Mechanical model and mechanical property analysis of fibre-reinforced hybrid composite pipes

Compared to conventional fibre-reinforced composite pipes, fibre-reinforced hybrid composite pipes are more complex and are characterised by the use of hybrid fibres, hybrid matrices, and multiple fibre winding angles. In this study, based on the mechanical model of conventional fibre-reinforced composite pipes, the cross-section division method, the radial pressure on the adjacent layer by spiral wound rope structures, and the calculation method of axial force in each layer were improved. Furthermore, the von Mises stresses in each layer were calculated to discriminate the failure to establish a mechanical model of fibre-reinforced hybrid composite pipes with any number of reinforced layers under axial tension, internal pressure, and external pressure. Experimental data and the finite element method (FEM) were used to verify the reliability of the established model, with the axial tensile mechanical properties analysed based on the established model. The results showed that the large-angle fibres no longer withstood the axial tensile load when the winding angle of the large-angle fibres was greater than 45°. The matrices yielding was much earlier than the fibre breakage. The matrices hybrid methods have a large influence on the axial tensile properties of fibre-reinforced hybrid composite pipes, and improving the material properties of the inner and outer liners can significantly improve the axial tensile properties of fibre-reinforced hybrid composite pipes.     

Thermal expansion of pipe-in-pipe systems

This paper presents a comprehensive mathematical model for the thermal expansion of pipe-in-pipe and bundle systems that are used in the offshore oil and gas industry. The inner pipe and the outer pipes are assumed to have structural connections through bulkheads at extremities and spacers or centralisers to prevent contact of the inner and the outer pipes. The aim is to calculate the displacement and forces on the bulkheads and axial force in the inner pipe.In addition to protective pipe-in-pipes, short and long pipe-in-pipes are defined and the limits between the two are clearly delineated. Analytical methods are extended to study the effects of exponential temperature gradients along both the inner and the outer pipes, the pipe-in-pipe length, tie-in spoolpieces, inner pipe weight, seabed and spacer friction and relative axial stiffness of the inner and the outer pipes on the thermal expansion characteristics. The iterative approach to solve thermal expansion characteristics proposed can be replaced by analytical calculation in most practical situations. Simple analytical formulae are suggested when the outer pipe temperature is constant. Analytical solutions indicate good agreement with finite element numerical results.     

挖泥船耐磨复合管铸造新工艺及性能研究

介绍一种挖泥船双金属复合材料输泥管离心铸造新工艺,研究高铬合金铸铁内层与ZG35外层复合管的组织构造、硬度特性。通过对复合管内层高铬合金铸铁材料进行多种冲蚀角度的泥沙磨损实验,分析探讨高铬合金铸铁材料的磨损机理。     

Buckle propagation of damaged SHCC sandwich pipes: Experimental tests and numerical simulation

Sandwich pipe (SP) combining high-strength performance and thermal insulation has been considered an effective solution for oil and gas transportation in ultra-deepwater. Strain hardening cementitious composite (SHCC) is well known for its capacity to withstand both tensile load and external hydrostatic pressure. The sandwich pipe considered in the research is constituted of concentric steel pipes with SHCC annular layer. In the present research work, the SHCC was manufactured, and full scale sandwich pipes were assembled. Intact and damaged specimens were submitted to controlled external pressure in a hyperbaric chamber to obtain the collapse and propagation pressures, respectively. Modeling and simulation of the buckle propagation of the SPs were correlated with the experimental results. The results show that sandwich pipe with SHCC core has an excellent structural strength under high external pressure in both intact and damaged conditions. Moreover, the results also show that the interaction between the annular and the inner/outer pipes provides a significant contribution to the buckling resistance under propagation pressure.     

Exact and simplified estimations for elastic buckling pressures of structural pipe-in-pipe cross sections under external hydrostatic pressure

Structural pipe-in-pipe cross sections have significant potential for application in offshore oil and gas production systems because they combine thermal insulation performance with structural strength and self weight in an integrated way. Such cross sections comprise inner and outer thin-walled pipes with the annulus between them fully filled by a selectable filler material to impart an appropriate combination of properties. Structural pipe-in-pipe cross sections can exhibit several different collapse mechanisms, and the basis of the preferential occurrence of one over the others is of interest. This article presents an exact analysis for predicting the elastic buckling behaviours of a structural pipe-in-pipe cross section when subjected to external hydrostatic pressure. Simplified approximations are also investigated for elastic buckling pressure and mode when the outer pipe and its contact with the filler material is considered as a pipe on an elastic foundation. Results are presented to show the variation of elastic buckling pressure with the relative elastic modulus of the filler and pipe materials, the filler thickness, and the thicknesses of the inner and outer pipes. Case studies based on realistic application scenarios are used to show that the simplified approximations are sufficiently accurate for practical structural design purposes.     

船体复合材料帽型加筋板渐进破坏分析

复合材料加筋板复杂的破坏过程与失效形式增加了应用难度。以面外均布载荷与面内压缩联合作用下的夹芯复合材料帽型加筋板为研究对象,在通过试验结果验证非线性有限元方法准确性的基础上,基于复合材料的hashin准则与胶层界面的最大应力准则展开渐进破坏分析,讨论了极限载荷、破坏模式及失效机理。采用有限元子模型技术对中段破坏区域建模,基于Shokrieh-Hashin准则进行局部破坏分析,讨论蒙皮的铺层损伤规律。结果表明:加筋板呈整体一阶屈曲破坏,极限载荷为316.8 kN;壁板下蒙皮的纤维压缩失效是导致加筋板整体破坏的原因;各铺层的面内失效规律基本相同,蒙皮的纤维压缩失效从外层逐渐向内层扩展,且扩展速率逐渐降低。     

An investigation on flexible pipes birdcaging triggering

An investigation on triggering mechanisms for the birdcaging failure mode of flexible pipes, used in offshore oil and gas production, is carried out. From previous experimental observations, a conjecture is made: the local axisymmetric instability of the external plastic layer, caused by the high radial loading which is internally applied due to the helical armor wires tendency to expand when the pipe is subjected to compression, would be this trigger. A simple instability onset criterion for the external plastic layer, namely, the polymer intrinsic yielding limit stress, is proposed and assessed, analytically, numerically and experimentally for HDPE tubes. Then, previous birdcaging experimental observations are investigated further, focusing on the flexible pipe external plastic layer, to assess the proposed criterion. Strong evidences of validity are obtained.     

A finite element model for flexible pipe armor wire instability

The constructive disposition of metallic and plastic layers confers flexible pipes with high and low axial stiffness respectively when tensile and compressive loads are applied. Under certain conditions typically found during deepwater installation or operation, flexible pipes may be subjected to high axial compression, sometimes accompanied by bending. If not properly designed, the structure may not be able to withstand this loading and fails. From practical experience observed offshore and in laboratory tests two principal mechanisms, which will be discussed in this paper, have been identified regarding the configuration of the armor wires. When the pipe fails by compression the armor wires may exhibit localized lateral or radial deflections, consequently permanent damage is observed in the armor wires with a sudden reduction of the structure’s axial stiffness. The pressure armor may also unlock, thus causing potential fluid leakage.In this work a finite element model is developed to estimate the critical instability load and failure modes. An axi-symmetric model is constructed employing a complex combination of beam and spring elements. For each armor layer only one wire needs to be modeled, hence the computational cost is minimized without compromising the phenomenon characterization. A parametric case study is performed for a typical flexible pipe structure, where the friction coefficient between the wire armors and the external pressure are varied, and the critical instability loads and failure modes are obtained and results are discussed.     

2519铝合金表面微弧氧化膜的结构与耐蚀性能

研究了2519铝合金微弧氧化膜表面形貌、截面形貌特征与成分分布特点、相结构以及微弧氧化膜的耐蚀性能.结果表明,氧化膜为55 μm厚膜时主要由α-A12O3、γ-A12O3和A16Si2O13组成,并有非晶相;截面形貌呈现明显的两层结构特征,致密层厚约35 μm,表面疏松层厚约20 μm.致密层中Al、Cu、O含量均高于表面疏松层的,而表面疏松层Si含量明显高于致密层的,A16Si2O13主要分布于表面疏松层.该氧化膜使铝合金试样的Icorr减小3个数量级以上,并明显提高了腐蚀电位.     

多层声学覆盖层复合的有限长弹性圆柱壳声辐射特性研究

针对水下双层圆柱壳内外壳体各表面敷设隔声阻尼层的情况,建立了有限长多层复合加实肋板的双层圆柱壳水下声辐射计算模型.对模型采用模态展开法,系统考虑壳体与隔声层和实肋板耦合,外表面声学覆盖层作用和外部声场耦合,并以状态矢量对应的矩阵形式导出复合壳体辐射声功率的计算表达式.数值计算了隔声阻尼层和外场声学覆盖层层参数,实肋板参数和壳体阻尼对模型辐射声功率的影响.研究结果表明:有实肋板时阻尼层的降噪量最高接近15dB,实肋板的声短路作用限制了隔声阻尼层的降噪效果;双层隔声阻尼层比单层隔声阻尼层降噪效果好3-4dB.外场声学覆盖层受实肋板影响较阻尼层小,其降噪量达10dB左右.     

A finite element methodology for birdcaging analysis of flexible pipes with damaged outer layers

Flexible pipes are commonly exposed to damages on the outer layers due to abrasion with seafloor or improper installation and operation, which may render them vulnerable to birdcaging failures. This paper presents a finite element model for the residual axial compressive strength evaluation of a flexible pipe with local damage on the outer layers. The elastoplastic nonlinearity of tensile armour steel layers and hyperelasticity of polymeric outer sheath are taken into account. This model is verified against existing test data. Parametric studies are then performed by varying the damage size in either the pipe axial or circumferential directions. The flexible pipe axial resistance, deformations, as well as the tensile armour wires layers stress states near the damaged section under different damage and axial compression conditions are discussed. The case studies show that damage on the outer layer, especially the anti-birdcage tape layer, is highly detrimental to flexible pipe residual strength against axial compression. The present results and discussions are instructive in understanding the flexible pipe birdcaging mechanism.     

Research on the fragment impact resistance of a composite mast

Due to the unique structural mode and material property of a composite sandwich plate, related research such as fragment impact resistance of a composite mast is short of publication and urgent in this field. In this paper, the commonly accepted sandwich core board theory was modified. Damage caused by a fragment attack was simulated onto a sandwich plate model built with solid and shell elements. It was shown that shear failure and vast matrix cracking are the main reasons for outer coat damage, and tension failure and partial matrix cracking are the cause for inner coat damage. Additionally, according to complexities in actual sea battles, different work conditions of missile attacks were set. Ballistic limit values of different fragment sizes were also obtained, which provides references for enhancing the fragment impact resistance of a composite mast.     

复合材料层合板螺栓连接接头极限强度分析

对基于不同渐进失效准则计算复合材料层合板螺栓连接接头极限承载力的高精度预报方法展开研究。基于Abaqus有限元软件,采用USDFLD子程序对接头进行渐进失效分析。分别采用最大应力准则、蔡-希尔失效判据、霍夫曼失效准则、蔡-吴失效准则、哈辛失效准则等5种失效准则进行数值计算。建立不同的场变量描述纤维、基体、界面的损伤状态,研究复合材料层合板螺栓连接接头在拉伸载荷作用下的损伤发展过程。研究表明,基于这5种失效准则计算的有限元仿真结果均与试验值较为接近,其中采用纤维失效和基体失效分开考虑的哈辛失效准则计算的复合材料层合板螺栓连接接头的极限强度与试验结果的准确度吻合最好,较适用于复合材料螺栓连接结构的有限元仿真。     

组合式活塞的装配间隙和预紧扭矩的计算方法

在内燃机中组合式活塞结构应用广泛,例如钢顶铝裙活塞、内外组合活塞等。但由于对组合活塞的零件配合间隙(过盈)值选择不当而引起的活塞损坏事故也时有发生。本文给出一种组合活塞配合间隙(过盈)值的计算方法,可以替代以往单凭经验估算的传统方法。 本文还介绍了计算组合活塞螺纹预紧扭矩的新方法,并获得了预紧扭矩与活塞应力的关系曲线,可以对组合活塞的螺纹预紧扭矩进行选择。 作者使用上述两项计算方法对K48E150ZC柴油机活塞进行了计算分析,探明了该活塞长期存在的问题,指出了在配合间隙和预紧扭矩方面的改进措施,为该柴油机顺利通过耐久考核试验和技术鉴定作出贡献。     

高速船复合材料层合板非线性动力失稳分析

对高速船复合材料层合板在轴向线性增长载荷作用下的非线性动力失稳进行了研究。基于极的大挠度基本假设,导出四边简支矩形层合板的非线性动力方程及变形及协调方程;用级数展开把非线性偏微分方程组化为易于求解的Kronecker内积形式的二阶常微分方程组,并由四阶Runge-kutta法数值求解,讨论了加载速率对复合材料层合板动力失稳的影响。由于本文在方程求解中采用了Kronecker内积,故提高了解的精度及效率。     

On the effect of the ply stacking sequence on the failure of composite pipes under external pressure

The use of high performance structural composites has become very important over the last decades, especially where weight is an essential factor. Particularly in the oil and gas industry, several designs of composite pipes for deep water applications have been recently proposed as competitive solutions against traditional steel pipes. Thus, it is important to assess the performance of composite pipes under high external pressure in order to avoid pipe failure or overconservative designs. In this paper, experimental tests of different composite pipe configurations are performed and then compared to analytical and numerical predictions. Unlike the case of internal pressure loads, the collapse pressure of composite pipes depends on the initial ovality and on the ply stacking sequence. The collapse resistance of different composite pipes is firstly studied through simplified analytical equations combined with different failure criteria. Then, a finite element model is developed using a progressive failure criterion [1]. Both analytical and numerical failure predictions were compared to experimental tests carried out on four composite pipes produced with different ply stacking sequence by the filament winding method [2]. An experimental-numerical-analytical comparison shows that numerical and analytical models provide results in good agreement with those obtained experimentally. Finally, a parametric analysis is carried out to show the effect of ovality and ply stacking sequence on the failure pressure of composite pipes.     

基于复合材料的水下耐压结构拓扑优化探究

探究基于复合材料的拓扑优化设计方法在水下耐压结构设计中的应用.本文方法是在等值线方法、SIMP(Solid Isotropic Material with Penalization)模型、灵敏度过滤技术的基础上,推导复合材料的等效刚度矩阵.通过经典桥形结构优化算例、静水压作用下的结构拓扑优化设计以及空心水下耐压结构优化设计,分析了在拓扑相关载荷作用下,复合材料对于水下耐压结构的最优拓扑形式的影响.发现复合材料与各向同性材料结构的优化结果比较相似,而复合材料的铺层方式及角度的变化可能对优化结果产生较大的影响,本文对空心耐压结构的优化结果与MIT团队提出的耐压壳概念相类似,说明复合材料的拓扑优化研究对于未来水下耐压结构的设计具有重要的参考价值及指导意义.     

RFID wireless system for detection of water in the annulus of a flexible pipe

Corrosive environments are responsible for the highest degree of degradation and failure in marine structures. The presence of sea water in marine structures such as flexible pipes can cause a significant reduction in their operational life, especially when associated with permeated gases, which could lead to corrosion related failure mechanisms such as corrosion-fatigue and hydrogen cracking. The ingress of sea water into flexible pipes can occur either due to ruptures in their external polymeric sheath or to permeation of condensed water from the pipe bore. This event since flooding of the so-called annular space of flexible pipes is the trigger for all knows corrosion assisted failure modes, it is clear that a system that is able to reliably detect the presence of water in the structure is highly desirable. This work will describe a radio frequency identification (RFID) system designed for this purpose; it relies on the measurement of shifts in the resonance frequency of specially-designed tags which would be inserted within the layers of the flexible pipe during manufacturing. This paper shows the design and validation process of these tags and also of a reader which is meant to be scanned along the outside surface of the pipe by a remotely-operated vehicle (ROV). The study was performed through a finite element analysis and a test in which the tags were inserted within a full-scale mock-up of a flexible riser, which was then flooded with synthetic seawater. Results show that the shift in response due to sea water is clearly identifiable and distinguishable from other effects.     

A finite element model for unbonded flexible pipe under combined axisymmetric and bending loads

Flexible pipes are key equipment for offshore oil and gas production systems, conveying fluids between the platform and subsea wells. The structural arrangement of unbonded flexible pipes is quite complex, encompassing several layers with polymeric, metallic and textile materials. Different topologies and a large amount of intricate nonlinear contact interactions between and within their components, especially because of the relative stick-slip mechanism during bending, makes numerical analysis challenging. This paper presents an alternative three-dimensional nonlinear finite element model that describes the response of flexible pipes subjected to combined axisymmetric and bending loads. To simulate the response of a flexible pipe under axial tension or compression combined with uniform curvature, an equivalent thermal loading is employed on the external sheath, which is modelled as an orthotropic thermal expansion material with temperature-independent mechanical properties. To assess the feasibility of the proposed model, the bending moment versus curvature of the finite element solution is compared with experimental results obtained in literature and good agreements are found between them. Detailed finite element results such as contact pressures, armour wire slip displacements and friction, normal and transverse bending stresses are also shown and compared with available analytical models.     

Analysis of impact damage characteristics of marine carbon fiber composite laminates embedded with PEI film北大核心CSCD

[目的]在传统船用碳纤维复合材料层合板层间添加热塑性相材料能有效提升船用复合材料的抗冲击性能,为探究其冲击损伤特性,开展实验研究。[方法]使用光学显微镜观察层合板的热塑性/热固性界面,分析两相材料的结合方式;对不同结构的复合材料层合板进行低、中、高3种不同能量的低速冲击;通过超声C扫描与电子显微镜,对各试件的损伤形貌进行观测,以研究各试件的冲击响应及损伤机理。[结果]结果显示,相较于碳纤维层合板,含热塑性相的船用复合材料层合板具有更好的损伤阻抗;内部嵌膜层合板试件在冲击能量为8和12 J的冲击下,内部分层损伤分别减少了19%和39%,且受到12 J冲击后,内部结构损伤较小,完整性较好。[结论]将PEI热塑性膜嵌于内部能提升层合板的韧性,显著减少内部分层损伤,明显提升内部嵌膜层合板的抗冲击性能。