrites in the< 001 >direction. The microstructure was mainly austenitic in the SS 316L layers with a lower fraction of ferrite while precipitates were noticed in the IN625 layers within the austenitic matrix. Yield strength (YS) and tensile strength (UTS) of SS 316L and IN625 were comparable with wrought ones. All the IF samples at 90° failed in the SS 316L region because of the lower UTS in comparison to IN625 and the mode of fracture was ductile. Microhardness measurements depicted the gradual change of hardness along the building direction. The present work highlights the potential of WAAM to fabricate FGM with required properties and is a viable manufacturing alternative to the traditional manufacturing techniques for producingFGM's. © 2022 CIRP

In the present study, functionally graded material (FGM) of Austenitic Stainless Steel-SS 316L and Nickel-based superalloy-Inconel 625 (IN625) was manufactured via Gas Metal Arc Welding (GMAW) based Wire Arc Additive Manufacturing (WAAM). WAAM processed FGM was well-formed without any defects and solidification cracking was not observed at the bi-metallic interface (IF) region. Microstructural features show a sharp transition at the IF with a discontinued dendritic structure. Energy-dispersive X-ray spectroscopy (EDS) examination confirmed the fine dissolution of elements at the IF and no major difference in the composition was observed. Electron Backscatter Diffraction (EBSD) maps confirmed that the grains are dominantly columnar while the IF revealed the smooth crystallographic growth along with large elongated dendrites in the< 001 >direction. The microstructure was mainly austenitic in the SS 316L layers with a lower fraction of ferrite while precipitates were noticed in the IN625 layers within the austenitic matrix. Yield strength (YS) and tensile strength (UTS) of SS 316L and IN625 were comparable with wrought ones. All the IF samples at 90° failed in the SS 316L region because of the lower UTS in comparison to IN625 and the mode of fracture was ductile. Microhardness measurements depicted the gradual change of hardness along the building direction. The present work highlights the potential of WAAM to fabricate FGM with required properties and is a viable manufacturing alternative to the traditional manufacturing techniques for producingFGM's. © 2022 CIRP

The tribological and thermal properties enable iron based sintered materials with hard phase ceramic reinforcements as promising friction material for heavy-duty wind turbines. In wind turbines, the braking system consists of aerodynamic and mechanical braking systems. During application of mechanical brakes, the friction materials are pressed against the rotating low-speed shaft. The desired braking efficiency is achieved by utilizing a number of friction materials, which in turn are joined in a steel backing plate. Though this arrangement increases the braking efficiency, the hard phase ceramic reinforcement particles reduces the bonding strength between the friction material and steel backing plate. The joint failure leads to catastrophic failure of wind turbine. Therefore, the need of the hour is to develop friction materials with functional gradients that have high wear resistance (contact area) and high bond strength (interface). In this study, an attempt is made to fabricate and characterize a friction material with gradient profile of composition along the cross section to provide functional gradient property. The functional gradient friction material is synthesized by gradient deposition of Fe, Cu, Cg, SiC and fly ash powders which is then compacted and sintered. The prepared functional gradient friction material was characterized in terms of microstructure and microhardness. The tribological performance (wear rate and coefficient of friction) of the developed functionally gradient friction material was investigated at various loads using pin-on disc apparatus. The results show that as the load increases, the wear rate decreases and at the same time the COF tends to increase at higher loads. The predominant wear mechanism was deduced from the morphology of the worn surface.

The tribological and thermal properties enable iron based sintered materials with hard phase ceramic reinforcements as promising friction material for heavy-duty wind turbines. In wind turbines, the braking system consists of aerodynamic and mechanical braking systems. During application of mechanical brakes, the friction materials are pressed against the rotating low-speed shaft. The desired braking efficiency is achieved by utilizing a number of friction materials, which in turn are joined in a steel backing plate. Though this arrangement increases the braking efficiency, the hard phase ceramic reinforcement particles reduces the bonding strength between the friction material and steel backing plate. The joint failure leads to catastrophic failure of wind turbine. Therefore, the need of the hour is to develop friction materials with functional gradients that have high wear resistance (contact area) and high bond strength (interface). In this study, an attempt is made to fabricate and characterize a friction material with gradient profile of composition along the cross section to provide functional gradient property. The functional gradient friction material is synthesized by gradient deposition of Fe, Cu, Cg, SiC and fly ash powders which is then compacted and sintered. The prepared functional gradient friction material was characterized in terms of microstructure and microhardness. The tribological performance (wear rate and coefficient of friction) of the developed functionally gradient friction material was investigated at various loads using pin-on disc apparatus. The results show that as the load increases, the wear rate decreases and at the same time the COF tends to increase at higher loads. The predominant wear mechanism was deduced from the morphology of the worn surface.

A matrix $A$ is totally positive (or non-negative) of order $k$, denoted $TP_k$ (or $TN_k$), if all minors of size $\leq k$ are positive (or non-negative). It is well-known that such matrices are characterized by the variation diminishing property together with the sign non-reversal property. We do away with the former, and show that $A$ is $TP_k$ if and only if every submatrix formed from at most $k$ consecutive rows and columns has the sign non-reversal property. In fact this can be strengthened to only consider test vectors in $\mathbb{R}^k$ with alternating signs. We also show a similar characterization for all $TN_k$ matrices - more strongly, both of these characterizations use a single vector (with alternating signs) for each square submatrix. These characterizations are novel, and similar in spirit to the fundamental results characterizing $TP$ matrices by Gantmacher-Krein [Compos. Math. 1937] and $P$-matrices by Gale-Nikaido [Math. Ann. 1965]. As an application, we study the interval hull $\mathbb{I}(A,B)$ of two $m \times n$ matrices $A=(a_{ij})$ and $B = (b_{ij})$. This is the collection of $C \in \mathbb{R}^{m \times n}$ such that each $c_{ij}$ is between $a_{ij}$ and $b_{ij}$. Using the sign non-reversal property, we identify a two-element subset of $\mathbb{I}(A,B)$ that detects the $TP_k$ property for all of $\mathbb{I}(A,B)$ for arbitrary $k \geq 1$. In particular, this provides a test for total positivity (of any order), simultaneously for an entire class of rectangular matrices. In parallel, we also provide a finite set to test the total non-negativity (of any order) of an interval hull $\mathbb{I}(A,B)$., Comment: Final version, to appear in Bulletin of the London Mathematical Society. 9 pages, no figures

We establish a characterization of almost $P$-matrices via a sign non-reversal property. In this we are inspired by the analogous results for $N$-matrices. Next, the interval hull of two $m \times n$ matrices $A=(a_{ij})$ and $B = (b_{ij})$, denoted by $\mathbb{I}(A,B)$, is the collection of all matrices $C \in \mathbb{R}^{m \times n}$ such that each $c_{ij}$ is a convex combination of $a_{ij}$ and $b_{ij}$. Using the sign non-reversal property, we identify a finite subset of $\mathbb{I}(A,B)$ that determines if all matrices in $\mathbb{I}(A,B)$ are $N$-matrices/almost $P$-matrices. This provides a test for an entire class of matrices simultaneously to be $N$-matrices/almost $P$-matrices. We also establish analogous results for semipositive and minimally semipositive matrices. These characterizations may be considered similar in spirit to that of $P$-matrices by Bialas-Garloff [Linear Algebra Appl. 1984] and Rohn-Rex [SIMAX 1996], and of positive definite matrices by Rohn [SIMAX 1994].

The present study was intended to evaluate the various pharmacognostical procedures in the leaves of Capparis sepiaria Linn., (Capparidaceae). The various pharmacognostical parameters were carried out as per WHO guidelines procedure i.e., bitterness, fineness, microscopical sections, loss on drying, water and alcoholic extractive values, water insoluble ash, acid soluble ash, total ash, swelling index, foaming index, heavy metal analysis, phytochemical analysis and toxicity studies (acute, subacute and chronic toxicity). The study was extended with analyzing the chemical compounds identification in the EECS (ethanolic extract of Capparis sepiaria by using GC-MS. The presence of various phytoconstituents such as glycosides, reducing sugars, flavonoids, saponins, starch and terpenoids is evidenced in EECS & AECS. The results showed that acid insoluble ash (1.70%), total ash (8.68%), water soluble ash (3.42%), water extractive (31.55%), alcohol extractive (5.06%), foaming index (105.26 Unit), loss on drying (9.84%), swelling index (4.16%), acute toxicity (nil), sub-acute toxicity (nil), chronic toxicity (nil). The study was concluded with the plant has standardized as per the World Health Organization procedures. The result of the pharmacognostical standardization of this plant serves as a reference piece and helps in future identification and authentication of this plant specimen. Might be the plant C. sepiaria has potential property by the standardization and it can be included in the normal flora of the plant kingdom.Keywords: C. sepiaria; Microscopical; Macroscopical standardization.