Search

In the engineering context of island blowing and reclamation, the modification effect of graphene oxide on the mechanical properties of calcareous sand cement mortar is analyzed, and the modification mechanism is elaborated from the microscopic perspective. The experimental results show that graphene oxide promotes the hydration reaction of calcareous sand-cement mortar, and the amount of graphene oxide doping significantly affects the modification effect. The modification effect gradually enhances when the graphene oxide doping amount increases from 0 to 0.06%, and the unconfined compressive strength of the specimens increases up to 36.96%. However, the modification effect decreases when the doping amount is 0.1% compared with that of 0.06%. The results of scanning electron micrographs and energy dispersive spectrometer tests indicate that the addition of graphene oxide accelerates the agglomeration of C-S-H gel produced by the reaction of calcareous sand cement mortar, forming a dense mesh-like structure, which enhances the unconfined compressive strength of the specimens. The oxygen-containing functional groups in graphene oxide are interlinked with the free Ca2+ in the hydration products, eventually producing crystals with the chemical formula (3CaO·Al2O3·CaSO4·12H2O). The generation of crystals leads to the reduction of pores inside the cement mortar and improves the specimen's compression strength. [ABSTRACT FROM AUTHOR]

Alkali-activated slag and fly ash (FA)-blended seawater sea sand concrete (AASC) is a new type of concrete produced without Portland cement or river sand. The advantages of utilising industrial waste and marine resources are that they are not only eco-friendly but cost-saving. This study aimed to investigate the properties of AASC exposed to elevated temperatures. Slag and FA were activated using NaOH and water glass solutions for mixing AASC. Heating and compressive tests were conducted to analyse the thermal and compressive properties of the AASC. The results showed that the AASC with higher FA content (Type II) had fewer flaky structures and more integral interfacial transition zones than the other type of AASC (Type I) after exposure to 600 °C. Type I AASC had better mechanical performance at temperatures below 400 °C but was inferior to Type II AASC beyond 600 °C. A compressive constitutive model was proposed for AASC. [ABSTRACT FROM AUTHOR]

The great efforts to reduce the environmental impact of composite materials by replacing synthetic components with bio-based ones are involving also sandwich structures. Agglomerated cork proved to be a feasible alternative to traditional polymeric foam as core material. Sandwich structures are extremely prone to impact events which can cause the direct exposure of the core material to the external environment making fundamental to know how its out-of-plane properties can be influenced by external factors such as sunlight and rain. The present work assessed the effects of UV accelerated aging and freeze–thaw (FT) cycles on the compressive behavior of two agglomerated corks with different densities providing also a direct comparison with a traditional PVC foam. Agglomerated cork compressive properties increase when exposed to UV accelerated aging up to 600 h, determining an increase of 31 % and 9 % in the compressive modulus for the less dense and denser cork, respectively. No significant changes were observed for the synthetic foam. FT cycles on as-received specimens induce a decrease in cores compressive properties after 30-day cycling, with a reduction in compressive modulus of approximately 11 % for PVC foam and of 12 % and 11 % for the less dense and denser cork, respectively. [ABSTRACT FROM AUTHOR]

The present research is aimed at examining the changes in tensile and compressive properties of natural fiber-reinforced composites (NFRC) exposed to various humidity conditions; this is due to the fact that moisture content (MC) in fibers is generally assumed to be detrimental to composite performance. It was found that once moisture is exposed, compressive strength and strain of specimens would be higher than those of tensile, whereas modulus of elasticity would be lower. Due to increasing moisture content, although elongation in all tests was enhanced, tensile and compressive strength declined by 15% and modulus of elasticity decreased by 20%. In addition, Poisson's ratio for both compressive and tensile properties was nearly identical (0.33) in distinct moisture content. A new understanding of moisture's effects on mechanical behavior is presented in this study by finding an optimum point for exposing moisture to increase compressive and tensile strength. [ABSTRACT FROM AUTHOR]

A novel type of tubular structure with negative Poisson's ratio based on gyroid-type triply periodic minimal surfaces (TPMSs) is proposed in this study. This work is an attempt to design auxetic tubular structures based on TPMS. A series of auxetic tubular structures were designed and then fabricated using laser power bed fusion. Compressive behaviours of the fabricated auxetic tubular structures were investigated using experimental and numerical methods. To obtain optimal designs of tubular structures with controllable auxetic properties, the influence of several parameters were investigated comprehensively. Subsequently, several graded auxetic tubular structures were designed based on the parametric analysis and studied numerically. The mechanical properties of the tubular structures could be controlled effectively using the proposed approach. The proposed method can be used for guiding the design and optimisation of auxetic tubular structures, showing excellent potential for various applications such as biomedical devices, vehicle crashworthiness, and protective engineering. [ABSTRACT FROM AUTHOR]

Concrete with manufactured sand (MSC) requires adequate compressive properties, which may be caused by stone powder. This present study investigated the effect of different stone powder content (0%, 3%, 5%, 7%, 9% and 11%) on compressive properties of MSC. The properties of fresh MSC were evaluated by three tests, compressive strength, axial compressive strength and elastic modulus. Measure results showed that stone powder as part of fine aggregate replacement improved compressive properties of MSC. The content ranging from 5%–7% increased compressive strength. The content of 11% could greatly improve axial compressive strength. The elastic modulus had a slightly enhancement when the stone powder was within 9%. Predictive models were proposed for the prediction of long-term compressive strength of MSC. [ABSTRACT FROM AUTHOR]

Electron beam melted (EBM) Ti-6Al-4V functionally graded materials (FGM) with continuously graded densities are investigated for dimensional accuracy, compressive properties, fractography and build direction effect in comparison to uniform density counterparts of the same volume. It is found that FGMs exhibit progressive layer-by-layer deformation mode regardless of unit cell designs and build direction. This deformation behavior is highly favourable for uni-directional impact absorption applications compared to uniform density counterparts with random or diagonal failure. Overall, the EBM-built FGM exhibits superior energy absorption than counterparts of uniform density. Significant improvement in the quasi-elastic gradient and energy absorption is obtained by changing the build direction for specific designs. Compared with other FGM or uniform density lattice structures from the literature, the energy absorption of lattice structures with lower relative density could outperform those with higher relative density by changing the unit cell design or density profile. [ABSTRACT FROM AUTHOR]

3D-reticulated porous (3D-RP) SiC ceramic was fabricated by polymer sponge replica technique with SiC ceramic slurry (77 wt% solid content). Furthermore, pure alumina slurry and alumina slurry with Y2O3/CeO2 were used to fill up the triangle hollows in coated sponge by vacuum infiltration method respectively. The results show that the compressive strength of 3D-RP SiC ceramic, infiltrated by the alumina slurry or alumina slurry with Y2O3/CeO2, was significantly improved in comparison with those of non-infiltrated ones. Subsequently, 3D-RP SiC/Fe composite material was prepared successfully by casting technique. The microstructure and abrasive resistance of 3D-RP SiC/Fe composite materials based on the different 3D-RP SiC ceramics were discussed in detail. The results show that an excellent interface bonding between 3D-RP SiC ceramic and iron matrix formed and intermediate products not measured in the interface. Moreover, the abrasive resistance of SiC/Fe composite material, especially, 3D-RP SiC ceramics with addition of Y2O3/CeO2 and Ni respectively, is observably superior to that of gray cast iron. The wear mechanism of 3D-RP SiC/Fe composite material is predominantly oxidative wear and adhesive wear, together with partial abrasive wear if under a high load. [ABSTRACT FROM AUTHOR]

Wire diameter, sintering parameter, and porosity have great influences on porous structures and compressive properties of the stainless steel porous twisted wire materials with 30–92% porosities. Finer wires, higher sintering temperature, and longer sintering time will lead to narrower pore-size distributions, more compact porous structures, and stronger compressive yield strength. A random pore model and a twisted wire framework model are put forward to simulate the compressive process. The compressive deformation mechanism is a continuous densification process. The simulated and experimental stress-strain curves all exhibit elastic stage, plastic yield platform stage, and final densification stage. [ABSTRACT FROM PUBLISHER]

In this paper, various aluminium foam/piezoelectric damping composites were prepared by using magnesium niobate, lead zirconate titanate, conductive carbon black, aluminium foam and epoxy resin as raw materials, and the influences of piezoelectric phase content and surface treatment on compressive performance of the prepared composites were investigated. Experimental results showed that the compressive strength of the composites could be effectively improved by using higher content of zirconate titanate or modifying the surface of zirconate titanate to optimise interfacial properties of the composites. [ABSTRACT FROM AUTHOR]

Compressive strength is one of the most important considerations when designing fibre-reinforced polymer (FRP) composite structures. This property is obtained from the stress-strain response of FRP specimen loaded in compression. Compression tests using shear-loading or end-loading methods usually cause premature failure of the specimens or failure near to/in tabs. Therefore, the purpose of this study is to design a test rig for compression testing that combines both shear- and end-loading methods. Computer-Aided Three-Dimensional Interactive Application software was used to design parts and the whole system of the test rig, namely UiTM dual guide compression test fixture. The performance of the test rig was evaluated by conducting compression tests on woven carbon, glass and Kevlar fibre-reinforced polymer composites samples. It was observed that all specimens failed within the specimen gauge length, implying that the tests were successful. [ABSTRACT FROM AUTHOR]

The compressive behaviors of nanoclay-reinforced syntactic foams filled by ceramic microballoons are investigated. Eighteen different types of nano syntactic foams are fabricated with three different microballoons volume fraction, each containing six different weight fraction of nanoclay in their matrix. Quasi-static tests are carried out using an Instron 5500 machine test and Split Hopkinson Pressure Bar (SHPB) apparatus is used to perform the high strain rate tests. Also, scanning electron microscopy (SEM) is used to understand the fracture mechanisms and the microstructure of the tested specimens. [ABSTRACT FROM AUTHOR]

A large-dimensional bulk nanocrystalline phase-based Fe–Al–Cr alloy with 10 wt.% Cr, which was about 200 mm in diameter and 10 mm in thickness, was prepared by an aluminothermic reaction casting and followed annealing at 1000 °C. Microstructures of the alloy were investigated by optical microscope, electron probe microscope, scanning electron microscope attached with electron backscattered diffraction, X-ray diffraction and transmission electron microscope. The magnetization curves of the alloy were tested by Lake Shore 7410 vibrating sample magnetometer. Compressive properties of the alloy were tested. The results show the alloy was consisted of a Fe–Al–Cr nanocrystalline matrix, Cr7C3phase and contaminants in micrometre. Average grain size of the nanocrystalline matrix was 19 nm. Volume fraction of the Cr7C3phase in the alloy was about 4.5%. After annealing, the saturated intensity of magnetization and the specific magnetic susceptibility of the alloy increased slightly from 99 emu/g and 0.083 emu/g Oe to 104 emu/g and 0.113 emu/g Oe, respectively. Compressive strength of the alloy was 1200 MPa and much higher than that of the small-scale nanocrystalline alloy and alloy with grains in micrometre. [ABSTRACT FROM AUTHOR]

The present study investigates the electrical conductivity and dielectric properties of untreated and alkali-treated Roystonea regia natural fiber-reinforced epoxy composites at different frequencies along with compression and water absorption properties. Fiber was treated with 5% NaOH and characterized by chemical, thermogravimetric, tensile test, and SEM methods before and after alkali treatment. The interface between matrix and fiber was studied by SEM. Conductivity of alkali-treated fiber composites is lower than that of untreated fiber composites and increased with increase in frequency. The dielectric constant and loss tangent values of the composites were found to decrease after alkali treatment, and these values decreased with increase in frequency. Alkali-treated fiber composites showed improvements in compressive strength and water resistance when compared with untreated fiber composites. [ABSTRACT FROM AUTHOR]

By using the quantum molecular dynamics technique, the compression of C60, C60F60 and C60H60 molecules was simulated, and their electronic structures under compression were calculated. According to the obtained results, the compressive mechanical properties of the three molecules, as well as the effects of compressive deformation on their electronic structures, were discussed. It is shown that (1) the load support and energy-absorbing capabilities of the three molecules both have the order of C60F60 > C60H60 > C60, but their deformation support capability is comparable, and (2) with the increase of compressive strain, the three molecules become more chemically active, but under the same compressive strain, the C60F60 and C60H60 molecules have better chemical stability than the C60 molecule. [ABSTRACT FROM AUTHOR]

A series of oil gels based on 4-tert-butylstyrene (tBS) and ethylene-10 propylene-diene (EPDM) cross-linked with determined amount of divinylbenzene (DVB) was synthesized by suspension polymerization. Toluene (Tol), cyclohexane (Cyclohex), and their mixtures with different compositions were used as pore-forming diluents. The influence of diluent type, dosage, and composition on swelling 15 behaviors, compressive properties, effective cross-link density (ne), average molecular weight between cross-links (Mc), and polymer-solvent interaction parameter (v1) of oil gels was studied in this work. [ABSTRACT FROM AUTHOR]

Al-based composites reinforced by icosahedral (i-) Al59Cu25.5Fe12.5B3 quasicrystalline particles were prepared by solid-state sintering. It was found that Al diffusion from the matrix to the quasicrystalline particles induces phase transformation into the ω-Al7Cu2Fe tetragonal phase. In order to preserve the i phase, we used an oxidation pre-treatment of the particles and studied its influence on the kinetics of the phase transformation (Al + i → ω) as a function of temperature by high energy X-ray diffraction. The oxide layer acts as a barrier, reducing efficiently the diffusion of Al up to a sintering temperature of 823 K, allowing the control of the phases in the composites. The mechanical properties and the friction behaviour of the composites were investigated and show the negative influence of the oxide on the interface strength. [ABSTRACT FROM AUTHOR]

In this study, bio-foam composites are produced using short sisal fiber as the reinforcement and modified castor oil as the matrix, respectively. The foam composites with an average cell size of 200 μm possess properties similar to those of commercial polyurethane foams. The effects of fiber loading, fiber length and foam density on the compressive properties of the foam composites are reported in relation to the interfacial interaction. It is found that the addition of chopped sisal alters cell structure of the foam. Surface pre-treatment of sisal by alkali or silane coupling agent helps to improve the mechanical properties and interfacial adhesion. The exposure of the fibers to the gas cells of the foam reduces the effectiveness of interfacial effect, which is different from the case of conventional bulk composites. As a result, the reinforcing ability of sisal fibers becomes a function of fiber length and so on. [ABSTRACT FROM AUTHOR]

Phenolic resin has the excellent properties of fire resistance, low smoke production during burning, and a good balance between its cost and mechanical properties compared with other types of resin used in fire-resistant polymers (FRPs). If phenolic resin can be employed as a matrix of FRP, such FRP can have a higher fire safety factor which will be a desirable property in the structures of vessels and railway carriages. However, for the case of the resole type of phenolic resin, water formed from the condensation reaction remains in the matrix, and this water evaporates resulting in the formation of voids during the curing process. In order to develop a new type of phenolic composite that can overcome this weakness, we used a foam type of phenolic resin and glass fibers as the matrix and the reinforcement, respectively. We, then, developed a new pultrusion technique for the new phenolic foam composite and examined its mechanical properties and thermal conductivity. In this paper, we report a new technique to mold not only a phenolic foam composite but also a sandwich beam in which the phenolic foam composite as a core and a thin phenolic FRP layer as a faceplate are used. We also investigated the compressive strength and elastic modulus under high temperatures and compared the result with that at room temperature. Finally, we show that the compressive properties of the phenolic foam composite and the sandwich beam are stable at higher temperatures. [ABSTRACT FROM AUTHOR]

In this article, the compressive behavior and anisotropy of both open- and closed-cell aluminum foams under different heat treatments were examined. For the closed-cell A356/SiCp foam, due to the age-hardening effect, the yield strength of the heat-treated specimens was found to be more than 200% of that of the as-cast specimens. The yield strength of the foam in the transverse direction was however only slightly higher than that in the longitudinal direction, which may be related to the relatively spherical cell structure of the foam. For open-cell Al6061 foams, heat treatment results in a significant increase in yield strength and also changes the failure mode from ductile to brittle. The open-cell foam further demonstrates a strong anisotropy. The causes of such phenomena are discussed in the article. [ABSTRACT FROM AUTHOR]