Biltu Mahato - Academia.edu (original) (raw)
Papers by Biltu Mahato
polymers, 2023
The temperature coefficient of resistance (TCR) determines the electrical performance of material... more The temperature coefficient of resistance (TCR) determines the electrical performance of materials in electronics. For a carbon nanotube (CNT) nanocomposite, change of resistivity with temperature depends on changes in CNT intrinsic conductivity, tunnelling thresholds and distances, matrix’ coefficient of thermal expansion, and other factors. In our study, we add one more influencing factor–the degree of cure. Complexities of the curing process cause difficulties to predict, or even measure, the curing state of the polymer matrix while uncertainty in the degree of cure influences TCR measurements leading to biased values. Here we study the influence of the cure state on the TCR of a single-walled CNT/epoxy polymer nanocomposite. For the given degree of cure, TCR measurements are conducted in the temperature range 25–100 ◦C, followed by the next 24 h of post-curing and a new cycle of measurements, 8 cycles in total. We find that contrary to industry practice to expect a high degree of cure after 3 h at 130 ◦C, the curing process is far from reaching the steady state of the material and continues at least for the next 72 h at 120 ◦C, as we observe by changes in the material electrical resistivity. If TCR measurements are conducted in this period, we find them significantly influenced by the post-curing process continuing in parallel, leading in particular to non-monotonic temperature dependence and the appearance of negative values. The unbiased TCR values we observe only when the material reaches the steady state are no longer influenced by the heat input. The dependence becomes steady, monotonically increasing from near zero value at room temperature to 0.001 1/◦C at 100 ◦C.
Composites Part A, 2023
Permeability measurements of engineering textiles exhibit large variability as no standardization... more Permeability measurements of engineering textiles exhibit large variability as no standardization method currently exists; numerical permeability prediction is thus an attractive alternative. It has all advantages of virtual material characterization, including the possibility to study the impact of material variability and small- scale parameters. This paper presents the results of an international virtual permeability benchmark, which is a first contribution to permeability predictions for fibrous reinforcements based on real images. In this first stage, the focus was on the microscale computation of fiber bundle permeability. In total 16 participants provided 50 results using different numerical methods, boundary conditions, permeability identification techniques. The scatter of the predicted axial permeability after the elimination of inconsistent results was found to be smaller (14%) than that of the transverse permeability (~24%). Dominant effects on the permeability were found to be the boundary conditions in tangential direction, number of sub-domains used in the renormalization approach, and the permeability identification technique.
International Journal of Bioprinting, 2023
Laser powder bed fusion (LPBF) is considered a promising technology for manufacturing porous, bio... more Laser powder bed fusion (LPBF) is considered a promising technology for manufacturing porous, biomimetic, and patient-specific scaffolds for bone repair. Scaffold permeability is one of the key factors to be considered for acquiring the required mass-transport properties in bone tissue engineering. This study aims to reveal the relationship between the design parameters of gyroid-based porous structure and scaffold permeability. A set of gyroid samples was manufactured from intermetallic NiTi alloy. Nine configurations of porous structures were obtained by varying the main design parameters, namely wall thickness and unit cell size. The in-plane method was employed to measure the permeability coefficient for the gyroid structures. Computational fluid dynamics simulations of the porous structures were performed to predict the targeted properties in an implant at the design stage before LPBF manufacturing. The results of the simulations were validated with the obtained experimental results. Geometrical accuracy and surface morphology of the as-built samples were investigated with various techniques. Biocompatibility assessment of the gyroid scaffolds was performed with human cell culture experiments.
Composite Science and Technology, 2023
In this research, a nanoscale modification with industrially available carbon nanotubes (CNT) mas... more In this research, a nanoscale modification with industrially available carbon nanotubes (CNT) masterbatch is explored to solve the problem of delamination and perform self-diagnostic and in-situ damage sensing and monitoring in composite laminates. Compared to other methods of introducing CNTs into laminate, the application of industrially available masterbatch is scalable, so that it is useful for large composite structures. The interleave is produced by painting the diluted masterbatch on the glass fiber prepregs. Two types of CNTs interleaves with a CNTs content of 0.6 wt% and 7.5 wt% were produced. The 0.6 wt% interleave has a detrimental effect of ~80% on Mode I initiation and propagation fracture toughness whereas, the 7.5 wt% interleave shows an improvement of 27% in initiation and 0.5% in propagation Mode I fracture toughness. The addition of CNTs interleaves turns unconductive laminate into a conductive laminate and hence, it was used for self-diagnostics of damage, targeting structural health monitoring applications. In-situ damage sensing and monitoring tests were performed by simultaneously measuring the resistance of the sample during the double cantilever beam test. The fractography of the interleaved composite laminates is studied and the hierarchical toughening mechanisms are identified and discussed.
IEEE Xplore, 2023
The curing cycles of thermoset polymers dictate the degree of cure and the subsequent material pr... more The curing cycles of thermoset polymers dictate
the degree of cure and the subsequent material properties and their performance. So, monitoring the degree of cure is crucial. The curing cycles are often changed during the manufacturing process to ensure an acceptable degree of cure while balancing manufacturing time and energy expenses. The conventional methods to monitor curing are expensive, time consuming, require suspension of production process, destructive, limited to few locations, cannot be performed directly on the production line, and come at the cost of increased complexity or compromised mechanical property. Here, we present a novel in-situ nano-engineered, low-cost, easy to operate sensor and non-destructive methodology for determining and continuous monitoring of curing process in a production line without any compromise on mechanical property. The sensor is based on the industrial carbon nanotube masterbatch for thermoset polymer materials. Application of such sensor improves and advances the quality control and increases the productivity of composite manufacturing.
Polymer Composites, 2019
The article experimentally investigates the interface strength of glass fibers in polypropylene (... more The article experimentally investigates the interface strength of glass fibers in polypropylene (PP) with two different levels of crystallinity. The different degrees of crystallinity, 46.6% and 52.5%, were achieved using fast (quenching, ~4500?C/min) and slow (~2?C/min) cooling, respectively, during production of the PP film. The degree of crystallinity was measured using the differential scanning calorimetry. The mechanical properties of the films were character- ized with the dynamic mechanical analysis and with a tensile test on Deben micro-tester. Interfacial shear strength (IFSS) of glass fiber/PP was determined using fiber fragmentation test. Interfacial normal strength (IFNS) was deter- mined using inverse identification based on finite-element modeling of trans- verse tensile loading of a single fiber (Deben micro-tester with digital image correlation-based observation of the debonding). The measurements have con- firmed the expected trend in mechanical properties of the film: increase of the storage and Young's moduli (room temperature) with the increase of degree of crystallinity, accompanied by the decrease in the loss modulus and tan δ. Inter- facial strength followed the trend of the PP stiffness: both the IFSS and IFNS values for the PP with high crystallinity (slow cooling) are three (IFSS) and four (IFNS) times higher than those for the low crystallinity (fast cooling) case.
polymers, 2023
Recently, polymeric nanofiber veils have gained lot of interest for various industrial and resear... more Recently, polymeric nanofiber veils have gained lot of interest for various industrial and research applications. Embedding polymeric veils has proven to be one of the most effective ways to prevent delamination caused by the poor out-of-plane properties of composite laminates. The polymeric veils are introduced between plies of a composite laminate, and their targeted effects on delamination initiation and propagation have been widely studied. This paper presents an overview of the application of nanofiber polymeric veils as toughening interleaves in fiber-reinforced composite laminates. It presents a systematic comparative analysis and summary of attainable fracture toughness improvements based on electrospun veil materials. Both Mode I and Mode II tests are covered. Various popular veil materials and their modifications are considered. The toughening mechanisms introduced by polymeric veils are identified, listed, and analyzed. The numerical modeling of failure in Mode I and Mode II delamination is also discussed. This analytical review can be used as guidance for veil material selection, for estimation of the achievable toughening effect, for understanding the toughening mechanism introduced by veils, and for the numerical modeling of delamination.
MDPI, 2022
In this study, three-dimensional (3D) polyvinyl alcohol (PVA)/aligned boron nitride (BN) aerogel ... more In this study, three-dimensional (3D) polyvinyl alcohol (PVA)/aligned boron nitride (BN) aerogel framework nanocomposites with high performance were fabricated by a facile strategy. The boron nitride powder was initially hydrolyzed and dispersed with a chemically cross-linked plasticizer, diethyl glycol (DEG), in the PVA polymer system. The boron nitride and DEG/PVA suspensions were then mixed well with different stoichiometric ratios to attain BN/PVA nanocomposites. Scanning electron microscopy revealed that BN platelets were well dispersed and successfully aligned/oriented in one direction in the PVA matrix by using a vacuum-assisted filtration technique. The formed BN/PVA aerogel cake composite showed excellent in-plane and out-of-plane thermal conductivities of 0.76 W/mK and 0.61 W/mK with a ratio of BN/PVA of (2:1) in comparison with 0.15 W/mK for the pure PVA matrix. These high thermal conductivities of BN aerogel could be attributed to the unidirectional orientation of boron nitride nano platelets with the post-two days vacuum drying of the specimens at elevated temperatures. This aerogel composite is unique of its kind and displayed such high thermal conductivity of the BN/PVA framework without impregnation by any external polymer. Moreover, the composites also presented good wettability results with water and displayed high electrical resistivity of ~1014 W cm. These nanocomposites, thus, with such exceptional characteristics, have a wide range of potential uses in packaging and electronics for thermal management applications.
polymers, 2023
As technology advances toward ongoing circuit miniaturization and device size reduction, followed... more As technology advances toward ongoing circuit miniaturization and device size reduction, followed by improved power density, heat dissipation is becoming a key challenge for electronic equipment. Heat accumulation can be prevented if the heat from electrical equipment is efficiently exported, ensuring a device’s lifespan and dependability and preventing otherwise possible mishaps or even explosions. Hence, thermal management applications, which include altering the role of aerogels from thermally insulative to thermally conductive, have recently been a hot topic for 3D-aerogel-based thermal interface materials. To completely comprehend three-dimensional (3D) networks, we categorized and comparatively analyzed aerogels based on carbon nanomaterials, namely fibers, nanotubes, graphene, and graphene oxide, which have capabilities that may be fused with boron nitride and impregnated for better thermal performance and mechanical stability by polymers, including epoxy, cellulose, and polydimethylsiloxane (PDMS). An alternative route is presented in the comparative analysis by carbonized cellulose. As a result, the development of structurally robust and stiff thermally conductive aerogels for electronic packaging has been predicted to increase polymer thermal management capabilities. The latest trends include the self-organization of an anisotropic structure on several hierarchical levels within a 3D framework. In this study, we highlight and analyze the recent advances in 3D-structured thermally conductive aerogels, their potential impact on the next generation of electronic components based on advanced nanocomposites, and their future prospects.
polymers, 2023
The problem of icing for surfaces of engineering structures requires attention more and more ever... more The problem of icing for surfaces of engineering structures requires attention more and more every year. Active industrialization in permafrost zones is currently underway; marine transport in Arctic areas targets new goals; the requirements for aerodynamically critical surfaces of wind generators and aerospace products, serving at low temperatures, are increasing; and fiber-reinforced polymer composites find wide applicability in these structural applications demanding the problem of anti/de-icing to be addressed. The traditional manufacturing approaches are superimposed with the new technologies, such as 3D printers and robotics, for laying heat wires or cheap and high-performance Thermal Sprayed methods for metallic cover manufacturing. Another next step in developing heaters for polymer structures is nano and micro additives to create electrically conductive heating networks within. In our study, we review and comparatively analyze the modern technologies of structure heating, based on resistive heating composites.
polymers, 2023
The temperature coefficient of resistance (TCR) determines the electrical performance of material... more The temperature coefficient of resistance (TCR) determines the electrical performance of materials in electronics. For a carbon nanotube (CNT) nanocomposite, change of resistivity with temperature depends on changes in CNT intrinsic conductivity, tunnelling thresholds and distances, matrix’ coefficient of thermal expansion, and other factors. In our study, we add one more influencing factor–the degree of cure. Complexities of the curing process cause difficulties to predict, or even measure, the curing state of the polymer matrix while uncertainty in the degree of cure influences TCR measurements leading to biased values. Here we study the influence of the cure state on the TCR of a single-walled CNT/epoxy polymer nanocomposite. For the given degree of cure, TCR measurements are conducted in the temperature range 25–100 ◦C, followed by the next 24 h of post-curing and a new cycle of measurements, 8 cycles in total. We find that contrary to industry practice to expect a high degree of cure after 3 h at 130 ◦C, the curing process is far from reaching the steady state of the material and continues at least for the next 72 h at 120 ◦C, as we observe by changes in the material electrical resistivity. If TCR measurements are conducted in this period, we find them significantly influenced by the post-curing process continuing in parallel, leading in particular to non-monotonic temperature dependence and the appearance of negative values. The unbiased TCR values we observe only when the material reaches the steady state are no longer influenced by the heat input. The dependence becomes steady, monotonically increasing from near zero value at room temperature to 0.001 1/◦C at 100 ◦C.
Composites Part A, 2023
Permeability measurements of engineering textiles exhibit large variability as no standardization... more Permeability measurements of engineering textiles exhibit large variability as no standardization method currently exists; numerical permeability prediction is thus an attractive alternative. It has all advantages of virtual material characterization, including the possibility to study the impact of material variability and small- scale parameters. This paper presents the results of an international virtual permeability benchmark, which is a first contribution to permeability predictions for fibrous reinforcements based on real images. In this first stage, the focus was on the microscale computation of fiber bundle permeability. In total 16 participants provided 50 results using different numerical methods, boundary conditions, permeability identification techniques. The scatter of the predicted axial permeability after the elimination of inconsistent results was found to be smaller (14%) than that of the transverse permeability (~24%). Dominant effects on the permeability were found to be the boundary conditions in tangential direction, number of sub-domains used in the renormalization approach, and the permeability identification technique.
International Journal of Bioprinting, 2023
Laser powder bed fusion (LPBF) is considered a promising technology for manufacturing porous, bio... more Laser powder bed fusion (LPBF) is considered a promising technology for manufacturing porous, biomimetic, and patient-specific scaffolds for bone repair. Scaffold permeability is one of the key factors to be considered for acquiring the required mass-transport properties in bone tissue engineering. This study aims to reveal the relationship between the design parameters of gyroid-based porous structure and scaffold permeability. A set of gyroid samples was manufactured from intermetallic NiTi alloy. Nine configurations of porous structures were obtained by varying the main design parameters, namely wall thickness and unit cell size. The in-plane method was employed to measure the permeability coefficient for the gyroid structures. Computational fluid dynamics simulations of the porous structures were performed to predict the targeted properties in an implant at the design stage before LPBF manufacturing. The results of the simulations were validated with the obtained experimental results. Geometrical accuracy and surface morphology of the as-built samples were investigated with various techniques. Biocompatibility assessment of the gyroid scaffolds was performed with human cell culture experiments.
Composite Science and Technology, 2023
In this research, a nanoscale modification with industrially available carbon nanotubes (CNT) mas... more In this research, a nanoscale modification with industrially available carbon nanotubes (CNT) masterbatch is explored to solve the problem of delamination and perform self-diagnostic and in-situ damage sensing and monitoring in composite laminates. Compared to other methods of introducing CNTs into laminate, the application of industrially available masterbatch is scalable, so that it is useful for large composite structures. The interleave is produced by painting the diluted masterbatch on the glass fiber prepregs. Two types of CNTs interleaves with a CNTs content of 0.6 wt% and 7.5 wt% were produced. The 0.6 wt% interleave has a detrimental effect of ~80% on Mode I initiation and propagation fracture toughness whereas, the 7.5 wt% interleave shows an improvement of 27% in initiation and 0.5% in propagation Mode I fracture toughness. The addition of CNTs interleaves turns unconductive laminate into a conductive laminate and hence, it was used for self-diagnostics of damage, targeting structural health monitoring applications. In-situ damage sensing and monitoring tests were performed by simultaneously measuring the resistance of the sample during the double cantilever beam test. The fractography of the interleaved composite laminates is studied and the hierarchical toughening mechanisms are identified and discussed.
IEEE Xplore, 2023
The curing cycles of thermoset polymers dictate the degree of cure and the subsequent material pr... more The curing cycles of thermoset polymers dictate
the degree of cure and the subsequent material properties and their performance. So, monitoring the degree of cure is crucial. The curing cycles are often changed during the manufacturing process to ensure an acceptable degree of cure while balancing manufacturing time and energy expenses. The conventional methods to monitor curing are expensive, time consuming, require suspension of production process, destructive, limited to few locations, cannot be performed directly on the production line, and come at the cost of increased complexity or compromised mechanical property. Here, we present a novel in-situ nano-engineered, low-cost, easy to operate sensor and non-destructive methodology for determining and continuous monitoring of curing process in a production line without any compromise on mechanical property. The sensor is based on the industrial carbon nanotube masterbatch for thermoset polymer materials. Application of such sensor improves and advances the quality control and increases the productivity of composite manufacturing.
Polymer Composites, 2019
The article experimentally investigates the interface strength of glass fibers in polypropylene (... more The article experimentally investigates the interface strength of glass fibers in polypropylene (PP) with two different levels of crystallinity. The different degrees of crystallinity, 46.6% and 52.5%, were achieved using fast (quenching, ~4500?C/min) and slow (~2?C/min) cooling, respectively, during production of the PP film. The degree of crystallinity was measured using the differential scanning calorimetry. The mechanical properties of the films were character- ized with the dynamic mechanical analysis and with a tensile test on Deben micro-tester. Interfacial shear strength (IFSS) of glass fiber/PP was determined using fiber fragmentation test. Interfacial normal strength (IFNS) was deter- mined using inverse identification based on finite-element modeling of trans- verse tensile loading of a single fiber (Deben micro-tester with digital image correlation-based observation of the debonding). The measurements have con- firmed the expected trend in mechanical properties of the film: increase of the storage and Young's moduli (room temperature) with the increase of degree of crystallinity, accompanied by the decrease in the loss modulus and tan δ. Inter- facial strength followed the trend of the PP stiffness: both the IFSS and IFNS values for the PP with high crystallinity (slow cooling) are three (IFSS) and four (IFNS) times higher than those for the low crystallinity (fast cooling) case.
polymers, 2023
Recently, polymeric nanofiber veils have gained lot of interest for various industrial and resear... more Recently, polymeric nanofiber veils have gained lot of interest for various industrial and research applications. Embedding polymeric veils has proven to be one of the most effective ways to prevent delamination caused by the poor out-of-plane properties of composite laminates. The polymeric veils are introduced between plies of a composite laminate, and their targeted effects on delamination initiation and propagation have been widely studied. This paper presents an overview of the application of nanofiber polymeric veils as toughening interleaves in fiber-reinforced composite laminates. It presents a systematic comparative analysis and summary of attainable fracture toughness improvements based on electrospun veil materials. Both Mode I and Mode II tests are covered. Various popular veil materials and their modifications are considered. The toughening mechanisms introduced by polymeric veils are identified, listed, and analyzed. The numerical modeling of failure in Mode I and Mode II delamination is also discussed. This analytical review can be used as guidance for veil material selection, for estimation of the achievable toughening effect, for understanding the toughening mechanism introduced by veils, and for the numerical modeling of delamination.
MDPI, 2022
In this study, three-dimensional (3D) polyvinyl alcohol (PVA)/aligned boron nitride (BN) aerogel ... more In this study, three-dimensional (3D) polyvinyl alcohol (PVA)/aligned boron nitride (BN) aerogel framework nanocomposites with high performance were fabricated by a facile strategy. The boron nitride powder was initially hydrolyzed and dispersed with a chemically cross-linked plasticizer, diethyl glycol (DEG), in the PVA polymer system. The boron nitride and DEG/PVA suspensions were then mixed well with different stoichiometric ratios to attain BN/PVA nanocomposites. Scanning electron microscopy revealed that BN platelets were well dispersed and successfully aligned/oriented in one direction in the PVA matrix by using a vacuum-assisted filtration technique. The formed BN/PVA aerogel cake composite showed excellent in-plane and out-of-plane thermal conductivities of 0.76 W/mK and 0.61 W/mK with a ratio of BN/PVA of (2:1) in comparison with 0.15 W/mK for the pure PVA matrix. These high thermal conductivities of BN aerogel could be attributed to the unidirectional orientation of boron nitride nano platelets with the post-two days vacuum drying of the specimens at elevated temperatures. This aerogel composite is unique of its kind and displayed such high thermal conductivity of the BN/PVA framework without impregnation by any external polymer. Moreover, the composites also presented good wettability results with water and displayed high electrical resistivity of ~1014 W cm. These nanocomposites, thus, with such exceptional characteristics, have a wide range of potential uses in packaging and electronics for thermal management applications.
polymers, 2023
As technology advances toward ongoing circuit miniaturization and device size reduction, followed... more As technology advances toward ongoing circuit miniaturization and device size reduction, followed by improved power density, heat dissipation is becoming a key challenge for electronic equipment. Heat accumulation can be prevented if the heat from electrical equipment is efficiently exported, ensuring a device’s lifespan and dependability and preventing otherwise possible mishaps or even explosions. Hence, thermal management applications, which include altering the role of aerogels from thermally insulative to thermally conductive, have recently been a hot topic for 3D-aerogel-based thermal interface materials. To completely comprehend three-dimensional (3D) networks, we categorized and comparatively analyzed aerogels based on carbon nanomaterials, namely fibers, nanotubes, graphene, and graphene oxide, which have capabilities that may be fused with boron nitride and impregnated for better thermal performance and mechanical stability by polymers, including epoxy, cellulose, and polydimethylsiloxane (PDMS). An alternative route is presented in the comparative analysis by carbonized cellulose. As a result, the development of structurally robust and stiff thermally conductive aerogels for electronic packaging has been predicted to increase polymer thermal management capabilities. The latest trends include the self-organization of an anisotropic structure on several hierarchical levels within a 3D framework. In this study, we highlight and analyze the recent advances in 3D-structured thermally conductive aerogels, their potential impact on the next generation of electronic components based on advanced nanocomposites, and their future prospects.
polymers, 2023
The problem of icing for surfaces of engineering structures requires attention more and more ever... more The problem of icing for surfaces of engineering structures requires attention more and more every year. Active industrialization in permafrost zones is currently underway; marine transport in Arctic areas targets new goals; the requirements for aerodynamically critical surfaces of wind generators and aerospace products, serving at low temperatures, are increasing; and fiber-reinforced polymer composites find wide applicability in these structural applications demanding the problem of anti/de-icing to be addressed. The traditional manufacturing approaches are superimposed with the new technologies, such as 3D printers and robotics, for laying heat wires or cheap and high-performance Thermal Sprayed methods for metallic cover manufacturing. Another next step in developing heaters for polymer structures is nano and micro additives to create electrically conductive heating networks within. In our study, we review and comparatively analyze the modern technologies of structure heating, based on resistive heating composites.