Rajnish kumar - Academia.edu (original) (raw)

Papers by Rajnish kumar

Materials

This paper presents an analytical model that quantifies the stress ratio between two test specime... more This paper presents an analytical model that quantifies the stress ratio between two test specimens for the same probability of failure based on the Weibull weakest link theory. The model takes into account the test specimen geometry, i.e., its shape and volume, and the related non-constant stress state along the specimen. The proposed model is a valuable tool for quantifying the effect of a change of specimen geometry on the probability of failure. This is essential to distinguish size scaling from the actual improvement in measured strength when specimen geometry is optimized, aiming for failure in the gauge section. For unidirectional carbon fibre composites with Weibull modulus m in the range 10–40, it can be calculated by the model that strength measured with a straight-sided specimen will be 1–2% lower than the strength measured with a specific waisted butterfly-shaped specimen solely due to the difference in test specimen shape and volume.

Materials, 2021

This paper presents an experimental method for tensile testing of unidirectional carbon fibre com... more This paper presents an experimental method for tensile testing of unidirectional carbon fibre composites. It uses a novel combination of a new specimen geometry, protective layer, and a robust data analysis method. The experiments were designed to test and analyze unprotected (with conventional end-tabs) and protected (with continuous end-tabs) carbon fibre composite specimens with three different specimen geometries (straight-sided, butterfly, and X-butterfly). Initial stiffness and strain to failure were determined from second-order polynomial fitted stress–strain curves. A good agreement between back-calculated and measured stress–strain curves is found, on both composite and fibre level. For unprotected carbon composites, the effect of changing specimen geometry from straight-sided to X-butterfly was an increase in strain to failure from 1.31 to 1.44%. The effect of protection on X-butterfly specimens was an increase in strain to failure from 1.44 to 1.53%. For protected X-butte...

IOP Conference Series: Materials Science and Engineering, 2020

Accurate characterization of fibres is crucial for the understanding the properties and behaviour... more Accurate characterization of fibres is crucial for the understanding the properties and behaviour of fibre-reinforced composite materials. Fibre properties are key parameters for composite design, modelling and analysis. In this study, characterization of mechanical properties of glass and carbon fibres has been performed using a semi-automated single-fibre testing machine. Based on a sample set of 150 glass and carbon fibers fibres, engineering and true stress-strain curves are analyzed. Different modulus determination methods are discussed based on true stress-strain and tangent modulus-strain relationships. For glass fibres, the true stress-strain based tangent modulus is found to be independent of applied strain, whereas for carbon fibres, a tendency of tangent modulus to increase with applied strain is observed. The modulus of glass fibres is found to be independent of fibre diameter, whereas carbon fibres with smaller diameter show higher modulus compared with carbon fibres wi...

Industrial & Engineering Chemistry Research, 2004

The esterification of palmitic acid with ethanol was investigated at various temperatures (35-70°... more The esterification of palmitic acid with ethanol was investigated at various temperatures (35-70°C) in the presence of three lipases (Novozym 435, Lipolase 100T, and hog pancreas lipase) in supercritical carbon dioxide (SCCO 2) and under solvent-free conditions. All enzymes showed an optimum temperature of 55°C under both conditions. The effect of water and ethanol addition on the esterification of acid was also investigated. The conversion obtained in SCCO 2 and under solvent-free conditions with Novozym at optimal conditions was 74 and 97%, respectively. Although a higher apparent yield was obtained under the solvent-free conditions due to higher substrate and enzyme concentrations, the reaction in supercritical carbon dioxide is better because of lower enzyme loading, higher reaction rates and easier downstream processing.

Industrial & Engineering Chemistry Research, 2004

Octyl palmitate was enzymatically synthesized from palmitic acid and octanol. The synthesis of oc... more Octyl palmitate was enzymatically synthesized from palmitic acid and octanol. The synthesis of octyl palmitate was investigated in three supercritical fluids, namely, carbon dioxide, methane, and ethane, using three different enzymes. The effects of temperature, initial water content, alcohol concentration, and enzyme loading on the conversion were determined. Among the enzymes, Novozym 435 (immobilized) catalyzed the reaction, resulting in the highest conversion compared to the other lipases, irrespective of the solvent used. Further ...

Fuel, 2004

Biodiesel, an alternative biodegradable diesel fuel, is derived from triglycerides by transesteri... more Biodiesel, an alternative biodegradable diesel fuel, is derived from triglycerides by transesterification with alcohols. In this work, the transesterification of sunflower oil was investigated in supercritical methanol and supercritical ethanol at various temperatures (200–400° C) at 200 bar. The rate coefficients and the activation energies of the reaction were also determined. Biodiesel was also enzymatically synthesized in supercritical carbon dioxide. The effect of enzyme loading, oil to alcohol ratio, reaction time and temperature ...

Biochemical Engineering Journal, 2005

The esterification of fatty acids of different chain lengths with isoamyl alcohol was studied in ... more The esterification of fatty acids of different chain lengths with isoamyl alcohol was studied in solvent free conditions and in supercritical carbon dioxide (SCCO 2). Three different commercial lipases, Hog pancreas lipase (HPL), Lipolase 100T, and Novozym 435 were used for the synthesis of the esters. The results indicate that Novozym gave high conversion for the esterification of all acids, while HPL and Lipolase favored the conversion of higher and lower chain lengths of fatty acids, respectively.

The solubility of water in the organic solutions, containing hydrocarbons, has traditionally been... more The solubility of water in the organic solutions, containing hydrocarbons, has traditionally been modeled by using empirical correlations. In this communication, an extended Setschenow model is proposed for predicting the organic solubility of water in a 5-100% tri-n-butyl phosphate/diluent-nitric acid-water biphasic system at 298.2 K. The literature data on water solubility were correlated to aqueous acid concentration and diluent concentration in the solvents. The proposed model was extended for temperature dependency of the solubility.

Materials

This paper presents an analytical model that quantifies the stress ratio between two test specime... more This paper presents an analytical model that quantifies the stress ratio between two test specimens for the same probability of failure based on the Weibull weakest link theory. The model takes into account the test specimen geometry, i.e., its shape and volume, and the related non-constant stress state along the specimen. The proposed model is a valuable tool for quantifying the effect of a change of specimen geometry on the probability of failure. This is essential to distinguish size scaling from the actual improvement in measured strength when specimen geometry is optimized, aiming for failure in the gauge section. For unidirectional carbon fibre composites with Weibull modulus m in the range 10–40, it can be calculated by the model that strength measured with a straight-sided specimen will be 1–2% lower than the strength measured with a specific waisted butterfly-shaped specimen solely due to the difference in test specimen shape and volume.

Materials, 2021

This paper presents an experimental method for tensile testing of unidirectional carbon fibre com... more This paper presents an experimental method for tensile testing of unidirectional carbon fibre composites. It uses a novel combination of a new specimen geometry, protective layer, and a robust data analysis method. The experiments were designed to test and analyze unprotected (with conventional end-tabs) and protected (with continuous end-tabs) carbon fibre composite specimens with three different specimen geometries (straight-sided, butterfly, and X-butterfly). Initial stiffness and strain to failure were determined from second-order polynomial fitted stress–strain curves. A good agreement between back-calculated and measured stress–strain curves is found, on both composite and fibre level. For unprotected carbon composites, the effect of changing specimen geometry from straight-sided to X-butterfly was an increase in strain to failure from 1.31 to 1.44%. The effect of protection on X-butterfly specimens was an increase in strain to failure from 1.44 to 1.53%. For protected X-butte...

IOP Conference Series: Materials Science and Engineering, 2020

Accurate characterization of fibres is crucial for the understanding the properties and behaviour... more Accurate characterization of fibres is crucial for the understanding the properties and behaviour of fibre-reinforced composite materials. Fibre properties are key parameters for composite design, modelling and analysis. In this study, characterization of mechanical properties of glass and carbon fibres has been performed using a semi-automated single-fibre testing machine. Based on a sample set of 150 glass and carbon fibers fibres, engineering and true stress-strain curves are analyzed. Different modulus determination methods are discussed based on true stress-strain and tangent modulus-strain relationships. For glass fibres, the true stress-strain based tangent modulus is found to be independent of applied strain, whereas for carbon fibres, a tendency of tangent modulus to increase with applied strain is observed. The modulus of glass fibres is found to be independent of fibre diameter, whereas carbon fibres with smaller diameter show higher modulus compared with carbon fibres wi...

Industrial & Engineering Chemistry Research, 2004

The esterification of palmitic acid with ethanol was investigated at various temperatures (35-70°... more The esterification of palmitic acid with ethanol was investigated at various temperatures (35-70°C) in the presence of three lipases (Novozym 435, Lipolase 100T, and hog pancreas lipase) in supercritical carbon dioxide (SCCO 2) and under solvent-free conditions. All enzymes showed an optimum temperature of 55°C under both conditions. The effect of water and ethanol addition on the esterification of acid was also investigated. The conversion obtained in SCCO 2 and under solvent-free conditions with Novozym at optimal conditions was 74 and 97%, respectively. Although a higher apparent yield was obtained under the solvent-free conditions due to higher substrate and enzyme concentrations, the reaction in supercritical carbon dioxide is better because of lower enzyme loading, higher reaction rates and easier downstream processing.

Industrial & Engineering Chemistry Research, 2004

Octyl palmitate was enzymatically synthesized from palmitic acid and octanol. The synthesis of oc... more Octyl palmitate was enzymatically synthesized from palmitic acid and octanol. The synthesis of octyl palmitate was investigated in three supercritical fluids, namely, carbon dioxide, methane, and ethane, using three different enzymes. The effects of temperature, initial water content, alcohol concentration, and enzyme loading on the conversion were determined. Among the enzymes, Novozym 435 (immobilized) catalyzed the reaction, resulting in the highest conversion compared to the other lipases, irrespective of the solvent used. Further ...

Fuel, 2004

Biodiesel, an alternative biodegradable diesel fuel, is derived from triglycerides by transesteri... more Biodiesel, an alternative biodegradable diesel fuel, is derived from triglycerides by transesterification with alcohols. In this work, the transesterification of sunflower oil was investigated in supercritical methanol and supercritical ethanol at various temperatures (200–400° C) at 200 bar. The rate coefficients and the activation energies of the reaction were also determined. Biodiesel was also enzymatically synthesized in supercritical carbon dioxide. The effect of enzyme loading, oil to alcohol ratio, reaction time and temperature ...

Biochemical Engineering Journal, 2005

The esterification of fatty acids of different chain lengths with isoamyl alcohol was studied in ... more The esterification of fatty acids of different chain lengths with isoamyl alcohol was studied in solvent free conditions and in supercritical carbon dioxide (SCCO 2). Three different commercial lipases, Hog pancreas lipase (HPL), Lipolase 100T, and Novozym 435 were used for the synthesis of the esters. The results indicate that Novozym gave high conversion for the esterification of all acids, while HPL and Lipolase favored the conversion of higher and lower chain lengths of fatty acids, respectively.

The solubility of water in the organic solutions, containing hydrocarbons, has traditionally been... more The solubility of water in the organic solutions, containing hydrocarbons, has traditionally been modeled by using empirical correlations. In this communication, an extended Setschenow model is proposed for predicting the organic solubility of water in a 5-100% tri-n-butyl phosphate/diluent-nitric acid-water biphasic system at 298.2 K. The literature data on water solubility were correlated to aqueous acid concentration and diluent concentration in the solvents. The proposed model was extended for temperature dependency of the solubility.