Composites Assembly for High Performance Fastener-less Structures
2: Biorefining and Advanced Materials Research Centre, SRUC, UK
Composites Assembly for High Performance Fastener-less Structures provides a broad and balanced span of information, covering both fundamentals and applications across academic and industrial state-of-the-art research and development on assembly, joining, inspection and repair of high-performance structures made from fibre-reinforced polymer composites and multifunctional nanocomposites. This knowledge is essential for the realisation of critical features in assembly and joining evolving procedures (across their design, development and performance analysis) in such multi-material systems, but also for the through-life maintenance of composite components used in a range of engineering applications such as those composite structures utilised for wind turbine blades, automotive parts, aircraft wings and fuselage. The book also addresses the non-destructive testing methods used to detect damage occurring in composite joints, which are essential to decide if the repair is needed.
The book begins by providing a fundamental description of the requirements for composite joining, assembly and repair. It goes on to address a variety of joining and repair procedures in composite structures from thermoset adhesive bonding to thermoplastic hybridisation, through-the-thickness reinforcement and sandwich structures. Further chapters cover the reliable assessment of structure's damage tolerance and failure assessment procedures, including non-destructive inspections and image processing based structural health monitoring, and provide understanding of the most likely deterioration mechanisms occurring in processing and assembly of composite materials and structures. The book is wrapped up with the ongoing state-of-the-arts in multifunctional nanocomposites with application for high-performance structures for self-sensing, energy harvesting and properties tailoring.
Composites Assembly for High Performance Fastener-less Structures brings together state-of-the-art practices for assembly, in-service damage and repair procedures along with the existing certification and repair regulations, followed by the futuristic opportunities for enabling and emerging polymer nanocomposites for smart structures, for an audience of academic researchers, advanced students, engineers and manufacturing professionals.
Inspec keywords: laminates; resins; fracture toughness; elastic constants; plastics industry; cracks; delamination; recycling; fracture; carbon fibre reinforced plastics
Other keywords: recycling; laminates; delamination; elastic constants; composites assembly; plastics industry; fracture; high performance fastener-less structures; cracks; resins; fracture toughness; carbon fibre reinforced plastics
Subjects: Engineering mechanics; General topics in manufacturing and production engineering; Rubber and plastics industry; Elasticity (mechanical engineering); Recycling; Fracture mechanics and hardness (mechanical engineering); Engineering materials
- Book DOI: 10.1049/PBME015E
- Chapter DOI: 10.1049/PBME015E
- ISBN: 9781839531491
- e-ISBN: 9781839531507
- Page count: 794
- Format: PDF
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Front Matter
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1 Overview on design and manufacturing of assembled composite aerostructures
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The aim of this chapter is to provide an overview on the methodologies used in the design and best practices applied in the manufacturing of assembled composite primary structures in the aerospace field.
Section 2 provides an overview on the general philosophy applied in the strength analysis, how its objectives are covered by the main product design phases and approach used for un-notched and notched composite laminates.
Sections 3 and 4 deal with the analysis process of fastened and bonded joints; in particular, they illustrate how the load is distributed in different configurations, an overview on how the stress analysis can be performed and typical modes of failure at joint. Section 5 introduces the processes used for assembly composite structures; in particular, the three main categories of joining of composites with thermoset matrices as co-curing, co-bonding and secondary bonding. Furthermore, the key factors to control adhesively bonded joint, together with relevant test cases in the space and aviation industry, have been illustrated.
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2 Processing of polymer composites: autoclave and microwave energy approaches
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In this chapter, autoclave and microwave applicator-based processing of polymer composites have been discussed. First, the principles and physics involved in the curing of polymer composites in both processes have been presented. The equipment details, process parameters, and processing steps have been discussed for both processes. The autoclave curing was compared with the microwave curing process for fabricating a fiber-reinforced polymer composite. The challenges in autoclave and microwave processing of polymer composites have been highlighted and possible future research directions have been discussed.
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3 Industry 4.0 for composites manufacturing
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This chapter reviews current theoretical and empirical studies related to the impact of Industry 4.0 on composites manufacturing. The aim is to identify industry trends and the gaps in the professional practice, making them available to the research community for further investigation.
The research scope is defined at an intersect of the three areas of interest: composites technology, business challenges, and Industry 4.0. The literature search is conducted by keyword search relevant to the areas of interest in academic databases. By further filtering of literature, the relevant papers were established, which were critically reviewed to establish key trends and gaps in professional practice. The critical review explored appropriate theoretical approaches for the area of interest, examined ethical position, and suggested a conceptual framework for investigating Industry 4.0 within composites industrial context.
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4 Development of fibre-reinforced polymer composites through direct digital manufacturing
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Direct digital manufacturing (DDM) is nothing but additive manufacturing (AM) digitally of three-dimensional (3D) printing. It has changed the way things are manufactured traditionally. The term DDM process undergoes from a digital blueprint of a product to a finished physical product. The technology is used to generate an object by computers and manufacture digitally to create real-world objects ranging from simple toy pieces to complex fighter jet parts. It is extensively adopted by many industries for product development such as toys, construction, medical devices, engineering components for automotive, marine, aerospace, space, and even human organs. One of the most important advantages of DDM is to manufacture the products with the high-dimensional accuracy where the cost and lead times can be reliably predicted. It is major breakthrough in manufacturing technology because this process can directly manufacture components without the need for expensive tooling, molding or machining to create complex geometries. In general, fibers have been traditionally used in many manufacturing processes for various reasons. However, using conventional methods, there are obstacles in obtaining the desired complex geometries and low setup costs. AM offers possible avoidance of these limitations. Bridging AM with fiber-reinforced materials offers a vast opportunity for lightweight and strong parts. Depending on the affinity, fibers with different structures can be mixed with different matrix materials and, thus, create stronger parts with improved mechanical properties. Process parameters like raster angle, infill speed, layer thickness, and nozzle temperature also strongly impact physical properties of fiber-reinforced AM products and are considered carefully. The products are used in many industries such as aerospace, motorsports, and biomedicine, where the weight, strength, and complexity of parts are critical. Fiber-reinforced polymer composites (FRP) are the leading engineering materials in twenty-first century. The manufacturing of FRP composites through DDM is a challenge. Therefore, this chapter focuses on the principle, manufacturing process, and its application to different products, and limitations are discussed.
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5 Joining and repair of resin-infused, continuous fibre-reinforced, thermoplastic acrylic-matrix composites for extended applicability
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With the growing demand for sustainable, high-performance materials, a greater need arises to exploit the numerous post-processing advantages that the use of thermoplastic acrylic matrices affords. Acrylic-matrix composites offer advantageous room-temperature processibility and remain recyclable, thermoformable and weldable even after consolidation. There are many attractive material- and process-based opportunities for addressing the open problems surrounding resource depletion and waste management. Owing to growing concerns over the environmental impacts associated with material/resource demand and waste management, repairability, recyclability and weldability are some of the most important material selection criteria within the composites industry. The ability to repair and recycle can considerably change the way end-of-life components are handled, ultimately providing alternatives to landfilling of waste. Joining can yield great weight-saving benefits (avoiding the use of fasteners) and enhance design flexibility for large-scale components and multi-material systems. Acrylic matrices as reshapable, recyclable and joinable materials, create a world of possibilities that must be explored. Moreover, cross-technological and inter-disciplinary research activities can contribute to the success of these explorations, which will undoubtedly have positive environmental and cost implications.
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6 Aerospace composites' repair: integrated processes' feasibility
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Repairs of aerospace composite structures are demanding: many different complex processes are performed while maintaining a strict process control and considering the stringent regulatory framework. Composite materials are becoming a standard for aircraft structure design, so the maintenance, repair and overhaul (MRO) industry needs to be ready to face the new associated challenges.
Different stages are considered in a composite repair: inspection, material removal, surface preparation, patch design, manufacturing and application and post-repair inspection. Many technologies can be applied to each of these tasks; consequently, there is not any agreement on a single solution to guarantee a fast, reliable and efficient repair.
The aim of this research was to analyse all the available technologies in order to suggest an integrated system capable of addressing all the involved steps in a cost-efficient way. The proposed system includes a two-stage non-destructive inspection (NDI), combining pulsed thermography and ultrasonic testing. Its execution is automated, carried out by a robotic arm, which also performs other tasks such as material removal or patch application to increase reliability and repeatability. A laser system is integrated for both micro-machining and surface preparation; this is a future-proofing feature, as laser technology is expected to become a standard for composites processing.
To validate the system feasibility, three main areas are covered. First, NDI experiments are performed to analyse if the information obtained is enough to ensure a fast and reliable damage assessment. Then, CAD modelling is done to integrate all the equipment in a portable platform. Finally, cost analysis guarantees the economic viability of the design and technologies used.
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7 Augmented reality-equipped composites bonded repair
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The prosperity of aircraft transportation together with revolutionary promotion of composite components employed in commercial aircrafts poses enormous challenges (uncertainties associated with polymer process control, zero-thickness defects and non-destructive inspection and testing capability to inspect process-induced defects, etc.) to the industry of aircraft composite repairing. An industry solution owning merits on efficiency, reliability and repeatability is in highly demand.
Augmented reality (AR), a human-computer interaction technology built up above the development of virtual reality, possesses its exclusive superiority on its capability of inflicting digital mock-up into physical environment. The above property of AR provides colossal opportunities to be utilised into the industry territory to contribute to the realisation of automatic, efficient, streamlined and reliable production line. The current project aimed at developing an AR system to explore its way of putting AR technology into aircraft composite repairing industry as a guidance tool to instruct technicians' repairing operation, mitigate human errors, and reduce the duration of repair and assembly. Stepped scarf repair embedded with soft composite patches was selected as the archetype to be brought into effect though hard patches were partially examined as well.
The developed AR system focuses on patch installation and vacuum bagging processes to address the predicament of miscellaneous steps and fibre directions to be followed. It contributes to provide a reliable, repeatable, reproductive and efficient composite assembly operation.
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8 3D printing of multi-material polymer composite systems
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This report overviews the 6-month address into building a multiphysics application to study the behaviour of multi-functional composites in 3D printing systems. Considering the huge number of 3D printing systems, this project lies spotlight on Fused Deposition Modelling (FDM), due to its accessibility and simplicity for embedding reinforcement filler. The study is built in COMSOL Multiphysics 5.6. It performs a non-Newtonian study on the flow of molten polymer through an E3D v6 HotEnd assembly. The study was built with Acrylonitrile butadiene styrene (ABS) as a validation case. The rest of the model being parametric and simple to simulate other isotropic, nano-particulate reinforcement in a polymer matrix. Another study allows the capability to estimate some thermo-physical properties to aid the development of examining select specimens for the flow study. Results include temperature distribution and phase shear plots to correctly identify best operating procedure for select specimens. Finally, details of possible future work have been noted.
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9 3D printing of composites for space applications
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Additive manufacturing (AM) has recently been adopting a wide variety of materials ranging from plastics, metals as well as their composites and alloys. Food, fabric, concrete and cement are amongst the new printable materials that have been considered commercially. The application areas of AM have also ever been expanding toward the field of space engineering beyond terrestrial applications. Researchers and entrepreneurs are actively investigating the potential of three-dimensional (3D)-printed composites to achieve the short-term goal of affordable access to space and the long-term goal of mankind's prolonged existence beyond Earth, namely, space habitats on the Moon, Mars, etc. The short-term goal involves AM of composites and metals, whilst the long-term goal necessitates AM of new printable materials encompassing nearly all facets of our everyday lives. Materials types other than composites are left as future work in accordance with the advent of novel AM methods and space exploration campaigns [1-3]. The focus of this chapter is to introduce (1) applications where spacecraft components made of 3D-printed composites can be used and (2) how these manufactured components can be assembled into a space system or structure.
The process of 3D-printing parts for space systems may occur on the ground (Earth) beforehand or in situ on orbits. There are several examples in which rocket engines or satellite components were 3D printed and then assembled into a ready-to-launch system on the ground. SpaceX first used a 3D-printed component in 2014, which was a liquid oxygen valve in one of the nine engines inside the Falcon nine rocket - nowadays, an entire engine of a small rocket can be 3D manufactured using large-scale metal printers with robotic arms, which reduce the number of assembled engine parts by an order of magnitude [4, 5]. These 3D metal printers are heavy and power-consuming because of their laser melting process. Composite 3D printers, on the other hand, are free from these constraints because composites have much lower melting points than metals. Composite 3D printers have been installed in the International Space Station (ISS) for astronauts' use. Different versions and brands of commercial 3D printers have proved their functionality under microgravity. They are not being used outside the ISS under harsh space conditions such as vacuum, radiation, micrometeorites, etc. The first automated on-orbit AM will be demonstrated in the near future to produce structural components with large dimensions and aspect ratios. In light of this background and context, the latest development of AM technologies for composite manufacturing and assembling will be discussed within mechanical, electrical, electrochemical and medical applications in space.
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10 Development and manufacturing of thermoplastic composite booms for drag augmentation system of a small satellite
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In recent years, the number of small satellite launches has increased significantly due to technological advancement allowing space to be more accessible and to be commercialised. As of the end 2020, market research shows that the number of small satellite launches has reached a record number high bringing it up to a total of 1,163 small satellites, which is more than triple the amount to previous 2019 record reported by market research. The increase in launches has added to the already substantial amount of object into the low Earth orbit. Space debris is widely recognised as a critical threat by major space agencies as it creates a hazardous environment for future missions. Therefore, there is a need for a cost-effective drag augmented system to de-orbit satellite at the end-of-life missions as required by Inter-Agency Debris Committee (IADC). A drag augmented system called the de-orbit mechanism (DOM) was subsequently developed at Cranfield University, which uses a drag sail to de-orbit satellites in low Earth orbit, which enables satellites to be compliant with the debris mitigation requirement set upon by the IADC. The current DOM uses a copper beryllium (CuBe) boom and a lightweight alternative was needed. This project looks at different designs for lightweight composite booms via the use of finite element analysis. Lastly, the project explores the cost-effective way of additive manufacturing (AM), and using Markforged onyx series FDM printer, a set of collapsible tubular mast (CTM) booms were created.
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11 Adhesively bonded polymer composite joints
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Adhesive bonding is a key technology for many different technological sectors, representing an effective, practical and versatile joining technology. In fact, adhesive bonding is especially important for applications where composite components must be assembled, since it provides a relatively uniform stress distribution, does not require drilling holes or other modifications and can have excellent adhesion to a wide range of substrates. There are, however, some important issues associated to composite bonding that must be fully understood, such as the susceptibility to delamination, which occurs due to the peeling loads generated by the adhesive layer on the low transverse strength substrates. In this chapter, the main considerations for bonding composite substrates are initially discussed, and a set of specific and recent research topics related to composite joints and adhesives are discussed in more detail. These include the use of modifications in the composite adherends, the use of functionally graded substrates, the mechanics and uses of bi-adhesive joints and the growing use of composite adhesives, especially those reinforced with natural materials.
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12 Design principles and recent developments in adhesively bonded joints of fibre-reinforced plastic composite structures
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Fibre-reinforced plastic (FRP) composite components must be joined such that the overall structure maintains its structural integrity while it is under mechanical and environmental loads. This chapter introduces adhesively bonded joints (ABJs) as a main joining technique of FRP composite structures, their design principles, characterisation methods and recent developments. Advantages and disadvantages of ABJs are discussed and their performance is compared with mechanical joining techniques. Design considerations and effective parameters such as adhesive properties, surface preparation, joint configuration and environmental factors on the joint behaviour are described. Different techniques for characterising ABJs' static and in-service performances such as fatigue and ageing are briefly discussed. A summary of the analytical and numerical methods developed for stress analysis of ABJ is also provided. Novel trends on ABJs, including bio-inspired designs to reduce stress concentration, self-healing and mechanical interlocking, are briefed, given new directions for research and design of ABJ of FRP composite structures.
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13 Mechanical degradation of composite bonded joints subjected to environmental effects
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The purpose of the current study was to evaluate the joint strength of a composite single lap joint (SLJ) adhesively bonded, exposed to a hostile environment. The aged joints under hygrothermal cycles were tested under static and fatigue load. A combined experimental-numerical cohesive zone model (CZM) predicted the joint strength degradation and damage propagation. The composite SLJ of T800/M21 bonded with FM94 was subjected to hygrothermal cycles in an environmental chamber (maximum 70°C and minimum 20°C), at maximum 85% RH.
The mechanical test results showed that the strength degraded with the increase in the number of cycles. The strength was reduced by 42% under static load after 714 cycles when compared to unaged joints. The degradation was accelerated in the initial 84 cycles but fell away slightly after this point. The fatigue life was evaluated at 30, 40 and 45% (ultimate static load) to a maximum of 1,000,000 cycles, resulting in a continuous fatigue life reduction with the increase in the number of ageing cycles. A characterization of the moisture diffusion parameters was performed on the adhesive (FM94) and composite laminate (T800/M21) subjected to hygrothermal cycles. Finding that the adhesive reached its moisture saturation level of 1.54% wt, while composite laminate was 0.68% wt, in both cases, the moisture diffusion obeyed Fick's second law. A displacement-diffusion analysis was conducted to determine the effect of moisture on the elasticity of the adhesive, predicting an elasticity modulus reduction of 20%.
The displacement-diffusion model results and shear lap test results were employed to establish the degradation parameters of the CZM, thus predicting the degradation of the joint with an accuracy of 13% at 714 hygrothermal cycles.
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14 Performance of aerospace composites in the presence of process-induced defects
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This particular research constitutes a research and development project; a novel technique for the embedment of highly thin (nearly zero-thickness) defects in aerospace grade adhesively bonded composite joints is the dominant subject. These defects consist a representative of poor polymer processing and impact induced defects, while this project studies the mechanical response of the joints in the presence of such defects. This was assessed using composite-to-composite single-lap joint (SLJ) specimens having different width and defect type. With respect to this project, two categories of defects with two different widths were recognised for laboratory testing; therefore, four configurations were considered. The joints were manufactured via manual lay-up of carbon fibre-reinforced composite prepreg and autoclave curing, followed by non-destructive inspection (ultrasonic C-scan, pulsed-echo thermography and infrared thermography) as an attempt for detecting embedded zero-thickness defects. The joints were then subjected to mechanical tension loading to determine the ultimate failure load and displacement. Finally, the fracture area of the failed joints in the bond area was observed with optical microscopy to visualise and determine the failure mechanisms, i.e. cohesive and adhesion failure.
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15 Interleaving in composites
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Fibre-reinforced polymer (FRP) composite laminates have absence of fibre reinforcements in their thickness direction. This means their through thickness stiffness, strength and toughness are weak, relative to their in-plane properties. In multi-directional FRP laminates, first failures in the form of cracks tend to initiate and propagate between the plies of different fibre orientations. This type of cracking is commonly known as delamination, which can be considered a critical weakness of FRP composites. The resistance to delamination can be improved by introducing some form of composite toughening to improve the interlaminar fracture toughness of the material. These toughening concepts can be introduced in the form of intrinsic or extrinsic toughening.
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16 A deep learning-based tool to predict delamination induced interlaminar stresses in composite structures
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A Neural Network (NN) algorithm was developed to predict the interlaminar stresses in a multi-layered composite panel, given the ply orientations and the 2-D in-plane stresses as sole inputs, usually obtained from classical plate or shell analyses. In particular, the developed tool eliminates the need for any three-dimensional (3-D) analysis or similar approaches to obtain the interlaminar stresses. For training the deep learning NN algorithm, a large dataset was generated to extract the interlaminar stresses in a composite shell with a hole, through time-intensive shell-cohesive analysis using commercial FEA Software (ABAQUS). Automated scripting interface using Python was used to automatically generate the training, validation, and testing datasets. Upon completion of the model training, stress distribution, performance measure, error distribution and regression plots were analysed and discussed. The results showed an overall good prediction of the interlaminar stresses in composite panels with a mean accuracy of 95%. Insights on the model accuracy and the predictions, and possible directions of further improvement were suggested. The resulting tool can be quite handy for composites analysis and design engineers for quickly obtaining interlaminar stresses from a 2-D plate/shell analysis, without resorting to time-intensive 3-D finite element analysis.
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17 Damage assessment of composites based on non-destructive pulsed thermographic inspection
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Thermography is a relatively new technique for non-destructive testing (NDT), which has been gathering increasing interest due to its relatively low-cost hardware and extremely fast data acquisition properties. This technique is especially promising in the area of rapid automated damage detection and quantification. This study introduces a coefficient clustering analysis (CCA) method to detect and quantitatively measure damage occurring in composite materials using non-destructive pulsed thermographic inspection. This method is based on fitting a low-order polynomial model for temperature decay curves, which a) provides an enhanced visual confirmation and size measurement of the damage, b) provides the reference point for sound material for further damage depth measurement and c) reduces the burden in computational time. The performance of the proposed method is evaluated through a practical case study with carbon fibre-reinforced polymer (CFRP) laminates, which were subjected to a drop impact test with varying energy levels.
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18 Augmented reality-equipped composite monitoring
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This project has been partially based on a work produced by Dr. Hamed Yazdani Nezhad and his partners, entitled "Numerical Analysis of Low Velocity Rigid Body Impact Response of Composite Panels." This report has gone through the reverse finite element analysis (FEA), simulating an experimental process involving measuring the damage caused by a body impacting a composite panel at low velocity. It has shown that a numerical simulation of an experimental procedure involving composite materials can produce an accurate representation/prediction of the experimental results. Using this assumption, the following project has been carried out.
Presuming that a composite laminate's structural integrity may be difficult to monitor without using invasive methods, a procedure requiring only visual surface data would be a major advancement in the structural health monitoring (SHM) of composite panels. Therefore, the purpose of this research was to explore the use of virtual technologies like AR or XR and question the validity of their use in the SHM of composite structures. Using photogrammetry and light detection and ranging (LiDAR), a composite panel's three-point bend deformation was measured, through which a three-dimensional (3D) model was created and analysed.
This study has shown that the use of LIDAR is superior to that of photogrammetry for capturing surface data of a flat composite panel. Although a MATLAB® code computing the stresses and strains of the panel from the surface deformation data was unable to be implemented, an Abaqus simulation was used to provide the required relationships. The latter was used to be visualized through AR using the Unity 3D Engine. If explored further, the use of surface scanning and AR visualisation of computed data from said surface scanning can indeed revolutionise the SHM of composites.
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19 Energy harvesting and self-sensing multi-functional polymer composites
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Frequently, the technical standards for the properties of materials to be utilised in products surpass the capabilities of a single material class, such as polymers, metals or ceramics. Such limits may sometimes be circumvented by mixing two types of materials in a single product, i.e., by creating a composite. In such composites, one of the two material classes oversees supplying one set of desired features, while the other material is in charge of giving a separate set of desirable (but related) traits [1].
Because of their combination of high strength, high stiffness and low density, advanced polymer composite materials are gaining popularity for applications need high strength, stiffness and low density, such as automobile and aerospace industries [2]. While the main role of these composites has historically been to support certain loads, there is a rising tendency in research to include various secondary functions into composite structures. There is a growing need for materials that combine required functional qualities like load sensing, energy harvesting, temperature monitoring, actuation, etc. with mechanical performance [1]. Moreover, aviation safety standards and assuring structural integrity dependability are critical elements that drive the usage of such materials in aircraft structures. To meet both requirements, non-destructive inspection of the structure is performed, which is more difficult and expensive than inspecting metallic structures. As a result, new in situ health monitoring approaches must be developed [3].
In the quest to decrease maintenance costs, remote monitoring of components in systems and structures has become vital. Typically, a health monitoring module with a sensor, wireless telemetry and processing capacity is spread across complicated structures and must function remotely utilising battery power. A battery can only provide power for a certain amount of time before it must be recharged or replaced, resulting in a cost of maintenance. A wireless data transmission module, sensors and an energy harvesting device are often included in a self-powered health monitoring module. Systems have been extensively researched to convert energy from widely accessible sources such as vibration, human motion, water, air, heat, light and chemical processes into usable electrical energy.
In this chapter, we briefly describe energy harvesting and self-sensing polymer composites.
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20 Tailoring thermo-mechanical properties of hybrid composite-metal bonded joint
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The metallic substrates and polymer adhesive in composite-metal joints have a large coefficient of thermal expansion (CTE) mismatch, which is a barrier in the growing market of electric vehicles and their battery structures. It is known that adding carbon nanotubes (CNTs) to the adhesive reduces the CTE of the CNT-adhesive multi-material system, therefore, when used in adhesively bonded joints it would, theoretically, result in low CTE mismatch in the joint system, and thus would reduce the risk of joint failure at high temperatures. In this research, the influence of two specific mass ratios of CNTs on the CTE of the polymer was evaluated. A laser extensometer was utilised to measure the thermal strains over the surface of thin specimens representative of joint's substrates (composite and metal) subjected to uniform and gradually increasing temperature from 30 to 120. The CTEs of the specimens were calculated, compared and analysed.
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21 High-performance nanocomposites for strain self-sensing applications in composite joints
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Carbon nanotubes (CNTs) are inherently multifunctional, conductive and possess piezo-resistive characteristics. They are able to enhance various characteristics of everyday materials and even widen the spectrum of tasks these materials can be used for. Aiming at the multi-functionality of materials, nanocomposites made of epoxy resin with embedded CNTs are a promising solution for strain self-sensing applications. A composite structure with an embedded network of conductive CNTs will see its electrical conductivity vary as it is strained during service. A critical parameter to achieve repeatable and reliable measure is the nanotube dispersion state in the resin. Nanocomposites made of CNTs dispersed in aerospace grade epoxy resin were created using a simple process. More specifically, probe sonication and magnetic stirring were used alongside different concentrations of surfactants. To investigate the resistance-based strain gauge abilities of such material, a testing apparatus was set-up and real-time measurement of strain and resistance were recorded. Gauge factor (GF) of around one was calculated when loading in the elastic region. Load versus strain curves for pure cured epoxy were compared to the fabricated nanocomposite, and mechanical properties were investigated. Raman characterisation of CNT sample, as well as scanning electron microscope (SEM) imaging was performed to investigate dispersion and quality of nanotubes. In the end, the feasibility of nanocomposites made with a simple process using CNTs produced was demonstrated.
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Back Matter
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