Mechanical behaviour and microstructural characterization of 3D four‐directional braided SiO2f/SiO2 composites

In this paper, SiO_2f/SiO₂ composites reinforced by 3D four‐directional braided quartz preform were prepared by the silica sol‐infiltration‐sintering method in a relatively low sintering temperature (450 °C). To characterize the mechanical properties of the composites, mechanical testing was carried out under various loading conditions, including tensile, flexural and shear loading. The microstructure and the fracture behaviour of the 3D four‐directional braided SiO_2f/SiO₂ composites were studied. The tensile strength, flexural strength and the in‐plane shear strength were 30.8 MPa, 64.0 MPa and 22.0 MPa, respectively. The as‐fabricated composite exhibited highly nonlinear stress–strain behaviour under all the three types of loading. The tensile and flexural fracture mechanisms were fully discussed. The fracture mode of the 3D four‐directional braided SiO_2f/SiO₂ composite in the Iosipescu shear testing was based on a mixed mechanism because of the multi‐directivity of the composite. Owing to low sintered temperature, the fibre/matrix interfacial strength was weak. The SiO_2f/SiO₂ composites showed non‐catastrophic behaviour resulting from extensive fibre pull‐out during the failure process.     

The dispersion of SWCNTs treated by dispersing agents in glass fiber reinforced polymer composites

It is an obstacle issue for carbon nanotubes (CNTs) particularly for single-wall carbon nanotubes (SWCNTs) with nano-level dispersion in fiber reinforced polymer matrix composites. In this paper, the dispersing agents such as Volan and BYK-9076 were employed to treat SWCNTs to improve their dispersion in the glass fiber/epoxy (GF/EP) composites. The dispersing results of SWCNTs in composites were observed by scanning electron microscopy (SEM). Then the glass transition temperature (T_g) of these kinds of composites with treated and untreated SWCNTs were obtained by dynamic mechanical thermal analysis (DMTA). Moreover, the flexural tests were performed on these composites. Based on the experiment results, the dispersion of SWCNTs was improved and the flexural property of SWCNTs/GF/EP composite was enhanced too.     

Assessment of three oxide/oxide ceramic matrix composites: Mechanical performance and effects of heat treatments

Mechanical performance of three oxide/oxide ceramic matrix composites (CMCs) based on Nextel 610 fibers and SiOC, alumina, and mullite/SiOC matrices respectively, is evaluated herein. Tensile strength and stiffness of all materials decreased at 1000 °C and 1200 °C, probably because of degradation of fiber properties beyond 1000 °C. Microstructural changes in the composites during exposure at 1000 °C and 1200 °C for 50 h reduce their flexural strength, fracture toughness and work of fracture. A literature review regarding mechanical properties of several oxide/oxide CMCs revealed lower influence of fiber properties on composite strength compared with elastic modulus. The tested composites exhibit comparable stiffness and strength but higher fracture toughness compared with average values determined from a literature review. Considering CMCs with different compositions, we observed an interesting linear trend between strength and fracture toughness. The validity of the linear relationship between fracture strength and flexural toughness for CMCs is discussed.     

Development and analysis of high density poly ethylene (HDPE) nano SiO2 and wood powder reinforced polymer matrix hybrid nano composites

ABSTRACT

The Hybrid composites are the emerging materials which uses two or more reinforced particles or fibres simultaneously. As potential applications of the composites, wood reinforced thermoplastic composites are commercially attractive for high volume applications, but their properties can be enhanced by adding Nano SiO₂ particles. Wood powder and nano SiO₂ were mixed with high density polyethylene as matrix material. Wood powder with fixed 5 wt. % and Nano SiO₂ with varying weight % (3, 5, 7 wt. %) are reinforced in HDPE to manufacture composite materials by compression moulding process. Mechanical properties including tensile strength, flexural strength and Izod impact strength were evaluated and it was revealed that tensile strength and flexural strength were obtained maximum at 5 wt. % of Nano SiO₂ and impact strength was obtained maximum at 3 wt. % of Nano SiO₂.     

Fabrication of toughened Cf/SiC whisker composites and their mechanical properties

In this paper, dense short carbon fiber reinforced silicon carbide matrix composites had been fabricated by hot-pressed (HP) sintering using Al₂O₃ and La₂O₃ as sintering additives. The results showed that the combination of Al₂O₃ and La₂O₃ system was effective to promote densification of short cut carbon fiber reinforced silicon carbide composites (Cf/SiC). The whisker structure of silicon carbide was formed during the annealed treatment at 2023 K for 1 h. However, it was noted that this structure was not observed in the as-received HP material. The mechanism of forming whisker structure was not clear, but this kind of whisker structure was helpful to improve mechanical properties. The combination of grain bridging, crack deflection and whisker debonding would improve the fracture toughness of the Cf/SiC composites.     

Development of kenaf-glass reinforced unsaturated polyester hybrid composite for structural applications

The main aim of this paper is to develop kenaf-glass (KG) fibres reinforced unsaturated polyester hybrid composite on a source of green composite using sheet moulding compound process. Unsaturated polyester resin (UPE) and KG fibres in mat form were used at a ratio of 70:30 (by volume) with treated and untreated kenaf fibre. The kenaf fibre was treated with 6% sodium hydroxide (NaOH) diluted solution for 3 h using mercerization method. The hybrid composites were tested for flexural, tensile and Izod impact strength using ASTM D790-03, ASTM D618 and ASTM D256-04 standards respectively. The highest flexural, tensile and impact strength were obtained from treated kenaf with 15/15 v/v KG fibres reinforced UPE hybrid composite in this investigation.Scanning electron microscopy fractography showed fibre cracking, debonding and fibre pulled-out as the main fracture mode of composites and kenaf treated 15/15 v/v KG reinforced hybrid composite exhibited better interfacial bonding between the matrix and reinforcement compared to other combinations.     

Improvement of SiCf/SiC density by slurry infiltration and tape stacking

SiC fiber-reinforced SiC–matrix ceramic composites (SiC_f/SiC) were fabricated by vacuum infiltration of a SiC slurry into Tyranno™-SA grade-3 fabrics coated with a 200 nm-thick pyrolytic carbon (PyC) layer followed by hot pressing using a transient eutectic-phase. The density of the composite was improved using a special infiltration apparatus with a pressure gradient and alternating tape insertion between fabrics. Their overall properties were compared with those of monolithic SiC and composite containing chopped fibers. Although the density of the composites decreased with increasing fiber fraction, SiC_f/SiC containing 50 vol.% fibers had a density of 3.13 g/cm³, which is the highest reported thus far. The composites containing continuous fibers had a maximum flexural strength of 607 MPa and a step increase in the stress–displacement behavior during the three-point bending test due to fiber reinforcement, which was not observed in the monolith.     

Multiscale fiber reinforced composites based on a carbon nanofiber/epoxy nanophased polymer matrix: Synthesis, mechanical, and thermomechanical behavior

Vacuum assisted resin infusion molding (VARIM) was used to produce multiscale fiber reinforced composites (M-FRCs) based on carbon nanofibers dispersed in an epoxy resin. Flexural, interlaminar shear strength (ILSS) and thermomechanical tests are presented for the 0.1 wt% and 1 wt% M-FRCs and compared with the neat fiber reinforced composites (FRCs). Flexural strength and modulus increased (16–20%) and (23–26%), respectively for the 0.1 wt% and 1 wt% M-FRCs when compared to the neat FRCs. ILSS properties increased (6% and 25%) for the 0.1 wt% and 1 wt% M-FRCs, respectively when compared to neat FRCs. The glass transition temperatures (T_g) of both M-FRC samples were 25 °C higher than the neat FRC. Coefficients of thermal expansion (CTE) of the M-FRC samples improved compared to the neat FRC. The improved T_g and CTE properties in the M-FRC samples are attributed to synergistic interactions between the CNF/PNC matrix and glass fibers.     

Using response surface methodology for modeling and optimizing tensile and impact strength properties of fiber orientated quaternary hybrid nano composite

In current study, weight percentage of nano silica and nano clay and also fiber orientation have been chosen as independent variables and the affect of these variables on tensile and izod impact strength of epoxy/glass fiber/SiO₂/clay hybrid laminate composite has been investigated. Central composite design (CCD) which is subset of response surface methodology has been employed to present mathematical models as function of physical factors to predict tensile and impact behavior of new mentioned hybrid nano composite and also optimizing mentioned mechanical properties. Totally 20 experiments were designed with 6 replicates at center point. The maximum and minimum value of tensile strength were 450.90 MPa and 158.16 MPa which occurred in design levels 1 and 14 respectively, also the maximum and minimum of izod impact strength were 10.47 kJ/m² and 2.56 kJ/m² which occurred in design levels 13 and 14 respectively. The optimization results using optimization part of Minitab software showed that the best tensile strength was obtained 488.53 MPa and occurred in 3.5 wt% of nano silica, 1.1 wt% of nano clay and 9° of fiber orientation and after preparing and testing five samples average value of tensile strength was obtained about 480 MPa. Also the results showed that the best impact strength obtained from software was 11.35 kJ/m² and occurred in 4.03 wt% of nano clay, 5 wt% of nano silica and 0° of fiber orientation. The optimization results also showed that tensile and impact strength at optimum values improved up to 6.4% and 203.5% compared to level 1 and 14 and 6.02% and 303.6% compared to level 13 and 14 respectively. In addition, the fracture surface morphologies of the quaternary nano composites were investigated by scanning electron microscopy (SEM).     

Fabrication and oxidation resistance of silicon nitride fiber reinforced silica matrix wave-transparent composites

Wave-transparent ceramic matrix composites for the high temperature use should possess excellent oxidation resistance. In this work, Si_3N_(4f)/SiO_2 composites with different fiber content were fabricated by filament winding and sol gel method. The oxidation resistance was investigated by tracking the response of flexural strength to the testing temperature. The results show that the flexural strength and toughness of the composites with fiber content of over 37% can reach high levels at around 175.0 MPa and 6.2 MPa m1/2, respectively. After 1 h oxidation at 1100?C, the flexural strength drops a lot but can still reach 114.4 MPa, which is high enough to ensure the safety of structures. However, when the oxidation temperature rises to 1200–1400?C, the flexural strengths continue to fall to a relatively low level at 50.0–66.4 MPa. The degradation at high temperatures is caused by the combination of over strong interfacial bonding, the damage of fiber and the crystallization of silica matrix.     

Microstructure and mechanical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites were prepared by isothermal chemical vapor infiltration. The phase compositions, microstructures and mechanical properties of the composites were investigated. The results show that the multilayered matrix consists of alternate layers of PyC and β-SiC deposited on carbon fibers. The flexural strength and toughness of C/(PyC–SiC)_n composites with a density of 1.43 g/cm³ are 204.4 MPa and 3028 kJ/m³ respectively, which are 63.4% and 133.3% higher than those of carbon/carbon composites with a density of 1.75 g/cm³. The enhanced mechanical properties of C/(PyC–SiC)_n composites are attributed to the presence of multilayered (PyC–SiC)_n matrix. Cracks deflect and propagate at both fiber/matrix and PyC–SiC interfaces resulting in a step-like fracture mode, which is conducive to fracture energy dissipation. These results demonstrate that the C/(PyC–SiC)_n composite is a promising structural material with low density and high flexural strength and toughness.     

Hybrid effect of nanoparticles with carbon fibers on the mechanical and wear properties of polymer composites

Polyetheretherketone (PEEK) composites reinforced with carbon fibers (CFs) and nano-ZrO₂ particles were prepared by incorporating nanoparticles into PEEK/CF composites via twin-screw extrusion. The effects of nanoparticles on the mechanical and wear properties of the PEEK/CF composites were studied. The results showed that the incorporation of nano-ZrO₂ particles with carbon fiber could effectively enhance the tensile properties of the composites. The tensile strength and Young’s modulus of the composites increased with the increasing nano-ZrO₂ content. The enhancement effect of the particle was more significant in the hybrid reinforced composites. The compounding of the two fillers also remarkably improved the wear resistance of the composites under water condition especially under high pressures. It was revealed that the excellent wear resistance of the PEEK/CF/ZrO₂ composites was due to a synergy effect between the nano-ZrO₂ particles and CF. CF carried the majority of load during sliding process and prevented severe wear to the matrix. The incorporation of nano-ZrO₂ effectively inhibited the CF failures through reducing the stress concentration on the carbon fibers interface and the shear stress between two sliding surfaces. It was also indicated that the wear rates of the hybrid composites decreased with the increasing applied load and sliding distance under water lubrication. And low friction coefficient and low wear rate could be achieved at high sliding velocity.     

Tunable BT@SiO2 core@shell filler reinforced polymer composite with high breakdown strength and release energy density

Barium titanate@silicon dioxide (BT@SiO₂) core@shell fillers with an average diameter of 100 nm were prepared by a facile sol–gel synthesis. The thickness of SiO₂ shell can be easily tuned by varying different mass ratio of BT to tetraethyl orthosilicate (TEOS). Polyvinylidene fluoride (PVDF) based composite films reinforced by BT and BT@SiO₂ were fabricated via a solution casting method. The effects of SiO₂ shell on morphology structure, wettability, interfacial adhesion, dielectric, electrical and energy performances of composites were investigated. Compared with BT/PVDF, BT@SiO₂/PVDF composites show significantly increased breakdown strength due to enhanced interfacial adhesion and suppressed charge carrier conduction. Benefiting from enhanced breakdown strength and reduced remnant polarization induced by SiO₂ shell, BT@SiO₂/PVDF shows increased release energy density (energy density which can be fully discharged and applicable). Especially, BT@SiO₂/PVDF with SiO₂ thickness of 4 nm exhibits the highest release energy density of 1.08 J/cm³ under applied electric field of 145 kV/mm.     

表面改性对Cf/HA-PMMA混杂生物复合材料的结构及性能的影响

采用原位合成与溶液共混相结合的方法,制备了短切碳纤维(C_f) 增强纳米羟基磷灰石(HA)-聚甲基丙烯酸甲酯(PMMA)生物复合材料。重点研究了短切碳纤维和纳米HA粒子表面改性前后对C_f/HA-PMMA复合材料微观结构和力学性能的影响。采用XRD、FTIR、XPS和SEM等对纳米HA粒子、碳纤维和复合材料的组成结构及断面的微观形貌等进行测试和表征,使用万能材料试验机测试其弯曲、压缩性能。结果表明：经表面氧化的碳纤维和用卵磷脂改性后的纳米HA与PMMA基体的界面结合性明显得到改善;采用卵磷脂表面改性后的纳米HA及表面预氧化后的碳纤维制备的C_f/HA-PMMA复合材料的弯曲性能得到显著提高,与采用未表面改性纳米HA和未表面氧化碳纤维所制备的C_f/HA-PMMA复合材料相比,弯曲、压缩强度和弹性模量分别提高1.6倍、2倍和4.3倍。     

Hybridization effect on the mechanical properties of curaua/glass fiber composites

The aim of this paper was to evaluate the effect of hybridizing glass and curaua fibers on the mechanical properties of their composites. These composites were produced by hot compression molding, with distinct overall fiber volume fraction, being either pure curaua fiber, pure glass fiber or hybrid. The mechanical characterization was performed by tensile, flexural, short beam, Iosipescu and also nondestructive testing. From the obtained results, it was observed that the tensile strength and modulus increased with glass fiber incorporation and for higher overall fiber volume fraction (%V_f). The short beam strength increased up to %V_f of 30 vol.%, evidencing a maximum in terms of overall fiber/matrix interface and composite quality. Hybridization has been successfully applied to vegetable/synthetic fiber reinforced polyester composites in a way that the various properties responded satisfactorily to the incorporation of a third component.     

Biocomposites from Musa textilis and polypropylene: Evaluation of flexural properties and impact strength

Abaca (Musa textilis)-reinforced polypropylene composites have been prepared and their flexural mechanical properties studied. Due to their characteristic properties, M. textilis has a great economic importance and its fibers are used for specialty papers. Due to its high price and despite possessing very distinctive mechanical properties, to date abaca fibers had not been tested in fiber-reinforced composites. Analysis of materials prepared showed that, in spite of reduced interface adhesion, flexural properties of the PP composites increased linearly with fiber content up to 50 wt.%. Addition of a maleated polypropylene coupling agent still enhanced the stress transfer from the matrix to the reinforcement fiber. As a result, composites with improved flexural properties were obtained. The mechanical properties of matrix and reinforcing fiber were evaluated and used for modelling both the flexural strength and modulus of its composites. In addition, the impact strength of materials was evaluated. Comparison with mechanical properties of composites reinforced with fiberglass points out the potentiality of abaca-reinforced polypropylene composites as suitable substitutes in applications with low impact strength demands.     

Effects of Cf/C density on microstructure and properties of 3-D Cf/ZrC composites prepared by liquid metal infiltration

Three-dimensional braided carbon fiber-reinforced ZrC matrix composites, 3-D C_f/ZrC, were fabricated by Liquid metal infiltration process at 1200 °C. Porous carbon/carbon (C_f/C) composites with various densities were used as preforms, and the effects of C_f/C density on microstructure and properties of the 3-D C_f/ZrC composites were investigated. The results show that the composites are composed of carbon, ZrC and residual metal. Both microstructure and properties of the 3-D C_f/ZrC composites are apparently affected by C_f/C density. With increasing density of C_f/C preform, the density of 3-D C_f/ZrC composites decreases while the open porosity increases. The composites obtained from the C_f/C preform with a density of 1.12 g/cm³ have the best mechanical properties, with flexural strength of 286.2 ± 11.4 MPa, elastic modulus of 83.5 ± 6.8 GPa and fracture toughness of 9.2 ± 0.6 MPa m^1/2. The composites exhibit excellent ablation resistance, and the mass rate and the linear ablation rate under an oxyacetylene torch are as low as 5.1 ± 0.4 mg s⁻¹ and 1.1 ± 0.3 μm s⁻¹, respectively.     

Toughening effect of short carbon fibers in the ZrB2–ZrSi2 ceramic composites

The toughening effect of the short carbon fibers in the ZrB₂–ZrSi₂ ceramic composites were investigated, where the ZrB₂–ZrSi₂ ceramics without carbon fibers were used as the reference. The mechanical properties were evaluated by means of flexural and SENB tests, respectively. The microstructure was characterized by SEM equipped with EDS. The results found that the short carbon fibers were uniformly incorporated in the ZrB₂–ZrSi₂ matrix and the relative density was about 97.92%. The flexural strength of short carbon fiber-reinforced ZrB₂–ZrSi₂ composites is 437 MPa; the fracture toughness and the work of fracture are 6.89 MPa m^1/2 and 259 J/m², respectively, which increased significantly in comparing with composites without fibers. The microstructure analysis revealed that the improved fracture toughness could be attributed to the fiber bridging, the fiber–matrix interface debonding and the fiber pullout, which consumed more fracture energy during the fracture process.     

Oxidation behavior of 3D Hi–Nicalon/SiC composite

Oxidation behavior of a three dimensional (3D) Hi–Nicalon/SiC composite with CVD SiC coating was investigated in the simulated air using a thermogravimetric analysis (TGA) device. Below 1100 °C, the oxidation kinetics was controlled by gas diffusion through the defects in the SiC matrix and coating and resulted in the consumption of PyC interphase. The residual flexural strength did have not a remarkable fluctuation and the relationship between the residual strength to temperature and weight change to temperature of the 3D Hi–Nicalon/PyC/SiC composite indicated the same regularity. Above 1200 °C, the oxidation kinetics was controlled by oxygen diffusion through the SiO₂ scale formed on the SiC coating and matrix. And the residual flexural strength of the composites was governed by the strength degradation of the Hi–Nicalon fiber. After oxidation, the fracture displacement in flexural tests increased with the weight loss increasing and the fracture mode showed a non-brittle pattern.     

Fabrication and thermal conductivity of copper matrix composites reinforced with Mo2C or TiC coated graphite fibers

Graphite fiber reinforced Cu-based composites have good thermal conductivity, low coefficient of thermal expansion for heat sink applications. In these composites, the quality of interfacial bonding between the copper matrix and the graphite fibers has significant influence on the thermal properties of composites. In this study, two different carbide coatings (Mo₂C or TiC) were synthesized on graphite fiber to promote the interfacial bonding in composites. Fibers/Cu composites had been produced by spark plasma sintering process. The results showed that the densification, interfacial bonding and thermal conductivity of coated composites were improved distinctly compared to that of uncoated ones. The enhanced composites present 16–44% increase of thermal conductivity in X–Y plane. An original theoretical model was proposed to estimate the interface thermal resistance. The result showed that the interfacial thermal resistance was largely reduced by one order of magnitude with the introduction of carbide interlayer.