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In the world of fast-growing technology, switch from traditional wooden and metallic sports racquets to next generation powerful racquets is inevitable with the advent of carbon fibres, which offer benefits like increased strength, stiffness, impact, and efficient vibration and damping properties. The introduction of carbon fibres, however, comes with challenges of choosing a right matrix system that, in combination, provides the best solution without sacrificing performance. Non-crimp fabric thin C-Ply composites have the potential to suppress the micro cracks and delamination until the material’s ultimate strength. But still, their usage and the possible advantages they can offer in sports applications like tennis racquets, badminton racquets or table tennis bats and so on are yet to be explored. This article aims at exploring the niche benefits offered by thin C-Ply™ carbon fibres in combination with thermoset and thermoplastic matrices in sports applications, especially racquets. The composites comprised multi-axial reinforcement fabrics/non-crimp fabrics infused with a room-temperature cure epoxy or a thermoplastic resin having low mix viscosity (200 cps) suitable for vacuum-assisted resin infusion. The mechanical properties of carbon fibre thin C-Ply/(thermoplastic or thermoset) composites pivotal in racquets, like tensile and flexural stiffness and modulus, have been determined experimentally. Double cantilever beam Mode I tests are also carried out to determine the bonding strength between the plies and the matrix interface as most of the failures in sports equipment are accompanied by either bond failures or imperfections within the structure. The findings of testing of various specimens are presented and discussed.

Exposure to hygrothermal environments affects mechanical properties of laminated composites through two principle mechanisms, namely, moisture absorption and the structural deterioration due to it. Previous studies have indicated that moisture plays a positive role in carbon fiber reinforced polymer composites by alleviating their damage under impact. In this study, carbon fiber reinforced polymer composites were exposed to long-term hygrothermal ageing to investigate the possibility of the initiation of structural defects due to it and their influences on the various behaviors of the laminated composites. A major type of observable structural defects was identified and the related initiation mechanism was proposed. It was found for the first time that the structural defects formed during hygrothermal ageing in turn changed the moisture uptake profile of the laminated composites. The effects of structural defects on the impact resistance of carbon fiber reinforced polymer composites were exclusively evaluated after removing the absorbed moisture. Tensile testing on vacuum-oven-dried laminates was conducted to assist the understanding of the mechanical strength of the carbon fiber reinforced polymer composites exposed to the hygrothermal environments.

In this paper, a re-look into the upper and lower bound solution to the buckling of composite columns is presented in details and this includes the complete derivation of the expressions for the kinematical compatibility conditions. Included in this contribution are also the results of the current finite element simulation together with the results of the experiments. Moreover, further investigations are conducted to test whether the proposed three methods of calculating the effective flexural stiffness can be employed in cooperation with the developed mathematical model to form the desired upper and lower bounds for the buckling loads of both the perfect and single-delaminated fiber-reinforced composite beams for the various parameters that are studied. In these analyses, single-delaminated fiber-reinforced composite beams which consist of random ply-orientations and stacking sequences are employed to put up a stringent test on the generalness and applicability of these three methods. It is observed that for all the cases that were examined, these three means of evaluating the effective bending modulus of a fiber-reinforced composite beam pass are validated.

The mechanical and interfacial properties of single carbon fibres have been experimentally investigated. Longitudinal tensile strengths were determined using single filament as well as impregnated yarn specimens at various gauge lengths ranging from 5 to 200 mm. The tensile behaviour of the fibre depends on gauge length due to the presence of flaws along the fibre. Axial compressive strength was obtained by the tensile recoil method. The transverse modulus was measured by nano-indentation technique. Shear modulus was obtained by a torsional pendulum test. The apparent shear strength of carbon fibre/epoxy interface was characterised by a microbond fibre pull-out test. Data obtained in this work constitute important materials’ data input for the design and simulation of carbon fibre composite structures.

The major challenge for producing and manufacturing risers for oil and gas production is to make them light weight so as to reduce the operational cost and improve the overall system requirements to make them an attractive option for marine and offshore industries. In the current research, the composite and metal-composite pipes (1) GFRP only (2) Al-GFRP and (3) PE-GFRP have been manufactured using filament winding machine operated using CADFIL and CADWIND CNC packages. The use of liners (Al and PE) has ensured the fluid tightness and collapse resistance of the pipe system. Small prototype pipes are manufactured based on optimized pipe design parameters for collapse under external pressure and burst under internal pressure using ANSYS 13 FEA analysis software. Experiments are conducted to verify the axial and hoop compressive strengths of the pipes with analytical results. The details of pipe manufacturing process using filament winding machine, simulation procedure to optimize the pipe parameters and validation of the simulation results with experimental results are the focal points of the current work.

A novel finding about effects of moisture and cyclic hygrothermal conditions on the impact resistance of carbon fiber reinforced epoxy polymer (CFRP) composites are presented. The course of experiments began with the fabrication of specimens using unidirectional CFRP prepreg materials. As-fabricated specimens were exposed to two types of hygrothermal conditions which were designed to simulate in-service environment. Microstructure characterization of the specimens revealed that neither hygrothermal conditions brought about any evident defects to the laminates. Low-velocity impact testing was then carried out on the specimens with different moisture levels. It was found for the first time that moisture significantly alleviated impact induced damage in the CFRP unidirectional laminates. Detailed discussion about how the absorbed moisture influenced the impact behavior of the laminate was carried out based on the interpretation of the damage characteristics and impact testing data. The effects of absorbed moisture on the GIC of this material were explored to assist the understanding of the role played by the absorbed moisture during low-velocity impact testing.

Composite materials are prone to delamination as they are weaker in the thickness direction. Carbon nanotubes (CNTs) are introduced as a multiscale reinforcement into the fiber reinforced polymer composites to suppress the delamination phenomenon. This review paper presents the detailed progress made by the scientific and research community to-date in improving the Mode I and Mode II interlaminar fracture toughness (ILFT) by various methodologies including the effect of multiscale reinforcement. Methods of measuring the Mode I and Mode II fracture toughness of the composites along with the solutions to improve them are presented. The use of different methodologies and approaches along with their performance in enhancing the fracture toughness of the composites is summarized. The current state of polymer-fiber-nanotube composites and their future perspective are also deliberated. Published version

For mass production of structural composites, use of different textile patterns, custom preforming, room temperature cure high performance polymers and simplistic manufacturing approaches are desired. Woven fabrics are widely used for infusion processes owing to their high permeability but their localised mechanical performance is affected due to inherent associated crimps. The current investigation deals with manufacturing low-weight textile carbon non-crimp fabrics (NCFs) composites with a room temperature cure epoxy and a novel liquid Methyl methacrylate (MMA) thermoplastic matrix, Elium®. Vacuum assisted resin infusion (VARI) process is chosen as a cost effective manufacturing technique. Process parameters optimisation is required for thin NCFs due to intrinsic resistance it offers to the polymer flow. Cycles of repetitive manufacturing studies were carried out to optimise the NCF-thermoset (TS) and NCF with novel reactive thermoplastic (TP) resin. It was noticed that the controlled and optimised usage of flow mesh, vacuum level and flow speed during the resin infusion plays a significant part in deciding the final quality of the fabricated composites. The material selections, the challenges met during the manufacturing and the methods to overcome these are deliberated in this paper. An optimal three stage vacuum technique developed to manufacture the TP and TS composites with high fibre volume and lower void content is established and presented. Published version

Fibre reinforced polymer laminated composites are susceptible to impact damage during manufacture, normal operation, maintenance, and/or other stages of their life cycle. Initiation and growth of such damage lead to dramatic loss in the structural integrity and strength of laminates. This damage is generally difficult to detect and repair. This makes it important to find a preventive solution. There has been abundance of research dealing with the impact damage evolution of composite laminates and methods to mitigate and alleviate the damage initiation and growth. This article presents a comprehensive review of different strategies dealing with development of new composite materials investigated by several research groups that can be used to mitigate the low velocity impact damage in laminated composites. Hybrid composites, composites with tough thermoplastic resins, modified matrices, surface modification of fibres, translaminar reinforcements, and interlaminar modifications such as interleaving, short fibre reinforcement, and particle based interlayer are discussed in this article. A critical evaluation of various techniques capable of enhancing impact performance of laminated composites and future directions in this research field are presented in this article. Published version

This work provides a systematic approach to accurately predict damage progression in a composite structure subjected to bending load. Landing gear structures for unmanned aerial vehicles were fabricated from braided textile preforms and assessed for flexural behavior. A multiscale finite element analysis model was developed for analyzing the progressive damage of these structures under bending loads. Microscale and mesoscale analyses were carried out first. Subsequently, the results of microscale and mesoscale analyses were used as inputs in macroscale analyses that predicted the progressive damages in the entire landing gear structure. The numerical results were validated by experimental studies. Accepted version

Carbon fiber reinforced polymer composites, especially carbon/epoxy, have been attracting interest from offshore oil and gas industry as alternatives to metals for deepwater risers due to their very high performance besides being light weight. Composite risers, however, require an inner liner of metal to prevent leakage and damage to the outer composite layers. The bonding between the composites and the metal liner is critical for the overall integrity of the riser. In this study, two mechanical surface treatment methods, grit blasting and grooving, are used to modify aluminum liner surface. Representative composite pipe specimens consisting of these aluminum liners and carbon/epoxy composites were fabricated using filament winding process. Effects of the surface treatments on the liner-composites bonding are investigated by loading the specimens under axial compression. The liner-composite bonding, de-bonding process and the progressive failure mechanism were studied with the use of finite element simulation tools. The grooving method was found to provide a better bonding than the grit blasting process. Details of the fabrication and the testing, as well as the analysis of the results are presented in the paper. Published version

Low-velocity impact testing was conducted on carbon/epoxy composite laminates exposed to hygrothermal environments. Besides normal laminates, staggered lay-up structures were made from unidirectional prepreg materials. The specimens were immersed in water at 80℃ for different durations before impact testing. Experimental data showed that moisture played a positive role by improving the impact resistance of composite laminates. Laminates with higher moisture level could behave elastically up to higher strain levels and retain their resistance to the striking impactor to larger deflections. After absorbing moisture, more of the impact energy was dissipated by the specimen through elastic deformation and less damage was induced to the laminate. Little degradation in the fiber/matrix interface was observed from SEM graphs. It is postulated that absorbed moisture improved the ductility of the epoxy resin by promoting chain segmental mobility of the polymer molecules, which eventually lead to the better impact response of laminates with higher moisture content.

The overall objective of the investigation presented in this paper was to study the effect of selective dispersion core/shell microparticles (CSP) within the different ply interfaces on impact damage behaviour of glass/epoxy laminates. These laminates were fabricated with the 30 g/m2 CSP particle areal weight per interface. A series of impact experiments were done with instrumental drop tower device at impact energy of 7.8 J and impactor velocity of 2.4 m/s, which is within a practical low velocity impact range. The analysis of the impact load, contact duration indicates that the presence of CSP particles in the bottom layers has a more pronounced effect on the impact performance improvement as compared to the top layers. In the case of selective dispersion, the presence of particles in the middle plies slightly degrades the performance when compared to the selective dispersion of particles only in top or bottom plies.

The diffusion of moisture in composite materials is a complex phenomenon. In this investigation, effects of temperature, laminate architecture and cyclic hygrothermal conditions on the moisture absorption behavior of carbon/epoxy laminates were explored. Both woven and unidirectional laminates were fabricated from carbon fiber reinforced epoxy prepreg materials (CFRP). Specimens were later immersed in water at different temperatures, including room temperature (RT), 60°C and 80°C, or exposed to cyclic hydrothermal conditions. Within the temperature range studied, the diffusion of moisture inside the CFRP laminates followed the Ficks law. Both the diffusivity and the saturation moisture contents of the conditioned laminates increased with temperature. Furthermore, no weight variation was observed when the specimens were stored in a freezer at-30°C. The architecture of the reinforcement fibers also exhibited significant influence on the diffusion behavior of moisture in the laminates. Under the same temperature, the diffusivity of moisture in woven laminates was higher than that in unidirectional laminates.

This paper investigates fabrication and mechanical properties of L-930 carbon fiber reinforced polymer woven prepreg composites cured using three different techniques: (1) thermal, (2) microwave, and (3) the combination of microwave and thermal. The third technique was established through parametric studies and proved to be an efficient method in curing the carbon fiber reinforced polymer prepregs without compromising mechanical properties, but with significant energy and time saving. With 20 min in microwave at 510 W followed by 60 min thermal curing in convection oven at 120℃ provided optimum results in terms of time and energy saving. The process was 2.5 times faster than and consumed only 1/4th of energy required for the autoclave curing. The mechanical properties in tension and flexure of carbon fiber reinforced polymer [0/90] and [±45] laminates cured with this technique were 1–5% better than the autoclave cured laminates. The details of the composites fabrication, the curing techniques, the experiments conducted along with the rationale and underlying reasons for the success of the new “microwave–thermal” curing technique are presented in this paper.

This article presents the work carried out in evaluating the efficiency of embedded heat pipes in simulated satellite substrates subjected to localized heat sources. The experimental setup that comprises either an aluminum plate or an aluminum honeycomb sandwich panel with an electrical heating element was designed. Various experiments were conducted on the substrates with and without embedded heat pipes at various heating power inputs. Case studies with adjoined and inclined substrates, employing either one or two embedded heat pipes having different insertion lengths, were performed. With the help of COMSOL Multiphysics 3.5a software, an equivalent three-dimensional finite-element model of the experimental setup was created and analyzed under the same real-time conditions. Based on the experimental results, design guidelines are proposed for optimized heat management within a satellite substrate using embedded heat pipes.

Silica aerogels are very light and highly porous materials that are intriguingly and complexly networked with large internal surface area, high hydrophobicity with extremely low density and thermal conductivity. These features make them ideal choice for applications as thermal and acoustics insulators or as optical, electrical and energy storing devices. However, their exploitation for structural applications is primarily inhibited by their brittleness. The brittleness of the silica aerogels makes their processing and handling difficult. Volumetric shrinkage occurs, which becomes more apparent at elevated temperatures. While there are hybrid silica aerogels doped with materials such as polymer, ceramics, metals in the market, the improvements in the mechanical properties are compromised with tremendous increase in density and reduction in the insulation performance. Post synthesis binding treatment of silica aerogels composites are not extensively explored due to the chemically inert trimethylsilyl (TMS) terminal groups on the surface of the hydrophobic silica aerogels. This paper discusses a unique fabrication method of developing a ductile silica aerogel composite solid via post synthesis binding treatment. Gelatin silica aerogel (GSA) and GSA-sodium dodecyl sulfate (SDS) composite blocks were produced by mixing hydrophobic aerogel granulates in a gelatin-SDS foamed solution by frothing method. The entire fabrication process and grounds for using a controlled % of gelatin as the main binder and SDS as an additive are explained. The compression testing of the blocks is presented. The associated strain recovery, - an unusual phenomenon with brittle silica aerogels, observed upon unloading is highlighted and studied. The microstructure and surface characterization of these composites was examined via FESEM/EDX and XPS/ESCA respectively. The dependency of process variables involved were analyzed through Analysis of Variance (ANOVA) model. Empirical models that relate the composition of gelatin, aerogel and SDS to achieve the optimal strain recovery with the associated compressive modulus and strength and density are established. The transition from brittleness to ductility is measured in terms of compressive stress versus strain behavior for various mass fractions of gelatin and SDS. The test data presented indicate analogous behavior of these to creep-like behavior of a material typically identified as the primary, secondary and tertiary stages. The rationale and mechanisms behind such creep-like three stages are explained using schematic diagrams Accepter version

This paper discusses the research conducted on prepreg composites interfaces engineered with, either carbon nanotubes (CNTs), or core shell micro-particles (CSMs). The emphasis is given on the fractography details that highlight various mechanisms involved in strengthening the ply-to-ply surface contacts due to the addition of these nanoand micro-particles.

The overall objective of the investigation presented in this paper was to study the effect of dispersion of core–shell polymer (CSP) particles within the ply interfaces on damage evolution of glass/epoxy laminates under impact loading. These laminates were fabricated with the CSP particle dispersion controlled to 14 % of the total weight of the used prepreg. A series of impact experiments were done with instrumental drop tower device at all probable impact energies within a practical low velocity impact range. The damage phenomena occurring in the internal microstructure of the laminates were analysed with the help of scanning electron microscope and correlated to the structural response of the laminate. The predominant damage modes were dependent on the magnitude of the applied impact energy. The CSP particle incorporation does not change the sequence of the fracture events but it delays and mitigates the damage creation. The deformation of the CSP particles and the tearing of their outer shells absorb most of the impact energy thereby preventing initiation of matrix cracks at lower impact energies and delaying fibre damage at higher energies. The crushed particles along with their nano-size rubber cores impede crack propagation requiring the cracks to follow torturous paths consequently dissipating additional amount of energy. These particles also promote elastic energy absorption of the laminates minimizing their tendency to fracture easily under impact. The ultimate load bearing capability of the modified laminate showed 60 % improvement and the deflection characteristics indicated lower proneness to impact.

Thick laminated composites are manufactured commonly by vacuum bagging of fiber-resin mix or prepregs on a suitable mould and, subsequently curing the lay-up at high temperature and pressure in an either autoclave or oven. At these pressures and temperatures, excess resin bleeds out of the lay-up during the initial stages of the curing. The amount of resin bleed is also a function of the bleeder parameters. Bleeder is a porous fibrous media that is laid around stacked lay-up to provide pathway for volatiles as well as absorb and hold the excess resin. Thicker or highly porous bleeders generally absorb higher amount of resin resulting in a resin starved laminate whereas very thin or denser bleeder leads to resin-rich areas within the laminate. It is thus important to select optimum bleeder parameters in order to achieve a desired resin volume fraction and its uniformity in a composite laminate upon curing. This paper details the simulation of the manufacturing of a thick laminated composite, where a significant amount resin is likely to flow out of a curing lay-up, leading to an optimization of bleeder parameters. A coupled, transient FE analysis is conducted that involves not only the heat transfer, resin flow and cure reaction kinetics simulation but also the simulation of the compaction of the wet laminate and the bleeder layers until the laminate is fully cured. Details of an experiment conducted to find compression characteristics of bleeder of varying thickness and the number of layers and related data that was used in the FE analysis are discussed in this paper. It is found that bleeder thickness significantly affects the amount of resin bleeding out from the curing laminate. As a result, the resin volume fraction of the laminate is affected. Case studies carried out to highlight the optimum bleeder thickness for a lay-up, and the method used to decide the thickness and the number of bleeder layers, are presented.

A two-dimensional transient heat transfer, one-dimensional compaction and two-dimensional resin flow analysis of a thick laminated composites fabrication assembly including the bleeders and vacuum bagging is carried out in a fully coupled manner. Resin distribution within the laminate and the bleeders is controlled by their respective compaction behavior as well as permeability of the fiber network. Compaction behavior of dry bleeders is obtained from compression experiments carried out in-house and the derived relevant empirical parameters are used in the numerical simulation. The variations in the resin volume fraction within the laminate due to the resin outflow to the surrounding bleeder were tracked and updated as a function of time in the cure simulation. Four case studies were performed with temperature dependent as well as independent resin properties and pressure dependent and also pressure independent resin volume fractions. These simulations were carried out to understand the behavior of resin flow through the bleeder and its impact on the local variations in the resin content of the laminate. The results obtained show a significant disparity in the thermal overshoot at the center of the laminate and the pressure distribution within the laminate and the bleeder, when a complete coupling and the parametric changes as in the real situation are ignored in numerical simulation. It is shown that the complete coupling of various real-time phenomena helps in accurate prediction of temperature, pressure, resin viscosity, bleeder and fiber compaction, resin flow and associated changes in fiber volume content, and degree of cure distributions for thick composites as they are cured.

Aerogels are ultralight solids with nanoporous structure and are one of the world’s lightest materials available in the market. It is a dry gel, principally made up of 99.8 % of air and weighing just around three times that of air. The first aerogels were realized in 1931, when Kistler (J Phys Chem 36:52–64, 1932) attempted to remove liquid from a wet gel. It started out with the testing of the hypothesis that the liquid in a jelly can be replaced by a gas so as to avoid the collapse of the wet gel. He postulated that it was possible to slowly expand the supercritical fluid within a gel and obtain an air-filled non-collapsed gel structure. He subsequently succeeded in producing silica aerogels with densities in the range 20–100 kg/m3, as well as aerogels of alumina, tungsten, ferric, and stannic oxides. Today, silica aerogel is frequently used in nanocomposites for their light weight and excellent thermal insulating properties. In this chapter, we document some of the silica aerogel-filled carbon composite sandwich structures we have recently developed and also numerically examine the underlying mechanisms which enable silica aerogels to possess extreme insulation properties and especially how pore size plays a major role.

Silica aerogels are very light, highly porous nanomaterial with large internal surface area possessing excellent thermal insulation that may get affected when the binders and additives used in aggregation. The most significant of all the properties is the extremely low thermal conductivity, reportedly to be in the range 0.017–0.024 W/m-K as highlighted by Schmidt and Schwertfeger (J Non-Cryst Solids 225:364–368, 1998).

Acoustics is the interdisciplinary science that deals with the study of mechanical waves and vibrations in the three states of matter with the aid of a medium to propagate. Sound is often described as audible waves and vibrations in the spectrum of 20–20 kHz.

Most published literature analyzed the elastic modulus of silica aerogels by drawing inspiration from the cellular solids models. For example, Ashby and Gibson (Cellular solids—structure and properties. Cambridge University Press, Cambridge, 1997) describe the open cellular foam model compressive modulus to follow power law dependence on the relative density as shown in Eq. 5.1 where C and μ are geometric constants that depend on the topological features and microstructure undergoing cell wall bending as the dominant deformation.

The effects of incorporating core shell polymer (CSP) particles within interply interfaces on the impact response of CFRP prepreg laminates are investigated. The impact tests were conducted on samples without and with CSP particles into the ply interfaces. The loads versus time curves were examined to determine the impact response and the associated energy absorption by the laminates were studied. The results indicate that both, the peak load of the laminates improved by 41% and damping index (DI) reduced by 90% with the dispersion of 51 g/m2 of CSP particles within the prepreg ply interfaces of the laminates. It was noted that the CSP particles shielded the composites from the initial severity of impact. The energy absorbing mechanisms altered the supercritical response of the laminate to subcritical due to increase in the elastic energy stored within the laminates with CSP particles thereby changing the energy absorption modes. It was observed from macroscopic observations and SEM images of the damage sites that the damage mechanism and patterns changed and the extent of damage reduced with the addition of CSP particles.

There has been increasing attention to utilizing carbon nanotubes (CNTs) as nano-fillers in polymers and polymer matrix composite materials, such as carbon fiber reinforced plastics. However, the understanding of how randomly oriented CNTs affect mechanical properties of such CNT-engineered composites is limited. This paper serves to develop an analytical model for determining the elastic properties of CNT-engineered composite materials using a mechanics of materials approach. Analysis of the properties was constructed progressively using material unit cells starting from the nano level, to the micro level, and finally, to the macro level. MATLAB programming platform was used to facilitate simulation of the modeling process. Typical simulation cases of the CNT-engineered composite materials are presented in comparison with published experimental and other data, where appropriate.

The investigations on optimization of composite composition of nickel–zirconia for the functionally graded layered thermal barrier coating for the lowest but uniform stress field under thermal loading is presented. The procedure for obtaining temperature- and composition-dependent thermal and mechanical properties of various coating compositions is discussed. These material parameters were used in thermo-mechanical finite element stress analyses of a nickel substrate with the coating. The results showed that the Von-Mises stresses in the substrate and the interfaces were the lowest with the coating profile that followed a concave power law relationship with the index n ≈ 2.65. Accepted version

Pultrusion being the viable and economical process for producing constant cross-section composite products, many variants of it are being tried out. This paper embarks on the pultrusion with multi-materials; typically of polymer foam/glass fibre reinforced polymer (GFRP) sandwich panels. Unlike conventional composites pultrusion, this process with more than two material phases, one of them dry, poses a challenge in simulating the thermal co-curing within the die. In this paper, the formulation and development of three-dimensional, finite element/nodal control volume (FE/NCV) approach for such multi-material pultrusion is presented. The numerical features for handling the dry-wet material interfaces, material shrinkage, variations in pull speed and die heating, and foam-to-skin thickness ratio are discussed. Implementation of the FE/NCV procedure and its application in analyzing pultrusion of polymer foam/GFRP sandwich panels with multi-heater environment are presented. Accepted version

This article deals with the output of a thermal balance test performed on a thermal test model of a micro-satellite and a model correlation between the thermal analysis and the test observations. The test was conducted in a thermal vacuum chamber with the vacuum level higher than 10 − 5 mbar and the surrounding temperature of −85°C. Three test cases, namely, the sun-pointing solar array with part of orbit in eclipse (or Earth's shadow), the payload operation with part of orbit in eclipse, and the extreme worst hot case, were designed and conducted in such a way that the desired orbital environment could be simulated as closely as possible. The temperature data were monitored and sampled at 105 critical points distributed at different locations within the satellite body. These temperature versus time profiles and their agreements with the analytical results obtained using SINDA/G (a special software package for heat transfer analysis in space environment by Network Analysis, Inc.) are discussed. Main obser...

Silica Aerogel composites are ultra-low density, highly porous foam-like materials that exhibit excellent thermal insulation and high strain recovery characteristics. In the present work, environment-friendly silica aerogel composites are fabricated using silica aerogel granules with bio based porcine-gelatin as the binding agent dissolved in water and by further drying the mix at sub-zero condition. This article focuses on improvement studies carried on the mold design and the manufacturing process to achieve better geometric compliance for the silica aerogel composites. It also presents contact angle measurements, compressive behavior under different cycles of loading, time dependent behavior and flexural response of the composites. The influence of additives, such as fumed silica and carbon nanotubes on mechanical properties of the composites is also deliberated. Water droplet contact angle experiments confirmed the ultra-hydrophobic nature of the composites. The mechanical properties were characterized under cyclic loading-unloading compression and three-point flexure tests. On successive compression in three consecutive load cycles, the strain and thickness recovery were found to decrease by around 30%. The flexural properties of the aerogel composites were investigated using it as the core covered by thin carbon composite face sheets. It was found that the flexural strength and the failure strain of this aerogel sandwich composites is approximately half of the conventional nomex honeycomb sandwich equivalent.

The end effect of a capillary die was investigated on concentrated suspensions with different particle concentrations, using dies with different diameters and at different temperatures. Nonlinearity in the Bagley plots was observed experimentally, and the nonlinearity increased with increasing particle concentration, decreasing temperature, and smaller capillary dies. Calculated end pressures based on the nonlinear Bagley plots were compared with those measured using an orifice die. As the extruded melts tended to stick on the exit wall of the capillary die, measurements by orifice die registered (40–50%) higher losses than those obtained from Bagley corrections. The key factors, which include particle concentration, contraction ratio, temperature, and flow rate, were discussed for their effects on end pressure. A formula was proposed combining the effects of these factors. Good agreement was obtained between the calculated end pressures with predicted results by the proposed formula. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Corrections for viscosity measurements of concentrated suspension with capillary rheometer experiments were investigated. These corrections include end effects, Rabinowitsch effect, and wall slip. The effects of temperature, particle concentration, and contraction ratio on the end effects were studied and their effects were accounted for using an entrance and exit losses model. The non-Newtonian effect and the nonlinearity of slip velocity against wall shear stress were described using a slip model. The true viscosity of a concentrated suspension with glass powder suspended in a non-Newtonian binder system was calculated as a function of shear rate and effective particle concentration, taking into consideration particle migration, which is calculated by a diffusive numerical model. Particle size was found to affect significantly the viscosity of the suspension with viscosity decreasing with increasing particle size, which can be reflected by a decrease in the value of the power-law index in the Krieger model. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Four surfactants, namely, sodium n-decyl sulfate (SDeS), sodium n-hexadecyl sulfate (SHS), sodium n-dodecyl sulfate (SDS), and Triton X-100, were used as additives to study thermal behavior and sol–gel transformations in dilute aqueous hydroxypropyl methyl cellulose (HPMC)/surfactant mixtures using micro-differential scanning calorimetry. The influence of anionic surfactant, SDS on the gelation varied with SDS concentration where the sol–gel transition started at a higher temperature. Shape of the thermograms changed from single mode to dual mode at the SDS concentration of 6 mM and higher. SDeS and SHS, however, resulted in “salt-in” effect of a different magnitude during gelation. Triton X-100, being a non-ionic surfactant, showed a minor “salt-out” effect on the thermo-gelation process. On the basis of different thermal behavior of anionic and non-ionic surfactant/HPMC systems, a mechanism is proposed explaining how the chemical structure and electro-charge of the surfactants affect the polymer/surfactant binding and polymer/polymer aggregation because of hydrophobic interaction during the sol–gel transition. © 2009 Wiley Periodicals, Inc. Journal of Applied Polymer Science, 2009

Ultraviolet (UV) embossing, involving molding against micro-structured molds, is a quick and efficient method to mass produce high aspect ratio micro-features. A crucial challenge to the repeatability and large-scale application of this technique is successful demolding, which escalates in difficulty with increasing aspect ratio, due to increased polymer-mold mechanical interlocking. Some of the key factors affecting UV embossing include the crosslinked polymer shrinkage and material properties, interfacial strength between polymer to mold and the demolding method. This paper presents a new method to simulate the demolding of UV cured polymer from a nickel mold. Hyperelastic material model and rate-independent cohesive zone modeling were employed in the numerical simulation; linear elastic polymer response, although relatively easy to apply, was not adequate. Progressive shrinkage was implemented, leading to delamination of the polymer-mold interface. The subsequent peeling of the cured polymer from the mold was modeled with increasing prescribed displacement. The optimal shrinkage degree was found to increase from 0.92 to 1.9% with increasing mold aspect ratio (aspect ratio is defined as height to width ratio) from 5 to 10.

Tablets of three different grades of hydroxypropyl methyl cellulose (HPMC), having different viscosity, were prepared using the direct-compression technique with no additive or binder. The fluid uptake behavior of these HPMC tablets was studied in three types of bio-media – water, simulated gastric fluid (SGF), and simulated intestinal fluid (SIF). The amount of fluid uptake by the tablets followed a power law relationship with time for all three media. Variants such as pH value, type of salts and salt concentration in the media were found to have little influence on the swelling process for the tablet. On the contrary, viscosity and molecular weight of HPMC were the controlling parameters for the swelling process. Subsequently, Indomethacin was added in certain percentage to the tablets as a model drug. It was to examine and elucidate drug releasing properties of the HPMC tablets. The possible mechanisms involved in the process of drug dispersion are proposed and discussed.

Thermal behavior of aqueous hydroxypropylmethylcellulose (HPMC)/surfactant mixtures was studied in the dilute concentration regime using micro-differential scanning calorimetry (DSC). The surfactant used was sodium n-dodecyl sulfate (SDS). The heat capacity of HPMC gel with various concentrations of SDS was much higher than that of the pure HPMC gel. The addition of SDS at different concentrations showed dissimilar influences on the gelation of HPMC; SDS at lower concentrations (≤6 mM) did not affect gelation temperature significantly except for enhancing the heat capacity whilst SDS at higher concentrations (≥6 mM) not only resulted in the gelation of HPMC at higher temperatures but also changed the pattern of the gelation thermograph from a single mode to a bimodal. On the basis of the observed thermal behavior of HPMC/SDS systems, the mechanism behind the sol-gel transition was discussed in terms of the properties of the surfactant and their influences on the extent of polymer/surfactant binding and polymer/polymer hydrophobic association. Gelation kinetics was analysed using the results from the DSC measurements. The kinetic parameters were determined.

PurposeThis paper seeks to provide an insight into the design and development of the thermal test model (TTM) of X‐Sat, a 120 kg class micro‐satellite, being developed at the Centre. This model was specifically constructed for carrying out a thermal balance test (TBT) in a 4 m diameter vertical thermal vacuum chamber.Design/methodology/approachThe construction of the thermal model followed a structural mock‐up model which was modified thermally to suit the purpose. Specific and careful consideration was given to the geometry and, more importantly, thermal characteristics such as thermal mass, surface properties, etc. to mimic the actual satellite configuration as closely as possible. Test plans were devised to qualify the fabricated components to meet the out‐gassing and other thermal requirements for the model. Design and qualification of supporting frame and linkages for TBT are also covered.FindingsIt is possible to simulate the thermal characteristics of a micro‐satellite in orbit under a different mission scenario through proper scaling and using alternative material options while developing TTM.Originality/valueThe paper discusses in detail the simplified cost‐effective approach of constructing TTM and also outlines the various issues to be considered for a TBT. It provides valuable information needed for micro‐satellite designers.

The effects of various inorganic salts and isotopic solvents on the thermal gelation behavior of hydroxypropylmethylcellulose (HPMC) in aqueous solutions were examined by micro-differential scanning calorimetry and rheological measurements. It was found that salting-out salts, such as NaCl, promoted the sol–gel transition of HPMC at a lower temperature. An analysis of solvent isotope effects on the changes in the temperature at maximum heat capacity (Tm) with salt concentration showed that interchain hydrogen bonding (hydrogen bonding between the hydroxyl groups of different HPMC chains) was involved in the sol–gel transition, and its strength depended on the temperature and salt concentration. It was demonstrated that the effectiveness of anionic species in changing the Tm of the HPMC solutions was in the sequence of the Hofmeister series. Anionic species play a role in reducing Tm by their influence on the structure of the water, which in turn affects interactions between hydroxyl groups and water molecules, interchain hydrogen bonding, and the strength of the water cages prohibiting hydrophobic association. Rheological and microcalorimetric results indicated that the change in the thermodynamics of gelation of the HPMC aqueous solution was determined by the salt types and concentration, and the effect of monovalent salts was found to be more cooperative than that of multivalent salts on the sol–gel transition. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The effects of wall slip of concentrated suspension melts in capillary flows were investigated at elevated temperature. The modeled material is a mixture of polymer EVA (Ethylene Vinyl Acetate) and non-colloidal spherical powder (glass microspheres) with mean particle size within 53∼63 μm. The effect of particle concentration on wall slip was studied experimentally in a capillary rheometer. For suspensions with different particle loadings (35%, 40%, and 45% by volume), the slip velocity Vs increased with an increase of particle concentration at the same testing temperature. A master slip curve can be obtained by plotting slip velocity versus the product of wall shear stress and square root of particle concentration. As such, a new particle concentration-dependent slip model is proposed. A theoretical approach coupled with the new slip model and flow equation is employed to characterize the flow behavior of concentrated suspension in a capillary rheometer, with reasonable agreement obtained with experimental observations.

The current work deals with the gelation of methylcellulose (MC) in aqueous solutions under isothermal conditions. The isothermal gelation was monitored during two consecutive heating and cooling cycles. The gelation was observed to occur early during the second cycle and progress at a higher rate. Micelle-like structures were found to form in MC solutions during the first gelation cycle. These were largely responsible for the accelerated gelation during the second heating cycle. The influence from the state of water was examined by studying the gelation phenomenon for MC using either cold or hot DI water as solvent. The possible mechanism involved is discussed. A gel indexing method was established to provide a quantitative measure for the state of gelation achievable using different MC concentrations with either cold or hot water solvent. Stabilization kinetics for the gel under isothermal conditions was described using the Malkin and Kulichikhin model. The kinetics parameters were determined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A fibre optic sensor was developed for in-situ pressure measurement based on the principle of differential pressure in liquids. This sensor system is very simple and consists of fibre Bragg grating (FBG) done on a fibre with core diameter of 9 μm. A calibration study was carried out with a water column and the pressure sensitivity was found to be 1.636 × 10-2MPa-1. The results show that response of FBG to the rise of water level is linear and agrees well with the theoretical results. The reliability of the sensors is confirmed by repeating the measurements for three times. The sensor is useful in applications that involve in-situ resin pressure measurement in manufacturing of laminated composite materials. Published version

Astonishingly 3D printing has excited the world of aerospace. This paper takes stock of the popular 3D printing processes in aerospace. Reasons for their popularity over the traditional manufacturing processes are dwelled upon. Materials developed specially for aerospace applications along with their characteristics are discussed. Ongoing activities related to 3D printing at various companies and organisations around the world are looked into. Project works in the area of extra-terrestrial printing are also highlighted. Even though 3D printing processes are operationally simple, they do have limitations in terms of the type, quality, and quantity of the materials they can handle. This paper underlines these points while discussing drawbacks of the printed components. Challenges associated with 3D printing in microgravity are also touched upon. Finally, a glimpse is taken into the future appearance of aerospace industry with 3D printing. Accepted version

Silica aerogels are very light, highly porous nanomaterial with large internal surface area possessing excellent thermal insulation that may get affected when the binders and additives used in aggregation. This paper discusses the variations in thermal conductivity of a binder-treated gelatin silica aerogel-sodium dodecyl sulfate (GSA-SDS) composite blocks doped with COOH group functionalized multi-walled carbon nanotubes (FMWNT) prepared via freeze drying and frothing methods. The thermal conductivity of GSA-SDS and GSA-SDS/FMWNT composites was evaluated with several mass ratios of the composite mix for 1-D steady-state heat transfer at mean temperature, Tm (300-370K), using Lee’s Disc method. The effects of silica aerogel granule size and mass ratio of FMWNT on the thermal conductivity were investigated. The lowest thermal conductivity achieved for the composite block was 0.016 W/m-K when 0.042 wt% FMWNT was added to gelatin aerogel mass ratio of 0.1:0.9 without SDS. Thermal conductivity predictive models were developed based on the numerous experiments carried out as a function of the aerogel granule size and the mass ratio of constituent materials. The predictive models for composites with FMWNT were validated to approximately 94.3 ± 2.4% accuracy with reduction of 7% in the thermal conductivity when compared with of the GSA composites. Accepted version

Methylcellulose (MC) is a thermo-reversible physical hydrogel. This study investigates the thermodynamic characteristics of gelation mechanism for MC. The relative and absolute specific heat capacity values of the hydrogel system were modeled using an empirical formulation to facilitate calculation of thermodynamic parameters. Experiments verifying the assumptions for the model formulation were conducted and are discussed. Parameters such as enthalpy, entropy, and changes in their magnitude as a function of temperature were calculated and their trends were studied. The implications of these observations on the various stages of the gel formation process and the associated mechanisms are evaluated. The studies revealed that the gelation of MC is a temperature-driven process rather than only driven by the heat input, and it attains a state of equilibrium under isothermal conditions. During gelation, the entropy of the overall (MC+water) system increases due to an increase in the disorderliness of the MC system.