Optimization of mechanical properties of non-woven short sisal fibre-reinforced vinyl ester composite using factorial design and GA method

This work presents a systematic approach to evaluate and study the effect of process parameters on tensile, flexural and impact strength of untreated short sisal fibre-reinforced vinyl ester polymer-based composites and predicts the optimum properties of random natural fibre-reinforced composites. The natural fibre of sisal at lengths of 10, 30 and 50 mm and vinyl ester resin at loadings of 15, 30 and 45 (wt%) were prepared. The composite panel was then fabricated using hand lay method in cold process of size 180×160 mm². Samples were then cut from the panel and subjected to mechanical properties testing such as tensile, flexural and impact strengths. The average tensile strength ranges between 27·1 and 43·9 MPa. The flexural strength ranged between 26·9 and 49·5 MPa and the impact strength ranged between 16 and 93 J/m. The strength values were optimized using factorial design and genetic algorithm (GA) method. The predicted optimum process parameter values are in good agreement with the experimental results.     

两种双基体C/C复合材料的微观结构与力学性能

借助偏光显微镜、扫描电镜以及力学性能测试研究了两种双基体C/C复合材料的微观结构与力学性能。结果表明:基体碳在偏光显微镜下呈现出热解碳的光滑层组织,沥青碳的各向同性、镶嵌和流域组织。在SEM下普通沥青碳为"葡萄状"结构,中间相沥青碳为片层条带状结构。具有多层次界面结构的材料可以提高材料的弯曲强度,改善材料的断裂韧度,两种材料在载荷-位移曲线中载荷为台阶式下降,呈现出假塑性断裂特征。材料A和材料B的弯曲强度分别为206.68,243.66MPa,断裂韧度分别为8.06,9.66MPa·m1/2,材料B的弯曲强度、断裂韧度均优于材料A。     

Synthesis and properties of dental zirconia–leucite composites

The dental zirconia–leucite composites were synthesized by high temperature solid-state method using potash feldspar, potassium carbonate and zirconia as raw materials. The mechanical properties and the coefficient of thermal expansion (CTE) of the prepared zirconia–leucite composites were tested. The results show that the bending strength, the fracture toughness and the metal–ceramic bonding strength of the prepared samples are about 110 MPa, 3·5 MPa/m^1/2 and 45 MPa, respectively. The CTE was about 13·73×10^–6 °C^–1 and close to that of Ni–Cr dental alloy (14·0×10^–6 °C^–1). The results indicate that the introduction of zirconia is beneficial to the improvement in the mechanical properties and CTE adjustment of porcelain material. The clinical application of the zirconia–leucite composites with good metal–ceramic bonding strength in the dental restoration could be envisioned.     

聚合物浸渍裂解法制备C/C-ZrC复合材料及其性能

本文以低密度C/C复合材料为坯体,有机锆聚合物为前驱体,采用聚合物浸渍裂解法(PIP)制备C/C-ZrC复合材料,并对其微观结构、力学性能、烧蚀性能以及烧蚀机理进行了研究。结果表明ZrC在材料内分布均匀,密度为2.05g·cm~(-3)的C/C-ZrC复合材料其弯曲强度为89.70MPa,呈脆性断裂。经氢-氧焰烧蚀150s后其线烧蚀率为-2.2×10~(-3)mm·s~(-1),质量烧蚀率为-1.0×10-3g·s~(-1),远低于密度为1.86g·cm~(-3)的C/C复合材料(线烧蚀率:4.4×10~(-3) mm·s~(-1),质量烧蚀率:7.5×10~(-4)g·s~(-1));在烧蚀的过程中,ZrC表现出优先氧化,同时生成的ZrO_2阻挡层能有效阻挡热量的传递和氧气的渗透,提高了材料的抗烧蚀性能。     

薄层化碳布缝合碳/碳复合材料制备与性能

为获得高性能、低成本碳/碳复合材料,以商用级T700大丝束薄层化碳纤维展宽平纹布和航空航天级T300小丝束碳纤维缎纹布为原材料制备缝合预制体,采用化学气相沉积工艺方法制备了一系列缝合碳/碳复合材料,对材料的气相致密化特征、微观结构特征和力学性能进行了测试与分析。研究结果表明,碳布规格和缝合间距对材料气相致密化效果和力学性能有较大影响。当选用T700-12 K、展宽16 mm大丝束纤维编织的面密度100 g/m2的平纹布为原材料且预制体缝合间距为5 mm×5 mm时,制备的密度为1.781 g/cm3薄层化碳布缝合碳/碳复合材料表现出良好的气相沉积工艺适应性和优异的力学性能,材料拉伸强度、压缩强度、弯曲强度和层间剪切强度高达342.9 MPa、285.5 MPa、328.4 MPa和15.2 MPa。通过商用级大丝束薄层化碳纤维的应用,大幅降低了高性能碳/碳复合材料的原材料成本,且制备的碳/碳复合材料性能达到了国际先进水平。      

三维碳化硅/碳化硅陶瓷基编织体复合材料

采用化学气相浸渗法（CVI）,制备出三维Hi-Nicalon SiC/SiC陶瓷基纺织体复合材料,经30hCVI致密化处理后,复合材料的密度达到2．5g.cm^-3。所研制的三维SiC/SiC复合材料不仅具有较高的强度,而且表现出优异的韧性和类似金属材料非灾难性的断裂特征,复合材料的主要功能力学性能指标为：弯曲强度860MPa,断裂位移1．2mm,断裂韧性41．5MPa.m^1/2,断裂功28．1kJ.m^-2,冲击韧性360.0kJ.m^-2。     

Surface characteristics and fatigue performance of warm shot peened wrought magnesium alloy Mg–9Gd–2Y

Abstract

The surface characteristics and fatigue performance of the warm shot peened Mg–9Gd–2Y alloys were investigated. Compared to conventional shot peening (SP) at room temperature, warm shot peening (WSP) at 240°C induces higher subsurface hardening and larger maximum compressive residual stress in the subsurface of the specimens. The optimum Almen intensity of WSP is 0·15 mm N, whereas it is 0·10 mm N for SP. The main reason is that the surface of warm shot peened specimen is more plastically deformed but less damaged at the optimum Almen intensity due to the increase in plastic deformation ability of the tested alloys at elevated temperature. The fatigue strength of the tested alloy at 10⁷ cycles is increased from 125 to 175 MPa by optimum SP and to 185 MPa by optimum WSP.     

Preparation of TiC reinforced steel composites and their characterisation

Abstract

Carbide reinforced steel composites are useful in extensive wear resistance applications. Titanium carbide reinforced steel composites have been prepared by dissolving a TiC rich Fe–TiC master alloy in a liquid steel. The composites have been characterised by optical microscopy, energy dispersive X-ray scanning electron microscope analysis, image analysis, and X-ray diffraction studies. Tensile strength measurements showed that the ultimate tensile strengths varied between 790 and 880 MPa for composites containing 0·7–0·34 wt-%Ti. Some composites show better wear resistance properties in comparison with low alloy steels.     

响应面法优化CCMS / WG 复合包装膜制备工艺的研究

利用响应面分析法研究了CCMS/ WG 复合包装膜优化制备工艺,考察了谷朊粉、交联羧甲基玉米淀粉和丙三醇用量对CCMS/ WG 复合包装膜综合性能评定值的影响,得出了复合包装膜优化制备工艺的回归模型。结果表明,当谷朊粉用量为0. 65 g,交联羧甲基玉米淀粉用量为4. 77 g,丙三醇用量为1. 05 g 时,CCMS/ WG 复合包装膜性能最佳,其厚度为0. 096 mm,拉伸强度为20. 3 MPa,断裂伸长率为39. 1%,单位冲击破损能量为5. 73 J/ mm,水蒸气透过系数为3. 58 g·mm/ (m2 ·d·kPa),透氧系数为0. 69×10-15 cm3 ·cm / (m2 ·s·Pa),透光率为37. 6%,复合包装膜综合性能评定值最高达15. 73。     

石墨表面镀Si对石墨/Al复合材料热物理性能的影响

研究了石墨粒径及表面镀Si处理对石墨/Al复合材料热物理性能的影响。结果表明:在盐浴过程中石墨表面形成了SiC层,这不仅增强了石墨-Si/Al复合材料的界面结合力,而且抑制了Al4C3相的产生。随着石墨鳞片体积分数从50%增加到70%,复合材料X-Y方向的热导率从492 W/(m·K)增加到654 W/(m·K),而且体积分数为50%的镀Si石墨/Al复合材料抗弯强度达到了81 MPa,相比未镀覆的提高了53%,是理想的定向导热电子封装材料。随着石墨粒径从500μm减小到150μm,石墨-Si/Al复合材料X-Y面方向的热导率由654 W/(m·K)降低到445 W/(m·K),但Z方向的热导率和复合材料抗弯强度变化不明显。     

Microstructure and mechanical properties of BAS/SiC composites sintered by spark plasma sintering

High-density BAS/SiC composites were obtained from β-SiC starting powder by the spark plasma sintering technique. Various physical properties of the BAS/SiC composites were investigated in detail, such as densification, phase analysis, microstructures and mechanical properties. The results demonstrated that the relative density of the BAS/SiC composites reached over 99.4% at 1900 °C. The SiC grains were uniformly distributed in the continuous BAS matrix which is probably because of complete infiltration of the SiC particles in BAS liquid-phase formed during sintering. The pull-out of SiC particles, crack deflection and bridging were observed as the major toughening mechanism. The flexural strength and fracture toughness of the BAS/SiC composites sintered at 1900 °C were up to 560 MPa and 7.0 MPa·m^1/2, respectively.     

Effect of C/C preform density on microstructure and mechanical properties of C/C–SiC composites prepared by alloyed reactive melt infiltration

Abstract

Low cost C/C–SiC composites were prepared by alloyed reactive melt infiltration. Effects of the density of C/C preforms on mechanical properties and microstructure of the C/C–SiC composites are reviewed. The results show that with increasing the density of C/C preforms, the flexural strength of the resulting composites increases, while the density of the composites decreases. The flexural strength can reach 341 MPa for the composite produced from the C/C preform of 1·3 g cm^?3. The phases in the composites produced from low density C/C preforms are Si, SiC, ZrSi₂ and carbon, while no Si phase is found in the composites with high density C/C preforms. Furthermore, the mechanism of the microstructure evolution of the C/C–SiC composites is proposed.     

Preparation and characterization of ZrB2-SiC ultra-high temperature ceramics by microwave sintering

ZrB₂-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification of ZrB₂-SiC composites and almost fully dense ZrB₂-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of the ZrB₂-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m^1/2, respectively.     

石墨表面TiC涂层对高定向石墨/Cu复合材料热导率和抗弯强度的影响

以高温盐浴法对天然鳞片石墨粉体(GF)进行表面TiC镀层处理,然后采用真空热压烧结法制备TiCGF/Cu复合材料,研究了粉体表面涂层和GF体积分数对复合材料微观结构、热导率及抗弯强度的影响。系列测试结果表明:随着GF体积分数的降低以及粉体表面TiC镀层的形成,TiC-GF/Cu复合材料平行于GF片层方向的热导率有所降低,抗弯强度有所提升。其中在GF的体积分数占TiC-GF/Cu复合材料70%时,这种变化最为明显,平行于GF片层方向的TiC-GF/Cu复合材料热导率下降幅度最大,从676W/(m·K)下降到526 W/(m·K)。同时,TiC-GF/Cu复合材料的微观结构进一步说明,GF表面的TiC涂层对GF/Cu复合材料的断裂模型起着重要的作用。     

Preparation and characterization of ZrB<Subscript>2</Subscript>-SiC ultra-high temperature ceramics by microwave sintering

ZrB₂-SiC ultra-high temperature ceramic composites reinforced by nano-SiC whiskers and SiC particles were prepared by microwave sintering at 1850°C. XRD and SEM techniques were used to characterize the sintered samples. It was found that microwave sintering can promote the densification of the composites at lower temperatures. The addition of SiC also improved the densification of ZrB₂-SiC composites and almost fully dense ZrB₂-SiC composites were obtained when the amount of SiC increased up to 30vol.%. Flexural strength and fracture toughness of the ZrB₂-SiC composites were also enhanced; the maximum strength and toughness reached 625 MPa and 7.18 MPa·m^1/2, respectively.     

Preparation and characterization of silicon nitride-silicon carbide composites

Silicon nitride-silicon carbide (Si₃N₄-SiC) composites were prepared by varying the percentage of silicon nitride at temperatures of 1350 to 1450°C. The mechanical and thermal properties of these composites were determined. The modulus of rupture of the composites increases with increase of temperature whereas the thermal expansion decreases. Composites with 10% and 50% Si₃N₄ have modulus of rupture of 49 and 86 MPa at 1400°C and thermal expansion coefficients (25°–1000°C) of 4·4 × 10⁻⁶ and 3·2 × 10⁻⁶°C⁻¹ respectively.     

Effect of hydrothermal pretreatment on the properties of moso bamboo particles reinforced polyvinyl chloride composites

Bamboo plastic composites were fabricated from polyvinyl chloride (PVC) and moso bamboo particles (BP). In order to improve the interfacial interaction between BP and PVC, as well as to obtain composites with outstanding mechanical properties, the roles of hydrothermal treating temperatures (120, 140, 160, 180, 200, 220, 240, 260 and 280 °C) on characteristics of BP and properties of the PVC/BP composites were investigated. Results showed that hydrothermal modification improved the surface property of BP and wiped off hemicelluloses and pectin. A uniform dispersion of BP in PVC matrix was observed by SEM with hydrothermal treatment. Tensile strength, tensile modulus and flexural strength of the composites achieved their maximal values of 15.79 MPa, 6702.26 MPa and 39.57 MPa, respectively, with 180 °C hydrothermal treatment. The highest values of elongation at break and flexural deformation were 3.75 ± 0.20% with 200 °C hydrothermal modification and 36.22 ± 2.70% with 140 °C hydrothermal modification, respectively. Due to more decomposition of hemicellulose, the composites expressed lower water absorption and higher thermal stability when the hydrothermal treating temperature exceed 160 °C.     

Dynamic response for porous epoxy resin matrix composites filled with iron powder at different strain rates and constitutive relationships

The porous epoxy resin matrix composites filled with iron powder referenced in this work consist of both ferromagnetic base materials and porous materials, which have properties of electromagnetic shielding and impact energy absorbing. Aimed at the dynamic compressive properties of the composites at different high strain rates, two materials were studied: the first is Fe/ER-17 with 40% porosity and 17% mass fraction of iron powder; the other is Fe/ER-90 with 10% porosity and 90% mass fraction of iron powder. The investigation results showed: (1) the quasi-static compressive failure strengths of the two composites are much lower than their dynamic compressive failure strengths; (2) Fe/ER-17 exhibits obvious characteristics of a porous material at high strain rates (≥3000/s), whereas FE/ER-90 exhibits a visco-elastic response at all strain rates; (3) Fe/ER-17 and Fe/ER-90 show a strain rate hardening effect on dynamic yield strengths. The dynamic yield strengths of Fe/ER-17 change from 19.23 MPa at a strain rate of 850/s to 30.97 MPa at a strain rate of 6000/s, and dynamic yield strengths of Fe/ER-90 change from 114.93 MPa at a strain rate of 700/s to 136.95 MPa at a strain rate of 3600/s. The hardening effect of dynamic yield strengths is linear with the strain rate, and their linear strain rate hardening factors are very small (10 × 10^?4 and 0.6 × 10^?4, respectively). A constitutive model of series form for a porous material and a modified ZWT constitutive model for a visco-elastic material were adopted for Fe/ER-17 and Fe/ER-90, respectively. The constitutive relationships developed captured the dynamic compressive characteristics of the two materials.     

碳纤维-Ni/尼龙66复合材料的制备与性能表征

为制备低电阻率的尼龙66基复合材料,以碳纤维和镍粉(Ni)填充尼龙66制备碳纤维-Ni/尼龙66高导电复合材料。研究填料表面改性和含量对碳纤维-Ni/尼龙66复合材料导电性能和力学性能的影响。结果表明:KH550改性碳纤维和Ni有助于降低碳纤维-Ni/尼龙66复合材料的电阻率。碳纤维-Ni/尼龙66复合材料的电阻率随着碳纤维和Ni含量的增加而减小,且碳纤维和Ni填充尼龙66的导电逾渗阈值均为20wt%,此时制备的碳纤维-Ni/尼龙66复合材料的电阻率为455Ω·cm,熔融温度为202.2℃。碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度随着碳纤维或Ni含量的增加而先增大后减小。当Ni含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度在碳纤维含量分别为20wt%和10wt%时达到最大值,分别为98MPa和70 MPa;当碳纤维含量为20wt%时,碳纤维-Ni/尼龙66复合材料的弯曲强度和拉伸强度则在Ni含量为30wt%和20wt%时达到最大值,分别为120 MPa和67 MPa。     

Fabrication and properties of SiNO continuous fiber reinforced BN wave-transparent composites

SiNO continuous fiber reinforced boron nitride (BN) wave-transparent composites (SiNO _f /BN) have been fabricated by a precursor infiltration pyrolysis (PIP) method using borazine as the precursor. The densification behavior, microstructures, mechanical properties, and dielectric properties of the composites have been investigated. After four PIP cycles, the density of the composites had increased from 1.1 g·cm^?3 to 1.81 g·cm^?3. A flexural strength of 128.9 MPa and an elastic modulus of 23.5 GPa were achieved. The obtained composites have relatively high density and the fracture faces show distinct fiber pull-out and interface de-bonding features. The dielectric properties of the SiNO _f /BN composites, including the dielectric constant of 3.61 and the dielectric loss angle tangent of 5.7×10^?3, are excellent for application as wave-transparent materials.