Multilayered Wall Research Articles

Mechanical and microstructural investigation of multi-layered Inconel 825 wall fabricated using CMT-based WAAM

In this research, a multi-layered wall was produced using the Wire-Arc Additive Manufacturing (WAAM) technique, specifically employing the Cold Metal Transfer (CMT) method with Inconel 825 wire. The optimized CMT-WAAM parameters were identified using multivariate regression analysis. The mechanical and microstructural properties of the wall were assessed in its lower, middle, and upper sections. The tensile properties showed that the ultimate tensile strength (UTS) ranged from 505 MPa to 514 MPa, closely matching that of conventionally wrought Inconel 825 (505–514 MPa). The yield strength (YS) varied from 199 MPa to 207 MPa, while elongation values ranged from 49.7 % to 57.5 %, depending on the section of the wall. A gradual decrease in hardness was observed from the bottom (246.16 Hv) to the top (221.75 Hv) of the wall. Microscopy identified continuous and discontinuous cellular-dendritic microstructures across the sections. Tensile and impact test fractographs revealed a fibrous ductile fracture mode, with SEM images highlighting the presence of Laves phases and micro-voids, particularly in the upper sections. Despite the formation of Laves phases, which can act as crack initiation sites, the mechanical properties of the WAAM-fabricated wall were comparable to those of wrought Inconel 825.

Characterization of multi-layered wall paintings from a Roman domus in Santa Maria Capua Vetere

This paper regards the preliminary characterization of wall paintings sampled in a Roman domus located in the city of Santa Maria Capua Vetere. Despite its history and archaeological remains, there is a lack of scientific studies on Roman materials and techniques adopted in this site. Samples were taken from different walls of the villa. Pigments, binders, and mortars were analyzed by optical and electronic microscopies, vibrational spectroscopies including Fourier transform infrared and micro-Raman imaging, and mass-spectrometry coupled to gas and liquid chromatography. Altogether, the multi-layers preparation, the rich pigments palette (both natural and synthetic ones) and the variety of the organic ligands used (terpenic resins or animal glue) support the hypothesis of a very wealthy owner. The absence of calcite in the pictorial layer and the presence of organic binders clearly indicates an a secco technique.

An explicit multilevel power turbulent wall function based on the de-thresholding Douglas–Peucker algorithm

Wall functions are extensively applied in engineering simulations with turbulence. They facilitate a significant increase in the scale of the grids next to the wall, which in turn reduces the total number of grids needed. This optimization enhances computational efficiency, making the simulation process more effective and streamlined. However, the current commonly used wall functions, such as the Spalding wall function, are an implicit expression that needs to be solved iteratively, which affects the computational efficiency, and the multilayer segmented wall function is not smoothly articulated, which affects the fidelity. In this study, based on flat plate direct numerical simulation (DNS) data, combined with structural ensemble dynamics theory, the de-thresholding Douglas–Peucker algorithm is introduced to construct an explicit wall function expression in the form of multilevel power exponential concatenated multiplication. The comparison of the new wall function against DNS data reveals that it demonstrates superior fitting accuracy in contrast to the traditional ones, and eliminates the need for manual calibration, reduces subjective influence, and enhances reliability. The numerical simulation outcomes for the flat plate boundary layer and a series of airfoils showcase the new wall function's exceptional accuracy, which not only meets but also surpasses the demanding standards of engineering practice.

Numerical study and experimental validation of heat transfer in a CenoPCM reinforced multi-layered meta-material wall for energy efficient buildings

Numerical study and experimental validation of heat transfer in a CenoPCM reinforced multi-layered meta-material wall for energy efficient buildings

Hygrothermal performance of multilayer wall assemblies incorporating starch/beet pulp in France

This work focuses on the investigation of the hygrothermal performance of four different wall insulation assemblies including starch/beet pulp composite for an office in France under two climatic conditions. Subsequently, a comparative performance analysis is made on all studied assemblies by substituting the Starch/beet pulp composite with hemp concrete (HC). For each design, the overall energy performance, total water content, drying rate and condensation risk were evaluated through hygrothermal simulations using the WUFI® Plus software and mold growth risk assessment was conducted with WUFI®Bio software. Results showed that insulation assemblies based on Starch/Beet pulp exhibited a slightly improved effectiveness in potential energy savings and higher dryness rate while having a higher condensation risk, a lower dynamic thermal performance, and a higher susceptibility to mold growth risk. Moreover, insulation assemblies based on Starch/Beet pulp demonstrated better hygrothermal performance under Nancy’s climate compared to that of Marseille. Wall assemblies based on hemp concrete reduced total energy consumption by up to 35 % in Nancy’s climate and 24.9 % in Marseille’s climate. In comparison, starch/beet pulp concrete achieved reductions of up to 37.5 % and 26 % respectively. However, the mold growth risk for starch/beet pulp was 1.2–7.2 times higher than for hemp concrete. In Marseille’s climate, this risk was 2.3–8.9 times higher for starch/beet pulp and 4.7–17.8 times higher for hemp concrete compared to Nancy’s climate. The findings from these room-scale studies enhance the understanding of the hygrothermal behavior of the Starch/Beet pulp bio-composite material by comparing its performance, under the same conditions, to that of the well-studied hemp concrete material in the literature. Additionally, these studies provide greater insight into the impact of water on the overall energy consumption, service performance of a building and health hazards. Finally, this research also tackles the challenges of integrating innovative materials into the established construction industry.

Zafirlukast induces DNA condensation and has bactericidal effect on replicating Mycobacterium abscessus.

Mycobacterium abscessus infections are emerging in cystic fibrosis patients, and treatment success rate in these patients is only 33% due to extreme antibiotic resistance. Thus, new treatment options are essential. An interesting target could be Lsr2, a nucleoid-associated protein involved in mycobacterial virulence. Zafirlukast is a Food and Drug Administration (FDA)-approved drug against asthma that was shown to bind Lsr2. In this study, zafirlukast treatment is shown to reduce M. abscessus growth, with a minimal inhibitory concentration of 16 µM and a bactericidal concentration of 64 µM in replicating bacteria only. As an initial response, DNA condensation, a known stress response of mycobacteria, occurs after 1 h of treatment with zafirlukast. During continued zafirlukast treatment, the morphology of the bacteria alters and the structural integrity of the bacteria is lost. After 4 days of treatment, reduced viability is measured in different culture media, and growth of M. abscessus is reduced in a dose-dependent manner. Using transmission electron microscopy, we demonstrated that the hydrophobic multilayered cell wall and periplasm are disorganized and ribosomes are reduced in size and relocalized. In summary, our data demonstrate that zafirlukast alters the morphology of M. abscessus and is bactericidal at 64 µM. The bactericidal concentration of zafirlukast is relatively high, and it is only effective on replicating bacteria but as zafirlukast is an FDA-approved drug, and currently used as an anti-asthma treatment, it could be an interesting drug to further study in in vivo experiments to determine whether it could be used as an antibiotic for M. abscessus infections.

Abstract Mo032: Biofabrication of Small Vascular Graft using Human Amniotic Membrane

Vascular diseases encompass a spectrum of pathological conditions affecting blood vessels, including cerebrovascular disease, coronary heart disease, aneurysms, deep vein thrombosis, and peripheral arterial disease. In severe cases, surgical interventions such as bypass grafting or vascular replacement surgeries are necessary to restore blood flow by bypassing obstructed vessels with functional vascular substitutes. Autologous blood vessels harvested from patients are considered the gold standard for vascular surgeries. However, their availability is limited in patients with pre-existing chronic diseases or previous vessel harvest, and the associated morbidities of vessel harvesting and subsequent surgeries further restrict their therapeutic applicability. Synthetic grafts, including polytetrafluoroethylene (e-PTFE), polyethylene terephthalate (PET), and polyurethane (PU), have obtained FDA approval for clinical application and have shown satisfactory outcomes in large vessel surgeries (internal diameter > 6mm). However, clinical trials targeting medium (6-10 mm) to small (< 6mm) vessels often yield unsatisfactory results. This study aims to develop a small vascular graft using human amniotic membrane (HAM) that meets the structural, mechanical, and biological requirements for human vascular reconstructive surgeries. Fresh HAMs were decellularized with 1% Triton X-100 and 0.1% sodium dodecyl sulfate to prepare decellularized HAM (DAM). The DAM was trimmed into a rectangular shape and rolled around a catheter to prepare a tubular-shaped DAM vascular graft. After rolling, the DAM grafts were crosslinked with 1% genipin for 24 hours followed by thorough water washing. The final DAM vascular graft exhibited a multi-layered wall structure and comparable dimensions and mechanical properties to native arteries. The DAM vascular graft was further evaluated in vivo by replacing part of the rat abdominal aorta and part of the carotid artery in pigs. Both small and large animal studies demonstrated vascular patency with no neointimal hyperplasia (NIH), suggesting that the DAM graft holds significant promise as a small tissue-engineered vascular graft for future vascular reconstruction surgeries.

DEVELOPMENT OF MODELS COMPLEX OSCILLATIONS FOR AUTOMATION SYSTEMS OF VIBROACOUSTIC OPERATIONAL SAFETY CONTROL OF BUILDINGS AND STRUCTURES

Problem statement. Long-term safe operation of buildings and structures is impossible without determining the stability of their load-bearing elements, especially after shocks and dynamic loads under the influence of explosions and fires. In such conditions, reliable and productive monitoring of the reliability of buildings and structures is a critical element in increasing human safety. Vibroacoustic is an effective and informative method that allows for non-destructive assessment of the condition of concrete, reinforced concrete, brick, multi-layer walls and other types of structures. However, to increase the speed and quality of determining the state of objects, maximum automation of the vibroacoustic method is required. Purpose of the study. Increasing the productivity and reliability of vibroacoustic monitoring of buildings and structures by automating the impact action with specified parameters based on the development of dynamic models of complex oscillations. Methods. Analytical studies of dynamic and kinematic models of the exciter of mechanical vibrations, computer modeling, laboratory tests of the vibration generator control system. Research results. Models of complex oscillations have been developed to improve reliability and implement new control laws that are impossible for classical vibration systems and are necessary for automated vibroacoustic control of buildings and structures and ensure the safety of their operation. The use of reduced bit depth coefficients in the calculation scheme using the Jack W. Crenshaw algorithm is justified in a wider range of argument values than with initial coefficient values for controlling vibration systems with limited computational performance. This is necessary when creating executive bodies of modern systems for automated vibroacoustic monitoring of the cracks and violations of the homogeneity of load-bearing structures of buildings and structures. The oscillation exciter has been tested in laboratory conditions. Scientific novelty. New methods and algorithms for automatic control of vibration exciters have been developed to obtain polyfrequency oscillations, linear waves and wave fields with specified amplitude and frequency characteristics. Practical significance. An oscillation exciter has been developed for a system of automated vibroacoustic control of the buildings and structures operation safety. This provides a necessary and sufficient basis for improving methods for assessing changes in the environment as a result of the appearance of cracks and loss of homogeneity.

Conforming mesh modeling of multi-physics effect on residual stress in multi-layer powder bed fusion process

The current research aims to predict the residual stress accumulation and evolution in the powder bed fusion processed multi-layer thin wall structures through a conforming mesh modeling approach. It involves the discrete element method (DEM) interfaced with the volume of fluid (VOF) method using computational fluid dynamics (CFD) coupled with the finite element method (FEM). The conforming mesh approach developed in the research predicts multi-physics, its induced porosity, and the cumulative effect on the residual stress in the powder bed fusion processed Ti-6Al-4V thin wall structures. The results of the residual stress in the multi-layered component from this method were further quantitatively compared with the non-conforming finite element method. The results show the conforming mesh approach was not only effective in capturing the layer geometry, and defects induced during the printing, but also predicted the residual stress in the region of the defect more accurately than the non-conforming mesh methods.

Chloromonas rubrosalmonea sp. nov. (Chlorophyta) causes blooms of salmon-red snow due to high astaxanthin and low chlorophyll content

ABSTRACT Melting snowfields support microbial communities, including blooms of phototrophic psychrophiles. “Watermelon snow” and its flagship species Sanguina nivaloides are mostly found at exposed, alpine or polar sites. Here, we investigated an alga that is morphologically similar but likely less common, thriving in exposed or semi-exposed snowpacks at lower altitudes frequently close to the tree line, and causing characteristic, intensely salmon-red snow surface spots in Central European and Norwegian mountains. Our aim was to illustrate the taxonomic heterogeneity of red snow by performing a cellular and molecular characterization of this species. The phylogenetic analysis placed the alga into the genus Chloromonas, clade “group C”. Single-cell Sanger sequencing enabled us to link the cell morphotype to its genotype. In addition to light microscopy of the snow samples, applying 18S rRNA gene and ITS2 metabarcoding confirmed that this alga dominated the bloom communities. The cysts had multi-layered smooth cell walls, and had a broadly oval to fully spherical shape, in striking contrast to most other Chloromonas species found on snow surfaces. Another remarkable feature was a pronounced astaxanthin accumulation in relation to a low proportion of chlorophylls, occasionally accompanied by a significant reduction of thylakoid membranes. This likely caused the photosynthetic dormancy of mature cysts found in some samples. Based on these data, we describe the snow alga as Chloromonas rubrosalmonea, sp. nov.

Optimizing wall structure for enhanced thermal performance: A layer-specific dimensionless parameter analysis in multi-layer walls

Enhancing building energy efficiency and thermal comfort crucially involves optimizing the phase shift (PS) and decrement factor (DF) of exterior walls. Using the auxiliary function method, this paper presents analytical solutions for the DF and PS in double-layer walls, subsequently extending these to multi-layer walls. Insulation and structural material properties (density, thermal conductivity, specific heat capacity), thickness, internal and external convective heat transfer coefficients, outdoor temperature fluctuations, and insulation layering in multi-layered walls were taken into consideration in acquiring analytical solutions. Our findings in double-layer walls and analogous structures show that the DF and PS are largely governed by two dimensionless parameters per layer: thermal diffusivity index and Biot number. Regardless of Biot numbers (ε1 and ε2), an increase in thermal diffusivity indexes (δ1 and δ2) consistently reduces the DF and enhances the PS. Moreover, a larger ε1 with a smaller ε2 generally associates with a lower DF, but their impact on PS is less significant compared to thermal diffusivity index. In multi-layer walls, especially with mirror symmetry, we observe a dual extremum phenomenon, marked by prolonged PS and reduced DF. This underlines the importance of structural configuration in wall thermal performance. Thus, in double-layer structures, while the DF decreases and PS increases with increasing thermal diffusivity index, the influence of Biot numbers is comparatively minimal, highlighting the paramount role of thermal diffusivity index in optimizing thermal behavior. This discovery provides valuable guidance for identifying wall structures with minimal DF and maximal PS during the architectural design phase.

Thermal Behavior of Composite Material Based on Phase Change Material/Plaster as Thermal Energy Storage in Multilayer Wall: Experimental Study.

This study aims to explore the effects of augmenting the mass proportion of a composite comprising paraffin and beeswax (PBPCM) within plaster, which influences the thermal insulation of a dual wall. This work is primarily based on the thermal properties of the composite material PBPCM/plaster with varying percentages of PBPCM. Various essential parameters, such as density, thermal conductivity, specific heat capacity, thermal diffusivity, and latent heat, were assessed and juxtaposed with those of conventional plaster for the PBPCM/plaster composite material. The evaluation of this composite material was executed through an experimental device on a laboratory scale. The obtained results show that the increase in the mass fraction of PBPCM in the plaster decreased the thermal conductivity of plaster more than 3 times, whereas this increase of the PBPCM fraction in plaster enhances heat retention, specifically in specific heat capacity under constant conditions. Nevertheless, in a dynamic state, thermal effusivity has the lowest value for 50% PBPCM. The recommendation is to utilize 50% PBPCM, as it yields an optimal thermal effusivity, and significant values of specific heat capacity and latent heat have been noted for this percentage of PBPCM, measuring 1263.77 kJ/kg K and 18.9 kJ, respectively. Additionally, an increase in the PBPCM percentage narrows the temperature range suitable for effective thermal energy storage.

Effect of Interlayer Machining Interventions on the Geometric and Mechanical Properties of Wire Arc Directed Energy Deposition Parts

Abstract Wire Arc Directed Energy Deposition (Wire Arc DED) has become a popular metal additive manufacturing technique for its capability to print large metal parts at a high deposition rate while being economically efficient. However, the Wire Arc DED process exhibits geometric inaccuracies resulting from the variability in the bead geometry and demonstrates heterogeneity in microstructure and mechanical properties. This study investigates the use of tailored periodic machining interventions during the Wire Arc DED process to address these shortcomings. The as-built geometry and surface finish, microstructure, and microhardness of multi-layer wall structures produced with and without machining interventions carried out at different temperatures are compared. The machining interventions are found to reduce the uncertainty in bead geometry evolution and significantly improve the surface roughness of the as-built walls, thus reducing the need for further post-processing of the wall surfaces. Although the microstructure constituents of the as-built wall structures with and without machining interventions are similar, the machining interventions result in finer grains in the interior of the part. Machining interventions are found to yield a statistically significant increase in microhardness, indicating increased strength compared to Wire Arc DED alone. In addition, the spread of the microhardness distribution is reduced in Hybrid-Wire Arc DED, indicating improved homogeneity of the grain size distribution compared to Wire Arc DED alone. The study shows that the proposed hybrid manufacturing technique has the potential to control and improve the geometric and mechanical properties of additively manufactured metal components.

Mechanical and corrosion performance of WAAM printed steel structure

Wire plus arc additive manufacturing (WAAM) is rapidly growing into a popular and cost-effective technology for manufacturing medium-large complex structured components. WAAM is a novel metal additive manufacturing method that deposits material layer by layer using an electric arc as a heat source, allowing the creation of metal components with high mechanical characteristics. The procedure allows for the construction of a near-net-shape structure at a rapid pace of production (50–130 gm/min) and material utilization efficiency (80–90 %). The present study mainly focuses on the fabrication of the WAAM structure and a detailed investigation of the mechanical and corrosion performance of multi-layer fabricated wall components. The most versatile and widely applicable stainless steel SS316L material is employed to build multi-layered wall structures. The average micro-hardness of the WAAM-built structure along the building direction was found to be 197.43±1.46 HV0.3 and that of the commercially available counterpart was found to be 187.26±1.17 HV0.3. Moreover, the maximum hardness was observed close to the bottom region (201.86±1.44 HV0.3) which further reduces with the building height. The ultimate tensile strength, and yield strength of the WAAM printed wall obtained as 573.81±2.3 MPa, and 275.41±1.1 MPa respectively found to have improved mechanical strength to that of wrought counter-part however the ductility in the form of percent elongation gets slightly reduced. Furthermore, comparable corrosion resistance was observed for the WAAM fabricated wall structure and conventionally manufactured SS316L structure. The bottom region experiences better corrosion resistance compared to the upper region in both saline environment and acidic corrosion solution with an average corrosion rate of 0.0276 mm/yr, and 0.0366 mm/yr respectively.

Thermal analysis of permanent magnet synchronous linear motor accounting for three-phase current unbalance

Three-phase current unbalance is a common winding fault of the motor, which will bring local overheating, cause security risks and economic losses, accurate temperature rise calculation and thermal flux characteristics analysis of the motor working in three-phase current unbalance are necessary and challenging. However, little research has been conducted on the thermal characteristics and analysis methods for the permanent magnet synchronous linear motor (PMSLM) working in three-phase current unbalance. To address this problem, a multilayer composite flat wall model contained heat source of the primary is proposed firstly to analysis the heat transfer characteristics of the PMSLM caused by three-phase current unbalance qualitatively. Then, the heat transfer and temperature distribution characteristics of the PMSLM are obtained by calculating the fluid-thermal coupling model of the PMSLM directly. What's more, the effect of current grade on heat transfer is analyzed by comparing the heat transfer characteristics of the PMSLM working in four different three-phase current balance cases. Finally, the qualitative analysis and fluid-thermal analysis results are verified experimentally with a PMSLM adopting four different three-phase current unbalance conditions. Thermal analysis of the PMSLM working in three-phase current unbalance makes it is possible to prevent local heat accumulation and avoid unexpected interruptions for the redundant motor system and the fault tolerant motor system.

Metallic Wood through Deep-Cell-Wall Metallization: Synthesis and Applications.

Metallic wood combines the unique structural benefits of wood and the properties of metals and is thus promising for applications ranging from heat transfer to electromagnetic shielding to energy conversion. However, achieving metallic wood with full use of wood structural benefits such as anisotropy and multiscale porosity is challenging. A key reason is the limited mass transfer in bulk wood where fibers have closed ends. In this work, programmed removal of cell-wall components (delignification and hemicellulose extraction) was introduced to improve the accessibility of cell walls and mass diffusion in wood. Subsequent low-temperature electroless Cu plating resulted in a uniform continuous Cu coating on the cell wall, and, furthermore, Cu nanoparticles (NPs) insertion into the wood cell wall. A novel Cu NPs-embedded multilayered cell-wall structure was created. The unique structure benefits compressible metal-composite foam, appealing for stress sensors, where the multilayered cell wall contributes to the compressibility and stability. The technology developed for wood metallization here could be transferred to other functionalizations aimed at reaching fine structure in bulk wood.

Heat transfer through a three-layer wall considering the contribution of phase change: A novel approach to the modelling of the process

A novel analytical solution to the time-dependent heat transfer equation for a multi-layer wall considering the contribution of phase change is obtained. Based on this solution a new numerical algorithm is developed for the analysis of variations in temperature and heat flux in a three-layer wall of a building in the presence of transient ambient temperature. In this algorithm, the new analytical solution at the end of the previous time step is used as the initial condition for the following time step with adjusted values of input parameters (ambient temperature). The novel algorithm is verified based on a comparison of the predictions of COMSOL Multiphysics (version 6.1) with its predictions for the same input parameters assuming that the time dependence of the ambient temperature follows the sine law. The new code is used for the analysis of heat transfer through a three-layer building wall assuming typical continental climate conditions. The inner and outer layers were filled with polyurethane foam, while a thin middle layer, located in the centre of the wall, was filled with the phase-change material (paraffin). Using the new numerical algorithm it is demonstrated that the presence of the thin paraffin layer in the wall leads to two orders of magnitude reduction in the amplitude of temperature oscillations on the room side of the wall compared to those on its outer side. It is shown that the presence of paraffin layer in the wall leads to an increase in the phase shift between the temperature on the outer side of the wall and the heat flux on the room side from about 1 hour (homogeneous wall) to about 5.5 hours (wall with the paraffin layer).

Influence of heat treatment on the microstructure and mechanical properties of Al–Mg–Si alloy fabricated by double wires + arc additive manufacturing

Al-3.4Mg-1.7Si alloy single-pass and multi-layer thin wall components were fabricated with double wires + arc additive manufacturing procedure. Heat treatment was performed to further process the component. The microstructure and mechanical properties of the as-deposited and heat-treated components were comparatively investigated. After heat treatment, the grains grow up slightly, and the phase particles change to distribute semi-continuously, and a large number of nanoscale monoclinic β″ precipitated phases generate. The porosity increases to 0.0486% from as-deposited 0.0348%. The microhardness, ultimate tensile strength and yield strength are respectively improved by 25%,79%, and 228% with heat treatment process, with the hardness uniformity and elongation decreased.

THE INFLUENCE OF THE MATERIAL AND THE THICKNESS OF THE INSULATION LAYER ON THE HEAT FLOW THROUGH A MULTI-LAYER EXTERNAL WALL PANEL OF A RESIDENTIAL BUILDING

Solved the actual problem of heat flow research through a multi-layer external wall panel of a residential building, depending on the material and thickness of the heat-insulating layer.

Functionally graded thick-walled tubes analysis by numerical methods

Functionally graded materials are increasingly used in the practice of engineering design, as is the case with thick-walled tubes. The use of these constructive elements requires a calculation, which should be as accurate, as accessible and as fast as possible. The present work responds to these requirements. For the calculation of tubes with thick walls made of functionally graded materials, two new ways were used, based on the concepts of multilayer (material) wall and equivalent material. The multi-layered wall concept considers the tube wall made of several layers, as in the case of the well-known multilayer plates, and the equivalent material concept considers the thick-walled tube made of homogeneous and isotropic material, but with fictitious properties, equivalent in behavior to the functionally graded material. The influence of Poisson's ratio is illustrated by some comparative results. The development of the calculus, the validation of the models and the analysis of the results are based on the numerical calculus using the finite element method. The models used, the transverse plane model, the axial-symmetric plane model and the 3D longitudinal model, are made in several variants regarding the fineness of the mesh. The paper also analyzes the influence of the Poisson ratio variation, compared to adopting a constant value. The results of the study, the models and concepts used are useful to specialists and designers of structures of this type, they have a high degree of generality and present openings for the use of other calculation methods.