Porosity Of Composites Research Articles

Research of tribological properties of surface MAO composites on D16T alloy

Operation of mechanical engineering products operating under conditions of intensive wear at high rotation speeds and loads leads to their inevitable wear and significant metal losses. One of the methods for obtaining wear-resistant surfaces on products, for example, friction pair parts, is the microarc oxidation (MAO) method of aluminum alloys. The method allows obtaining dense hard surface wear-resistant composites based on α-Al2O3 (corundum) and γ-Al2O3. The structure, composition and surface quality of the resulting MAO coating significantly affect the performance characteristics of the product surface. The aim of the work is to determine the effect of porosity (10 and 16%) and surface roughness (Ra, equal to 2.7 and 0.51 μm) of MAO composites on D16T alloy on tribological properties and to evaluate the possibility of using MAO coatings in friction pairs, including end seals, under dry friction conditions. Comparative tests were carried out on an SMT-1 machine under dry friction conditions at a specific pressure in the friction pair of P = 0.5 MPa; the duration of the experiment was 90 – 91 min for each friction pair. The studies have shown that in many friction pairs, various types of damage (destruction) of the coating integrity, as well as deep abrasive wear, occurred. The porosity of the MAO coating in the range of 10 – 16% at different roughness values does not affect the abrasive wear of the coating. However, a porosity of 10% and a surface roughness of no more than Ra ≤ 0.51 ± 0.12 μm are preferable for achieving better tribological characteristics of surface MAO composites on D16T aluminum alloy.

Facile preparation and properties of foamed fly‐ash/slag‐based hollow glass microspheres/geopolymer composites

AbstractIn order to reuse the multiple solid waste and improve the porosity of geopolymer composites, a unique foaming process was developed to fabricate novel green foamed fly‐ash/slag‐based hollow glass microspheres/geopolymer (HGMs/FSGP) composites. A thorough investigation was carried out on the synergic effects of cetyltrimethylammonium bromide (CTAB), hydrogen peroxide (H2O2) and HGMs on the microstructure, strength and thermal conductivity. Results showed that the foamed HGMs/FSGP composites with the amorphous structure could be fabricated by foaming combined with HGMs at room temperature. The density of the samples changed from 1.16 to 0.47 g/cm3 with 1–5 wt.% H2O2. The acceptable compressive strength (0.71–15.05 MPa) of the HGMs/FSGP composites was attributed to the fractured HGMs, the good bond between HGMs and geopolymer matrix, and crack deflection across the HGMs. With proper H2O2 and HGMs, the composites obtained their lowest thermal conductivity of 0.116 W/(m⋅K), which could find use in insulation fields.

Effect of Alumina Proportion on the Microstructure and Technical and Mechanical Characteristics of Zirconia-Based Porous Ceramics

The current study investigates the process of preparing and analysing porous-structured ceramics made from zirconium, aluminium, and magnesium ceramic oxides. The starch consolidation casting (SCC) technique, with different types of starches (potato and tapioca), was used for this purpose. Our objective was to methodically examine the impact of different processing factors, such as the temperature at which pre-sintering and sintering occur, and the proportions of ceramic powders, on the microstructure, mechanical characteristics, and porosity of the resultant composites. Pre-sintering effectively reduced the rate of shrinkage during the final sintering stage; this resulted in more controlled and predictable shrinkage, leading to better dimensional stability and reduced risk of defects in the final product. A higher alumina content was associated with an increase in apparent porosity and a reduction in volume shrinkage and apparent densities. The mercury intrusion porosimetry (MIP) findings concluded that the prepared porous ceramics have a multi-modal pore structure. The highest calculated compressive strength was 76.89 MPa for a sample with a porous structure, which was manufactured using 20 wt.% tapioca starch and 30 wt.% alumina content. The main advantage of alumina is its ability to improve compressive strength by refining the grain structure and serving as a barrier against fracture development.

Investigation of the effect of urease bioadditives on porosity and water absorption of cement composites

The results of the application of the biomineralization process in concrete to improve concrete properties such as porosity and water absorption are presented. As a result of the research, an assessment of the activity of various bioadditives based on the Bacillus subtilis strain and isolates isolated from samples of chernozem soil of the Yelets district of the Lipetsk region was given.It was found that the immobilized bacteria slightly differ from the native form in terms of urease activity, however, when stored for more than 50 days. they maintain their activity at a high level, and native microorganisms lose their ability to function, reducing urease activity by 10 times practically to minimum values. It was also revealed that when using Portland cement of various types, there is a decrease in water absorption up to 30%, and porosity decreases up to 40%.The use of different types of fine aggregate also affects porosity, so when using the same parts of sand P1 and P2, porosity is lower than with a homogeneous fine aggregate.It was also noted that all samples had increased strength characteristics – compressive strength and bending strength by 15–25%, respectively. Thus, the use of bioadditives is optimal to achieve improved concrete characteristics.

Decision Support System for the Design Process of Apatite Biopolymer Composite Parts

Abstract In connection with the increase in the number and severity of various types of bone tissue injuries received as a result of wounds during military operations in Ukraine, an important issue in orthopedics and traumatology is making informed decisions about the possibility of restoring the integrity and functions of bone tissue when using different types of composition, porosity and strength of apatite-biopolymer composites. The scientific direction of research is the development of principles and methods for making scientifically based decisions in the design and additive manufacturing of bone substitutes based on apatite-biopolymer composites with functional properties depending on the nature of the localization of the cavity bone defect and its size. A set of methods for analyzing images of bone tissue, taking into account its spatial structure, which are obtained by sensors of different physical nature, with the use of neural network models, development of methods of their design, optimization and training is proposed. The new knowledge obtained as a result of the project will become the necessary basis for making optimal decisions in practice for the introduction of the latest methods of treatment and prosthetics in trauma surgery, oncology, cranio-maxillofacial surgery, dentistry, taking into account the risks of biocompatibility of apatite-biopolymer composites. Software development of an intelligent decision support system will be used to design bone substitutes with controlled composition, structure, porosity and mechanical strength for the further selection of additive technology for its production from apatite-polymer composites, which will contribute to increasing the efficiency of treatment and prosthetics in orthopedics and traumatology.

The novel incorporation of lignin-based systems for the preparation of antimicrobial cement composites

This paper, for the first time, presents a potential application of titanium(IV) oxide and silicon(IV) oxide combined with lignin through a solvent-free mechanical process as admixtures for cement composites. The designed TiO2–SiO2 (1:1 wt./wt.) hybrid materials mixed with lignin were extensively characterized using Fourier transform infrared spectroscopy (FTIR), electrokinetic potential analysis, thermal analysis (TGA/DTG), and porous structure properties. In addition, particle size distributions and scanning electron microscopy (SEM) were conducted to evaluate morphological and microstructural properties. In the next step, the effect of the TiO2–SiO2/lignin hybrid admixture on the workability, hydration process, microstructure, porosity, mechanical, and antimicrobial properties of the cement composites was evaluated. It was observed that appropriately designed hybrid systems based on lignin contributed to better workability, with an improvement of 25 mm, and reduced porosity of cement composites, decreasing from 14.4 % to 13.3 % in the most favorable sample. Additionally, a higher microstructure density was observed, and with increasing amounts of hybrid material admixture, the mechanical parameters also improved. In addition, the TiO2–SiO2/lignin hybrid systems had significant potential due to their high microbial purity, suggesting their effectiveness in minimizing microbial accumulation on surfaces. The final stage of analysis involved employing response surface methodology (RSM) to ascertain the optimum composition of cement composites. The results obtained indicate that the TiO2–SiO2/lignin admixtures are a promising approach for the valorization of lignin waste flows in the design of cement composites.

Wood fibers with natural blowing agents for extrusion and injection molding of polypropylene

ABSTRACT This paper presents a new two-step approach of foaming polypropylene (PP) containing wood fibers (WF) with tri-sodium citrate dihydrate as the low-temperature chemical blowing agent (CBA) and sucrose as the high-temperature CBA. The first CBA was intentionally selected to thermally degrade during extrusion (lower temperature range), whereas the second CBA during the injection molding (higher temperature range). The CBAs were dissolved in water, and WF were soaked in these solutions, afterward dried, ground, and then mixed with PP and extruded. The extruded granules were then injection molded to produce dumbbell-shaped samples. The porosity, thermal degradation, PP crystallization, mechanical and thermomechanical properties of the wood-polymer composites (WPCs), as well as their susceptibility to acoustic damping, were determined. It was shown that sucrose can be an effective CBA for injection-molded WPC samples. However, the effectiveness of this additive is improved by the addition of tri-sodium citrate dihydrate, which decomposed during extrusion.

Ablation resistance and mechanical properties of C/C-HfC-SiC composites with a bulletproof-like layer

Two structural designs are based on the arapaima fish scale structure to enhance the performance of composites. A double-layer SiC/PyC coating was deposited to modify C/C-HfC-SiC composites by chemical vapor deposition. The introduction of PyC coating reduced the porosity and roughness of composites. Ar-O2-Al2O3 plasma ablation system was used to assess the composites. The composites with arapaima fish scale structure showed good flexural and ultra-temperature particle erosion resistance. The samples with the introduction of PyC layer showed higher flexural strength of 220 MPa, which is 40.13 % higher than that of without. After ablation 40 s, the linear ablation rates decreased from 5.95 μm/s to −4.6 μm/s. This study provides new ideas to develop C/C composites with improved ablation-resistant and mechanical properties.

Control of tungsten-epoxy composite porosity prepared using a high-energy ball milling method: An engineering aspect of backing layer fabrication

Tungsten-epoxy composite is commonly used as a backing layer substrate of piezoelectric-based ultrasonic transducers. The physical properties of this composite, such as porosity, play a significant role in controlling the behavior and specifications of transducer fabrication. Therefore, this study aimed to investigate the effects of tungsten content in epoxy to control porosity and determine the engineering aspects of ultrasonic transducer fabrication. The experiment was conducted using a shaker-type high-energy ball milling method, where non-spherical and faceted tungsten particles with a mean size of 1 μm were composited into epoxy resin as a matrix at various tungsten-epoxy weight ratios of 0:1 to 10:1. The prepared composite surface morphological and elemental, tungsten loading, particles, and epoxy bonding were examined and analyzed. Furthermore, analysis was carried out on the relationship between tungsten content and the parameters corresponding to the composite acoustic characteristics, such as sound velocity, acoustic attenuation, and acoustic impedance. The results showed that composite porosity increased in the range of 12.40–31.87%, corresponding to acoustic impedance from 3.04 to 9.37 Mrayl (below 10 Mrayl for biomedical ultrasonic transducers) when the tungsten-epoxy weight ratio varied from 0:1 to 10:1. This showed the significant influence of tungsten particle loading on controlling porosity of tungsten-epoxy composite by precisely tuning the weight ratio, contributing to engineering process in the fabrication. In conclusion, porosity was adjusted by controlling the tungsten loading content in epoxy.

Tailored directional porosity in ceramic matrix composites (CMCs) for hypersonic applications

AbstractIn the field of hypersonic systems and their missions, the occurring flows impose extreme mechanical and thermal loads on the materials used. At the German Aerospace Center (DLR), extensive research is conducted in this area, ranging from design and specification to the development of suitable materials concluding with the proof of concept under realistic conditions in wind tunnels. In recent years, ceramic matrix composites (CMCs) have been investigated for specific aspects of hypersonics. These materials exhibit consistent mechanical behavior over a wide temperature range (up to 1600 °C), coupled with high damage tolerance and thermal shock resistance, distinguishing them from metals and superalloys. Particularly, special porous C/C–SiC ceramics (carbon-fiber-reinforced carbon with silicon carbide) enable innovative material applications for components in transpiration cooling, fuel injection, or boundary-layer transition control. The work presented focuses on the next generation of porous C/C–SiC ceramics currently in development. By deliberately modifying the textile preform, the resulting microstructure and pore morphology are influenced, allowing for control over both the total volume and the orientation of the pores. Relevant parameters influencing porosity have been determined based on the results, and an initial characterization has been conducted. It has been demonstrated that there is a preferred direction of porosity within the sample thickness (Z-axis), and in terms of hypersonic-relevant properties, an absorption coefficient of 0.58 for an acoustic wave at 500 kHz (static pressure of 15 kPa), as well as a length-specific flow resistance of 3.4 MPa s/m2 and an overall porosity of 12.25% were determined. Building upon these promising initial findings, the goal is to further expand the understanding of the parameters influencing porosity and to generate a tailored material for different application scenarios by correlating them with hypersonic properties.

Investigation of the Influence of UV Radiation on Compositions of Polylactide with Graphite Nanoplates

Composites of polyether polylactide (PLA) synthesized from natural raw materials with graphite nanoplates (GNP), which represent a new type of composite materials based on biodegradable polymers, were obtained by solid-phase method under the action of shear deformations. The porosity of composites was evaluated and their electrical and mechanical properties were studied. The effect of UV radiation on the molecular weight and molecular weight distribution of PLA in PLA-GNP composites of different compositions was investigated using the method of excision chromatography (EC), and the effect of the GNP nanofiller content on the change of their mechanical characteristics in the process of radiation was shown.

Effect of Na2SiO3/NaOH rate and natural zeolite content on basalt fiber reinforced eco-efficient slag-based geopolymer mortar synthesis

Considering that industrial wastes such as granulated blast furnace slag (GBFS) and fly ash (FA) will be released less or more in the future, developing geopolymer composites with natural pozzolans is a critical issue today. In this study, geopolymer composites with different SS (sodium silicate)/SH (sodium hydroxide) rates (2.0, 2.5 and 3.0) were produced by NZ reinforcement at 5%, 10% and 15%, and their physicomechanical, transport, high-temperature resistance, microstructure, carbon footprint and cost features were investigated. Geopolymer composites had been heat-cured for 8 h at 80 °C. The porosity of geopolymer composites varies between 5.2 and 7.2%, while their water absorption is between 3.4 and 6.9%. The dry unit weight of all geopolymer composites is less than 2300 kg/m3. The compressive strength of the geopolymer composite with an SS/SH rate of 3 and an NZ rate of 5% was about 75 MPa, and the compressive strength of the geopolymer composite with an SS/SH rate of 2 and an NZ rate of 15% was about 40 MPa. The capillary water absorption value of geopolymer composites is generally less than 1 kg/m2. While the compressive strength of geopolymer composites exposed to 600 °C ranged from 21.2 to 40.5 MPa, using 5% and 10% NZ generally improved the high-temperature resistance. The carbon emission of geopolymer composites was between 391.4 and 400.8 kgCO2/kg, while the cost increased only slightly with increasing NZ content. As a result, NZ content of 10% when the SS/SH rate is 2.5 and NZ content of 5% when the SS/SH rate is 3 improves many features of geopolymer composites.

Wire-arc additive manufacturing of TiB/Ti6Al4V composites using Ti-TiB2 cored wire: processing, microstructure and mechanical properties

ABSTRACT A novel wire-arc additive manufacturing (WAAM) process utilising titanium flux-cored wire (FCW) containing TiB2, Al60V40 and Ti6Al4V powders was proposed for fabricating TiB/Ti6Al4V composites. The FCW exhibited the capability in customising the composition of TiB/Ti6Al4V composites from hypoeutectic to hypereutectic by tailoring the proportion of TiB2 in blended powders. The comprehensive influence of TiB2 content on molten pool flow, compositional homogeneity and porosity of as-printed composites was attributed to the reduction of melt flowability, driven by viscosity escalation. It was unravelled the porosity was the intrinsic deficiency for the FCW-WAAM process, originating from the gases within FCW, while the interlayered TiB clusters were caused by the lagging melt of TiB2 powders. Due to directional solidification, TiB whiskers possessed a large aspect ratio and were partial to upward growth in hypoeutectic composites, which enhanced the load transfer strengthening. However, the porosity degraded the ductility of composites and caused the variation in mechanical performance.

Preparation and Characterization of Hydroxyapatite Based Composite Material via Cold Sintering Process

This study focuses on the synthesis of hydroxyapatite (HA) from bovine bones through calcination and subsequent combination with Polyvinyl Alcohol (PVA) using the Cold Sintering Process (CSP). The CSP, operating at lower temperatures than conventional methods, aims to preserve the bioactivity and biocompatibility of HA, crucial for biomedical applications. The research investigates the influence of HA composition, sintering temperature, and PVA content on the porosity and compressive strength of the HA-PVA composite. The Hydroxyapatite powder, obtained from calcinated bovine bones, exhibits irregular shapes and sizes with a maximum grain size of 10µm, confirmed by SEM analysis. XRD analysis validates the successful production of Hydroxyapatite, showcasing characteristic peaks. The HA/PVA composite's XRD pattern indicates the dominance of HA, with PVA present as well. The study produces 27 specimens through the CSP, varying HA composition and sintering temperature. Porosity increases with higher HA content and sintering temperature, attributed to the role of PVA in binding HA particles. Compressive strength rises with increased HA content, emphasizing HA's role in enhancing mechanical strength. The presence of porosity is mitigated by a strong bond between HA and PVA, contributing to structural integrity. This research provides insights into tailoring HA-PVA materials for biomedical applications, considering controlled porosity and mechanical strength. The CSP, with its unique advantages, emerges as a promising method for developing customized materials to meet diverse biomedical needs.

Micro- and macro- mechanical properties of an Al2O3/Al2O3 ceramic matrix composite after thermal aging at 1400 °C

The evolution mechanism of mechanical properties at elevated temperature is particularly crucial to the oxide/oxide composites. In this work, an Al2O3/Al2O3 ceramic matrix composite was prepared by laminating with high solid content slurry. The microstructure, micro- and macro- mechanical properties of the composites before and after thermal aging at 1400 °C were examined. The density and porosity of the original composite were ∼2.60 g/cm3 and ∼27.2 %, respectively. The sintering phenomenon of matrix in the composite after thermal aging was clearly visible, resulting in the matrix modulus increased by 83.5 % and the interfacial shear strength increased by 154.9 % compared with those of the original composite. The fundamental mechanics theory of composites stated that the significant increase of interfacial shear strength was the main reason that the flexural strength retention ratio of the composite decreased to ∼55 % after thermal aging.

Adaptation to appropriate sub-freezing temperatures through reduction of mycelial porosity and alteration of cell wall composition in Stropharia rugosoannulata

Sub-zero temperatures are avoided for storing mushrooms due to freeze damage. Stropharia rugosoannulata (S. rugosoannulata) often encounter such low temperatures prior to harvest. To preserve S. rugosoannulata, sub-freezing was studied at −2 °C, −6 °C, and −10 °C. The mechanism that caused the differences in the quality was analyzed from the perspective of water distribution and microstructure. The results revealed that at −2 ℃, S. rugosoannulata achieved a firmness and flavor that was comparable to that of the fresh samples. Water migration was observed at −2 ℃. However, at this temperature, S. rugosoannulata exhibited a lower drip loss compared to the fresh samples, and there was no significant variation in the malondialdehyde (MDA) and the electrolyte leakage rate (EL). Despite the swelling of the cells, the mycelial porosity decreased and the cell wall protein and water-soluble polysaccharide content increased to acclimate to the low temperature. In summary, the results of this study imply that it is possible to store S. rugosoannulata at suitable sub-freezing temperatures.

Effect of lubricant functional groups on tribological properties of epoxy/graphene composites

AbstractThe functional group in the molecular chain of lubricants is a key factor for a boundary lubricating film, which can further enhance the friction performance by interfacial tribochemistry. In this paper, the tribological behavior of epoxy/graphene (EP/Gra) composites was investigated through varying lubrication conditions, including dry friction, or different lubricants (such as water, hexadecane, oleylamine, and oleic acid). The porosity and Shore hardness (SHD) of the EP composites were significantly improved by the addition of graphene. Results showed that the porosity of the EP/0.75 wt.% Gra composites was reduced by 75.6% and their SHD increased by 5.4 compared with the EP/0.05 wt.% Gra composites. The average coefficient of friction (COF) of the composites was reduced by at least 27.3% under dry friction conditions. For water as lubricant, the EP/0.5 wt.% Gra composite exhibited the lowest COF (0.0455). The EP/0.75 wt.% Gra composite displayed the lowest COF (0.0466) when hexadecane acted as lubricant. By contrast, EP/0.05 wt.% Gra showed the lowest COF (0.0389) with oleylamine as lubricant, and the EP/0.25 wt.% Gra composites gave the lowest COF (0.0433) under oleic acid. The amine group of oleylamine reacted with the EP group to form a hydroxyl group, resulting in a polymer with low friction adhered to the friction interface. Simultaneously, the EP group reacted with the carboxyl group, forming a network of hydrogen bonds with graphene, which reduced the shear stress on the friction interface. Therefore, the functional groups of lubricants have a vital influence on the tribological properties of frictional composites, which may provide a new approach to solving the problem of wear.

Facile construction of porous epoxy resin/geopolymer composites using red mud and slag by well‐distributed dual‐blending

AbstractPorous geopolymer composite (E51) reinforced by E51 epoxy resin was prepared by well‐distributed dual‐blending using red mud, metakaolin, and slag as raw materials. The effects of E51 content on microstructure, porosity, mechanical properties, and thermal insulation properties of the porous composites were investigated. The addition of E51 changed the setting time and viscosity of the slurry with high content of solid wastes (80%), which play an important role in the formation of pores during the direct foaming process. The addition of E51 had great influence on the porous properties of geopolymer composites, which in turn affected their compressive strength (0.19–1.44 MPa) and thermal conductivity (0.09–0.12 W/mK). The addition of E51 enabled the production of geopolymer composites in a rather large range of total porosity (67.3–81.1 vol%), with an optimal sample possessing a total porosity of up to 78.7 vol%, a thermal conductivity of 0.086 W/mK, and a compression strength of 0.47 MPa.

Local defect resonance and nonlinearity of porosity air bubbles in solids

Acoustics of bubbles is quite developed field mainly due to multiple cavitation-related ultrasonic applications in liquids. New applications, which require detailed studies of ultrasound encounter with bubble in solid materials, have become apparent recently and are concerned with detectability of porosity in advanced solid materials based on layered technology, like composite and additive manufactured structures. To elucidate the transition from liquids to solids the present paper starts from theoretical similarity between both and proceeds to experimental study of the resonance acoustic effects of air bubbles in epoxy resin. The LDR frequencies are shown to be reciprocal to the bubble radius so that the latter can be evaluated if the frequency is known. The bubbles excited at the LDR frequencies and their subharmonics (superharmonic resonance) manifest extraordinary wide higher harmonic spectra that implies a nonlinear means for nondestructive testing of porosity in composites and other materials.

Leveraging Vision Transformers for Detecting Porosity in Wind Energy Composites

The structural robustness and operational efficiency of wind turbine rotor blades are crucial for the overall effectiveness of wind energy systems, often constructed with fiber-reinforced polymers (FRPs) and adhesives. However, porosity within these materials poses a significant threat, weakening structural strength and effectiveness. Air pockets lead to stress concentration points, reducing load-carrying capacity and elevating the risk of blade failure, especially under dynamic wind loads. Manual detection of these air pockets is laborious, necessitating automated inspection techniques. Advanced imaging technologies, such as computed tomography (CT) scanning and deep learning, hold promise for identifying and quantifying porosity in FRPs and adhesives, reducing labor while enhancing accuracy. The study introduces a transformer-based model for porosity detection, departing from convolution-based methods, emphasizing the incorporation of global context throughout the network. Leveraging Vision Transformer (ViT) framework advances, the model is applied to porosity segmentation in wind energy blades, showing promising results with limited datasets. The prospect of using larger datasets suggests potential for a versatile solution in segmenting porosity or voids in various wind energy blade composites, including adhesives.