热压成型与冷压成型粉煤灰基试块特性研究

试验研究了热压(120℃、20MPa)与冷压(20℃、20MPa)成型方法对粉煤灰基试块抗压强度的影响。采用XRD、FT-IR、SEM、TGA分析手段,分别对两种试块的矿物组成、成键结构、微观形貌和热失重特性进行对比分析。结果表明,热压成型试块的抗压强度是冷压成型的2.5倍;与冷压成型试块相比,热压试块的XRD谱图中检测出更加明显的硅铝酸盐水化产物衍射峰;FT-IR谱图中的[SiO_2]吸收峰强弱为:粉煤灰原样冷压成型试块热压成型试块;热压试块SEM图片中的颗粒痕迹更加模糊,有更为大量的絮状物微观形貌,且能谱中的钙硅原子比(Ca/Si)约为0.7,该比值为冷压型块的近1/3;热压和冷压试块的自由水失重率分别为3.0%和4.5%,硅铝酸盐水化物失重率分别为1.2%和0.3%。说明粉煤灰基热压成型试块较冷压成型试块具有更加明显和更加深刻的水化反应。     

骨料对工业废渣陶粒混凝土性能的影响

研究了不同等级陶粒骨料及砂率对陶粒混凝土性能的影响。结果表明:采用800级,600级陶粒为骨料制备工业废渣陶粒混凝土,随骨料用量增加,容重降低有限,但会导致强度和比强度大幅度降低。采用较高等级骨料制备轻混凝土时,通过增加骨料用量降低容重不可取。以400级陶粒为骨料,随骨料用量增加容重有明显降低趋势,但强度变化不大。与骨料等级和用量相比,砂率对不同等级废渣陶粒混凝土的强度和容重的影响要小得多。骨料用量及砂率对废渣陶粒混凝土的软化系数影响不明显,但骨料等级的影响显著,骨料越轻、陶粒混凝土容重越小,软化系数越大。     

复配阻燃剂对硬质聚氨酯泡沫塑料阻燃性能的影响

研究了甲基膦酸二甲酯(DMMP)、尿素(UC)、磷酸三乙酯(TEP)单独添加及复配使用对硬质聚氨酯泡沫塑料(RPUF)阻燃性能的影响。结果表明,UC与DMMP及TEP复配是气相和凝聚相双相协同阻燃机理的复合阻燃剂;UC与DMMP,UC与TEP复配阻燃RPUF,可达到垂直燃烧分级V0级;UC／DMMP复配使用,UC和DMMP含量分别为15%和25%时,其阻燃RPUF的氧指数最高,为27.3%,阻燃性能优于UC／TEP复配阻燃RPUF;复配阻燃RPUF的压缩强度比单独填充UC体系高,呈现协同作用。     

碳纤维增强轻质耐压复合材料的制备及性能研究

通过模压工艺制备了短切碳纤维/空心玻璃微珠(K46)/环氧树脂复合材料,并对复合材料的断面形貌、密度、抗压强度和吸水率进行了研究。研究结果表明,随着碳纤维含量的增加,复合材料密度变化较小,抗压强度上升,当碳纤维含量为4%时,抗压强度最大,微珠含量分别为50%、55%、60%的复合材料的抗压强度分别为68.9MPa、65.1MPa、57.2MPa;随碳纤维含量的增加,复合材料饱和吸水率下降,当碳纤维含量为4%时,微珠含量为55%、60%的复合材料达到最小饱和吸水率,分别为0.81%、1.15%。     

THE DEVELOPMENT OF A MANDREL PEEL TEST FOR THE MEASUREMENT OF ADHESIVE FRACTURE TOUGHNESS OF EPOXY-METAL LAMINATES

A mandrel peel test is established for measuring the adhesive fracture toughness of a metal/rubber-toughened epoxy laminate system. By adopting an energy balance analysis it is possible to determine directly both adhesive fracture toughness and plastic work in bending the peel arm around the mandrel. The suitability of the procedure is examined for various types of metal peel arms, which are classified in terms of their ability to deform plastically during the test. The plastic work is also predicted theoretically, and comparisons are made between the measured and calculated values. The fracture energies determined from the mandrel tests are compared with those obtained from 90° fixed-arm peel tests. For the calculations of plastic work in bending in the fixed arm test, various options are used when modelling the tensile stress-strain behaviour of the peel arm material. In addition, the adhesive layer thickness is considered in terms of its influence on the calculation of adhesive fracture toughness.     

激光烧结制备塑料功能件

采用选择性激光烧结技术(SLS)直接制备高强度塑料功能件，考察了激光功率、扫描速度、单层层厚等工艺参数及无机填料对成型件强度的影响。在激光功率10W、扫描速度1500mm／s、单层层厚0．15mm的较佳烧结工艺参数下，制备了拉伸强度、弯曲强度、冲击强度分别达到44MPa、50．8MPa、37．214／m^2的SLS成型件。随着填料用量的增加，烧结件的拉伸强度略有增加，冲击强度下降，在填料用量为40％(质量含量，下同)时弯曲强度达到最大值。     

Strength of Some Grades of Steel and Armco Iron under Shock Compression and Rarefaction at Pressures of 2 – 200 GPa

This paper reports results from a comparative experimental study of the dynamic strength of St. 20 and 09G2S steels (which are of interest as structural materials for the loadbearing casings of explosionproof chambers) under shock compression and tension (spalling) at shockfront pressures of 1–5 GPa and strain rates of 10³ – 10⁴ sec^-1. A comparative analysis is performed of the obtained and available data on the dynamic yield point and spall strength of St. 3, St. 20, 09G2S, 12Kh18N10T, ÉI712, 30KhGSA, 36NKhTYu, KhVG, and 35Kh3NM steels and armco iron, whose strengths and ductilities under static loading conditions differ by a factor of up to five. Experiments are described in which spheres of St. 3, St. 20, 12Kh18N10T, and 30KhGSA steels with markedly different strengths and ductilities are loaded by a convergent quasispherical shock wave with a pressure at the center of 200 GPa and a strain rate of 10⁵sec^-1.     

Effect of Cr3C2 on Valence-Electron Structure and Plasticity of Rim Phase in Ti(C,N)-Based Cermets

Based on the empirical electron theory of solids and molecules, the valence-electron structure (VES) of the rim phase in Ti(C,N)-based cermets was calculated, and the relationship between the VES and plasticity was determined. The results indicated that the plasticity of the rim phase in a Ti(C,N)-based cermet could be defined using the sum of the n _a values for the covalent bonds, and that chromium dissolution in the rim phase improved the plasticity of the rim phase. Moreover, a series of experiments showed that adding Cr₂C₃ to a typical Ti(C,N)-based cermet strengthened the interface. Based on those results, a Ti(C,N)-based cermet with added Cr₃C₂ was manufactured; the new cermet had more than twice the transverse rupture strength of a typical cermet.     

Effect of SiO2 content on the microstructure,mechanical and dielectric properties of Si3N4 ceramics

This study investigated the effect of SiO₂ content in the Y₂O₃–Al₂O₃ additive system on the microstructure, mechanical and dielectric properties of silicon nitride (Si₃N₄) ceramics. The total sintering additive content was fixed at 8 wt% and the amount of SiO₂ was varied from 0 to 7 wt%. The crystalline phases of the samples were determined by X-ray diffraction analysis. Complete α-to-β transformation of the Si₃N₄ occurred during sintering of all of the samples, which indicated that the phase transformation was unaffected by the SiO₂ content. However, the microstructures showed that the aspect ratio of the β-Si₃N₄ grains decreased and the residual porosity increased with increasing SiO₂ content. Additionally, the flexural strength and the dielectric constant decreased with increasing SiO₂ content because of the residual porosity and the formation of the Si₂N₂O phase via a reaction of SiO₂ with Si₃N₄.     

Mechanical and optical properties of spark plasma sintered transparent Y2O3 ceramics

Commercial Y₂O₃ nanopowder was used to fabricate transparent Y₂O₃ ceramics by spark plasma sintering under the pressure of 100 MPa for 20 min with the heating rate of 100 °C/min. The microstructures, mechanical and optical properties of the Y₂O₃ ceramics sintered at different temperatures were investigated in detail. Densification occurred up to a sintering temperature of 1500 °C, and above 1500 °C, rapid grain growth and pore growth occurred. The highest relative density of 99.58% and the minimum average grain size of 0.58±0.11 µm were obtained at 1500 °C. The flexural strength, hardness and fracture toughness of the optimal spark plasma sintered Y₂O₃ ceramic were 122 MPa, 7.60 GPa and 2.06 MPa.m^1/2, respectively. The Y₂O₃ ceramic sintered at 1500 °C had the in-line transmission of about 11–54% and 80% in the wavelength range of 400–800 nm and 3–5 µm, respectively.