Kevlar－49芳纶纤维表面接枝改性

采用空气等离子体处理Ｋｅｖｌａｒ－４９并在活化处理后的纤维表面接枝聚丙烯酸（ＰＡＡ）、聚丙烯酸乙酯（ＰＥＡ）及丙烯酸和丙烯酸乙酯的共聚物（ＰＡＡ／ＥＡ）。单丝拔出实验研究表明，空气等离子体改性的Ｋｅｖｌａｒ－４９／环氧树脂体系的界面结合强度和界面破坏能均有明显提高，其中接枝了Ｐ（ＡＡ／ＥＡ）的Ｋｅｖｌａｒ－４９／环氧树脂体系的界面破坏能（５５Ｊ／ｍ２）比未改性体系的界面破坏能（２７．８Ｊ／ｍ２）提高了一倍。     

The tensile and fatigue behaviour of Kevlar-49 (PRD-49) fibre

The tensile, creep and tension-tension fatigue properties of Kevlar-49 fibre (formerly known as PRD-49) have been determined. The fracture morphology of the fibre has been examined and is shown to be complex due to considerable splitting. The fibre quickly stabilizes under a steady load but failure due to creep can occur when it is loaded very near to its simple tensile breaking load. Kevlar-49 has been found to fail by fatigue, and its fatigue lifetime is dependent on the amplitude of the applied oscillatory load as well as the maximum load to which the fibre is cycled.     

Excess loss of single-mode jacketed optical fiber at low temperature

This paper describes excess loss of single-mode jacketed optical fibers at low temperature. A structural model is proposed for the jacketed fiber in order to investigate the relationship between the structure and excess loss. This model clarifies the excess loss increase mechanism that any initial irregularity existing in the jacketed fiber increases due to shrinkage of the jacket and causes excess loss. These results show that reducing the buffer diameter and controlling the fiber deformation inside the jacket are effective in suppressing excess loss at low temperature.     

Long term physical ageing of polycarbonate at room temperature: dynamic mechanical measurements

The loss peak, called α′, appearing as a shoulder in the left wing of the α peak in dynamic mechanical measurements is used to follow the very long term ageing at room temperature of samples of Polycarbonate rejuvenated by cold rolling or by quenching prior to ageing. This peak shifts to higher temperature with increasing ageing time t_a. An approximate linear increase with ln t_a is found with a similar slope of about 8 K/decade for both kinds of samples. The shape and the magnitude of the peak are strongly dependent on the treatment given to the samples before ageing. It is assumed that ageing at room temperature and below results from an activated process additive to the annealing process prevailing at higher temperatures up to T_g. This ageing process which depends of the pretreatment is characterized by a lower activation energy than the annealing one. Taking these assumptions into account, experimental data are shown to agree reasonably with the predictions of a model previously proposed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Very low temperature thermal conductivity of Kevlar 49

We measured the thermal conductivity of a Kevlar 49 in the temperature range. The data were fitted with a power-law: . Kevlar 49 is a candidate material for the supports of CUORE experiment.     

玄武岩纤维在低温下的传热特性试验研究

为研究多孔介质在低温下的传热特性,进行了抽真空条件下试验件中填充和不填充玄武岩纤维的低温传热试验.在两种状态下分别测得了温度变化曲线、系统压力变化曲线和质量变化曲线.对比分析后发现,在低温抽真空条件下填充玄武岩纤维对试验件在传热方面有明显的强化作用,能有效降低并稳定试验件的温度,但液氮的消耗量有所增加.     

Compression strength of carbon,glass and Kevlar-49 fibre reinforced polyester resins

The compression behaviour of a series of polyester resins of various compositions and in different states of cure has been investigated. Their mechanical characteristics having been established, the same range of resins was then used as a matrix material for a series of composites reinforced with carbon, glass and aromatic polyamide fibres. The composites were unidirectionally reinforced, having been manufactured by pultrusion, and were compression tested in the fibre direction after a series of experiments to assess the validity of a simple testing procedure. Rule of Mixtures behaviour occurred in glass-polyester composites up to limiting volume fractions (V _f) of 0.31 for strength and 0.46 for elastic modulus, the compression modulus being equal to the tensile modulus, and the apparent fibre strength being in the range 1.3 to 1.6 GPa at this limiting V _f. At a V _f of 0.31 the strengths of reinforced polyesters were proportional to the matrix yield strength, _my, and their moduli were an inverse exponential function of _my. For the same matrix yield strength a composite with an epoxy resin matrix was stronger than polyester based composites. At V _f=0.30, Kevlar fibre composites behaved as though their compression modulus and strength were much smaller than their tensile modulus and strength, while carbon fibre composites were only slightly less stiff and weaker in compression than in tension. The compression strengths of the polyester resins were found to be proportional to their elastic moduli.     

Long term analysis of citation counts at the micro-level

Analysis over a 13 year period of citation counts to research papers in pursuit of a new scientific hypothesis on the mechanism of action of oestrogen hormones, which therefore could be defined at the micro-level, revealed that during a period of expansion of the field there was an overall fall in mean citation counts, even to papers bywith hindsight still successful groups. This fall appeared to be related to a relatively greater increase in the number of papers to be cited than in the number of citing papers.     

碳纤维复合材料低温热导率测试方法

针对碳纤维复合材料在X、Y、Z 3个方向的各向异性特点,分析其传热机理,讨论分析了碳纤维复合材料低温热导率测试方法.采用两种不同方法分别测试出碳纤维复合材料3个方向的低温热导率数据.根据测试结果,讨论了影响测试精度的主要因素,如温度、试样装配、试样厚度的影响等,给出了部分碳纤维复合材料低温热导率与温度关系曲线.     

Fracture analysis of Kevlar-49/epoxy and e-glass/epoxy doublers for reinforcement of cracked aluminum plates

Adhesively bonded composite patch repair is efficient means to regain load carrying capacity, alleviate the crack growth, and improve the service life of the damaged structure. In this paper, three dimensional finite element models are developed to examine the fracture behavior of a single edge V-notched Aluminum plate repaired with Kevlar-49/epoxy or e-glass/epoxy pre-preg patches on both sides. Contour integral method was used for evaluating the stress intensity factor (SIF), an indicator of the crack stability. The load transfer mechanisms, stress distribution, damage variable (D), and crack mouth opening displacement (CMOD), were also presented to estimate the effectiveness of composite patch repair. The influence of the patch material, crack length and the adhesive thickness has been investigated. Results have shown that the crack induced damage increased nonlinearly with a larger crack size. With the composite patch repairs, SIF is reduced to 1/7–1/10 of that of the bare plate and CMOD decreased by 79%. The damage variable is reduced significantly and the load capacity is increased. A thinner adhesive layer results in a higher percentage of load shared by the composite patch.     

Simulation of crack growth under low cycle fatigue at high temperature in a single crystal superalloy

Crack growth tests have been performed at 950 °C with Single Edge Notch specimens of the Ni-based single crystal superalloy PWA1483. In particular, several orientations and frequencies have been investigated, thus allowing the assessment of the influence of these parameters on the crack growth rate. In addition, oxidation experiments have been carried out to characterize the kinetics of the outer oxide scale growth at the same temperature.On the other side, crack growth has been simulated with the Finite Element program ABAQUS in real test conditions by the node release technique. The nodes are released according to the measured crack growth rate.The simulation results are compared with the test results on the basis of the computed Crack Tip Opening Displacement (CTOD). For this purpose, the crack is propagated until a stabilized value of the CTOD is obtained. This is usually the case when the crack has crossed the initial plastic zone. The procedure provides an evaluation of the effects of cycle frequency, crystal orientation, plasticity and oxide induced crack closure.     

纳米金红石型TiO2的低温制备

分别在中性，碱性和酸性环境下对钛酸四丁酯溶液进行水解以制备纳米二氧化钛。在中性和碱性环境下水解产物是非晶态的，当温度低于700℃煅烧只能得到脱钛矿型二氧化钛。在酸性环境下，通过调整酸和水的加入量将溶液在低温下（40－50℃）水解合成了从纯锐钛矿相到不同比例锐钛矿－金红石混晶相，再到纯金红石相的纳米二氧化钛，乙醇的加入促进凝胶的形成以及锐钛相向金红石相的转化。