浅析直升机复合材料修理技术

复合材料在直升机上的广泛应用可有效地改善直升机的性能,随着这种应用的增加并为更有效地使用复合材料,迫切地需要发展可靠的修补技术。简单介绍直升机复合材料的修理原则、无损检测,并叙述复合材料的修补方法。     

民航飞机复合材料修理

本文深入浅出向读者介绍我国民航飞机复合材料修理技术，通过对本文阅读能让读者系统学习目前我国民航飞机复合材料修理程序及掌握相关修理工具设备的应用。     

挖补修理复合材料层合板疲劳性能研究进展

随着纤维增强复合材料结构的应用更加广泛,其结构修理问题日渐凸显。挖补修理在复合材料层合板修理中具有重要地位,而修理后结构的疲劳性能是评价结构修理质量的重要依据,因此对复合材料挖补修理层合板疲劳性能的研究意义重大。文中从模型和试验两方面总结了挖补修理复合材料层合板疲劳性能研究现状,指出了当前挖补修理复合材料层合板疲劳性能研究存在的问题,可为复合材料结构挖补修理研究和工程应用提供参考。     

先进复合材料可制造性中的成本估算理论框架

飞行器复合材料构件的可制造性评价是其结构制造工艺方案决策的重要依据,成本是评价体系中的一个重要指标。本文概述了先进复合材料可制造性中的成本概念及组成,应用过程估算方法建立了成本指标的估算理论框架及初步模型。通过对工时估算理论的分析,提出了适合于过程估算方法的工时概念关系式。应用本文所提出的先进复合材料可制造性成本估算理论,能够有效地建立较为实用的可制造性成本评价估算模型。     

飞机复合材料结构修理设计渐进损伤研究

复合材料在现代飞机结构中所占比重越来越大。从现阶段大量的金属飞机结构繁重的维修任务可以看出,未来复合材料飞机结构维修任务的艰巨性。复合材料结构修理渐进损伤研究已经成为未来复合材料技术研究的重要方向。本文从复合材料层合板贴补修理分析与强度预测分析入手,讨论复合材料层合板挖补修理技术。     

复合材料螺接修理结构参数化建模分析工具开发及验证

螺接修理在复合材料结构的临时性修理,尤其是战伤修理中应用较广泛。然而其修理设计过程较复杂,建模分析难度较大,难以满足工程快速定参的需要。本文针对含穿透损伤复合材料层合板的螺接修理问题,采用VB.NET结合p型有限元技术,开发了一套参数化的建模分析工具。分析工具通过界面读取修理结构的几何参数、螺栓布局、螺栓大小、载荷、材料属性等参数,自动创建有限元模型并进行求解。根据求解结果,分析工具可为用户提供修理结构的螺栓载荷、钉载比例、危险孔孔边应力等。另外,通过引入有限断裂力学,结合两级模型分析技术可预测得到修理结构的失效强度和失效位置。最后,采用典型算例对分析工具的有效性进行了验证。     

复合材料胶接修理层合板拉伸性能及影响参数

胶接修理是效率较高、应用较广的复合材料结构修补技术。对采用不同参数进行挖补和贴补修理的复合材料层合板的拉伸性能进行实验研究。结果表明:挖补修理实验件的强度恢复率约为66%~91%,贴补修理实验件的强度恢复率约为44%~61%。在挖补修理实验件中,减小挖补斜度、采用双面挖补、使用热压罐固化,在贴补修理实验件中,采用双面贴补、增大补片尺寸,均可得到更高的强度恢复率。在实验基础上建立的有限元模型,能够有效预测实验件的失效载荷、破坏模式,并可分析实验件的应力分布和渐进损伤过程,为设计修理方案提供参考。     

结合国情和需要努力发展我国的复合材料技术

结合国情和需要努力发展我国的复合材料技术中国航空工业总公司张登高一、先进复合材料当前的发展动向先进复合材料是材料大家族中近一、二十年来迅速崛起的一颗“新星”，特别是在航空工业中占有相当重要的地位。下面首先简要介绍国外对于先进复合材料技术的研究、应用和...     

先进树脂基复合材料制造技术进展

国内先进树脂基复合材料制造技术经过30多年的发展, 已初步形成以热熔预浸料制造、 热压罐和树脂传递模塑(RTM)成型技术为代表的先进树脂基复合材料制造技术体系, 所制备的先进树脂基复合材料已在航空领域得到大量应用。本文中主要介绍国内先进树脂基复合材料热压罐成型技术、 RTM成型技术和自动铺放技术的最新进展以及先进树脂基复合材料制造过程模拟与优化技术, 讨论了国内先进树脂基复合材料制造技术的主要发展方向。     

先进树脂基复合材料制造技术进展

国内先进树脂基复合材料制造技术经过30多年的发展,已初步形成以热熔预浸料制造、热压罐和树脂传递模塑(RTM)成型技术为代表的先进树脂基复合材料制造技术体系,所制备的先进树脂基复合材料已在航空领域得到大量应用.本文中主要介绍国内先进树脂基复合材料热压罐成型技术、RTM成型技术和自动铺放技术的最新进展以及先进树脂基复合材料制造过程模拟与优化技术,讨论了国内先进树脂基复合材料制造技术的主要发展方向.     

Application of bonded composites in the repair of ships structures – A 15-year service experience

The carbon fibre composite overlays (patches) installed on a Royal Australian Navy frigate to inhibit the recurrence of superstructure fatigue cracking have been in service for 15 years now. The service life these composite repairs have accumulated is now sufficient for the ship to have gone through several complete maintenance cycles. The ship has also had a major upgrade/modification programme and been exposed to a full range of environmental conditions while it has served on its many active deployments. This paper examines the success of this repair methodology in the light of ship owner’s expectations. These expectations have two major aspects which are addressed here.The first is the effectiveness of the composite repair in restoring the strength and function of the damaged structure, the cost and timeliness in effecting that repair and the disruption incurred prior to and during the repair.The second aspect to determining the success of the composite repair is more long term. This comprises the durability and repairability of the composite repair itself, including the availability of clear, objective, and documented criteria for inspecting the repair in future years and authorising its continued service. Furthermore, the ease with which the repair itself can be removed and replaced to facilitate subsequent maintenance work or modifications to the parent structure, and the ability to survey the parent structure behind the repair all make up this second facet. Unfortunately, this aspect is less obvious to the repair team but quickly becomes apparent to the ongoing custodians of the structure. These custodians are also the ones most likely to be authorising the repair method to be used for similar damage in the future and so they are important stakeholders to keep ‘on side’.This paper reviews the service history of the carbon fibre overlays since their installation and comments on both the short and long term success of the repair methodology.     

Design of Emergency Aircraft Repairs Using Composite Patches

The increasing demand for fatigue life extension of both military and civilian aircraft has led to advances in repair technology for cracked metallic structures. Conventional structural repairs may significantly degrade the aircraft fatigue life and lower its aerodynamic performance. Adhesively bonded composite reinforcement is a new technology of great importance due to the remarkable advantages obtained, such as mechanical efficiency and repair time and cost reduction. In this article, bonded composite patch repairs were designed for quick application to aircraft under emergency conditions, such as aircraft battle damage repair (ABDR). A formulated method was developed, to be applied when damage has to be restored quickly, without restrictions to safety of flight. Different damage cases were investigated using finite-element analysis (FEA), taking into account specific parameters of the structure under repair. Based on the FEA results, a quick design procedure using composite patch repairs for the most frequent damage cases is proposed.     

A self-healing thermosetting composite material

Strategies for the repair or replacement of thermosetting composite components are essential for their safe operation in many applications. To achieve this, complex repair strategies are often employed, requiring gross manual intervention. This is appropriate for extensive damage, but for minor damage can prove inefficient and not worthwhile given the damage that the repair process often inflicts on the structure. Therefore, self-repair techniques for composites have been demonstrated by a number of authors. This paper discusses a novel self-repair technique employing a solid-state repair system for a thermosetting resin that has been shown to be capable of recovering between 50% and 70% of its pre-fracture strength after healing. E-glass fibre composites, produced using this resin, demonstrated that a reduction of delamination area and healing of matrix cracking can be achieved in practice.     

Fracture toughness analysis of inclined crack in cylindrical shell repaired with bonded composite patch

Adhesively bonded composite patch repair has been widely used to restore or extend the service life of cracked structural components due to its efficiency and cost-effectiveness compared to mechanical repair technique. Current available knowledge on patch repair mainly focus on flat damaged structures and the corresponding analysis methods and empirical databases are computationally efficient. In contrast, only limited work has contributed to studying patch repair to curved damaged structures. Authors have developed an adhesive element in conjunction with a shell element to investigate the effect of curvature on the adhesive stresses and mode I fracture toughness of the cracked host shell in the curved repairs. In this paper, this technology is again employed to model an adhesively bonded composite patch repair to a cylindrical shell embedded with an inclined through-thickness crack. The total strain energy release rate (SERR), calculated by the modified virtual crack closure technique (VCCT), is used to evaluate the mix-mode fracture toughness of the damaged structure and further to estimate the efficiency of patch repair. An automatic mesh generation scheme is proposed to conduct a quick parametric analysis, which can also be used to structural optimization design of composite patch repair. The numerical results are presented to show the effect of curvature and inclined angle of the through-thickness crack on fracture toughness of the repaired structure subject to different loads.     

层压板修理设计中的参数选择问题

复合材料层压板的修理问题是复合材料结构修理中的基础性研究课题。其中,贴补法和挖补法是两种基本的修理方法。通过有限元方法对贴补法和挖补法进行了研究,给出了贴补修理和挖补修理的最佳设计参数选择方案。对于大多数贴补修理设计,补片的厚度应该是母板厚度的一半,搭接长度大约在25mm;对于挖补修理,通常可采用6°的挖补角度。试验结果表明,通过计算分析得出的最佳修理设计参数对工程实际具有很好的指导意义。      

Fatigue crack growth behavior of cracked aluminum plate repaired with composite patch

In this study, we investigated the fatigue crack growth behavior of cracked aluminum plate repaired with bonded composite patch especially in thick plate. Adhesively bonded composite patch repair technique has been successfully applied to military aircraft repair and expanded its application to commercial aircraft industry recently. Also this technique has been expanded its application to the repair of load bearing primary structure from secondary structure repair. Therefore, a through understanding of crack growth behavior of thick panel repaired with bonded composite patch is needed. We investigated the fatigue crack growth behavior of thick panel repaired with bonded composite patch using the stress intensity factor range (ΔK) and fatigue crack growth rate (da/dN). The stress intensity factor of patched crack was determined from experimental result by comparing the crack growth behavior of specimens with and without repair. Also, by considering the three-dimensional (3D) stress state of patch crack, 3D finite element analyses were performed to obtain the stress intensity factor of crack repaired by bonded composite patch. Two types of crack front modeling, i.e. uniform crack front model and skew crack front model, were used. The stress intensity factor calculated using FEM was compared with the experimentally determined values.     

FE analysis of the behaviour of octagonal bonded composite repair in aircraft structures

Bonded composite repair has been recognized as an efficient and economical method to extend the fatigue life of cracked aluminium components. In this work, the finite element method is applied to analyze the central crack’s behaviour repaired by a boron/epoxy composite patch. The knowledge of the stress distribution in the neighbourhood of cracks has an importance for the analysis of their repair according to the patch geometry. The effects of mechanical and geometrical properties of the patch on the variation of the stress intensity factor at the crack tip were highlighted. The obtained results show that the stress intensity factor at the repaired crack with composite patch of height 2c/3 is reduced about 5% compared to cracks repaired with octagonal patch of size c. For patch height of c/3 the reduction is about 7%. The adhesive properties must be optimised in order to increase the repair performances and to avoid the adhesive failure.     

氧化石墨烯增强PVA-PAA复合水凝胶的制备及性能研究

水凝胶具有高含水、低摩擦、良好生物相容性等优良性能,被认为是最具潜力的软骨修复材料,但传统水凝胶因为力学强度低限制了其应用。本实验将氧化石墨烯(GO)作为增强剂,通过冷冻-解冻与退火法相结合制备了高强度的聚乙烯醇-聚丙烯酸-氧化石墨烯(PVA-PAA-GO)复合水凝胶。结果表明:PVA-PAA-GO复合水凝胶具有多孔网状结构和良好的力学强度,随着GO含量的增加,复合水凝胶的力学强度呈先上升后下降的趋势,GO含量为0.05%时,力学强度可达34 MPa,GO含量为0.05%、1%时,PVA-PAA-GO复合水凝胶的损耗因子小于0.1,与天然软骨的动态力学性能相似。     

Repair of floating offshore units using bonded fibre composite materials

On ships, tankers and similar vessels structural defects such as cracks and corrosion damage are typically repaired by welding. However, welding is unwanted hotwork on floating offshore units (FOUs) such as floating, production, storage and offloading (FPSO) and floating, storage and offloading (FSO) vessels because it requires shutdown of parts of the vessel thus resulting in expensive production delays. Bonded fibre composite material patch repairs can be used as an alternative to overcome the hazards of hotwork associated with welding. The patches are bonded over the defect and the integrity of the original structure is hence restored. The patch repair technology can also be utilised to provide upgrades, such as life extensions and higher design requirements.A recommended practice (RP) has been developed that describes requirements for patch repairs used in FOUs. To provide flexibility and to fit different repair needs, the RP defines a range of Repair Classes that can be used depending on the urgency of the repair and the need for optimisation. The qualification effort increases with the degree of optimisation. The requirements are based on an extensive test program carried out in the laboratory (reported elsewhere) as well as experience from full-scale repair demonstrators.Two full-scale repair demonstrators were carried out on actual FOUs to demonstrate the feasibility of the RP for bonded composite patch repair. In addition the demonstrators also showed the viability of using bonded composite repairs under harsh conditions encountered in oil and gas exploration and production environments. The first repair was carried out to arrest a fatigue crack that had developed from the corner of a door, while the second repair was carried out to restore material loss on a heavily pitted deck floor. Both repair cases are used as examples to demonstrate the proposed qualification procedures whilst at the same time discussing the challenges and potential applications of this patch repair technology for FOUs in the oil and gas industry.