Browsing by Author "Ayre, David"
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Item Open Access Adhesively bonded composite testing(Cranfield University, 2017-06-01 10:43) Yazdani Nezhad, Hamed; Ayre, DavidDataset used in Figure 2 in "Tensile Response of Adhesively Bonded Composite-to-composite Single-lap Joints in the Presence of Bond Deficiency" (doi:10.1016/j.procir.2016.09.021). Also used in "A novel process-linked assembly failure model for adhesively bonded composite structures" (doi:10.1016/j.cirp.2017.04.103).Item Open Access Carbon nano materials based composites for energy storage.(Cranfield University, 2022-04) He, Shojun; Ayre, DavidThe development of human industrial technology has increased the requirement for electric energy. At present, the rapid development of various smart devices has led to an increasing demand for high-performance batteries. The emergence of various wearable devices has led to a need for flexible electrodes. Aerogels and paper, as two good flexible porous materials, have attracted many scholarly studies in recent years. Combining carbon materials, which have excellent electrochemical properties, with aerogel and paper can result in flexible electrodes with good performance. This research presents a series of aerogel and carbon paper samples prepared using three different production processes. For the aerogel samples, the effects of graphene addition and manufacturing route were investigated. The study resulted in a recommended material and process to produce a porous aerogel sample with high electrochemical cycle stability. For carbon paper samples, the relationship between variables such as surfactant, paper, conductive material and the sample properties was examined. Initial work indicates that carbon paper manufacturing routes are simpler than others reported elsewhere and provide materials that have electrochemical properties with potential for use as electrodes in supercapacitors and other energy storage devices. Of course, cost and environmental protection have also been considered in this project.Item Open Access Carbon nanotube embedded adhesives for real-time monitoring of adhesion failure in high performance adhesively bonded joints(Springer Nature, 2020-10-08) Bregar, Tadej; An, Donglan; Gharavian, Somayeh; Burda, Marek; Durazo-Cardenas, Isidro; Thakur, Vijay Kumar; Ayre, David; Słoma, Marcin; Hardiman, Mark; McCarthy, Conor; Nezhad, Hamed YazdaniCarbon nanotubes (CNTs) embedded polymers are of increasing interest to scientific and industrial communities for multi-functional applications. In this article, CNTs have been introduced to high-strength epoxy adhesive for enabling in-situ strain sensing in adhesively bonded aluminium-to-aluminium single-lap joints to accurately indicate the onset and propagation of adhesion failure to the evolution of piezo-resistivity in varying mechanical loads. The CNT modified adhesive in bonded joints and the CNT modified adhesive alone have been tested under monothonic and cyclic tensile loads up to ultimate failure. The changes in the piezo-resistivity induced by the CNTs have been monitored in situ with respect to loading. A novel interpretation method has been developed for progressive, instantaneous adhesion failure estimation under cyclic tensile stresses from a resistivity baseline. The method indicates that the in-situ resistivity changes and the rate of the changes with strain, i.e. sensitivity, strongly correlate with the adhesion failure progression, irrespective of the CNT dispersion quality. Moreover, the effect of bond thickness on the evolution of piezo-resistivity and adhesion failure have been studied. It was observed that relatively thin adhesive bonds (0.18mm thickness), possessing higher CNT contact points than thick bonds (0.43mm thicknes), provide 100 times higher sensitivity to varying cyclic loadsItem Open Access A comparative analysis of acoustic emission sensor embedding in glass fibre composite(Elsevier, 2023-12-21) Ghadarah, Noor Salam; Ayre, DavidThe manufacturing process of composite structures permits fully embedding acoustic emission (AE) sensors. While the embedding process may pose challenges, its advantages, if proven, can outweigh the challenges. The increased sensitivity resulting from embedding acoustic emission sensors in composites is still not definitively established. A test was set up with pre-determined AE initiation locations (surface and sub-surface) and pre-determined receiving sensor's location (surface and sub-surface) to ensure any sensitivity increase was evident. The receiving sensor's attenuation along (at 90°) and across the fibres (at 45°) was assessed using two test methods: pencil lead breaking (PLB) and actuator methods. The actuator method involved using two pulse generators, the TGP110 pulse generator and the Mistras FieldCal. A range of specific frequencies were utilised, 30, 60, 150 and 300 kHz, using the FieldCal. The results obtained from the test methods were not in agreement with each other. For example, comparing the sensitivity using surface cracks, the PLB method showed decreased sensitivity when embedding the receiving sensor compared to the actuator method, which demonstrated minimal changes in sensitivity. The research aims to clarify the sensitivity increase obtained when embedding an AE sensor while taking into account the crack's position and frequency.Item Open Access Comparative life cycle assessment of aluminium and CFRP composites: the case of aerospace manufacturing(Springer, 2024-02-24) Atescan Yuksek, Yagmur; Mills, Andrew; Ayre, David; Koziol, Krzysztof K. K.; Salonitis, KonstantinosAs climate change intensifies and existing resources are depleted, the need for sustainable industries becomes more important. The aviation industry is actively addressing environmental concerns by enhancing fuel efficiency and adopting lighter materials, especially carbon fibre composites. Research has proven that the use of carbon fibre composites provides cumulative benefits in reducing fuel consumption over the entire life cycle of an aircraft. However, existing studies are lack of a comprehensive exploration of the diverse impacts associated with composite manufacturing processes and recycling methods. To address this gap, a comparative life cycle assessment analysis covering the materials’ manufacturing, operation, and end-of-life phases is conducted. This analysis includes aluminium alloy and five different carbon fibre composite materials produced with varied constituents and manufacturing methods. Composite manufacturing processes, encompassing carbon fibre production, resin selection, and composite manufacturing methods, are considered. Weight savings based on the mechanical properties of utilised composite type are also taken into account. Results highlight the potential to mitigate the environmental impact of composite materials through strategic choices in constituent types, manufacturing processes, and disposal scenarios. Moreover, break-even distances indicate that aluminium becomes more environmentally detrimental than the analysed composite structures beyond a flight distance of 300,000 km.Item Open Access Data supporting: 'Electromagnetic Field Controlled Domain Wall Displacement for Induced Strain Tailoring in BaTiO3-Epoxy Nanocomposite'(Cranfield University, 2022-08-31 13:30) Yazdani Nezhad, Hamed; Li, Danning; Barrington, James; James, Stephen; Ayre, David; Sloma, Marcin; Lin, Meng-FangThis dataset is comprised of 4 files: 100W_strains, 100W_temperature, 440W_strains, and 440W_temperature.Failure in an epoxy polymer composite material is prone to initiate by the coalescence of microcracks in its polymer matrix. As such, matrix toughening via addition of a second phase as rigid or/and rubber nano/micro-particles is one of the most popular approaches to improve the fracture toughness across multiple scales in a polymer composite, which dissipates fracture energy via deformation mechanisms and microcracks arrest. Few studies have focused on tailorable and variable toughening, so-called ‘active toughening’, mainly suggesting thermally induced strains which offer slow and irreversible toughening due to polymer’s poor thermal conductivity. The research presented in the current article has developed an instantaneous, reversible active toughening composite based upon contact-less introduction of a microscopic compressive extrinsic strain field via remote electromagnetic radiation. Quantification of the extrinsic strain evolving in the composite with the microwave energy has been conducted using in-situ realtime fibre optic sensing. A theoretical constitutive equation correlating the exposure energy to micro-strains has been developed, with its solution validating the experimental data and describing their underlying physics. The research has utilised functionalised dielectric ferroelectric nanomaterials, barium titanate (BaTiO3), as a second phase dispersed in an epoxy matrix, able to introduce microscopic electro-strains to their surrounding rigid epoxy subjected to an external electric field (microwaves, herein), as result of their domain walls dipole displacements. Epoxy Araldite LY1564, a diglycidyl ether of bisphenol A (DGEBA) associated with the curing agent Aradur 3487 were embedded with the BaTiO3 nanoparticles. The silane coupling agent for the nanoparticles’ surface functionalisation was 3-glycidoxypropyl trimethoxysilane (3-GPS). Hydrogen peroxide (H2O2, 30%) and acetic acid (C2H4O2, 99.9%) used as functionalisation aids, and the ethanol (C2H6O, 99.9%) used for BaTiO3 dispersion. Firstly, the crystal microstructure of the functionalised nanoparticles and the thermal and dielectric properties of the achieved epoxy composite materials have been characterised. It has been observed that the addition of the dielectric nanoparticles has a slight impact on the curing extent of the epoxy. Secondly, the surface-bonded fibre bragg grating (FBG) sensors have been employed to investigate the real-time variation of strain and temperature in the epoxy composites exposed to microwaves at 2.45 GHz and at different exposure energy. The strains developed due to the in-situ exposure at composite, adhesive and their holding fixture material were evaluated using the FBG. The domain wall induced extrinsic strains were distinguished from the thermally induced strains, and found that the increasing exposure energy has an instantaneously increasing effect on the development of compressive strains. Post-exposure Raman spectra showed no residual field in the composite indicating no remnant strain field examined under microwave powersItem Open Access Data Underpinning "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints"(Cranfield University, 2017-09-07 15:26) Colegrove, Paul; Joesbury, Adam; Ayre, David; Van Rymenant, Patrick; Ganguly, Supriyo; Williams, StewartFigures for article entitled "Weld-Bonded Stainless Steel to Carbon Fibre-Reinforced Plastic Joints"Item Open Access Development of damage tolerant composite laminates using ultra-thin interlaminar electrospun thermoplastic nanofibres(European Society for Composite Materials, 2018-06-30) Li, Danning; Prevost, Raphael; Ayre, David; Yoosefinejad, Ata; Lotfian, Saeid; Brennan, Feargal; Yazdani Nezhad, HamedCarbon 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.Item Open Access Effect of hygrothermal cycles on mechanical performance of composite adhesively bonded joints(European Society for Composite Materials, 2018-06-30) Rincon Urbina, Sonia; Ayre, David; Yazdani Nezhad, HamedThis 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.Item Open Access Electromagnetic field controlled domain wall displacement for induced strain tailoring in BaTiO3-epoxy nanocomposite(Nature, 2022-05-07) Li, Danning; Barrington, James; James, Stephen; Ayre, David; Sloma, Marcin; Lin, Meng-Fang; Yazdani Nezhad, HamedFailure in an epoxy polymer composite material is prone to initiate by the coalescence of microcracks in its polymer matrix. As such, matrix toughening via addition of a second phase as rigid or/and rubber nano/micro-particles is one of the most popular approaches to improve the fracture toughness across multiple scales in a polymer composite, which dissipates fracture energy via deformation mechanisms and microcracks arrest. Few studies have focused on tailorable and variable toughening, so-called ‘active toughening’, mainly suggesting thermally induced strains which offer slow and irreversible toughening due to polymer’s poor thermal conductivity. The research presented in the current article has developed an instantaneous, reversible extrinsic strain field via remote electromagnetic radiation. Quantification of the extrinsic strain evolving in the composite with the microwave energy has been conducted using in-situ real-time fibre optic sensing. A theoretical constitutive equation correlating the exposure energy to micro-strains has been developed, with its solution validating the experimental data and describing their underlying physics. The research has utilised functionalised dielectric ferroelectric nanomaterials, barium titanate (BaTiO3), as a second phase dispersed in an epoxy matrix, able to introduce microscopic electro-strains to their surrounding rigid epoxy subjected to an external electric field (microwaves, herein), as result of their domain walls dipole displacements. Epoxy Araldite LY1564, a diglycidyl ether of bisphenol A associated with the curing agent Aradur 3487 were embedded with the BaTiO3 nanoparticles. The silane coupling agent for the nanoparticles’ surface functionalisation was 3-glycidoxypropyl trimethoxysilane (3-GPS). Hydrogen peroxide (H2O2, 30%) and acetic acid (C2H4O2, 99.9%) used as functionalisation aids, and the ethanol (C2H6O, 99.9%) used for BaTiO3 dispersion. Firstly, the crystal microstructure of the functionalised nanoparticles and the thermal and dielectric properties of the achieved epoxy composite materials have been characterised. It has been observed that the addition of the dielectric nanoparticles has a slight impact on the curing extent of the epoxy. Secondly, the surface-bonded fibre Bragg grating (FBG) sensors have been employed to investigate the real-time variation of strain and temperature in the epoxy composites exposed to microwaves at 2.45 GHz and at different exposure energy. The strains developed due to the in-situ exposure at composite, adhesive and their holding fixture material were evaluated using the FBG. The domain wall induced extrinsic strains were distinguished from the thermally induced strains, and found that the increasing exposure energy has an instantaneously increasing effect on the development of such strains. Post-exposure Raman spectra showed no residual field in the composite indicating no remnant strain field examined under microwave powers < 1000 W, thus suggesting a reversible strain introduction mechanism, i.e. the composite retaining its nominal properties post exposure. The dielectric composite development and quantifications presented in this article proposes a novel active toughening technology for high-performance composite applications in numerous sectors.Item Open Access Experimental and numerical study of process-induced defects and their effect on fatigue debonding in composite joints(Elsevier, 2019-03-22) Liu, Yiding; Zhang, Xiang; Lemanski, Stuart; Yazdani Nezhad, Hamed; Ayre, DavidLaboratory coupon joints for fatigue debonding tests usually have narrow width and a through-width initial disbond. However, realistic structural joints are much wider and may contain process-induced defects and accidental damage; both are much smaller than the joint width. Small and discrete damage may behave differently from the idealised through-width disbond crack. This has brought a question on whether the laboratory coupon joint can accurately represent the fatigue behaviour of wider structural joints. This paper presents an experimental and numerical study of fatigue behaviour of a wide bonded lap joint with a process-induced defect of semi-circular shape. Fatigue debonding propagation was monitored by ultrasound inspection. Fatigue life was predicted using a normalised strain energy release rate parameter calculated by finite element method, and the adhesive material fatigue crack growth rate data measured under single and mixed mode conditions. Simulation of process-induced defect and validation by experiments have brought a better understanding of fatigue debonding behaviour in wide joints containing realistic damage. Suggestions are given for fatigue fracture tests of bonded joints.Item Open Access Fatigue cracking behaviour of epoxy-based marine coatings on steel substrate under cyclic tension(Elsevier, 2017-02-13) Wu, Tongyu; Irving, Phil E.; Ayre, David; Jackson, P.; Zhao, F.Strain controlled fatigue tests have been performed on two types of heavily filled epoxy corrosion protection coating sprayed onto a 6 mm steel substrate. Fatigue cycling was performed at R ratios of 0 and −1. The two coatings differed in their formulation and the major differences in mechanical performance were in their static strain to first crack development and their fracture toughness, where Coating A was significantly tougher than coating B. During strain cycling coating crack development was monitored using optical observations and surface replicas. It was found that in both coatings surface crack development began soon after the onset of cycling and proceeded via growth of surface channelling cracks and multiple initiation of new cracks. Detailed studies were made of crack development morphology and its relation to coating type and to the applied strain range. A definition of coating life as the first appearance of a 2 mm surface crack length was used. This represented the end of the life where the coating protected the substrate. Before this life was achieved, crack growth rates of single cracks were invariant with crack length. After this point further crack growth, multiple cracking and crack to crack interactions took place. Cracking in this region could be characterised with a new total crack length parameter shown to be strongly dependent on applied strain range.Item Open Access Fatigue life prediction of z-fibre pinned composite laminate under mode I loading(Elsevier, 2019-02-13) Tang, Suchao; Lemanski, Stuart; Zhang, Xiang; Ayre, DavidA hybrid method is presented combining linear elastic fracture mechanics with nonlinear damage mechanics that can predict the fatigue crack growth rate in z-fibre pinned composites under mode I loading. The strain energy release rate is evaluated using the virtual crack closure technique via finite element analysis. Cohesive elements are used in the pinned region to represent the crack bridging force generated by the pins. The reduction of the pins' bridging force under the fatigue loading is accommodated by applying a degradation law, based on damage mechanics with empirical fitting parameters. A modified degradation law is proposed which is capable of accumulating fatigue damage under varying crack opening displacement ranges experienced by the pins during fatigue loading. Fatigue testing was performed with a z-pinned double cantilever beam at two different values of applied displacement amplitude. The predictions show reasonably good agreement with the test results in terms of the fatigue crack propagation rate and fatigue life.Item Open Access A finite element model for predicting the static strength of a composite hybrid joint with reinforcement pins(MDPI, 2023-04-22) Bianchi, Francesco; Liu, Yiding; Joesbury, Adam M.; Ayre, David; Zhang, XiangThis paper presents a finite element model for predicting the performance and failure behaviour of a hybrid joint assembling fibrous composites to a metal part with reinforcement micro pins for enhancing the damage tolerance performance. A unit-strip model using the cohesive elements at the bond interface is employed to simulate the onset and propagation of debonding cracks. Two different traction–separation laws for the interface cohesive elements are employed, representing the fracture toughness properties of the plain adhesive bond and a pin-reinforced interface, respectively. This approach can account for the large-scale crack-bridging effect of the pins. It avoids using concentrated pin forces in the numerical model, thus removing mesh-size dependency, and permitting more accurate and robust computational analysis. Lap joints reinforced with various pin arrays were tested under quasi-static load. Predicted load versus applied displacement relations are in good agreement with the test results, especially for the debonding onset and early stage of crack propagation.Item Open Access A finite element study of fatigue crack propagation in single lap bonded joint with process-induced disbond(Elsevier, 2018-09-09) Liu, Yiding; Lemanski, Stuart; Zhang, Xiang; Ayre, David; Nezhad, Hamed YazdaniThis paper presents a method for predicting fatigue crack propagation in adhesive bonded composite joints with an initial full-width disbond using finite element analysis and numerical integration of the material's fatigue crack growth rate law. Fatigue tests were conducted on single lap joints. Crack lengths were monitored from four runout corners. In-situ crack growth measurements were performed by ink injection to identify the crack front profile during fatigue loading. The crack growth was modelled using a fracture mechanics criterion considering two different crack propagation patterns. The material's fatigue crack growth rate law was determined experimentally using the standard double cantilever beam and end notch flexure specimens. Using the total strain energy release rate and the two crack scenarios, the numerical model predicted the lower and upper bounds of the measured fatigue crack growth rates of the lap joint.Item Open Access Implications of substrate geometry and coating thickness on the cracking resistance of polymer-based protective coatings(Elsevier, 2018-12-31) Wray, Lesley-Anne; Ayre, David; Irving, Phil E.; Jackson, Paul A.; Jones, P. R.; Zhao, F.Welded steel T-sections of different weld fillet geometries coated with water ballast tank protective coatings were subjected to thermal cycling with a temperature range from 60°C to -10°C. Cracks developed in the coatings at the weld line, propagating longitudinally along it. The number of cycles required to create 1 mm cracks was strongly dependent on the weld geometry and the coating Dry Film Thickness (DFT). Finite Element Modelling (FEM) was employed to calculate thermally induced strain fields in the coatings subjected to the same temperature range. FEM predicted that the greatest strain concentrations are present at the coating surface within the weld fillet region. Increased DFT and decreased fillet radius leads to increased maximum principal strains. Numerical analysis predicts that greatest strain ranges promoting the earliest cracking/failure are found in thicker coatings applied to smaller weld radii. Experimental observations confirm this.Item Open Access Investigation of the fracture behaviour of epoxy-based water ballast(Cranfield University, 2015-07) Wu, Tongyu; Irving, Phil E.; Ayre, David; Dell'Anno, GiuseppeThe fracture of water ballast tank (WBT) coatings due to thermal stresses is widely recognised as an issue. Upon coating fracture, rapid corrosion of the tanker steel structure will occur, leading to expensive structure repairs or even tanker scrapping. In this project, the fracture behaviour of two experimental WBT coatings, referred to as A and B, in the forms of free film and substrated coatings was investigated. Static tensile tests and fatigue tests of the substrated coatings were performed. A finite element model of coating cracking was developed. Thermal stress and J-integral of surface cracking defects in substrated coatings were calculated using the model, in which the effects of defect size, coating thickness, and thermal strain on coating fracture were investigated. For the first time, fracture mechanics was used to explain WBT coating fracture behaviour. The J-integral of surface defects was used to predict the onset strain of coating cracking under mechanical strains in laboratory and under thermal strains in service. A theoretical comparison between the cracking drive forces in terms of J - integrals in WBT coatings under thermal strains and mechanical strains was performed.Item Open Access Investigation of the general properties and field-induced electromechanical response of polymer nanocomposites with surface-functionalised dielectric nanoparticles.(2022-02) Li, Danning; Ayre, David; Yazdani Nezhad, HamedFor the past several decades, polymer composite materials have become increasingly popular in various industrial sectors owing to their advantageous properties, such as light weight and high mechanical performance. Most of the failure modes of composite materials are initiated by the coalescence of microcracks in the matrix. Therefore, matrix toughening is one of the most popular approaches to improve the overall fracture toughness of polymer composite materials. The most widely known approach for matrix toughening is the addition of a second phase, such as rigid or/and rubber particles, to dissipate the fracture energy. Several studies have focused on another approach, known as ‘active toughening’, involves introducing a thermal-induced strain from the fillers to its surrounding matrix, but this approach could only deliver slow and irreversible toughening due to the polymer’s poor thermal conductivity. In this study, a new approach is presented that involves an instantaneous extrinsic strain field activated by remote electromagnetic radiation. Quantification of the real-time field-induced strain evolution with microwave radiation is conducted via fibre optic sensing technology (FBGs). Theoretical expressions correlating the field-induced strain with microwave power level and exposure time have been developed, with the theoretically calculated solution validating the experimental data and describing the underlying physics. This study has introduced functionalised ferroelectric barium titanate nanoparticles (BaTiO₃) as a second phase dispersed into an epoxy matrix. The embedded nanoparticles are capable of introducing electro-strains to their surrounding rigid epoxy when subject to an external electric field, which result from the domain wall movements due to polarisation orientation. A diglycidyl ether of bisphenol A epoxy with the hardener Aradur 3487 were modified with the BaTiO₃ nanoparticles embedment. The silane coupling agent for the nanoparticles’ surface functionalisation was 3-glycidoxypropyl trimethoxysilane (3-GPS). Ultrasonication and solvent-aided mixing (ethanol, C2H6O, 99.9%) are employed to facilitate the dispersion of BaTiO₃ nanoparticles. Firstly, the crystal microstructure of the functionalised BaTiO₃ nanoparticles and the mechanical, thermal, and dielectric properties of epoxy nanocomposite materials have been characterised via various conventional techniques. It has been observed that the addition of the nanoparticles only has an insignificant impact on the curing extent of the epoxy. After that, the surface-bonded fibre grating sensors have been employed to investigate the variation of strain and temperature change of the epoxy nanocomposite materials simultaneously in the microwave oven at 2.45GHz with different power levels. The strains developed in the nanocomposite, adhesive used for FBG bonding, and the holding fixture are then studied via FBG sensors to distinguish the strains induced by domain wall movement from thermally induced strains. Repeated compressive strain fields are observed as a decline in the FBGs strain measurements of epoxy nanocomposite samples with negligible temperature change when placed horizontally in the oven cavity. Raman spectra are used in this study to observe the post-microwave effect of the internal stress state. The blueshift of the characterisation peaks of BaTiO₃ has been identified, thus suggesting a residual stress field experienced by the nanoparticles. The multi-functional nanocomposite development and qualifications presented in this study proposed a novel active toughening technology for high-performance composite applications in numerous sectors.Item Open Access Mechanical degradation of composite structures subjected to environmental effects.(2018-04) Rincon Urbina, Sonia; Ayre, David; Yazdani, HamedPolymeric materials have inherent advantages thanks to the mechanical properties that they lend to a structure enhancing its useful life in factors of safety, reliability and aesthetics. Nevertheless, the durability may be affected by other considerations including environmental attack resulting in unexpected failures and maintenance costs, making it therefore essential to accurately predict the overall performance of these structures. This study was designed to evaluate the joint strength of an adhesively bonded composite Single Lap Joint (SLJ), exposed to a hostile environment i.e. cycles of temperature and moisture, mechanical damage and fatigue. The aged joints under hygrothermal cycles were tested under static and dynamic loads. A combined experimental-numerical Cohesive Zone Model (CZM) was calibrated to predict 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 % Relative Humidity (RH). The results showed that the strength degraded consequent to the increasing number of cycles. The strength reduced by 42 % under static load after 714 cycles in comparison to unaged joints. The fatigue life was evaluated at 30%, 40% and 45% ultimate static load to a maximum of one million cycles, resulting in a continuous fatigue life reduction with the increase in the number of aging cycles. A characterisation of the moisture diffusion parameters was performed on adhesive (FM94) and composite laminate (T800/M21) subjected to hygrothermal cycles. A displacement-diffusion analysis was conducted to determine the effect of moisture on the elasticity of the adhesive. 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.Item Open Access Mechanical performance of composite bonded joints in the presence of localised process-induced zero-thickness defects(Elsevier, 2018-11-02) Yazdani Nezhad, Hamed; Stratakis, Dimosthenis; Ayre, David; Addepalli, Sri; Zhao, YifanProcessing parameters and environmental conditions can introduce variation into the performance of adhesively bonded joints. The effect of such variation on the mechanical performance of the joints is not well understood. Moreover, there is no validated non-destructive inspection (NDI) available to ensure bond integrity post-process and in-service so as to guarantee initial and continued airworthiness in aerospace sector. This research studies polymer bond defects produced in the laboratory scale single-lap composite-to-composite joints that may represent the process-induced defects occurring in actual processing scenarios such as composite joining and repair in composite aircrafts. The effect of such defects on the degradation of a joint’s mechanical performance is then investigated via quasi-static testing in conjunction with NDI ultrasonic C-scanning and pulsed thermography. This research is divided into three main sections: 1- manufacturing carbon fibre-reinforced composite joints containing representative nearly zero-thickness bond defects, 2- mechanical testing of the composite joints, and 3- assessment of the NDI capability for detection of the bond defects in such joints.