Preliminary design of composite riser stress joints

The objective of this paper is to investigate the technical feasibility of using hybrid carbon and glass-fibre reinforced epoxy composite tubes as production risers for a tension leg oil platform tethered in 1000 m of water. The axial forces and bending moment distributions applied to the riser were calculated by hydrodynamic finite element analysis, taking into consideration the extreme environmental conditions, large displacements, waves, currents and platform motions, which could occur in a 100 year recurrent storm. Loads induced by pre-tensioning the riser, the weight of the riser, external water pressure and the internal pressure that could arise in the event of a blow-out in the well were also considered.The riser was of 220 mm internal diameter and the walls were reinforced with layers of carbon-fibre wound at ±20° to the tubes axis, sandwiched between circumferentially wound glass-fibre reinforced epoxy layers on the inner and outer surfaces. The thickness of the carbon-fibre reinforced layers tapered along the 24 m lengths of the top and bottom sections of the riser, which are described as tapered joints. The strengths at various sections of the composite tubes were calculated using orthotropic, laminated, thick cylinder theory and progressive failure analysis. The wall thicknesses were chosen by comparing the predicted first failure load and 1/3rd final failure load envelopes with the various combinations of axial tensile and bending loads and internal and external pressures that the tubes could encounter. The possibility of delamination occurring at the ply drop-offs in the walls of the tapered joints was investigated using finite element methods and fracture mechanics.The composite riser was shown to satisfy all the design requirements and to weigh less than half the weight of an equivalent steel component.     

Bio-inspired design of aerospace composite joints for improved damage tolerance

This paper uses a bio-inspired design strategy based on tree branch joints to improve the damage tolerance of co-cured composite T-joints. The design of tree branch joints at different length scales from the microstructural to the macro-length scale was investigated. X-ray computed tomography of a pine tree revealed three main features of tree branch joints which provide high structural efficiency and damage tolerance: integrated design with the branch embedded into the centre of the trunk; three-dimensional fibril lay-up in the principal stress directions; and variable fibril density to achieve iso-strain conditions through the joint connection. Research presented in this paper adapts the embedded structural feature of tree joints into a carbon/epoxy T-joint. The flange plies were embedded to 25%, 50% and 75% of the depth of the skin of the composite T-joint to mimic the design of tree branch joints. Experimental testing revealed that the bio-inspired T-joint design with integrated adherends had increased normalised inelastic strain energy (defined as ductility), increased normalised absorbed strain energy to failure, and higher load-carrying capacity following damage initiation (damage tolerance) compared to a conventionally bonded T-joint. However, these improvements were achieved at the expense of earlier onset of damage initiation in the T-joints.     

过盈配合和预紧力的混合作用对复合材料机械连接结构的影响及其机制

为研究钉孔过盈配合情况和紧固件预紧力及二者混合作用对复合材料连接强度的影响及其机制,提出了一种基于试验验证的有限元方法,在有限元模拟结果与两组不同配合复合材料与钛合金单剪双钉连接拉伸试验吻合良好的基础上,进一步模拟6种不同螺栓预紧力和7种不同钉孔配合模式的组合,共42种不同情况的结构承载能力。通过对模拟结果的分析发现：一定的干涉配合值和预紧力虽然可能导致钉孔周围在受载较小时提前出现较小破坏,但在载荷较大时反而可以改善孔周的接触条件,从而减小孔周的纤维破坏范围,并最终提高连接结构的破坏载荷。而且钉孔配合情况和螺栓预紧力对连接结构承载能力会相互影响,即在不同钉孔配合情况下所得到的紧固件预紧力优化值会有所不同,反之亦然。因此在进行复合材料机械连接结构承载能力优化时,必须同时考虑不同参数的影响,才能获得最优的结构设计。     

On design methods for bolted joints in composite aircraft structures

The problems related to the determination of the load distribution in a multirow fastener joint using the finite element method are discussed. Both simple and more advanced design methods used at Saab Military Aircraft are presented. The stress distributions obtained with an analytically based method and an FE-based method are compared. Results from failure predictions with a simple analytically based method and the more advanced FE-based method of multi-fastener tension and shear loaded test specimens are compared with experiments. Finally, complicating factors such as three-dimensional effects caused by secondary bending and fastener bending are discussed and suggestions for future research are given.     

Effect of the structural reinforcement of composite adherends on the mechanical strength of adhesive joints

This study proposes a novel method to strengthen fiber reinforced plastic (FRP) adherends in a single lap joint (SLJ) by using Kevlar threads. The adherend reinforcement procedure consists of applying a zigzag thread in the fiber glass layers that comprise the adherend in order to subsequently manufacture the adherends using the vacuum infusion method. For this study, three single lap joint configurations were used: Adherends without Kevlar reinforcement (SLJ₁), adherends with Kevlar reinforcement with a medium step zigzag (SLJ₂) and adherends with Kevlar reinforcement with a small step zigzag (SLJ₃). Mechanical tensile tests were carried out to determine the ultimate strength and displacement of the single lap joint configurations studied. Adherends reinforced by Kevlar threads increase the strength and displacement of the single lap joint. However, the influence of the step size of zigzag threads on the adherend does not significantly influence the strength, but significantly affects the maximum displacement of the single lap joint.     

Structural design of single lap joints with delaminated FRP composite adherends

This paper deals with the structural design of single lap joints (SLJs) with delaminated adherends using fracture mechanics principles. The interlaminar stresses and Strain Energy Release Rate (SERR) are considered as damage characterizing parameters used for designing the SLJ when delamination damages are pre-embedded in both the adherends at similar positions. Three dimensional geometrically non-linear finite element analyses (FEAs) of SLJ with delaminated adherends have been performed to determine the interlaminar and SERR values along the delamination fronts by simulating the simultaneous interaction delamination damages when pre-embedded at similar positions in both the adherends. SERR values are evaluated using Modified Crack Closure Technique (MCCI) which is based on energy principle. The delaminations are assumed to be of linear front, and have been considered to be embedded in both the laminated FRP composite adherends beneath the surface ply of the adhesively bonded SLJ. The delamination damages are presumed either to pre-exist or get evolved at the interlaminar locations. Such delaminations have been modelled using the sublaminate technique. The critical issues of modelling pre-embedded delamination damages are discussed in detail. The numerical results presented in this paper are based on the validated FE model compared with the available literature. Based on the present analyses, the structural design recommendations have been made for the SLJ when pre-embedded delamination damages are present in both the adherends. It is observed from the stress based design that the delamination damage when present in the bottom adherend is more detrimental for failure of SLJ compared to that for the case when it is present in the top adherend. Also, SERR based design reveals that the opening mode predominantly governs the propagation of delamination damage for all positions of the pre-embedded delaminations in both the adherends of the SLJ.     

Progressive damage analysis as a design tool for composite bonded joints

This paper discusses the application of progressive damage analysis (PDA) methods as a design tool. Two case studies are presented in which the effects of changing design features on the strength of bonded composite joints are evaluated. It is shown that the trends of parametric evaluations performed with full-featured PDA models can be unintuitive and the trends can be opposite to those obtained with traditional design criteria. The joint configurations that were tested exhibit multiple damage modes, requiring several different PDA tools to accurately predict the structural peak loads. For damage tolerant structures that exhibit complex sequences of multiple failure mechanisms, traditional failure prediction tools are insufficient. Parametric PDA models encompassing a bonded joint specimen's design space have the potential to reveal unintuitive and advantageous design changes.     

等温时效对新型Sn-Ag基复合钎料显微组织和力学性能的影响

研究了等温时效对Sn-3.5Ag共晶钎料及其复合钎料的力学性能和显微组织变化的影响。为了弥补传统复合钎料制备和服役中强化颗粒容易粗化的问题, 制备了不同种类最佳配比的具有纳米结构的有机无机笼型硅氧烷齐聚物(POSS)颗粒增强的Sn-Ag基复合钎料。对钎焊接头在不同温度（125、150、175℃）下进行时效,通过SEM和EDAX分析了钎料与基板间金属间化合物层(IMC)的生长情况。结果表明, 经过不同温度时效,复合钎料钎焊接头界面处金属间化合物的生长速率比Sn3.5Ag共晶钎料慢, 复合钎料的IMC生长的激活能分别为80、97和77kJ/mol,均高于Sn3.5Ag共晶钎料。经过150℃时效1000h后,复合钎料钎焊接头的剪切强度分别下降了22%、13%和18%,下降幅度相当或明显小于Sn-3.5Ag钎料钎焊接头。      

搭接区端部细观结构对受拉复合材料单搭接头力学响应的影响

在复合材料单搭接头的加工过程中,在搭接区端部会形成一些细观结构,从而在这些区域常存在比较严重的应力集中。应用实验和有限元方法研究了胶瘤和复合材料端部毛刺这2 种搭接区端部细观结构对受拉复合材料层合板单搭接头力学响应的影响。应用数字图像相关方法测量了搭接区端部的应变场分布情况,同时利用基于子模型技术的非线性有限元方法分析了搭接区端部细观结构的作用。实验结果与有限元分析结果吻合较好。实验和有限元结果都表明胶瘤分担了部分载荷,可以降低搭接区端部的应力集中。复合材料端部毛刺的作用与毛刺的具体结构关系密切,不同结构的毛刺对搭接区端部应力应变分布的影响是不同的。     

Robust economic control chart design

Designing a control chart involves making fundamental decisions about the control chart parameters. Traditionally, practitioners select design parameters using ad hoc procedures. Academic research has been challenging this tradition by introducing a more rigorous criterion for selecting the design parameters based on economic criteria. However, there has been limited success in implementing economic designs. This research develops the concept of Robust Economic Design of control charts where multiple economic and process scenarios are considered in control chart design. By developing a robust optimization technique for economic control chart design, we hope to promote a better understanding of industrial implementation of economic designs of control charts. The effectiveness of this technique is illustrated through examples and a sensitivity analysis.     

复合材料缠绕接头设计

复合材料接头由于其轻质、高强及可设计性好等特点,被越来越多地运用于国外大型民用飞机的结构设计中.本文通过有限元建模,对一种新型的复合材料缠绕接头在拉伸和压缩载荷下的力学响应进行研究.主要围绕基础型、梭型和锥型三种典型的接头形式,比较了不同构型对缠绕接头力学性能的影响.结果表明,三种典型构型的复合材料缠绕接头均具有较好的...     

Corrosion of composite welded joints

The process of corrosion of composite welded joints of 20 steel and 08Kh18N9T stainless steel produced by manual argon-arc welding is investigated by electrochemical methods. It is shown that a contact galvanic couple is formed in the zone of the welded joint and, as a result, the surface of 20 steel in the vicinity of the weld turns into the anode and intensely corrodes. For this reason, composite welded joints should not be used in heart-power engineering. Odessa State Academy of Food Technologies, Odessa. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6. pp. 33–36, November–December, 1996.     

Optimization design of control chart systems

This article proposes an algorithm to design an integrated control chart system consisting of several individual control charts, each of which is used to monitor a critical process stage in the manufacture of a product. The design algorithm considers all the charts within a system in an integrative and optimal manner. Consequently, the performance characteristics of the system as a whole can be significantly improved and the product quality will be further enhanced. Such an improvement is achieved without requiring additional cost and effort for on-line inspections. Furthermore, the floor operators can utilize and understand the optimal control chart system as easily as they do the existing system. Some useful guidelines have also been highlighted to aid the users to adjust the control limits of the control charts in a system.     

Resistance welding of thermosetting composite/thermoplastic composite joints

An investigation of the resistance welding between carbon fibre (CF)-reinforced polyetherimide (PEI) and CF-reinforced epoxy laminates is presented. A three-dimensional transient finite element model (FEM) featuring heat transfer, consolidation and thermal degradation was used for simulating the process. A hybrid interlayer made of a glass fibre (GF) fabric essentially impregnated with PEI on one side and with epoxy resin on the other side was produced to provide mechanical interlocking between the thermoplastic (TP) and the thermosetting (TS) systems. The ‘optimal’ resistance welding time based on the maximum lap shear strength (LSS) was determined for three power levels and correlated to the time required to achieve bonding predicted by the FEM. Consolidation quality and failure mechanisms were discussed in relation with processing parameters. Experimental and simulated processing windows were constructed and correlated to each other. However, thermal degradation as predicted by the model did not correlate to a reduction in performance of the joint.     

A review on the driving performance of FRP composite piles

Fibre composites have been a viable option in replacing traditional pile materials such as concrete, steel and timber in harsh environmental conditions. However, driving composite piles require more careful consideration due to their relatively low stiffness. Currently, there are no specific guidelines on the installation of composite piles which limits their acceptance in load-bearing applications. There is a need therefore to understand their behaviour during driving in order for composite piles to be safely and economically driven into the ground. This paper presents an overview on composite pile technologies and an examination on the different factors that affects their driving performance. Emphasis on the potential use of hollow fibre reinforced polymer (FRP) piles and the need for further study on their impact behaviour is highlighted. It is expected that the information provided in this paper will help researchers and engineers to develop efficient techniques and guidelines in driving composites piles.     

Simulation of pin-reinforced single-lap composite joints

A simple and efficient computational approach is presented for analyzing the benefits of through-thickness pins for restricting debond failure in joints. Experiments have shown that increases in debond resistance and ultimate strength depend on the material, size, density, location, and angle of deployment of the pins and the mechanisms of pin deformation, which are complex and strongly affected by the mode ratio of the debond crack. Here the mechanics problem is simplified by representing the effects of the pins by tractions acting on the fracture surfaces of the debond crack. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of competing failure mechanisms, including tensile or compressive failure of the adherends, joint debonding (creating leak, for example, if the joint is in a pipeline), and ultimate failure associated with pin rupture or pullout. Calculations illustrating complex mode ratio variations are presented for a lap joint specimen comprising curved laminate segments cut from pipes.     

Spectrum fatigue of composite bolted joints

The new Swedish fighter JAS39 Gripen has a large number of primary structures made of composites. On those structures a large number of bolted joints are used which during the aircraft's service life will be subjected to spectrum fatigue loading. Consequently it is important to study the spectrum fatigue life of bolted joints. Specimens with a double-lap configuration and six bolts have been fatigue loaded at the load ratios R=−0.2 and R=−5. Specimens were also fatigue loaded with a vertical fin spectrum which had different amounts of elimination of load cycles. A linear damage rule, Miner's rule, was used to predict the spectrum fatigue life. The experimental results show that the shortest fatigue life occurs for specimens loaded at R=−1 followed by specimens loaded at R=−0.2. The longest fatigue life occurred for specimens loaded at R=−5. It was found that 50% elimination of load cycles in the spectrum can be used without affecting the fatigue life. The Miner's rule predictions appeared to overestimate the spectrum fatigue life. From bolt failure it was found that the first bolt row transfers the largest amount of load in the specimens.     

复合材料负泊松比格栅结构设计及力学性能评价

对复合材料负泊松比格栅新结构的设计、制备与评价进行了研究,采用有限元方法模拟了负泊松比结构单元在轴压载荷作用下的力学行为,通过热压罐成型制备复合材料负泊松比格栅结构,并评估其成型质量、蒙皮及筋条的力学性能、结构抗轴压性能。数值模拟结果表明,负泊松比格栅结构与正交格栅结构相比,变形形式从马鞍形变为波纹形,横向膨胀量降低,应力分布均匀性提升,筋条-轴线夹角θ=30°时,负泊松比格栅结构达到最优。采用热压罐成型的MT300/603碳纤维/环氧树脂负泊松比格栅试件成型质量良好,蒙皮及筋条的力学性能优异。力学测试结果表明,筋条-轴线夹角θ=30°时,MT300/603负泊松比格栅结构轴压模量为65.92 GPa,轴压失效载荷为64.65 kN。轴压失效模式为筋条节点处的蒙皮-筋条开裂。筋条-轴线夹角θ=30°的MT300/603负泊松比格栅结构抗压强度高于正交格栅结构,且力学行为呈现明显的负泊松比特征,是一种具备优异综合力学性能的新格栅结构,在航天飞行器蒙皮结构等领域具有潜在的应用价值。      

Robust economic-statistical design of X-bar control chart

Control charts are developed to monitor the service and production processes. The fact that many processes have uncertain parameters is a barrier to obtain the best design of the control charts. In this paper, economic statistical design (ESD) of the X-bar control chart utilising robust optimisation approach that considers interval estimates of uncertain parameters is investigated. A heuristic algorithm is developed to obtain the robust scheme of the control chart. Robust design for an industrial problem is compared with traditional ESD, and heuristic design. Numerical analyses and simulation study show that the proposed X-bar control chart offers a better approach and more reliable solutions for practitioners.     

服役低温老化对铝合金-玄武岩纤维增强树脂复合材料粘接接头力学性能的影响及失效预测

为了给铝合金-玄武岩纤维增强树脂(BFRP)复合材料粘接结构在汽车工业中的应用提供参考和指导,加工了铝合金-BFRP复合材料粘接接头。结合汽车服役中的温度区间,选取?10℃和?40℃的低温老化环境,对接头进行0、10、20、30天的老化。对老化后的粘接接头进行准静态拉伸试验和剪切试验,得到不同老化时间下铝合金-BFRP粘接接头的准静态失效强度。结合DSC和FTIR分析低温老化对BFRP复合材料的影响,并对粘接接头的失效断面进行宏观分析和SEM分析。结果表明:在低温老化环境中,胶粘剂与BFRP复合材料的化学性质受低温老化作用影响不大,BFRP中的官能团与玻璃化转变温度(T_g)没有发生明显的变化,接头的失效强度和失效模式主要受胶粘剂与粘接基材的热应力影响。对于拉伸接头,随着低温老化时间的增加,BFRP复合材料纤维与树脂基体间的结合力降低,铝合金-BFRP复合材料接头的失效断面中纤维撕裂的比例逐渐减少,拉伸接头失效强度逐渐下降。老化后剪切接头仍为内聚失效,BFRP复合材料的低温老化对铝合金-BFRP复合材料剪切接头的失效强度几乎没有影响,剪切接头失效强度的下降主要是胶粘剂与粘接基材热膨胀系数不一致引起的热应力的影响。采用二次应力准则公式对?10℃和?40℃低温环境下,拉应力、剪应力值随老化时间的变化规律进行了拟合,在此失效准则的基础上,根据响应面原理,建立接头失效强度随老化时间变化的三维曲面,为粘接技术在车身结构中的工程应用提供参考。