Analysis of multi-layered filament-wound composite pipes under internal pressure

Composite pipes in this study are composed of multi-layered filament-wound (FW) structures. Each layer of the pipes is assumed to be anisotropy. Based on the three-dimensional (3-D) anisotropic elasticity, an exact elastic solution for stresses and deformations of the pipes under internal pressure is presented. Moreover, detailed stress and strain distributions for three given angle-ply pipe designs are investigated by using the present theory. The shear extension coupling is also considered because the lay-up angles with +φ and −φ layers cannot exist in the same radius. For cylindrical-pressure vessels with different angle-ply pipe, the ratio of applied hoop-to-axial stress in each layer is different. Even if quite a thin-walled pipe, the ratio of hoop-to-axial stress is no longer a constant of 2:1.     

Dynamic analysis of multi-layered filament-wound composite pipes subjected to cyclic internal pressure and cyclic temperature

Based on the three-dimensional anisotropic elasticity, the stress analysis of multi-layered filament-wound composite pipes subjected to cyclic internal pressure and temperature loading is conducted in this article. The time-dependent stress, strain and deformation distributions are numerically obtained by the use of the finite difference technique. The pressure and temperature are considered to be symmetrical about the axis of the cylinder and independent of the axial coordinate. Each layer of the pipes is made of a homogeneous, anisotropic and linearly elastic material and it is assumed that the material properties do not change with increasing the temperature. The shear extension coupling is also considered because of lay-up angles. Numerical results obtained from the present model are compared with other published results and good agreement has been achieved.     

轴心受压CFRP—铝合金组合管弹塑性屈曲性能分析

CFRP管具有轻质高强的特点,适合于建造大跨度空间网格结构,但其破坏呈脆性,且以节点连接破坏为主,不能充分发挥CFRP材料的优点,为此建议将CFRP与铝合金组合形成CFRP-铝合金组合管来改善其受力性能和构件连接性能。首先对CFRP-铝合金组合长管进行了轴心受压稳定试验研究,得到其基本受力性能与破坏模式。利用有限元方法对组合管的特征值屈曲进行分析,研究不同CFRP铺层角度、厚度和顺序的影响。根据特征值屈曲的分析结果,引入初始几何缺陷,对组合管进行了弹塑性屈曲分析,并将分析结果与试验结果进行了对比,确定了有限元分析模型的合理性,进一步研究了不同长细比、铺层角度和厚度对组合管弹塑性稳定性能的影响机理。最后基于试验结果与数值分析结果,通过修正Perry稳定计算公式,得到了CFRP-铝合金组合长管屈曲荷载的计算公式。     

Weibull analysis, extrapolations and implications for condition assessment of cast iron water mains

The applicability of Weibull statistics to the condition assessment of cast iron water distribution pipes has been considered. The effect of Weibull modulus, characteristic strength, sample size and mode of loading (tension or flexure) on the strength of cast iron water distribution pipes is investigated. The strength distribution of cast iron samples cut from sections of five different water distribution pipes recovered from the ground have been characterized. Strengths have been measured in flexure, at two different temperatures (ambient and 0 °C), and in tension at ambient temperature using two different sample sizes. It is shown that characteristic strength values in flexure decrease with increasing size of graphite flake and that there is no significant difference between the results at the two temperatures investigated. For samples of the same volume tested in tension and flexure, the reduced strength measured in tension is consistent with Weibull predictions. However, the strength of large samples tested in tension was not significantly different from the small samples, perhaps because the samples were of the same thickness and conventional Weibull scaling is not applicable. Finally, using a method which treats a large pipe as an assembly of small samples, the strength distributions from the small samples tested in tension are used to make a prediction of the strengths of 1 m span sections of pipe loaded in three‐point bending, which were reported in previous work. The predicted pipe strengths are close to the lower end of the measured pipe strength distribution. Overall, this work suggests that Weibull analysis is a useful tool to examine the strength distribution of removed from cast iron water pipes and so has the potential to contribute in the assessment of asset condition.     

纤维增强PE材料增韧效果的研究

以聚乙烯(PE)材料为基体,应用玻璃纤维随机或定向分布,增加材料的强度、刚度和断裂韧性,是发展高压大口径复合材料天然气管道的需要。本文基于PFRAC程序的动态断裂分析能力[1],增加了各向异性材料的本构条件,发展了对纤维增强复合材料未开裂和开裂管道的计算功能。由力学性能的试验结果,提供了材料的本构关系,对未开裂和开裂的管道进行了计算分析。结果表明,PE管道经纤维增强之后,与纯PE材料的管道相比,其环向位移下降到53%(纤维随机分布)~5%(纤维沿管道轴向80度分布);裂纹驱动力相应下降到50%~17%,充分反映了纤维对PE材料的增强和增韧效果。     

The long-term behaviour of an aluminium-reinforced polyethylene pressure pipe

The long-term behaviour of an aluminium-reinforced polyethylene pressure pipe has been explored by undertaking stress rupture tests at 60 and 80 °C. The results of the tests showed these macrocomposite pipes have a time-dependent strength, such that with an increasing time under load the strength declined. In addition the pipes were weaker at 80 °C when compared to the 60 °C strength. The analysis of the influence of time and temperature on strength showed these multilayer pipes can be considered to behave as do conventional homogeneously structured plastic pipes, and that to describe the influence of time on the pipe strength, the accepted procedures developed for conventional plastics pipes can be applied. In addition the mode of failure of the pipes was examined. Pipe failure initiates by the strain-controlled failure of the reinforcing aluminium layer. The polyethylene layers then fail almost instantaneously in a ductile mode. This analysis of the mode of failure was supported by freeze-thaw cycling tests to – 25 °C and the 60 and 80 °C stress rupture tests.     

Air cooling of concrete by means of embedded cooling pipes-Part I: Laboratory tests of heat transfer coefficients

Embedded cooling pipes can be used to reduce the temperature rise in massive structures as a measure against thermal cracking. When air is used as a cooling medium, relatively large diameters with profiles causing friction losses along the pipe are preferred. In this paper, heat transfer coefficients for two different types of cooling pipes have been determined for different pipe flows in combination with various temperature levels. This paper relates to the first part of the investigation dealing with the laboratory tests of heat transfer coefficients. The second part, dealing with application in design, is presented in “Air cooling of concrete by means of embedded cooling pipes-Part II: Applications in design” [1].     

客车空调压缩机排气管路失效分析与结构改进

采用ANSYS Workbench软件对客车空调压缩机排气管路进行失效分析和结构改进。以3种典型管路为研究对象,在压缩机端施加位移载荷进行管路失效分析,模拟结果与管路实际断裂位置一致。通过添加弯头、调整管路角度以及增加不锈钢波纹管长度等改进措施,可以降低管路的最大等效应力,延长管路的使用寿命。     

Microscopy of failure mechanisms in filament-wound pipe

Filament-wound pipes pressurized in one of two modes, to give biaxial or uniaxial stress conditions, have been examined using standard microscopic techniques. Whitening of the pipes which develops during testing has been correlated with different types of cracking. A mechanism for weepage in filament wound pipes by the crossing of transverse cracks in adjacent laminae is described. The types of crack present in the pipe at loads up to final failure were found to be consistent with predictions of the stresses acting in the pipe walls.     

Life extension technology for steam pipe systems—II. Development of life prediction methodology

Part II of this paper addresses the development of a fracture mechanics based life prediction methodology of steam pipes which operate at elevated temperatures but in the sub-creep temperature range. Elastic-plastic fracture mechanics concepts were employed to establish the remaining life prediction methodology and inspection criteria of steam pipes. Leak-before-break analyses were utilized to determine the flaw inspection criteria. Both tension and bending type loading conditions were considered in the life prediction analysis. The life assessment technology is concerned with the fatigue crack growth life of circumferential cracks in a pipe. The material properties of the A106B steam pipe steel reported in Part I of this paper were used to predict the fatigue life of steam pipes. The effects of operating parameters (e.g. stress and temperature), pipe size, and material properties on the remaining life and inspection intervals of steam pipes can be quantitatively evaluated.     

Performance measurements of a 7 mm-diameter hydrogen heat pipe

A gravity assisted heat pipe with 7-mm diameter has been developed and tested to cool a liquid hydrogen target for extracted beam experiments at COSY. The liquid flowing down from the condenser surface is separated from the vapor flowing up by a thin wall 3 mm diameter plastic tube located concentrically inside the heat pipe. The heat pipe was tested at different inclination angles with respect to the horizontal plane. The heat pipe showed good operating characteristics because of the low radiation heat load from the surroundings, low heat capacity due to the small mass, higher sensitivity to heat loads (to overcome the heat load before the complete vaporization of the liquid in the target cell) due to the higher vapor speed inside the heat pipe which transfers the heat load to the condenser.     

Theoretical investigations of hydrogen,nitrogen, and oxygen homogenous and annular wick heat pipes

In any heat pipe, the capillary pressure developed at the liquid-vapour interface balances the sum of the various pressure drops throughout the pipe. This study analyses the different contributions to pressure drop for both homogenous wick and annular wick heat pipes operating at low temperatures. The pressure drop in the wick structure is of primary importance for a homogenous wick heat pipe. The heat transfer capacity of an annular-wick heat pipe is strongly affected by the interphase pressure drop due to non-zero evaporation and condensation rates at the liquid—vapour interfaces. Theoretical heat transfer rates as functions of the vapour temperature have been computed for both homogenous and annular wick structures of heat pipes using hydrogen, nitrogen, and oxygen as working fluids. The heat transfer capacity of the annular wick design is more than an order of magnitude higher than that of the corresponding homogenous wick design.     

Analysis of Pipes Containing Plain and Gouged Dents

Abstract: The paper discusses numerical results obtained for pipes subjected to transverse denting by a rigid indenter. Dents produced by different shapes of indenters are assessed for the amount of cross‐sectional distortion of the pipe and for propagation of this distortion along the length of the pipe. The contact area between the rigid indenter and the deformable pipe, as well as between the pipe and the rigid support is calculated for different loading configurations and for different shapes of indenters. Pipe supports considered include elastic springs, a rigid saddle and a rigid plate. In numerical work, axial cracks and gouges of different sizes have been introduced to the pipe's outer surface. Damaged pipes are then subjected to denting and results, including denting forces, distortion of the cross‐sectional area and limit loads are compared with the corresponding results obtained for non‐dented and non‐gouged geometries as well as with non‐dented but gouged cases. Finally, selected numerical results are compared to experimental data in order to demonstrate the adequacy of the adopted modelling and analysis approach.     

Extension of the layer removal technique for the measurement of residual stresses in layered anisotropic cylinders

An extension of the layer removal technique is presented that allows the residual stresses within multilayered anisotropic pipes of any wall thickness to be determined. The method inherently satisfies the self-equilibrium requirement and limits the effects of measurement errors to the region local to the error. The thickness of each layer that is removed need not be uniform and is entirely independent of the thickness of each ply of material. Four example problems are considered. The first three allow results to be compared between the present method and previous work. The fourth problem demonstrates the method on a thick walled anisotropic pipe built up of +45°/-45° plies for which no solution was previously available.     

Heating and Melting of Paraffin in a Coaxial System under the Effect of High-Frequency Electromagnetic Radiation

The impact of a microwave electromagnetic field on the melting of paraffin in a coaxial system simulating an oil well is investigated. The schematic diagram is presented of the experimental facility for the investigation of melting of paraffin in a system consisting of an internal pipe and a coaxially arranged external pipe. In the interelectrode space of these two pipes, an electromagnetic field is induced with a frequency of 2400 MHz. It is shown that the distribution of temperature in the pipes is nonuniform, corresponding to the standing electromagnetic wave in the interelectrode space. The presence of paraffin in the interpipe space substantially accelerates the melting process in the entire coaxial system.     

High Tech Tabakpfeifen

High Tech Smoking Pipes High Tech materials are of interest not only for industrial applications but their use can be also of advantage for consumer goods. The bowls of smoking pipes frequently consist of wood which forms charcoal and together with condensated pyrolysis products of the tobacco a brittle crust. In consequence after a shorter or longer time period the smoker consequence after a shorter or longer time period the smoker has to abandon his pipe. Better suited are bowls consistening of temperature resistant materials, e.g., carbon which is used as lining of blast-furnaces. By utilizing the anisotropic properties of pyrographit a better temperature distribution within the tobacco stuffing can be achieved improving the burning rate and avoiding the formation of a pool at the bowl's bottom. Pyrographite and carbon fiber-reinforced carbon (CFC) which is also proposed for smoking pipes are used for rocket cones and nozzled, heat shields and other high temperature applications. CFC is less brittle than other carbon materials and the bowls of this material are “knockproof”. Although the benefits of carbon for smoking pipes are not controversial the substitution of the wood bowl will have to wait till the fashion orientated consumer's behavior is changed.     

Polarised infrared and differential scanning calorimetry studies on oriented vinyl pipe materials

The molecular orientation in a conventionally extruded PVC pipe, a uniaxially oriented PVC pipe and a biaxially oriented PVC pipe has been studied via Infrared dichroism. The degree of order or crystallinity has also been studied by Differential Scanning Calorimetry and also via Infrared Spectroscopy. The fundamental structural difference between the conventional and oriented pipes was that polymer chains were preferentially aligning in the hoop direction for oriented pipes whereas they were fairly isotropic in the conventional pipe with a slight preferential alignment in the axial direction. Analysis of the C–Cl stretching mode indicated that the uniaxially oriented pipe had much higher alignment of the C–Cl bond in the axial direction than the biaxial pipe, which correlates with higher fracture toughness for circumferential cracking in the biaxial pipe. Both DSC and Infrared spectroscopy detected little change in the crystallinity or order in the oriented pipes compared to the conventionally extruded pipes.     

The flow of conducting fluids through circular pipes having finite conductivity and finite thickness under uniform transverse magnetic fields

The steady flow of viscous, incompressible, electrically conducting fluids through circular pipes in the presence of an applied uniform transverse magnetic field is considered. In this analysis, the finite conductivity and wall thickness of the pipe have been taken into account. An exact solution and its numerical calculation have been presented. Some interesting results have been obtained.     

基于并层单元的大体积混凝土水管冷却温度场热-流耦合精细计算

热-流耦合精细算法能准确反映冷却水管附近温度梯度,从而精确计算大体积混凝土水管冷却温度场,然而该方法在有限元计算中存在前处理规模大、计算效率低的缺点;依据混凝土的热力学参数随龄期变化特性和混凝土水管冷却温度场分布规律,开发了一整套热-流耦合精细计算的前、后处理程序,在计算过程中依据龄期特性对混凝土单元不断进行并层处理,从而实现了大体积混凝土水管冷却温度场整体-局部一致模型的快速建立和高效精确数值模拟。数值计算算例表明该方法能在保证计算精度的同时,极大地降低有限元计算过程中的单元规模,有效地节约了计算时间,提高了计算效率,使得大体积混凝土温度场全过程精细数值仿真得以实现。