Good Compressive Properties Research Articles

Carbon fibers assisted 3D N-doped graphene aerogel on excellent adsorption capacity and mechanical property

In order to improve structural stability of aerogel, supported N-doped reduced graphene oxide aerogels are prepared by introducing fiber materials (biomass cellulose and carbon fibers) via self-assembly method. Thereinto, N-doped carbon fibers/reduced graphene oxide aerogel exhibits ultra-light density (7.19 mg/cm3), high specific surface area (329.6 m2/g), excellent superhydrophobicity, high adsorption capacity (206.38 g/g), which is superior to most reported cellulose aerogels. Moreover, regardless of multiple heating or squeezing cycles, adsorption capacity of this aerogel is also more than 90 %. In addition, N-doped carbon fibers/reduced graphene oxide aerogel shows good mechanical compressive property and thermal stability, which contributes to high-valued utilization in practice.

Light-weight concrete with artificial aggregate manufactured from plastic waste

The inclusion of an artificial aggregate manufactured using plastic waste to develop a light-weight concrete was studied. Five separate mixes were designed, progressively increasing the amount of artificial aggregate and measuring the fresh and hardened concrete properties, and it was found that the slump and density of the concrete decreased as the amount of artificial aggregate in the concrete increased. Both the compressive and the tensile Then the mix that was most suitable to the requirements of the study in terms of density and compressive strength was chosen for further investigation in stage two. Fifteen percent of the natural aggregate by weight was replaced in this optimal mix, which equals more than thirty-seven percent of the volume given the lower density of the manufactured aggregate compared to natural aggregate. A larger number of specimens and more detailed testing was undertaken for stage two when compared to stage one, including establishing the compressive stress–strain relationship and the modulus of elasticity of the newly developed concrete mix. The results indicated that plastic aggregates manufactured following shredding, palletisation and extrusion processes can be used to obtain a lightweight concrete (1800 kg/m3) while having relatively good compressive strength properties (20 MPa at 28 days). These results were higher than other results previously reported in the literature on the replacement of coarse aggregate with plastic, but were marginally lower than results reported in the literature for studies where fine aggregate was replaced with plastic. It was concluded that the concrete mix reported herein can be used for a wide spectrum of applications such as non-structural facades and sound barriers for highways. Further research is required to investigate the durability of concrete with the artificial aggregate included in the mix, especially if the product is to be subjected to wear and tear such as in driveways or warehouse slabs.

Microstructure and properties of aluminium-high entropy alloy composites fabricated by mechanical alloying and spark plasma sintering

High-quality aluminium-CuZrNiAlTiW high-entropy alloy (HEA) composites were fabricated by mechanical alloying and spark plasma sintering (SPS). The microstructures, mechanical properties and corrosion resistance of these composites were investigated. The as-milled HEA powders consist of a single body-centered cubic (BCC) solid solution phase. Besides the Al and BCC phases, the NiAl-rich B2 and WAl12 phases were in-situ formed in the sintered composites due to the large concentration gradient of Al between the matrix and HEA reinforcement. Compared to the SPS-ed Al bulk, the Al-HEA composites show higher microhardness and strength, caused by the dispersion strengthening of BCC phase and precipitation strengthening of B2 and WAl12 phases, as well as the serious lattice distortion. The core-shell microstructure in the composite with 10 vol.% HEA (Al10) contributes to its good compression properties with high yield strength and good plasticity. The Al20 composite exhibits a high fracture strength of 544 MPa, owing to the uniform size and distribution of BCC particles. Additionally, W and Ni could improve the stability of protective layer, and thus enhance the pitting resistance of the Al-HEA composites in seawater. The Al10 composite possesses the relatively positive corrosion potential and low corrosion rate, revealing a good general corrosion resistance.

Low Tortuous, Highly Conductive, and High-Areal-Capacity Battery Electrodes Enabled by Through-thickness Aligned Carbon Fiber Framework.

Thick electrode with high-areal-capacity is a practical and promising strategy to increase the energy density of batteries, but development toward thick electrode is limited by the electrochemical performance, mechanical properties, and manufacturing approaches. In this work, we overcome these limitations and report an ultrathick electrode structure, called fiber-aligned thick or FAT electrode, which offers a novel electrode design and a scalable manufacturing strategy for high-areal-capacity battery electrodes. The FAT electrode uses aligned carbon fibers to construct a through-thickness fiber-aligned electrode structure with features of high electrode material loading, low tortuosity, high electrical and thermal conductivity, and good compression property. The low tortuosity of FAT electrode enables fast electrolyte infusion and rapid electron/ion transport, exhibiting a higher capacity retention and lower charge transfer resistance than conventional slurry-casted thick electrode design.

Manufactory and Properties of Poly(<i>p</i>-Phenylenebenzobisoxazole) Aerogels Prepared by a Simple Freeze-Drying Procedure

Aerogels based on organic high performance fibers have been attracted great attention due to its excellent thermal and mechanical properties. Here, PBO nanofiber aerogel were prepared from the super-fiber PBO through a top-down process with a sol-gel process and a simple freeze-drying process, followed by thermal cross-linking. The prepared aerogel has a small volume shrinkage, a high specific surface area of 168.9 m2 /g and a small pore diameter of 1.356 nm. Because of its 3D porous structure, it results in a low density of 6 to 30 mg/cm3 and a high porosity (98%). The aerogel retains the molecular structure of PBO at the same time, which gives it initial thermal decomposition temperature up to 500 °C and a superior fire-retardant capability. PBO aerogel possesses good compressive properties with a yield stress of 0.44MPa at 80% strain and an elasticity modulus of 1.98 MPa which is higher than SiO2 and cellulose aerogel reported.

The effect of Cr additions and oxidation on densification, microstructure, phase constituents and mechanical properties of TiAlCr alloys produced by SPS

Ternary Ti-47.5Al-(1–3)Cr (at. %) and reference quaternary Ti-48Al-2Cr-2Nb (at. %) titanium aluminide alloys were processed from elemental powders utilizing mechanical milling, mechanical alloying and spark plasma sintering. The effect of Cr additions and oxidation on the densification behavior, microstructure, phase constituents and mechanical properties of the sintered alloys were investigated. The results point out that Cr additions and the presence of O play a significant role on the densification process i.e., compaction rates and sintering temperatures of the alloys. The microstructure and phase constituents of the alloys were studied based on historical experimental and theoretical data. Furthermore, the compression properties and fracture morphologies at experimental temperatures were found to be determined by a combination of response to densification, microstructural and phase evolutions effects as opposed to composition only. High additions of Cr coupled with the high level of oxidation impaired the compression properties of the ternary alloys, resulting in a 9% decrease in peak stress at higher testing temperatures. At these temperatures, the quaternary alloy showed good compression properties compared to the ternary alloys.

Establishing Test Methods to Gauge Attitudes to Full-Culm Bamboo as a Building Material in Housing: Initial Survey Results From Bangsar, Kuala Lumpur, Malaysia and Tanjung, Lombok, Indonesia

Tropical developing economies are some of the most vulnerable societies to natural disasters, and by 2050, some 50% of the world's population will live in the tropics. Tropical developing economies already have a shortage of housing which lacks structural quality, durability and is considered non-adequate. Tropical developing economies have an opportunity to utilize locally sourced lightweight natural materials such as bamboo. Tropical countries are substantial producers of bamboo. Bamboo is sustainable, relatively strong, with good tensile and compressive properties. It is a material that can be worked with simple tools and has the potential to be grown locally on a village or even a family scale. Many tropical countries grow an abundance of tropical woody bamboos which can also absorb CO2 at a fast rate, and their fibrous roots can reduce the effects of flooding and landslides. Bamboo can also stabilize slopes to tackle the effects of deforestation affecting many tropical countries including Malaysia and Indonesia which saw some of the highest rates of forest loss between 2000 and 2017. If we are to increase the use of sustainable materials, then we should look to non- or marginally-engineered building techniques to ensure that the most affordable form of bamboo, ‘full culm bamboo’, is enfranchised. Full-culm bamboo also has a low carbon footprint when sourced locally. A commonly claimed barrier to bamboo being more widely used in construction is the fact is that in many developing economies there is a perception of bamboo as the ‘poor man’s timber’ and this can negatively influence the choice of materials used in adequate housing. The reasons these perceptions are prevalent in contemporary society has not been fully explored. This paper documents an initial survey which was carried out using the Likert Scale in Kuala Lumpur (KL), Malaysia and Tanjung, Lombok, Indonesia in June 2019. The aim of this paper is to analyse the initial study design, sampling strategy, data collection instruments and procedures, and identify the main study variables. The outcome of this is to propose a test methodology to quantify a magnitude of the perception of bamboo as the ‘poor man’s timber’ and if surveying is a good means of learning about how we may be able to address negative societal attitudes to bamboo. By understanding societal attitudes to the material of bamboo in construction, we as architects can employ the information to address these concerns and design for the use of materials such as bamboo. Architects can then through inclusive and community participatory design practices, develop adequate housing for urban areas, which is functional and aesthetically pleasing for residents to democratically choose.

Lightweight multifunctional polypropylene/carbon nanotubes/carbon black nanocomposite foams with segregated structure, ultralow percolation threshold and enhanced electromagnetic interference shielding performance

Lightweight polypropylene (PP) composite materials are preferred to other polymer-matrix composites, in the conductive and electromagnetic interference (EMI) shielding industries, due to their pronounced advantages. However, facile and high-efficiency fabrication of low-density multifunctional PP composite foams, for EMI shielding, remains a challenge. In this study, we fabricated lightweight polypropylene (PP)/carbon nanotubes (CNTs)/carbon black (CB) nanocomposite foams by combining high-speed mechanical mixing, structural manipulation and solid-state supercritical carbon dioxide (ScCO2) foaming. Due to the “brick and mud” dense structure formed by high-speed mechanical mixing and structure manipulation, we obtained a low density (0.082–0.101 g/cm3) after solid-state ScCO2 foaming in the nanocomposite foams containing hybrid nanofiller (1:1). Specifically, segregated synergistic conductive networks were observed in the nanocomposite foams. With such networks, the nanocomposite foams containing hybrid nanofiller (1:1) exhibited the best electrical properties (~6.67 × 10−3 S/cm at 5 wt% hybrid filler), and the lowest percolation threshold (0.016 vol%) compared with other systems. Moreover, the nanocomposite foams containing 5 wt% hybrid nanofiller (1:1) showed enhanced specific EMI shielding effectiveness (~72.23 dB·cm3/g at X band), and absorption-dominated shielding characteristic. Furthermore, we found a good thermal insulation performance (61.2 mW·m−1·K−1) and compressive properties (~37.1 MPa·g−1·cm3 at 50% strain). Overall, our work provides a simple and versatile strategy for fabricating high-performance PP-based nanocomposite foams. These foams present lightweight, ultra-low percolation threshold, high strength, thermal insulation and good EMI shielding properties.

Hydrogel-Based Gas Sensors for NO2 and NH3.

In this study, an innovative gas sensing mechanism, self-responsive sensing mechanism, has been detected in the supramolecular hydrogel-based sensors. The self-responsive ability of as-fabricated hydrogel-based sensors to the target gas (e.g., NO2, NH3, etc.) is determined by three synergetic supramolecular interactions, namely, hydrogen bonding, molecule crystallization, and electrostatic interactions existing in hydroxyls, poly(vinyl alcohol) (PVA) crystallization, and poly(ionic liquids) of the intrinsic hydrogel networks, respectively. On account of unique synergetic supramolecular interactions, the sensors not only exhibit a rapid, reversible, and reproducible response but also show good tensile and compressive properties and excellent recovery property. The results demonstrate the potential of the self-responsive sensing mechanism as a pathway to realize a new generation of highly responsive hydrogel-based gas sensors.

Characterization of sandstones of eastern Slovakia

Abstract The main building material in the past was stone. Geological composition influenced the choice and type of building stone, which was used for the construction of the buildings. In eastern Slovakia sandstone was used in large quantities for its good compressive properties, good workability and aesthetic appearance. Sandstones were used for decorative but mainly construction purposes. The most common problem in historical stone structures is missing waterproofing insulation. Transmission and storage parameters of heat and water of historical materials are needed to assess the moisture condition of buildings and to correctly design measures. In this article are presented researches of sandstones properties abroad and locations of selected sandstones of eastern Slovakia, which were used for construction of historical buildings.

Fabrication of bimodal open-porous poly (butylene succinate)/cellulose nanocrystals composite scaffolds for tissue engineering application

The design of porous tissue engineering scaffold with multiscale open-pore architecture (i.e., bimodal structure) promotes cell attachment and growth, which facilitates nutrient and oxygen diffusion. In this study, a porous poly (butylene succinate) (PBS)/cellulose nanocrystals (CNCs) composite scaffold with a well-defined controllable bimodal open-pore interconnected structure was successfully fabricated. The bimodal open-porous scaffold architecture was designed by synergistic control of temperature variation and a two-step depressurization in a supercritical carbon dioxide (Sc-CO2) foaming process. The microstructure and properties of the bimodal open-porous PBS/CNCs scaffold, such as morphology, open porosity, hydrophilic and degradation performance, and mechanical compression properties, were analyzed. In the experiments, the scaffold with unimodal pore structure was used for comparison. The results showed that the bimodal open-porous PBS5 scaffold displayed a well-defined bimodal open-pore structure composed of large pore (~68.9 μm in diameter) and small pore (~11.0 μm in diameter), with a high open porosity (~95.2%). In addition, the scaffolds exhibited good mechanical compressive properties (compressive strength of 2.76 MPa at 50% strain), hydrophilicity (water contact angle of 71.7 °C) and in vitro degradation rate. Moreover, in vitro biocompatibility was determined with NIH-3T3 fibroblast cells using MTT assay and live/dead cell viability assay. Results indicated that the obtained bimodal open-porous scaffolds had a good biocompatibility and the viability of cells grown on the scaffolds reached up to 98% after 7th day of culture. Therefore, our work provides new insights into the use of biodegradable polymeric composite scaffolds with bimodal open-pore structure and balanced properties in tissue engineering.

Mechanical properties of lightweight 316L stainless steel lattice structures fabricated by selective laser melting

The performance of advanced and lightweight 316L stainless steel lattice structures fabricated by selective laser melting (SLM) was investigated using a range of laser energy densities (LED). A unique tetrakaidecahedron cell type was designed to construct a periodic lattice structure, which was compared with two common lattice structures of different unit cell topologies and deformation behaviors using mechanical property and quasi-static energy absorption. It was found that tetrakaidecahedron structure deserved good compressive properties and energy absorption capabilities. The fabricated strut morphology and internal porosity were investigated using confocal and scanning electron microscopy to correlate with the compressive properties of the structure. The porosity was found to increase firstly and then fluctuate smoothly with increasing LED, similar to yield strength. The yield strength and compression modulus were not independent of porosity, indicating that further improvements can be achieved by SLM process optimization. Meanwhile, nonlinear finite element analysis was used to analyze their compressive response and fracture behavior. Our results highlighted that a high performing unit cell geometry can be used for energy absorption and lightweight manufacturing applications of lattice structures.

Design, synthesis, and properties of novel amino-ester and amino-ester-alcohol polymer backbones

Simultaneous polymerization of polyacrylic, polyamine, and polyepoxy monomers offers the potential to generate a novel polymer backbone with new and beneficial properties. The Aza-Michael addition of amines to acrylates is fast and exothermic and can thus increase the rate of amine epoxy reactions producing poly amino-ester-alcohol polymer backbones. The polymerization is shown to be remarkably tolerant of organic and aqueous solvent interactions. The resultant polymers are transparent and possess good compressive and thermal properties that are amenable to polymer design. The polymers of this article are predicated on efficient polymerization of the acrylate and amine functionalized monomers, so preliminary rules for their polymerization are provided as a preamble to the hybrid polymers with polyepoxy monomers.

Microstructural evolution and compression property of a novel γʹ-strengthened directionally solidified CoNi-base superalloy

The microstructural evolution and compression property of a novel γʹ-strengthened CoNi-base superalloy have been investigated. The directionally solidified CoNi-base superalloy possesses a lower density of 9.03 g/cm3 and a higher γʹ solvus temperature of 1166 °C, compared with those of the Co–Al–W-base superalloys with high level of W element. After aging at 900–1100 °C, the alloy displays stable γ/γʹ two-phase microstructure with high volume fraction of the γʹ phase, and without detrimental topologically close-packed (TCP) phase. The CoNi-base superalloy shows good compression property. In the process of compression, the alloy exhibits positive temperature dependence of the 0.2% flow stress above 600 °C. With increasing temperature, the alloy displays a maximum of 0.2% flow stress of 607 MPa at 850 °C. The major deformation mechanisms of the CoNi-base alloy are pairs of a/2<110>-type dislocations shearing γʹ precipitates from room temperature to 850 °C and unpaired dislocations bypassing the γʹ precipitates above the peak temperature of 850 °C. In this alloy, high content of Ni improves the γʹ solvus temperature and microstructural stability, which leads to a good compression property at high temperatures.

PDMS-Based Capacitive Pressure Sensor for Flexible Transparent Electronics

We propose a flexible pressure sensor based on polydimethylsiloxane (PDMS) and transparent electrodes. The transmittance of the total device is 82% and the minimum bending radius is 18 mm. Besides, the effect of annealing temperature on the mechanical properties of PDMS is reported here. The results show that the PDMS film under lower annealing temperature of 80°C has good compression property but poor dynamic response. While for higher temperatures, the compression property of PDMS films significantly reduced. The best compromise of annealing temperature between compression property and dynamic response is found for PDMS film of about 110°C. The pressure sensor under 110°C curing temperature shows a good sensitivity of 0.025 kPa−1 and robust response property. The device shows a promising route for future intelligent transparent sensing applications.

Foaming and Compressive Properties of A359/SiC&lt;sub&gt;P&lt;/sub&gt; Metal Matrix Composites

In this work, a commercial MMC (A359-20% SiCP) was remelted, diluted to different particle contents (5 to 20 vol. %), and foamed at a fixed temperature using titanium hydride. In general, excellent foamability could be obtained for all SiC contents. Foam stability (retention of expansion), on the other hand, depended on SiC content. Remelting and diluting procedures also influenced the foam stability on account of varied oxide contents generated upon impeller stirring. The foam quality, in terms of cell wall integrity, improved with increasing SiC content. Despite the defect levels, good compression properties were obtained in these foams, which are close to model predictions. Overall, this system is very promising for producing good quality foams by melt processing technique.

Formation of cuboidal B2 nanoprecipitates and microstructural evolution in the body-centered-cubic Al0.7NiCoFe1.5Cr1.5 high-entropy alloy

The present work primarily investigated the formation of coherent cuboidal B2 nanoprecipitates in body-centered-cubic (BCC) Al0.7NiCoFe1.5Cr1.5 high-entropy alloy (HEA) and its microstructural evolution with temperature. Alloy samples were prepared by suction-cast processing and then heat-treated at different temperatures of 673–1273 K for 2 h, respectively. It was found that the coherent microstructure with cuboidal B2 nanoprecipitates in BCC matrix can be formed in the as-cast state and be stabilized up to 823 K with a particle size of 60–120 nm. Even after being heat-treated at 773 K for 1080 h, the cuboidal B2 nanoprecipitates were still stabilized without any coarsening. It was due to a moderate lattice misfit (ε = 0.4–0.5%) that favored the formation of coherent cuboidal B2 nanoprecipitates, resulting in a good compressive mechanical property. Meanwhile, the Fe/Cr-rich σ phase appeared and dominated after the treatment at 873 K, causing heavy brittleness. The face-centered-cubic (FCC) phase appeared at 973 K and became dominant above 1173 K, which softened the alloy. In addition, the thermodynamic calculations were carried out for further understanding the microstructural evolution with temperature. The influence of microstructures constituted by different phases on mechanical properties was studied, in which high strength caused by cuboidal B2 nanoprecipitates was discussed in light of the precipitation-strengthening mechanism.

Communication-Aware Waveform Design for MIMO Radar With Good Transmit Beampattern

Designing the radar waveform, which ensures spectral compatibility with the communication systems, is known to be challenging. In addition to having the desirable transmitter efficiency, it is also anticipated to share the good pulse compression property of the reference waveform. In this paper, we investigate the problem of waveform design for multiple-input multiple-output radar with good transmit beampattern under certain practical constraints (e.g., peak to average power ratio and similarity constraints) in coexistence with communication systems. The waveform is designed by minimizing a weighted summation of the beampattern integrated sidelobe-to-mainlobe ratio and waveform energy over the space-frequency bands. Since the resulting problem is NP-hard, two approximated primal-dual algorithms based on the alternating direction method of multipliers algorithm are proposed. Concretely, the proposed algorithms update the primal variable by minimizing the linearized and quadratic approximations of the augmented Lagrangian function of the original problem, respectively. The closed-form solution of each primal variable is provided. Moreover, both the convergence and computational complexities of these two algorithms are discussed. Numerical simulations are provided to demonstrate the effectiveness of the proposed approaches.

An ultra-lightweight recyclable carbon aerogel from bleached softwood kraft pulp for efficient oil and organic absorption

A carbon aerogel with porous structure was synthesized from bleached softwood kraft pulp (BSKP) via eco-friendly freezing-drying and carbonization steps. The obtained carbon aerogel exhibited a low density of 25.5 mg cm−3, high hydrophobicity with a water contact angle of 139.7° and good compressive properties. When used as an absorbent, the carbon aerogel could absorb 14 to 26 times its own weight in organic solvent and oil. Furthermore, the aerogel could be easily recovered and regenerated through burning, pressure recycling, and squeezing, and a high adsorption efficiency was maintained over a number of cycles. The use of biomass as a raw material, together with the excellent hydrophobicity and recyclability, make this carbon aerogel a suitable adsorbent for a variety of practical separation requirements.

Preparation and properties of three dimensional graphene/phenolic resin composites via in-situ polymerization in graphene hydrogels

Three dimensional graphene/phenolic resin (3DGP) composites were synthesized via in-situ polymerization in graphene hydrogels (GHs). The water in the GH was perfectly replaced with resole resin due to the infiltration of resole resin into the GH and the evaporation of water from the GH by heating in the appropriate temperature. The 3DGP composite was obtained successfully by in-situ polymerization. The prepared composite can retain the complete 3D network structure to achieve good dispersion of graphene sheets forming 3D conducting network in polymer. The mechanical and electrical properties were measured, and the results showed that the composite possessed good electrical conductivity and compressive property. The compressive strength of 3DGP composite (441.11 MPa) increased by 14.24% compared with that of pure phenolic resin. In addition, the electrical conductivity of 3DGP composite reached 2.73 S/cm with a graphene loading of 2.15 wt% due to the 3D interconnected structure.