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Machine Learning (ML) is useful in predictive analytic or prognostic modeling for materials and engineering. It is, however, challenging to gather sufficient and representative data. Experiments are possible only in small numbers due to specialty materials, manufacturing, infrastructure, and testing involved. Simulation and numerical models need skills and appropriate validation. If the dataset at hand is too small in size to train ML, professionals tend to create synthetic data, which may not necessarily meet the quality required of the new data. A Knowledge-based Data Boosting (KDB) process, named COMPOSITES, that rationally addresses data sparsity without losing data quality is systematically discussed in this paper. A study on inter-ply fracture toughness of carbon nanotube (CNT) engineered carbon fibre reinforced polymer (CFRP) composite laminates is used to demonstrate the KDB process. This involved strengthening of inter-ply interfaces using CNT advocated for improving delamination resistance of the CFRP composites. It is demonstrated that the KDB process helped augment the dataset reliably and improved the best fit regression lines. The process also made it possible to define boundaries and limitations of the augmented dataset. Such sanitised dataset is certainly valuable for prognostic modeling. Accepted version

Textile non-crimp carbon fabrics (NCCFs) are made of several dry uni-directional (UD) tows which are aligned straight and stitched together. The use of these reduces resin rich areas and stress concentrations that are likely found in woven fabrics composites during manufacturing. The use of spread tows to manufacture the thin plies leads to the fibre areal weight (FAW) of lower than 150 g/m2. This current research aims at investigating the tensile, flexure and interlaminar shear response of thin ply carbon composites with a view to deduce the failure mechanisms. The baseline comparison is carried out with conventional thick ply composites and differences in the failure mechanisms are studied. For tensile tests, reduced number of acoustic emission counts in the case of thin ply composites indicated that the stresses were unaffected until the laminate ultimate strength. In flexural tests, it was noticed that the resin rich sites near the stitches first initiated compression failure followed by translaminar cracking or longitudinal fibre fracture. This is due to the strong fibre-matrix adhesion in the case of thin ply composites. No interlaminar shear fracture was seen to occur throughout the laminate thickness and across the width, leading to a significant improvement in the flexural properties of the thin ply composites. These thin laminates have better interlaminar shear properties. It was observed through microscopy that thin ply laminates first undergo interlaminar shear followed by inelastic deformation at the ultimate strength of the material.

Non-crimp fabrics are fabric tapes stitched to an adjacent orthogonal fabric with no associated crimp. In the current research, the effect of fixation polyester stitches in improving through-the-thickness properties of non-crimp fabric composite laminates is investigated. Detailed experimental studies on interlaminar fracture toughness and static indentation properties of stitched and unstitched thin ply carbon fibre epoxy composites have been conducted. About 23% higher peak load and 37% higher energy absorption were noticed during static indentation tests for the stitched ply composites. A detailed SEM investigation has shown that the stitch-stitch interaction ‘within a bi-angle ply’ and ‘between the bi-angle ply’ plays a significant role in reducing the delamination extent. The critical energy release rate during Mode I fracture toughness of stitched composites was found to be 26.5% higher and SEM investigation depicted that the stitches promote the intra-laminar delamination and enhance the toughness of the composite. Nanyang Technological University The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors would like to acknowledge the financial support from Institute for Sports Research, Nanyang Technological University, Singapore and CHOMARAT, France and ARKEMA, France.

This paper presents a multi-scale progressive damage modeling strategy to investigate the damage and failure behaviors of 2D woven composites. The micro-scale and meso-scale RVEs are identified to sequentially consider the fiber/matrix scale and the tow architecture scale. The micromechanics failure criterion is then introduced to facilitate analysis of the damage initiation and evolution at the constituent level. An anisotropic damage model is also constructed based on the Murakami-Ohno damage tensor, and the damage evolution is governed by the material fracture energy during failure. The proposed multi-scale strategy is carried out by a user-material subroutine (UMAT) in ABAQUS, which predicts the detailed local responses and complex failure mechanisms of the woven composites. Moreover, experimental tensile and compressive tests are conducted to further validate the proposed model.

A scaled, 7.5-mm thick, unidirectional glass/epoxy wind turbine spar cap cured in a vacuum-assisted oven was found to have attained non-uniform thickness along its length. Edge deformations were severe, leading to noticeable edge curvature even at the vacuum pressure. These unforeseen discrepancies could only be predicted and/or dealt beforehand through a process simulation that integrates the complete processing physics. A fully coupled numerical simulation of composites manufacturing was established and implemented for a portion of a spar cap in multiphysics finite element software. Phenomena such as resin flow-induced compaction and cure-induced deformation were captured. The simulation results indicated that even though the distorted edge of the laminate is trimmed off, there will still be some curvature left within the part. It was noted that simulating percolation flow of resin alone leads to less accurate deformation predictions. Therefore, a method to include shear flow-induced deformation of the resin-saturated fiber beds were proposed and implemented. Such a fully coupled and integrated procedure is useful for optimizing process parameters to achieve intended final part with accurate dimensions and minimal manufacturing-induced defects or deformities.

Braided textile composite exhibits an efficient mechanism to distribute loads throughout its structure and have excellent impact resistant properties. Despite many works in the past, the successful prediction of braided textile composites strength still remains a challenge today. In this paper, a numerical simulation model based on a meso-scale approach is presented to predict the strength and damage behavior of braided textile composites. A meso-scale homogenized representative unit cell was built for the study using finite element analysis (FEA) method. 3D-Hashin and Stassi failure criteria were respectively selected for the yarn and the pure matrix, and coded in a subroutine in Abaqus finite element solver to study the individual constituents damages. From the different numerical studies, the failure mechanisms were observed to change with the braiding angle. The meso-scale computed results were also seen to agree closely with experimental and simulation results computed using a micro-mechanics failure approach.

A novel composite scarf joint is successfully fabricated with thermoplastic core shell microparticles incorporated into the interlaminar interface regions with a dual objective of mitigating the impact damage and improving the stiffness compatibility of the joint. The impact analysis of the joints revealed that the incorporation of microparticles led to a significant improvement of the impact load bearing capacity of joint and reduced the extent of the damage area. It is also observed from flexural tests that the microparticles reduces the stiffness of the laminate proportional to the weight fraction of the particles and thereby help design a joint adherend with controlled matching stiffness. This engineered scarf joint adherend configuration has the potential to minimise stiffness mismatch between a fatigue worn-out damaged composite part and the new scarf repair patch laminate designed for it. This shall help ensuring an easy restoration of uniform load distribution in the newly bonded composite scarf j...

This study details a fabrication methodology envisaged to manufacture Glass/BMI honeycomb core aerogel-filled sandwich panels. Silica aerogel granules are used as core fillers to provide thermal insulation properties with little weight increase. Experimental heat transfer studies are conducted on these panels to study the temperature distribution between their two surfaces. Numerical studies are also carried out to validate the results. Despite exhibiting good thermal shielding capabilities, the Glass/BMI sandwich panels are found to oxidise at 180 ºC if exposed directly to heat. In order to increase the temperature bearing capacity and the operating temperature range for these panels, a way of coating them from outside with high temperature spray paint was tried. With a silicone-based coating, the temperature sustainability of these sandwich panels is found to increase to 350 ºC. This proved the effectiveness of the formed manufacturing process, selected high temperature coating, the coating method as well as the envisaged sandwich panel concept. Published version

In order to build predictive analytic for engineering materials, large data is required for machine learning (ML). Gathering such a data can be demanding due to the challenges involved in producing specialty specimen and conducting ample experiments. Additionally, numerical simulations require efforts. Smaller datasets are still viable, however, they need to be boosted systematically for ML. A newly developed, knowledge-based data boosting (KBDB) process, named COMPOSITES, helps in logically enhancing the dataset size without further experimentation or detailed simulation. This process and its successful usage are discussed in this paper, using a combination of mode-I and mode-II inter-ply fracture toughness (IPFT) data on carbon nanotube (CNT) engineered carbon fiber reinforced polymer (CFRP) composites. The amount of CNT added to strengthen the mid-ply interface of CFRP vs the improvement in IPFT is studied. A simpler way of combining mode-I and mode-II values of IPFT to predict delamination resistance is presented. Every step of the 10-step KBDB process, its significance and implementation are explained and the results presented. The KBDB helped in not only adding a number of data points reliably, but also in finding boundaries and limitations of the augmented dataset. Such an authentically boosted dataset is vital for successful ML. Published version

Advanced manufacturing techniques, such as automated fiber placement and additive manufacturing enables the fabrication of fiber-reinforced polymer composite components with customized material and structural configurations. In order to take advantage of this customizability, the design process for fiber-reinforced polymer composite components needs to be improved. Machine learning methods have been identified as potential techniques capable of handling the complexity of the design problem. In this review, the applications of machine learning methods in various aspects of structural component design are discussed. They include studies on microstructure-based material design, applications of machine learning models in stress analysis, and topology optimization of fiber-reinforced polymer composites. A design automation framework for performance-optimized fiber-reinforced polymer composite components is also proposed. The proposed framework aims to provide a comprehensive and efficient approach for the design and optimization of fiber-reinforced polymer composite components. The challenges in building the models required for the proposed framework are also discussed briefly.

An experimental investigation focusing on the hygrothermal aging-structural degradation–mechanical property relationship of GLARE 4A laminates was conducted. Water immersion conditioning at 80 °C for up to 4 months was carried out on GLARE 4A laminates. It was found that although the outer aluminum layers effectively protected the glass/epoxy composite layers from hygrothermal attack, the composite layers absorbed moisture through the edges. Consequently, significant decrease in both, the tensile strength and fatigue life of the GLARE 4A laminates, was observed although no structural defects were apparently identifiable in the microstructures of the conditioned laminates. Detailed experimental investigation was conducted to study the mechanism of mechanical property decay due to hygrothermal aging. It is proposed that the strength of the S2-glass fibers was not fully realized due to the weakening of the fiber/matrix interface and the deterioration of the sizing, which consequently led to the reduction in the tensile strength and fatigue life of the GLARE 4A laminates. The stiffness degradation characteristics of GLARE 4A laminates under cyclic loading were also investigated. Keywords: Fiber metal laminates, GLARE, Glass fiber, Hygrothermal, Tensile, Fatigue

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 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.

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

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).

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

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

In this paper, practical aspects of employing the finite element/nodal control volume (FE/NCV) approach for modelling of prepreg moulding, resin transfer moulding and pultrusion of fibre reinforced polymer composites are discussed. Various NCV based formulations for simulating resin flow through fibrous media, resin cure, heat transfer in fabrication assemblies, changes in material properties with temperature and cure are explained. The development of a process-adaptive, modular, semi-steady simulation procedure that combines the benefits of a commercially available general-purpose FE package and user-defined computer programs for NCV grid is presented. The process is easily implementable for one-, two- or three-dimensional domains without re-meshing. Implications of ignoring the effects of the heat of exothermic cure reaction, the artificial loss of resin mass during the resin flow, and the die temperature on material properties are highlighted using example problems.

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.

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

In this study, a finite element model of a micro-satellite named X-SAT was developed to perform heat transfer analysis and design a passive thermal control scheme in the form of thermal coatings, film, and paints. To start with, the modeling philosophy and computational methodology were introduced along with the suitable assumptions made. A typical thermal control scheme was proposed and implemented using SINDA/G-NEVADA software. The sensitivity of the results to the software settings was then assessed. It was observed that the limits on the ray counts for Monte Carlo simulation in RENO and VEGAS routines play a vital role in deciding reliability of the results, especially the temperature gradients within solar panels. Subsequently, two types of solar panel designs, one with all-active solar strings and other with selectively active solar strings, were examined. When the panels with all-active type of solar cell strings were adopted, heat dissipation through shunt regulators posed a challenge for thermal ...

Spacecraft thermal control materials (TCMs) play a vital role in the entire service life of a spacecraft [NASA Preferred Reliability Practices: Spacecraft Thermal Control Coatings Design and Application (Practice No. PD-ED-1239), 1995, pp. 1–6] . Most of the conventional TCMs degrade in the harmful space environment [R.D. Karam, Satellite Thermal Control for Systems Engineers, AIAA, Virginia, USA, 1998, pp. 147–163] . In the previous study, plasma sprayed alumina (PSA) coating was established as a new and better TCM for spacecrafts, in view of its stability and reliability compared to the traditional TCMs [R.M. Li, S.C. Joshi, H.W. Ng, Presented in 2nd International Conference on Materials for Advanced Technologies & IUMRS, Singapore, 2003, pp. 1–4] . During the investigation, the surface roughness of PSA was found important, because the roughness affects the radiative heat exchange between the surface and its surroundings. Parameters such as root-mean-square roughness cannot properly evaluate surface roughness effects on radiative properties of opaque surfaces [M.F. Modest, Radiative Heat Transfer, 2nd ed., Academic Press/Elsevier Science, USA, 2003, pp. 90–92] . Some models have been developed earlier to predict the effects, such as Davies’ model [H. Davies, Proceedings of IEEE vol. 101, part IV, 1954, pp. 209–214] , Tang and Buckius's statistical geometric optics model [K. Tang, R.O. Buckius, Int. J. Heat Mass Transfer 44 (2001) 4059–4073] . However, they are valid only in their own specific situations. In this paper, an energy absorption geometry model was developed and applied to investigate the roughness effects with the help of 2D surface profile of PSA coated substrate scanned at micron level. This model predicts effective normal solar absorptance ( α ne ) and effective hemispherical infrared emittance ( ɛ he ) of a rough PSA surface. These values, if used in the heat transfer analysis of an equivalent, smooth and optically flat surface, lead to the prediction of the same rate of heat exchange and temperature as that of for the rough PSA surface. The model was validated through comparison between a smooth and a rough PSA coated surfaces. Even though not tested for other types of materials, the model formulation is generic and can be used to incorporate the rough surface effects for other types of thermal coatings, provided the baseline values of normal solar absorptance ( α n ) and hemispherical infrared emittance ( ɛ h ) are available for a generic surface of the same material.

PurposeNowadays, many micro‐satellites rely on three‐axis stabilization using at least three reaction wheels (RWs) for attitude control. Typically, RWs are mounted separately within the satellite and leads to long wires from each RW to the associated electronics. Placement and other constraints may also arise during integration. Furthermore, the large number of mounting holes required for mounting the RWs directly on the structural panels may weaken the integrity of the structure. This paper highlights a need for a special housing to be designed for mounting three to four RWs as a group at one location for simple and easy three‐axis stabilization of typical micro‐satellites.Design/methodology/approachDetails about the development of the design methodology for such housing are discussed. The basic idea is to place the RWs onto the proposed housing, which will be then mounted on to one of the honeycomb panels used for the satellite structure. Requirements analysis, design, validation, and manufacturing process are covered.FindingsThe outcome is a dimensionally optimized housing structure for four RWs with a frequency safety factor of three.Originality/valueIn summary, the designed product satisfied all requirements. In addition, the exercise set out a planned procedure for designing similar housings for other satellite components.

Optimization studies are performed on the pultrusion of a thermosetting composite. The three-dimensional finite element/nodal control volume procedure developed for simulation and optimization of the process is employed for this purpose. The aim of optimization is to achieve the desired degree of cure with minimum local variations across the pultrudate cross-section. The die-heating environment is optimized for a few cases with different initial temperatures for a glass/epoxy wet preform and for the cooler installed within the pultrusion die near its entrance. The role of these temperature parameters in moderating the optimization constraints is examined. Simultaneous optimization of die-heater temperatures and pull-speed is also considered. It is observed that the temperature overshoot within the composite pultrudate can be reduced and better optimization results can be achieved by a proper choice of a pre-die temperature for the composite and the die-cooler temperature.

This article deals with the computation of effective elastic properties of braided textile composites assisted by finite element analysis. In this approach, dynamic representative unit cells are first constructed to model typical geometry of braided textile preform. After establishing the elastic properties of braiding yarns, the effective Young’s moduli, shear moduli and Poisson’s ratios corresponding to varying braiding angles are obtained by analysing these geometric models of preform with the help of the commercial finite element analysis code Abaqus. Effects of fibre volume fraction on the elastic properties of both biaxial and triaxial composite unit cells are also examined. Finally, the bending behaviour of a simply supported beam with braided composite skin is evaluated via the finite element analysis assisted multi-scale modelling, which is further verified experimentally. The predicted results were compared favourably with the experiment, backing the accuracy of the proposed modelling approach.

Wavefront sensing systems measure the slope or curvature of a surface by calculating the centroid displacement of two focal spot images. Accurately finding the centroid of each focal spot determines the measurement results. This paper studied several widely used centroid-finding techniques and observed that thresholding is the most critical factor affecting the centroid-finding accuracy. Since the focal spot image of a freeform surface usually suffers from various types of image degradation, it is difficult and sometimes impossible to set a best threshold value for the whole image. We propose an adaptive centroid-finding algorithm to tackle this problem and have experimentally proven its effectiveness in measuring freeform surfaces. Published version

PurposeWith the advent of micro‐satellites technology, passive thermal controls in the form of surface coatings have become important for onboard thermal management. The thermal coatings, however, suffer outgassing and mass loss due to their direct exposure to harsh thermal environment and high vacuum in space. The purpose of this paper is to discuss testing and evaluation on outgassing of AA6061‐T6 specimen surfaces treated with various types of anodized coatings of different thicknesses and the related mass loss before and after thermal exposure.Design/methodology/approachSamples of chromic acid, polytetrafluroethylene polymer, and black‐ and brown‐colour anodized aluminum coupons were subjected to high vacuum (∼1×10−6 mbar), before and after thermal baking at 120°C. Spectrum analysis of the outgassed material to know their quantities and proportion was conducted subsequently using a Quadrupole mass analyzer.FindingsThe surface coatings under study complied with the spacecraft requirements for the mass loss of less than 1 percent of the total mass of the coating material used for that surface. The mass spectrum analysis of the outgassed material indicated that the majority of the coating mass loss was on account of water vapours and organic solvents like ethylene.Practical implicationsThese results provided a good insight into the reliability of the coating materials studied and the bonding between the aluminum substrates and the coatings.Originality/valueThe coatings and the technology needed for their application on aluminum are readily available. The present work on outgassing and mass loss in a simulated space environment will provide useful insight on their usage for micro‐satellites.

This paper presents a simulation procedure for the mould-filling processes in which a field-analysis module of a general-purpose finite-element package is employed. The formulations used in this procedure are based on the finite element/nodal control-volume approach. The numerical concepts employed for modelling the effects of convective heat transfer on temperature and resin cure are discussed. Numerical implementation of the procedure is presented. The procedure was applied to simulate different mould-filling examples under isothermal and non-isothermal conditions. The results show that the simulation procedure developed is numerically valid and stable, and provides reasonably accurate predictions. Accepted version