Fibre bridging during high temperature fatigue crack growth in Ti/SiC composites

Synchrotron X-ray diffraction has been used to map the crack tip stress field, load redistribution and the variation in interfacial shear stress along bridging fibres local to a matrix crack during fatigue crack growth in Ti-6Al-4V/unidirectional SCS-6 SiC monofilament composite at elevated temperature. Quasi-static fatigue cycles were applied in a diffractometer at the same stress amplitudes and temperatures (120 and 300 °C) as those used in prior off-line fatigue testing. The elastic fibre strains were measured ply by ply along the fibres and in the matrix in the region of the crack. In this manner the crack affected zone was mapped, and subsequently the interfacial shear stress levels deduced as a function of distance from the crack at these temperatures. The results are compared with previous studies of load redistribution at room temperature and the fibre sliding stresses compared with those needed to slide pristine fibres to evaluate degradation of the interfacial shear strength caused by interfacial wear during fatigue. The implications for the use of such composites at elevated temperatures, for example in aero engines, are discussed.     

Defining the physical structure and properties in novel monofilaments with potential for use as absorbable surgical sutures based on a lactide containing block terpolymer

Monofilaments of a block terpolymer of l-lactide, ?-caprolactone and glycolide have been melt spun for potential use as absorbable surgical sutures. As-spun fibres of the terpolymers produced by melt spinning were elastic, amorphous and isotropic. A two-stage process involving hot drawing was employed to enhance their mechanical properties. WAXS and SAXS results coupled with DSC demonstrated that hot drawing leads to an orientated amorphous matrix containing small highly aligned crystals. Hot drawing was carried out at a range of temperatures using the highest possible draw rate commensurate with maintaining continuity of the fibre. A novel WAXS analysis based on a spherical harmonic analysis allowed a separation of the scattering into three components: oriented crystalline, oriented amorphous, and an isotropic amorphous. There is a steady increase in the fraction of oriented crystalline material with increasing hot draw temperature, although the level of crystallinity is ultimately limited by the statistical nature of the terpolymer. The material shows highly promising potential properties for use as a monofilament suture.     

Completed double layer boundary element method for periodic fibre suspension in viscoelastic fluid

A numerical method to simulate the periodic fibre suspension in viscoelastic fluid is developed with the completed double layer boundary element method (CDLBEM). The periodic summations that arise in the formulation were well handled by Ewald summation technique to speed up the convergence rate in the computation. The formulation for velocity field in periodic fibre suspension in viscoelastic fluid is derived and is used to simulate multiple fibres suspended in a viscoelastic shear flow. Simulations are carried out for various fibre aspect ratios and volume fractions ranging from dilute to concentrated regimes. Numerical results of macroscopic rheological properties of the system are compared to available experiments on viscoelastic fibre suspensions, and are found to agree reasonably well with the experimental data.     

Anti-Nutritional Components, Fibre, Sinapine and Glucosinolate Content, in Australian Canola (Brassica napus L.) Meal

Canola meal is highly regarded as a component of animal feed with a high protein content and a desirable amino acid profile. The presence of some components, in particular glucosinolates, sinapine and fibre, affects the value of the meal and reduces the amount that can be used in animal feed formulations. Glucosinolates in traditional cultivars (rapeseed) had very high amounts and this severely limited the usefulness of the meal. Canola breeding programs have successfully reduced glucosinolate content to trace amounts. However sinapine remains at levels sufficiently high to cause problems, particularly in poultry feed. The relatively high fibre level in canola also reduces the value of the product for animal feed. This study has determined the level of sinapine, glucosinolates and fibre in current cultivars of canola in Australia to illustrate advances made by breeding programs and limitations which still remain to raise the usefulness of a potentially valuable feedstock. Although glucosinolate levels in meal were shown to have been reduced to 11 μmol/g in some cases, sinapine remained at traditional levels of about 12–15 g/kg and neutral detergent fibre levels were about 30–40%. These issues are important priorities for canola breeders.     

香蕉采摘机械手夹持装置仿真优化设计

香蕉机械化自动采摘的采摘对象为成串香蕉,要求采摘机械手的夹持装置具有一定的强度和刚度。针对此特点,在提出一种香蕉采摘机械手夹持装置结构的基础上,用三维建模软件Pro/E进行了夹持装置的参数化建模设计;对所构造的三维模型,应用ANSYS Workbench对夹持装置关键部件夹持杆及支撑杆的结构设计参数进行了多目标优化设计,分析了载荷与变形之间的关系,得到优化的结构方案,并制作实体样机验证了优化设计的可行性,为香蕉采摘夹持装置的结构设计提供了理论依据。     

Tencel纤维织物染整工艺

1　前言Tencel纤维 (纤维分类属 Lyocell)是天然纤维素纤维 ,它是采用溶剂纺由木浆粕衍生而成 ,木浆粕来源于树木 ,因而是一个取之不尽的资源。使用的纺丝溶剂为 N-甲基吗啉 - N-氧化物 ( NMMO) ,通过溶解 ,纺丝和后处理得到 Tencel纤维。由于其生产过程无污染溶剂 ,NMMO无毒且几乎能全部回收 ,符合环保要求 ,所以被誉为“2 1世纪绿色纤维”。2　 Tencel纤维性能Tencel纤维具有所有纤维素纤维的天然性质 ,包括较好的吸湿性 ,服用舒适性 ,柔和的光泽 ,优良的染色特性和生物降解性。表 1　 Tencel纤维性质项目　　种类 Tencel 涤　纶棉…     

Green biorefinery (GBR) scenarios for a two-cut silage system: Investigating the impacts of sward botanical composition, N fertilisation rate and biomass availability on GBR profitability and price offered to farmers

In Ireland, grass is a readily available bioresource. It has previously been established that Green biorefinery (GBR) could become a potential use of Irish grasslands, and a blueprint for a sustainable GBR industry in Ireland has been developed. The objective of this paper is to use scenario analysis to investigate the sensitivity of the profitability of the GBR blueprint to variations in grass quantity and quality as a function of botanical composition, fertiliser application, and biomass availability. As an outcome of these scenario analyses, the price the GBR can offer to farmers above their production costs (€ t⁻¹ dry matter) was calculated. Results of the scenario analyses determined that GBR systems located in a catchment area of permanent pasture (Lolium perenne > 60%) with annual grass yields in the range of 9-12 t dry matter (DM) ha⁻¹, and supplied with grass biomass with a fibre content of 500-555 g kg⁻¹ DM and a protein content of 110-130 g kg⁻¹ DM, were viable. The most profitable scenarios were generated when nitrogen fertiliser application was greater than 90 kg ha⁻¹ a⁻¹. Biomass availability of less than 30% resulted in reduced profitability and for some scenarios resulted in a loss for both the GBR and farmer due to increased transport costs. Within the scenario assumptions of this study, grass feedstock was valued at €4-€56 t⁻¹ dry matter above production costs. However, this value depended on the yields and biomass availability of the GBR catchment area.     

Determination of lifetime probabilities of carbon fibre composite plates and pressure vessels for hydrogen storage

It is shown that an analogy can be made between the failure of unidirectional carbon fibre reinforced epoxy plates and filament wound carbon fibre composite pressure vessels and that their strengths and failure probabilities can be determined. Fibres in filament wound composite structures are placed on geodesic paths around the mandrel, which becomes the liner; so that when the structure is pressurised the fibres are only subjected to tensile forces, as in a unidirectional composite. Multiscale modelling reveals that composite failure is controlled by fibre breakage and that clustering of fibre breaks determines ultimate reliability of the structure. Time dependent relaxation of the matrix leads to delayed failure of the elastic fibres. A statistical study, using the stochastic properties of the fibres, determines the range of lifetimes which will be obtained in a given class of pressure vessel, leading to an evaluation of failure probabilities as a function of internal pressures. In this way the definition of safety factors, based on an understanding of the physical processes governing damage accumulation, becomes possible.     

The effect of ionic strength, polyphosphates type, pH, cooking temperature and preblending on the functional properties of normal and pale, soft, exudative (PSE) pork

Compared to processed meat product made from normal pork, products made from pale soft exudative (PSE) pork have higher cook loss (CL) and weaker texture. In this study interactions between a range of processing conditions (ionic strength, polyphosphate addition, polyphosphate chain length, pH, cooking temperature and time between preparation and cooking), and their effect on the texture [shear stress (SS), true shear strain (TSS)] and CL of gels made from normal and PSE pork were examined. Of the processing conditions studied, ionic strength, polyphosphate addition and polyphosphate chain length affected the functional properties of normal and PSE pork differently. Generally, the functional properties of normal pork were superior to PSE pork, with no combination of conditions making all the functional properties of PSE pork equal to those of normal pork under the same conditions. The combination of conditions that was most effective in reducing the difference between normal and PSE pork was high ionic strength in the presence of added polyphosphate. Under these conditions there was no significant difference in CL between normal and PSE pork, although the texture (SS and TSS) of the PSE pork samples was still inferior.     

Investigation on germanium oxide-based glasses for infrared optical fibre development

We demonstrate the suitability of GeO₂ for fibre engineering by compositional modifications of core and cladding glasses using the rod-in-tube technique, which have been matched for fibre drawing. The methods adopted for identifying the core–clad combination (56GeO₂–31PbO–9Na₂O–4Ga₂O₃ and 55GeO₂–30PbO–11Na₂O–4Ga₂O₃) are explained, based on the thermal, viscosity, and optical properties. We specially point out to the relatively high transformation temperature range (T_g > 380 °C) of the glass, which is suitable for chemical sensing and metrological applications in the 150–200 °C. The total intrinsic loss is compared with the measured loss in multi- and single-mode fibres from 0.532 to 2.02 μm, with loss less than 2.5 dB m⁻¹ in the 1000–1600 nm range. The origin of larger loss outside this region is explained.