高强高模聚乙烯醇纤维的研究进展

从聚合方法和引发方式综述了国内外合成高相对分子质量及高立构规整度聚乙烯醇(PVA)的研究进展;详述了通过聚新戊酸乙烯酯的醇解来制备PVA微纤的方法;简述了高强高模PVA纤维的特性及应用;指出今后高强高模PVA纤维的研究应在聚合方法、开发新的高效引发剂和醇解工艺作进一步探索。     

制备聚丙烯腈基高模量碳纤维的高温热处理技术

指出高温热处理是制备高模量碳纤维的关键技术;介绍了制备PAN基高模量碳纤维的3种高温热处理技术。     

高强高模维纶纤维的表面修饰及其在水泥中的分散性

目前高强高模维纶纤维由于缺乏合理的分散方案且分散性不佳,极大地限制了在工程领域的应用。为了解决这一问题,采用聚乙烯醇磷酸酯（TFOPVA）分散剂对高强高模维纶纤维进行表面涂层改性处理,并以此为基础制备维纶纤维/水泥基复合材料。利用X射线光电子能谱仪（XPS）、场发射扫描电子显微镜（SEM）、万能材料试验机、纤维强伸度仪（XQ-1A）等对改性前后的维纶纤维的分散性及其复合材料的力学性能进行测试和表征。结果表明：当TFOPVA上浆质量分数和吸附量分别为1%和5mg/g时纤维分散效果最佳;维纶纤维短丝在水泥基体中的分散系数提高33.3%;TFOPVA处理后的维纶纤维单丝断裂强度增加4.5%,与维纶纤维之间能牢固结合;TFOPVA改性后的维纶纤维/水泥复合材料的抗压强度和抗折强度相比改性前分别提高了27.9%和21.2%。     

高模量沥青及其混合料低温性能研究进展

高模量沥青混合料因其出众的抗车辙性能和抗疲劳性能成为构建重载交通长寿命路面的理想材料,但低温性能差成为制约其应用和发展的最重要因素。近年来,如何改善高模量沥青及其混合料低温性能成为了路面领域的研究热点。本文综述了在胶结料中添加热塑性弹性体、油基改性剂、纳米材料以及在混合料中添加纤维这4种主要技术路径,重点阐述了这4种技术路径的改性材料用量、改性工艺参数与改性效果之间的关联,并对其改性机理进行总结。最后展望了高模量沥青及其混合料在低温性能方面的未来研究重点和发展趋势,即旨在克服高模量沥青混合料应用范围的限制,进而推动高模量沥青混合料在重载长寿命路面中的应用。     

高温碳化张力对碳纤维性能影响

在碳纤维生产过程中张力贯穿于整个工艺过程,张力控制的划分可分为两个部分,一是预氧化张力控制;二是碳化张力控制。借助在线张力仪详细研究了特定工艺条件下的高温碳化张力对6K碳纤维拉伸强度、弹性模量和密度的影响。     

Effects of end conditions on compressive strength and static elastic modulus of very high strength concrete

The use of bonded and unbonded caps in testing very high strength concrete cylinders has been investigated experimentally. A hundred and ninety-two concrete cylinder specimens of 150-mm diameter and 300-mm height were cast and tested using packing with softboard, neat cement paste, neoprene pad and sulfur mortar. The design strength level of 75-100 MPa was achieved using water-cementitious material ratios of 0.22, 0.26 and 0.31. The results of the study were compared considering compressive strength and static elastic moduli values. A two-way analysis of variance was performed at a .01 level of significance in order to compare the effect of end conditions. It was found that the overall mean compressive strengths of specimens capped with neat cement paste, neoprene pad sulfur mortar were not significantly different. The packed specimens exhibited a significant difference from the others. On the other hand, there was no statistical difference in the static elastic moduli values when different capping types were used. Several modulus prediction equations were also examined. Experimental values were consistently higher than the predicted values.     

一种中温固化高强度环氧胶粘剂的研制

以E-51、E-44为主体树脂,加入奇士增韧剂研制出一种中温固化高强度环氧胶粘剂.该胶粘剂在加入占粘料质量分数30%左右的增韧剂后,选用自制固化剂SL-1,在50 ℃×1 h+80 ℃×1 h条件下固化,其拉伸剪切强度可达42.1 MPa.     

Elastic modulus of powder beds—the effects of wall friction: a model compared to experimental data

A model was developed to predict the effects of wall friction upon the elastic modulus of powder beds. The model combined a Janssen stress distribution with non-linear contact mechanics. Overall bed properties were predicted by integrating strain over the bed depth and relating this to applied stress to find the apparent spring constant of the bed.This model was compared to the experimental data of Yanagida et al., for particulate materials subject to low-magnitude vibration. These data cover a range of particulate materials in test cells ranging from 0.0345 to 0.15 m in diameter.The model gave excellent qualitative correspondence with the experimental data, showing the following points:

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for shallow beds, first peak frequencies are independent of cell diameter and only dependent upon cell depth,

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for intermediate bed depths, first peak frequency is dependent upon both bed depth and cell diameter,

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there are indications that, for deeper beds, first peak frequency may be independent of bed depth and only dependent upon cell diameter.

Quantitative comparisons were made with the experimental data by three methods, with two or three fitted parameters from the model. One method gave good quantitative agreement with physically realistic values of the fitted parameters. This method determined an elastic parameter from shallow bed data, where first peak frequency is proportional to bed depth to the power −5/6. Two stress distribution constants were then determined by a least squares of error method on the data.     

Compressive strength of lumber at high temperatures

A model was developed to predict the residual strength in compression parallel to grain for dimension lumber subjected to axial loads at elevated temperatures while braced to prevent buckling. Prediction of the time‐dependent temperature profile within the cross‐section of a lumber member was achieved by adapting a two‐dimensional heat transfer model. An extensive literature review examined seven models proposed by various authors to predict residual strength under various temperature regimes. With knowledge of the temperature‐history and material properties, it was possible to predict the time to failure by crushing of axially loaded members exposed to elevated temperatures. Initially, predicted times to failure did not show as good an agreement with those measured in an experimental programme as had been hoped. However, when a new residual strength‐temperature model was developed and used to simulate the axial load capacity of nominal 38 mm × 89 mm studs exposed to fire, the results obtained showed good agreement with experimental results. Copyright © 2004 John Wiley & Sons, Ltd.     

新型碳纤维用原丝——高强高模Lyocell纤维纺丝工艺研究

采用天然高相对分子质量纤维素脱脂棉为原料 ,制备了高强高模纤维素纤维 ( L yocell纤维 ) ,并用此作为碳纤维原丝 ,成功制得了强度优于粘胶基碳纤维的 L yocell基碳纤维。考察了高相对分子质量纤维素的溶解特点 ,纺丝工艺对 L yocell纤维聚集态及性能的影响 ,比较了 L yocell纤维和粘胶原丝的表面及截面形态。实验表明 :高相对分子质量纤维素溶解的静溶胀时间和温度对其溶解有明显的影响 ;纺丝过程中 ,大的气隙长度对提高纤维的性能有利 ;随着凝固浴中 N -甲基吗啉 N -氧化物( NMMO )的浓度增加 ,纤维的强度和模量增加 ,当其在凝固浴中的质量分数达到 10 %时 ,强度模量最大 ,浓度继续增加 ,纤维的力学性能开始下降 ;拉伸比增加 ,L yocell纤维的强度模量增加 ,当拉伸比大于 3.0时 ,纤维的性能略有下降     

冷制高强快干淀粉胶粘剂

介绍了一种以淀粉为主要原料,在复合催化剂作用下,经双氧水室温氧化并添加高强快干添加剂和其他助剂,制备高强快干淀粉胶的方法,讨论了对淀粉胶性能的影响因素及其简要的作用机理,确定了能够满足最佳上机要求的配方。应用本方法制出的胶粘剂,通过中试制板,证明该胶具有干燥速度快、强度高等优点。     

适用于低温固化的低黏度高强度环氧树脂结构胶

以碳酸丙烯酯(PC)为活性稀释剂、自制增韧型421固化剂/快固型DETA(二乙烯三胺)固化剂作为复合固化剂,制备环氧树脂(EP)结构胶。研究结果表明:当m(EP)∶m(PC)∶m(421)∶m(DETA)=100∶20∶24∶6.0时,EP结构胶的初始黏度(60 mPa.s)相对较低,其强度和韧性俱佳(拉伸强度为45 MPa、压缩强度为70 MPa和钢/钢剪切强度为12.0 MPa);该EP结构胶可低温固化(5℃或常温固化7 d后的拉伸强度基本一致),也是一款适用于冬季施工的低黏度高强度EP结构胶。     

室温固化高剥离耐热环氧树脂胶粘剂

介绍了一种具有高剥离强度和剪切强度的室温固化耐热胶粘剂。室温固化10d后,室温剥离强度可达到7．0kN／m;室温剪切强度为30．8MPa,150℃剪切强度可达14．5MPa。重点讨论了环氧树脂种类、复配合固化剂比例以及促进剂用量对胶粘剂粘接强度和耐热性能的影响。     

Elastic modulus prediction based on thermal conductivity for silica aerogels and fiber reinforced composites

The speed of sound is a critical parameter in the test of mechanical and thermal properties. In this work, we proposed a testing method to obtain the elastic modulus of silica aerogel from the sound speed formulas. The solid thermal conductivity of the silica aerogel is experimentally measured for predicting the sound speeds, and then the elastic modulus is calculated based on the elasticity sound speed model. The experimental data of the solid thermal conductivity of silica aerogels with different densities are employed and the obtained elastic modulus is fitted as a power-law exponential function of the density. Two existing sound speed models and three groups of available experimental data are also employed to validate the present fitting relation, and good agreement is obtained for the silica aerogel in the density range of 150–350 kg/m³. The fitting formula can also be extended to estimate the elastic modulus of the glass fiber-reinforced silica aerogel composite. The results show that the elastic modulus of the aerogel composite is sensitive to the glass fiber volume fraction, while the thermal conductivity is weakly dependent on the glass fiber volume fraction at room temperature in the studied range of fiber volume fraction.     

一种中温固化高强度耐烧蚀环氧结构胶的特性

介绍了一种中温固化、粘接强度高、氧-乙炔烧蚀性能好的环氧胶粘剂,讨论了树脂和填料等对组分性能和工艺的影响。满足了小型固体火箭发动机中金属和玻璃钢之间的粘接及其耐烧蚀性能的要求。     

In situ characterization of high temperature elastic modulus and fracture toughness in air plasma sprayed thermal barrier coatings under bending by using digital image correlation

The evolutions of elastic modulus and fracture toughness are the key factors affecting the failure mechanism and durability of thermal barrier coatings (TBCs). Combined the high temperature three-point bending with the digital image correlation (DIC) method, the variations of high temperature elastic modulus and fracture toughness of air plasma sprayed TBCs with temperature are determined. The surface and interfacial cracking information can be monitored real-time by DIC system. The results show that when the temperature rises from 30 °C to 800 °C, the elastic modulus and fracture toughness of TC decrease from 20.3 GPa to 13.1 GPa and from 1.31 MPa m^1/2 to 1.16 MPa m^1/2, respectively. And the interfacial fracture toughness increases from 83.7 J/m² to 156.3 J/m². These results are consistent with the available values determined in literatures, which ensures the validity of this method.     

低温等离子体处理对高强聚乙烯纤维表面影响的研究

采用空气低温等离子体处理高强聚乙烯纤维,测试处理前后纤维表面摩擦系数的变化,并采用电子扫描显微镜（SEM）和原子力显微镜（AFM）对纤维表面形貌进行观察分析。结果发现,空气低温等离子体处理的刻蚀作用会在纤维表面形成致密的＂小坑群＂,使得纤维表面产生剥落、联结,造成纤维表面的粗糙程度有所增加,其处理后的纤维表面静、动摩擦系数有所提高。     

Microstructure and interface-adhesion of thermally sprayed continuous gradient elastic modulus FeCrAl-ceramic coatings

The bond strength between thermally sprayed metal bond-coats and ceramic top-coats is a key factor in determining their service life. However, most studies focus on interface modifications. In this research, based on FeCrAl bond-coats prepared by arc spraying, top-coats (Al₂O₃-40 wt% TiO₂) were prepared by plasma spraying, and heat treatment was carried out in a hypoxic atmosphere. Continuous gradient elastic modulus FeCrAl-ceramic coatings were successfully prepared, and the microstructural and mechanical properties from the substrate to the top-coats were systematically investigated. The Al₂O₃ content gradually decreased from the top-coats to the substrate, forming continuous gradient elastic modulus FeCrAl-ceramic coatings. The oxide formed during the heat treatment filled the defects in the bond-coats and greatly improved the mechanical properties of the coating. The bonding strength of the continuous gradient elastic modulus coating was 21.7% greater than that of the as-received coating.     

高温和超高温极端环境下陶瓷管材弹性模量评价新技术

本文综述了从室温到2200°C范围内陶瓷材料弹性模量的传统测试方法和新技术。针对脆性陶瓷管材在高温及超高温下弹性模量的评价难题,我们提出一种结合相对法和缺口环法的新方法,即相对缺口环法。通过比较缺口环与刚性圆块的横梁位移得到缺口环在高温及超高温下的真实变形量计算出精确的弹性模量。对典型的石英玻璃管、氧化铝陶瓷管、C/SiC/ZrB_2复合陶瓷管以及石墨管进行测试所得到的结果表明相对缺口环法准确有效,为高温及超高温等极端环境下脆性管材的结构安全提供了一种简便可靠的评价方法。