硬聚氯乙烯厚样品的光分解-氧化反应之分布型式——Ⅰ.自然气候老化

用红外光谱等方法研究了R-PVC厚样品的自然气候老化历程,成功地测定了10微米以内表面层的化学变化。发现高的光分解-氧化速率发生在表面层,体层的氧化速率受氧扩散作用控制,反应程度随深度的增加而急剧下降。指出这种特征反应分布型式对R-PVC制品的户外使用耐久性起决定性的影响。     

硬质聚氯乙烯用复合发泡剂的研究

采用活化剂(尿素、碳酸锌)和碳酸氢钠对偶氮二甲酰胺(AC)改性制备硬质聚氯乙烯(R-PVC)用复合发泡剂,并用热分析和放气量检测对复合发泡剂进行了表征。结果表明当AC、NaHCO3、尿素和碳酸锌的质量比为10:10:2.5:2.5时所得的复合发泡剂分解温度处于R-PVC成型加工范围内,吸-放热基本平衡,放气量大且无突发性。采用这种复合发泡剂制备的硬质聚氯乙烯发泡材料具有较好的力学性能和微孔结构。     

高径比对W纤维/Zr基非晶复合材料压缩性能的影响

采用渗流铸造法制备W纤维/Zr基非晶复合材料,研究高径比的变化对复合材料室温压缩力学性能的影响。结果表明,复合材料的屈服强度随样品高径比的增大先降低,高径比大于1时趋于平稳。高径比大于或等于1.25时,复合材料的压缩塑性应变变化不大。高径比小于1.25时,复合材料的压缩塑性应变均大于50%。压头与样品端部摩擦力的作用、W纤维之间非晶丝高径比的变化和W纤维与非晶基体之间变形的不匹配综合作用最终导致小高径比的复合材料样品具有更好的压缩力学性能。     

He对仅含位错的纯Fe力学性能的影响研究

在反应堆运行过程中,核材料中的He通过核反应产生,并对材料性能的影响较大。通常认为,He会造成材料强度的上升,韧塑性的下降。制备了不同变形量的仅含位错的纯铁样品,开展了He原子对于样品力学性能影响研究,并对影响机理进行了初步分析。结果表明,不同的变形量下,He的注入使得样品的拉伸强度或有所提升,或变化不大,但所有样品的延伸率均得到了不同程度的提高。该结果与通常认为的"氦脆"现象不相一致,由此可见,He并不总是降低金属材料的力学性能。     

多孔铝合金连通孔对压缩性能的影响

根据多孔铝渗流制备过程中孔结构的形成规律建立了单元模型,其中改变渗流压力引起的通孔度变化所产生的孔隙率变化规律符合物理模型.通过对不同孔隙率的孔结构单元模型计算,结合实验研究了孔隙率变化引起的孔结构变化,并计算了通孔多孔铝力学性能的影响规律.结果表明,模型计算得到的材料弹性模量,塑性变形平台应力与实验结果基本相符,孔与孔之间通孔度的变化决定了通孔多孔铝的孔隙率变化,受压缩时在连通孔处的应力集中是其力学性能对孔隙率敏感的直接因素.     

单晶凝固组织的样品尺寸效应

通过对不同直径的单晶样品的凝固实验，研究了样品尺寸对单晶凝固组织的影响规律，研究发现，随样品尺寸减小，单晶凝固组织被细化，尤其一次枝晶间距λ1和枝晶间γ′相尺寸对样品尺寸的依赖性更为明显；样品尺寸影响的要质在于此表面积的变化，进而对凝固过程温度梯度产生影响，最终作用于凝固组织和力学性能，一次枝晶间距λ1和枝晶间γ′尺寸与样品的比表面积近拟呈线性关系，样品尺寸变化，明显改变了单晶生长过程的温度梯度和合金的高温持久寿命。     

无粘结剂天然鳞片石墨电极的结构与力学性能

以天然鳞片石墨为原料采用无粘结剂冷压成型方式制备得到了天然鳞片石墨块状样品,研究了经预压块状样品在等静压后的结构特征以及鳞片石墨取向对力学性能的影响。结果表明,预压块状样品等静压后,在不同方向收缩率发生了变化,在Z轴约为10%~11%,在X、Y轴约为7%~8%。等静压后与等静压前相比,样品变得更加密实,抗折强度提高。天然鳞片石墨在块状样品中的取向是随着径向位置而变化的,块状样品的抗折强度与成型时鳞片石墨的取向有关。文章中还对天然鳞片石墨块状样品的微观结构和抗折强度之间的关系。进行了定性分析。     

高Nb-TiAl合金的凝固组织与力学性能研究

研究了Al含量变化对高Nb-TiAl合金的凝固组织与力学性能的影响.结果表明:随着Al含量的增加,TiAl合金晶粒尺寸呈增加趋势;当Al含量为45.7%时,凝固过程中局部区域发生包晶转变,使晶粒尺寸显著增大;室温及700℃高温拉伸强度随着Al含量的增加而呈增加的趋势,但发生包晶转变致使室温及700℃高温拉伸强度下降约200MPa;Al含量对延伸率不敏感,持久性能随Al含量的增加呈增加趋势.为控制铸锭凝固后的组织与力学性能,尽量避开包晶转变区,合金中Al含量应低于45.7%.     

中间退火温度对新锆合金性能影响的研究

研究了两种新锆合金经不同中间退火组合后的力学性能和高压釜内含锂水中的耐蚀性能.结果表明:采用低温中间退火组合的样品具有更好的机械性能;对高Nb合金来说也有益于耐蚀性能的提高,低Nb合金在耐蚀性能不随中间退火组合温度的变化而改变.文中从第二相的角度对引起性能变化的原因进行了分析.     

制样工艺对3D打印制品的拉伸性能影响研究

本文选用PLA材料,选取FDM成型技术,对比不同的沉积方向和制样工艺对拉伸性能结果的影响,为3D打印产品的力学性能测试方法标准化研究工作提供指导。结果表明：采用FDM技术沉积的PLA制品的力学性能具有明显的各向异性,与堆积方向一致的方向上拥有最佳的力学性能,评价3D打印制品力学性能时,应充分考虑堆积方向对其造成的影响;直接打印测试样品与机械加工测试样品的测试结果存在较大差异,机械加工样品测试结果表现更佳,因此,应充分考虑不同的制样方式对结果的影响。     

Impact of natural weathering on medium-term self-healing performance of fiber reinforced cementitious composites with intrinsic crack-width control capability

The paper investigates the medium-term self-healing performance of fiber reinforced cementitious composites with intrinsic crack-width control capability under natural weathering. The pre-cracked specimens with different damage levels are exposed to various humidity conditions, namely, water submersion, natural weathering, and a laboratory environment with constant humidity. The medium-term self-healing performance is evaluated using a resonant frequency test, tensile test, SEM, and EDX. It is concluded that the medium-term cracked specimens can moderately recover their mechanical properties within 90 days after being submerged in water or exposed to natural weathering. In particular, they are able to resume the multiple cracking behavior and exhibit a reloading strength larger than the preloading strength. Furthermore, the identified compositions of the medium-term healing products for specimens exposed to water and natural weathering conditions are similarly characterized. The reported results imply that effective medium-term self-healing can be realized in fiber reinforced cementitious composites with intrinsic crack-width control capability under natural weathering.     

Natural and accelerated weathering of PVC and polypropylene waste-water pipes

Plastic pipes and plumbing accessories for waste water are gaining popularity and replace the more conventional metal and asbestos-cement products. The main disadvantage of these pipes is their relative poor durability when exposed to external weathering conditions, particularly to the UV solar radiation. The work presented deals with the weathering behaviour of polyvinylchloride (PVC) and polypropylene (PP) pipes. Commerical pipes were exposed to natural and artificial-accelerated conditions and their mechanical properties tested after various periods of exposure. The results show that both the PVC and PP pipes are damaged by the accelerated and natural weathering within a short time, resulting in a rapid deterioration in the ultimate elongation. The drop in the extensibility of the PVC pipe is more gradual than that of the PP. The tensile strength, in both cases, is hardly affected—as expected—proving that the deterioration is mainly a surface phenomenon and depends on the cracking of the exposed surface.     

Modelling of drying induced stress of clay: elastic and viscoelastic behaviours

The aim of this work is to study the influence of the mechanical behaviour of a porous saturated material on its predicted response to drying. A convective drying model is applied on a kaolin rectangular sample. Two mechanical behaviours are studied: elastic and viscoelastic. Numerical results show a significant difference between the stress evolutions obtained for both behaviours. The simulation result of viscoelastic model is consistent with what actually happens during drying and describes more the behaviour of the kaolin sample.     

混杂纤维复合材料的混杂效应

本文分析了混杂纤维复合材料力学行为中的混杂效应,对现行的各种理论和假说作了概要的介绍。影响混杂效应的主要因素有组分材料、混杂结构及其界面状态。HC中纤维断裂延伸率及强度的混杂效应可以用断裂力学、微观(统计)力学等理论解释;而断裂能的混杂效应则主要决定于混杂结构和受力方式,混杂效应的提出和研究对HC的实际工程应用有一定参考价值。      

NANOCRYSTALLIZATION OF METALS AND COMPOSITES PROCESSED MECHANICALLY IN THE SOLID STATE

Extreme plastic deformation encountered in a variety of mechanical processes may yield nanostructured and nanophase materials with a broad range of chemical composition and microstructure. This paper discusses several such examples including the deformation induced nanophase formation in powder particles, thin foil sandwich structures, and at the surface of metals and alloys exposed to friction induced wear conditions. The deformation processes occurring within powder samples during mechanical attrition are important for fundamental studies on the effect of extreme mechanical deformation on the microstructure and its stability.     

用聚乙烯片连续测量太阳紫外辐射的研究

本文对用聚乙烯作为潜在的廉价的光接收体以测量抵达地面的太阳紫外辐射进行了研究。发现含特定添加剂的厚度0.2mm的聚乙烯片可用来连续累积测定波长范围300～400hm的太阳与天空紫外光的辐照量,按照光电法仪器的订定,投射到聚乙烯片曝露表面的太阳与天空紫外光的辐照量是归属为由聚乙烯的光降解导致生成的末端乙烯基的909cm~(-1)红外吸收峰的吸光度增量的幂函数。同时聚乙烯的光降解亦与其他气候因素有关,但它们的影响可以通过由曝露期间的平均气温建立的经验式予以修正,用本法在广州进行的全年连续监测结果表明,它的测量值与以光电转换为工作原理的仪器之测量值比较,偏差小于10％。     

Degradation Characterization of Ethylene-Propylene-Diene Monomer (EPDM) Rubber in Artificial Weathering Environment

Ethylene-propylene-diene monomer containing 5-ethylidene-2-norbornene as diene was exposed to artificial weathering environment produced by a xenon lamp light exposure and weathering equipment for different periods of time. The changes of surface color and mechanical properties were monitored by spectrophotometer, computer-controlled tensile testing and hardness measurements. Crosslink density of ethylene-propylene-diene monomer specimens was measured by the solvent swell method. The results showed that the surface of ethylene-propylene-diene monomer became yellower due to the form of carbonyl group. The degradation process proceeded predominantly via cross-linking. With increase in crosslink density, the tensile strength increased and the elongation at fracture decreased.     

原位复合法复合PA6/巴基管复合材料的试验研究

经过硝酸处理的利用ＣＶＤ法生产的巴基管与ＰＡ６采用原位复合法进行复合时，将以其外壁上联结的羟基－ＯＨ和羧基－ＣＯＯＨ参与己内酰胺合成ＰＡ６的缩水聚合反应，从而结合到ＰＡ６的网状大分子结构中，同时也阻止ＰＡ６分子长大，并产生较大应力。