26 research outputs found

    Effect of hygrothermal cycles on mechanical performance of composite adhesively bonded joints

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    This paper numerically and experimentally studied mechanical performance of composite adhesively bonded single-lap joints in the presence of hygrothermal cycles, under static tensile loading. Joint performance was predicted by the development of a coupled experimental-numerical approach based on cohesive zone modelling. Composite adherends of aerospace grade carbon fibre-reinforced Hexply® M21/T800 pre-impregnated plies, bonded using a 25mm × 25mm bond overlap. Bond interface was exposed to cyclic moisture and temperature loads by introduction of 2mm sharp cracks at joint runouts. Pre-cracked joint specimens were subjected to hygrothermal cycles in environmental chamber under conditions representative of aircraft operational cycles. Testing proved that joint degradation occurred with increased cycle numbers. Strength reduced by 42% under static load after 714 cycles compared to unaged joints. Degradation accelerated in the initial 84 cycles, but was reduced for higher cycles attributed to adhesive bulk moisture saturation. Moisture diffusion parameters were characterised for both adhesive and composite subjected to hygrothermal cycles. Adhesive reached moisture saturation level of 1.54%wt, while composite laminate was 0.68%wt. In both cases, moisture diffusion followed Fick's second law. Displacement-diffusion analysis determined effect of moisture on elasticity of adhesive. This analysis plus the single-lap test data were coupled to develop degradation parameters required for CZM, demonstrating an 87% accuracy at 714 hygrothermal cycles

    Comparative study of strain energy storage mechanisms between carbon fibre-reinforced peek and epoxy composites subjected to static and cyclic loading

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    Experimental studies were performed on the strain energy storage behaviour of aerospace grade PEEK and toughened epoxy carbon fibre-reinforced composite prepreg laminates having identical fibre content. The strain energy stored up to failure was recorded at the highest point of deflection for static three point bending (3PtB) samples laminates with different thicknesses. Ductile and brittle behaviors at failure have been the key focuses of this study therefore cyclic loading tests were also performed. Firstly, high strain 3PtB fatigue loading was carried out on the two prepregs with identical quasiisotropic stacking sequences, and secondly in order to characterise the plasticity parameters for the two laminates cyclic shear tests at high strain levels was carried out. The results have shown that the strain energy storage characteristics of the PEEK laminates are much better than those of the epoxy laminates in several ways; such as the independence of the strain energy storage level to thickness. Furthermore, at the same level of applied stress, the PEEK laminates tend not to lose strain energy compared to the toughened epoxy laminates. This study shows that the thermoplastic nature of the PEEK gives it an improved plasticity level which enhances its strain energy storage capability. PEEK carbon laminates are therefore serious candidates for spring applications

    Prospects of sustainable polymers

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    Synthetic polymers have shown a great impact on every aspect of our life and attained an exponential rise in their production and utilization in the past decades due to their durability, flexibility, moldability, and inexpensive nature. However, the use of natural polymers or development of safe and environment-friendly synthetic bio-based polymers is continuously undergoing for a sustainable future owing to the exhaustion of petroleum-based resources or fossil-based materials, disposal and economical concerns, including government guidelines. In this regard, the development of new sustainable polymers or materials will step up and build a genuinely circular economy by decreasing manufacture or utilization of fossil-based materials as limited reserves

    Towards the use of electrospun piezoelectric nanofibre layers for enabling in-situ measurement in high performance composite laminates

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    The aim of this research is to highlight the effects from composite manufacturing on the piezoelectric properties of fibre-reinforced composite laminates internally modified by layers of low-density piezoelectric thermoplastic nanofibres in association with a conductive electrode layer. for in-situ deformation measurement of aerospace and renewable energy composite structures through enabling electrical signal change. Several methods have been used to analyse the effects such as phase characterisation of the piezoelectric thermoplastic nanofibres and non-destructive inspection of the laminates, during processing an Inter Digital Electrode (IDE) made by conductive epoxy-graphene resin, and pre-preg autoclave manufacturing aerospace grade laminates. The purpose of fabrication of such IDE layer was to embed the same resin type (HexFlow® RTM6) for the conductive layer as that used for the laminates, in order to sustain the structural integrity via mitigation of downgrading effects on the bonding quality and interlaminar properties between plies, rising from materials mismatch and discontinuous interplay stress transfer. XRD, FTIR, EDS and SEM analyses have been carried out in the material characterisation phase, whereas pulsed thermography and ultrasonic C-scanning were used for the localisation of conductive resin embedded within the composite laminates. This study has shown promising results for enabling internally embedded piezoelectricity (and thus health monitoring capabilities) in high performance composite laminates such as those in aerospace, automotive and energy sectors

    Development of damage tolerant composite laminates using ultra-thin interlaminar electrospun thermoplastic nanofibres

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    Carbon fibre-reinforced polymer (CFRP) composites are extensively used in high performance transport and renewable energy structures. However, composite laminates face the recurrent problem of being prone to damage in dynamic and impact events due to extensive interlaminar delamination. Therefore, interlaminar tougheners such as thermoplastic veils are introduced between pre-impregnated composite plies or through-thickness reinforcement techniques such as tufting are employed. However, these reinforcements are additional steps in the process which will add a degree of complexity and time in preparing composite lay-ups. A novel material and laying-up process is proposed in this paper that uses highly stretched electrospun thermoplastic nanofibers (TNF) that can enhance structural integrity with almost zero weight penalty (having 0.2gsm compared to the 300gsm CFRP plies), ensuring a smooth stress transfer through different layers, and serves directional property tailoring, with no interference with geometric features e.g. thickness. Aerospace grade pre-impregnated CFRP composite laminates have been modified with the TNFs (each layer having an average thickness of <1 micron) electrospun on each ply, and autoclave manufactured, and the effect of the nanofibers on the fracture toughness has been studied. Interlaminar fracture toughness specimens were manufactured for Mode I (double cantilever beam) and Mode II (end notched flextural) fracture tests. Such thin low-density TNF layers added an improvement of 20% in failure loads and fracture toughness in modes I and II

    Autonomous systems imaging of aerospace structures

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    Aircraft manufacturers are constantly improving their aircraft ensuring they are more cost-efficient to do this the weight of the aircraft needs to be reduced, which results in less fuel required to power the aircraft. This has led to an increased use of composite materials within an aircraft. Carbon fibre reinforced polymer (CFRP) composite is used in industries where high strength and rigidity are required in relation to weight. e.g. in aviation – transport. The fibre-reinforced matrix systems are extremely strong (i.e. have excellent mechanical properties and high resistance to corrosion). However, because of the nature of the CFRP, it does not dint or bend, as aluminium would do when damaged, it makes it difficult to locate structural damage, especially subsurface. Non Destructive Testing (NDT) is a wide group of analysis techniques used to evaluate the properties of a material, component or system without causing damage to the operator or material. Active Thermography is one of the NDT risk-free methods used successfully in the evaluation of composite materials. This approach has the ability to provide both qualitative and quantitative information about hidden defects or features in a composite structure. Aircraft has to undergo routine maintenance – inspection to check for any critical damage and thus to ensure its safety. This work aims to address the challenge of NDT automated inspection and improve the defects’ detection by performing automated aerial inspection using a Unmanned Aerial Vehicle (UAV) thermographic imaging system. The concept of active thermography is discussed and presented in the inspection of aircraft’s CFRP panels along with the mission planning for aerial inspection using the UAV for real time inspection. Results indicate that this inspection approach could significantly reduce the inspection time, cost, and workload, whilst potentially increasing the probability of detection

    A critical review of the current progress of plastic waste recycling technology in structural materials

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    One of the main environmentally threatening factors is plastic waste which generates in great quantity and causes severe damage to both inhabitants and the environment. Commonly, plastic waste generated on the land ends up in water bodies, resulting in detrimental solid impacts on the aquatics via poisoning and flooding the marine ecosystem. Exploring various approaches to convert plastic wastes into new products known as an efficient way to manage them and to enhance the sustainability of the environment, discussed in this article. Moreover, The limitation of the application of plastic waste for construction purposes is also considered. It is wind up that the usage of plastic waste for construction purposes will significantly rectify the sustainability of our environment and also be regarded as a trustworthy source of materials for applying in conventional materials such as concrete and asphalt

    A Review on biomedical application of polysaccharide-based hydrogels with a focus on drug delivery systems

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    Over the last years of research on drug delivery systems (DDSs), natural polymer-based 18 hydrogels have shown many scientific advances due to their intrinsic properties and a wide variety 19 of potential applications. While drug efficacy and cytotoxicity play a key role, adopting a proper 20 DDS is crucial to preserve the drug along the route of administration and possess desired therapeu-21 tic effect at the targeted site. Thus, drug delivery technology can be used to overcome the difficulties 22 of maintaining drugs at a physiologically related serum concentration for prolonged periods. Due 23 to their outstanding biocompatibility, polysaccharides have been thoroughly researched as a bio-24 logical material for DDS advancement. To formulate a modified DDS, polysaccharides can cross-25 link with different molecules, resulting in hydrogels. According to our recent findings, targeted 26 drug delivery at a certain spot occurs due to external stimulation like temperature, pH, glucose, or 27 light. As an adjustable biomedical device, the hydrogel has tremendous potential for nanotech ap-28 plications in the involved health area like pharmaceutical and biomedical engineering. An overview 29 of hydrogel characteristics and functionalities is provided in this review. We focus on discussing 30 the various kinds of hydrogel-based on their potential for effectively delivering drugs that are made 31 of polysaccharides

    PVP2011-57695 STUDY OF CREEP RELAXATION BEHAVIOUR OF 316H AUSTENITIC STEELS UNDER MECHANICALLY INDUCED RESIDUAL STRESS

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    ABSTRACT Compact tension 316H austenitic steel specimens, extracted from an as-received ex-service pressure vessel header, have been pre-compresse
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