This paper deals with modelling the mechanical behaviour of silica-alumina open-cell porous ceramics obtained by viscous flow sintering. The modelling approach is based on the similarity of the material microstructure to a truss of sintering bridges connecting alumina particles. This makes it possible to use two-node elements, leading to a low computational cost. The method includes the building of a random packing of spheres (alumina particles) and the setup of connections between their centres (silica sintering bridges). An equivalent stiffness is then assigned to each bridge, based on the material parameters. The macroscale elasticity constants have been derived from the natural frequencies of such micrometric cylindrical volume elements made of thousands of particles. The reliability of the underlying assumptions is discussed and the dependence to the material parameters is emphasized. The method is suitable to handle more complex behaviours, which opens the door to fracture modelling.

This paper focuses on evaluating the security challenges faced by mobile field hospitals, which play a crucial role in emergency response and disaster management in remote and austere environments. The authors conducted a penetration test using the Open Source Security Testing Methodology Manual (OSSTMM) framework to assess the security posture of a mobile field hospital. The methodology employed in the study included a combination of automated and manual techniques such as network scanning, vulnerability assessments, social engineering, and exploitation. The penetration test revealed several security vulnerabilities in the mobile field hospital, including weak passwords, unpatched software, and inadequate network segmentation. Additionally, the study identified vulnerabilities in the hospital's medical devices and equipment, posing a risk of cyber-attacks that could disrupt operations and compromise patient safety. The results underscore the importance of implementing enhanced security measures in mobile field hospitals to mitigate cyber threats and ensure the uninterrupted functioning of medical operations during emergencies and disasters. This study provides a comprehensive analysis of the mobile field hospital's security posture using the OSSTMM framework and emphasizes the urgent need for improved security practices in such settings. Keywords: Cybersecurity, Healthcare, Penetration Testing, Mobile Field Hospitals, Data, Emergency Response, Open Source, Security Testing, Ethical Hacking, Security Frameworks, Proceedings Citation Format Ahmed, N.B., Daclin, N., Olivaux, M. & 4usserre, G. (2023): Addressing the Dilemma of a “Crisis within a crisis”: Exploring the Penetration Testing challenges in a Mobile Field Hospital Setting. Proceedings of the Cyber Secure Nigeria Conference. Nigerian Army Resource Centre (NARC) Abuja, Nigeria. 11-12th July, 2023. Pp 67-80 https://www.csean.org.ng/. dx.doi.org/10.22624/AIMS/CSEAN-SMART2023P9

Potential contributions of 3D-Digital Image Correlation are investigated to understand the dilatant behaviour of a refractory concrete during high-temperature creep experiments. An experimental analysis of high-temperature image quality is performed. The measurement uncertainty is assessed and compared to the sensitivity of computed kinematic fields to the parameters of the Drucker-Prager model that control the dilatancy. Promising results are found i) concerning deflection and neutral axis location measurement in bending creep tests and ii) contactless measurement of axial strain in compression creep tests, iii) to support the assumption of dilatant behaviour from bending and diametral compression tests and iv) to provide data for a rough parameter identification from compression creep tests.

The reliability of a two-temperature model is assessed in the case of longitudinal heat transfer in unidirectional composites. One interest is that it makes it possible to apply separate boundary conditions or source terms on the fibre and the matrix (emissivity for example), without necessitating an explicit description of the fibre and matrix domains. For the sake of simplicity, the model under study is based on a fin-approximation in both fibre and matrix, which implies a high interfacial thermal resistance. The range of validity of this assumption is investigated by comparing the model to an axisymmetric one-temperature model, using non-dimension variables and Dirichlet boundary conditions. It turns out that this range of validity is strongly dependent on the parameters.

Carbon fibre reinforced composites with matrix consisting of porous glass-ceramics obtained by high temperature heat-treatment of geopolymer based material are studied. The matrix is obtained from a slurry. Several composites have been manufactured by in-laboratory stratification of pre-impregnated plies with slurries diluted at various rates. Slurry dilution changes the porosity and leads to pseudo-ductile behaviour of the composite. Dilution implies a drop of non-linearity stress threshold together with a slower decrease of the strength. An optimal dilution rate is evidenced, which exhibits high strength but lower non-linearity stress threshold, and then, a significant failure strain. The optimized prepreg material is compared with a reference composite processed by an industrial prepreg process. The origin of the pseudo-ductility is related to decohesion at the interface between tows and inter-tow matrix. RTM also provides a pseudo-ductile composite but with very low non-linearity stress threshold, in relation to poorly impregnated tows.

Oxide/oxide ceramic composites can be used for structural applications operating continuously at temperatures between 500°C and 900°C under oxidizing environment, such as in areas close to aircraft engines. In particular, composites based on a matrix combining alumina and silica are promising because this system has good mechanical properties up to 1000°C and allows to limit the grain coarsening in Nextel 610 alumina fibers. In this work, the mechanical behavior of a Nextel 610/alumina-silica oxide/oxide ceramic matrix composite is studied. The matrix system initially associates submicron particles of alumina (AKP-50, d50 = 200 nm, Sumitomo Chemical Co. Ltd.) and colloidal particles of silica (Ludox AS-40, d50 = 20 nm, Grace Davison). Unidirectional composite plates were manufactured. The fibers were impregnated with the suspension by contact molding and the green body was subsequently sintered. The composite material was then characterized. In particular, the elastic properties and the behaviors in diametral compression and in 4-point bending were determined. The mechanical behavior of the material is closely related to its microstructure which results from the flow of the viscous silica phase during sintering. In addition, the influence of the alumina-silica ratio is discussed. Relationships between processing/microstructure/properties were finally established by considering the behavior of the matrix system during the various stages of the manufacturing.

This paper studies the rheological behavior of aqueous suspensions of fine grained (d50 = 200 nm) alumina. Rheological measurements were performed on suspensions containing various amounts of solid and 0.26 wt% of ammonium polymethacrylate in order to ensure a good state of dispersion. Brownian motions, colloidal interactions and hydrodynamic interactions dictate the behavior. The viscosity is mainly influenced by the shear rate and by the solid volume fraction. A Maron and Pierce model was used to describe this last effect in the hydrodynamic regime. The maximum packing fraction was found to be 40 vol%. This value is related to the colloidal stability as described by the DLVO theory. In fact, the maximum packing fraction leads to a surface-to-surface separation distance of about 46 nm because of the repulsive potential. Finally, a dimensionless approach was achieved to quantitatively identify, on the rheogram, the different flow regimes associated to each dominant interaction type.

This study investigates the effects of desizing by heat cleaning on tensile properties of basalt-based mineral fibers.Two heat treatments, which lead to a complete removal of the sizing layer, were considered: one at low temperature (350°C) for a long time (10 h) and one at high temperature (600°C) for a short time (35 min).Desizing greatly affects tensile strength.High temperature and short time treatment conditions lead to the most severe strength degradation (66%).SEM micrographs reveal that failure originates from surface defects.Mechanisms responsible for strength loss were investigated by X-ray diffraction analyses, density measurements and differential thermal analyses.Strength degradation is ascribed to sizing layer removal and to thermally activated structural rearrangement of basalt.

Geopolymer-based glass-ceramic matrix composites can be processed at room temperature and a heat treatment below 100 degrees C leads to matrix hardening thanks to the geopolymerization mechanisms. The stabilization of the matrix into glass-ceramics is achieved via a post-curing at high temperature. This paves the way of the utilization of cost-effective liquid composite molding processes, for which all the necessary equipment is already available for processing temperature ranges related to polymer matrix composites, provided that the rheological behavior of the precursor is suitable to conveniently permeate the fibrous preform. The paper describes the thixotropic rheological behavior of a reference suspension at processing temperature (10 degrees C-20 degrees C) and its evolution along aging at -18 degrees C. The changes are interpreted in terms of geopolymerization mechanisms (dissolution and polycondensation) and suspension rheology (predominance of hydrodynamic effects at high shear rate). On this basis, a phenomenological modeling framework, combining two Krieger-Dougherty equations, is proposed to build a relationship between the effective viscosity of the suspension and the phenomena involved during aging (dissolution of aluminosilicate particles) and shearing (microstructure scalar variable).

Heteroaggregation corresponds to an attraction between two different types of particles. It can either lead to stable or instable systems, depending on the conditions. In this paper heteroaggregation in binary mixtures of alumina and silica colloids is studied, by coupling an experimental approach and Brownian dynamics simulations. Two main objectives are targeted. The first one is to bridge the gap between coagulation and dispersion, by examining the effect of the relative concentrations of silica and alumina. The second one is to study the effect of the volume fraction of solid, which impacts strongly the aggregation mechanism. The coagulation or the dispersion are evidenced by sedimentation tests, granulometry, and rheological measurements, supported by zeta potential measurements. Heteroaggregates could be observed by transmission electron microscopy. Brownian dynamics simulations give more insight into the very first moments of the process, to predict the adsorption kinetic and the heteroaggregates structure. A very good agreement is obtained between experiments and simulations, which both show adsorption of silica leads to the bridging of alumina particles and thus coagulation at low concentration. This adsorption is rapidly limited by electrostatic interactions, then hindering alumina agglomeration by repulsive interactions. For the higher solid fractions, alumina aggregation is more likely, as two alumina particles can easier encounter before their surface is enough covered by the silica to avoid their aggregation.

This paper investigates the effects of temperature cycles between -55 degrees C and 125 degrees C (the temperature range for intended space application) on the strength and microstructure of spray deposited Si-Al CE9F alloy. After 500 cycles, the strength is significantly improved of 9% (i.e., 26 MPa). Moreover the Weibull modulus also undergoes a significant increase. Microstructure characterizations by XRD, SEM, EBSD and DSC evidence recovery and recrystallization processes in the Al phase, and subgrain development at grain boundaries in the Si phase, leading to lower crystallite size. A Hall-Petch dependence of mean strength to average crystallite size in Si is proposed as strengthening mechanism.

Cette etude s’interesse a l’influence du desensimage par traitement thermique sur les proprietes mecaniques de fibres de basalte. Le traitement thermique a 350 °C pendant 10h, considere dans ces travaux, permet d’obtenir un desensimage complet des fibres. Les proprietes mecaniques des fibres de basalte avant et apres desensimage ont ete evaluees par essais de traction sur monofilaments. Une diminution de 34% de la resistance mecanique a ete observee suite au desensimage tandis qu’aucune difference significative n’a ete constatee sur le module d’Young. L’observation au MEB des facies de rupture montre que les defauts presents a la surface des fibres sont responsables de la rupture. La structure du basalte n’etant pas modifiee au cours du traitement, la perte de resistance mecanique est exclusivement attribuee au desensimage. Celui-ci a revele les defauts surfaciques des fibres et aggrave leur criticite. Des eprouvettes en materiaux composites unidirectionnels ont ete fabriquees avec une matrice epoxy et testees en considerant les deux etats de fibres. Les differences de proprietes mecaniques observees sur les composites correspondent a celles observees sur les monofilaments. Autrement dit, la presence de la matrice ne permet pas de « proteger » les defauts surfaciques des fibres reveles par le desensimage, comme pouvait le faire l’ensimage.

The rheological behavior of mechanically dewatered sewage sludges is complex but essential as it affects almost all treatment, utilization and disposal operations, such as storage, pumping, land-spreading, or drying. In this work, a specific methodology coupling experiments and modelling is developed to characterize the rheological and textural properties of highly concentrated sludge. The experimental part based on a uniaxial compression method has been presented in a previous paper (Liang et al., 2017). This article is dedicated to the modelling part, which includes the behavior identification and the parameters optimization. Previous and additional mechanical tests allow the identification of a visco-elasto-plastic behavior. This behavior is then modelled with a Burgers-Ludwik model, with 7 rheological parameters. This model is able to simulate the viscoelastic behavior of sludge under the yield stress, and the visco-elasto-plastic hardening behavior over the yield stress. The optimization of model parameters is carried out in two steps and relies on the calculation of basins of attraction and confidence intervals with initial conditions estimated from the mechanical tests. Finally, the entire characterization methodology, from experimental mechanical tests to model parameter optimization, is applied to sludge samples at different operating conditions and structural states. The determination of the rheological properties of sludge is achieved with excellent matching between simulation and experimental results. Being able to take into account these impact factors, the rheological model can be used to predict the sludge behavior in various operating conditions.

The use of structural adhesive bonding has increased in recent years for its comparatively superior properties. Recent advances in the technology aims to offer industrials a reliable process for bonding assemblies. One part of this project implies to simulate the shape of the adhesive, at the end of the docking process, which will be done using the Volume of Fluid method (VOF) implemented in OpenFoam ® , an open source CFD toolbox. In order to validate, the numerical model is then compared to analytical solutions for cylindrical models and will be further extended to more complex geometries.

The effect of dicumyl peroxide (DCPO) concentration on the polymerization kinetics of a polysilazane system has been investigated through DSC analyses. DCPO acts as polymerization initiator by activating the polyaddition of vinyl groups. The overall heat of reaction is found to be a linear function of the DCPO concentration above 1.5 wt%, due to the addition of the heat of fully initiated polymerization and the heat of DCPO decomposition. Below 1.5 wt% of DCPO, the polymerisation of polysilazane is not fully initiated and only part of the reaction occurs. The resulting overall heat of reaction is therefore lower than that provided by the linear law valid for higher concentrations. A two‐reaction kinetic model built on this interpretation leads to a satisfactory representation of the DSC analyses performed for each DCPO concentration between 0.1 and 20 wt%. POLYM. ENG. SCI., 58:859–869, 2018. © 2017 Society of Plastics Engineers

This publication presents new advances in the field of refractories characterization. These laboratory methods that combine experiments and numerical analyses and concern both the thermomechanical and thermochemical behaviour are illustrated through different examples: identification of asymmetrical creep, determination of elastic and inelastic properties, measurements of macroscopic deformation, phase transformations or corrosion kinetics. These advanced techniques offer the refractory community new opportunities to improve the knowledge and the prediction of the phenomena of degradation of the refractories.

Thermostable resins, such as cyanates esters (CEs), exhibit thermal stability at high temperature. However, CEs are highly exothermic during the curing process. Thus, a thorough understanding of the polymerization during the RTM process (Resin Transfer Molding) is important in order to achieve a full conversion and then good mechanical characteristics for the final product. This article deals with cure kinetics of Primaset PT30 ® resin studied by DSC scans which falls under two methods, dynamic and isothermal. The enthalpy of reaction HT is evaluated by using the dynamic method and the isothermal method evaluates both, the reaction rate dα dt and the curing degree α. In addition, the model expression proposed in this study is Kamal-Sourour model in order to predict the isothermal curing. Mots Clés: cyanates esters, RTM, étude cinétique, DSC

Thermostable resins, such as cyanate esters (CEs), exhibit thermal stability at high temperature. However, CEs are highly exothermic during the curing process. Thus, a thorough understanding of the polymerization during the RTM process (Resin Transfer Molding) is important in order to achieve a full conversion and then good mechanical characteristics for the final product, while preventing any degradation of the matrix. This article deals with cure kinetics of Primaset PT30 ® resin studied by DSC scans which falls under two methods, dynamic and isothermal. The enthalpy of reaction HT is evaluated by using the dynamic method and the isothermal method evaluates both the reaction rate dα dt and the curing degree α. In addition, the model expression proposed in this study is Kamal-Sourour model in order to predict the matrix curing.

The mechanically dewatered sewage sludge with total solid content around 20% on a weight basis is very similar to yield stress fluid, its complex transition between solid and fluid states is not perfectly reversible and especially challenging in terms of pumping, land spreading and drying. To characterize the rheological and textural properties of highly concentrated sludge, a specific methodology based on uniaxial single and cyclic compression tests is developed. Three types of sludge samples (fresh original, fresh premixed and aged original ones) are extruded into cylinders and pressed between two parallel plates using a material testing machine. In single compression, the bioyield point beyond which the sludge fractures is around 7.3 kPa with true strain equal to 0.21. The cyclic compression tests reveal that the sludge behaves as a viscoelastic body when the true strain is smaller than 0.05 and as a visco-elastoplastic once exceeding the yield stress. The elastic module is around 78 kPa; the viscosity is deduced, in the order of magnitude 104-105 Pa " s and the yield stress is estimated about 4 kPa. In the unloading phase, the sludge behaves again as a viscoelastic body with clear hysteresis. With the increase of compression speed, the viscosity declines, which confirms that the sludge is a shear-thinning material. The yield stress and the bioyield increase with compression speed, but it does not induce extra internal damage in the samples since the resilience and the cohesiveness are unaltered. The reliability and sensitivity of the method is justified by highlighting the changes of sludge behavior due to aging and premixing effects: both decrease the strain energy density, but do aggravate the adhesiveness of the sludge; the aging makes the sludge less cohesive, while the premixing does not modify its cohesiveness. In spite of changes in test conditions, the elastic module of sludge samples remains unchanged. (C) 2017 Elsevier Ltd. All rights reserved.