Browsing by Author "Yazdani Nezhad, Hamed"
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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 Application of NDT thermographic imaging of aerospace structures(Elsevier, 2019-02-13) Deane, Shakeb; Avdelidis, Nicolas Peter; Ibarra-Castanedo, Clemente; Zhang, Hai; Yazdani Nezhad, Hamed; Williamson, Alex A.; Mackley, Tim; Davis, Maxwell J.; Maldague, Xavier P. V.; Tsourdos, AntoniosThis work aims to address the effectiveness and challenges of Non-Destructive Testing (NDT) inspection and improve the detection of defects without causing damage to the material or operator. It focuses on two types of NDT methods; pulsed thermography and vibrothermography. The paper also explores the possibility of performing automated aerial inspection using an unmanned aerial vehicle (UAV) provided with a thermographic imaging system. The concept of active thermography is discussed for inspecting aircraft CFRP panels along with the proposal for performing aerial inspection using the UAV for real time inspection. Static NDT results and the further UAV research indicate that the UAV inspection approach could significantly reduce the inspection time, cost, and workload, whilst potentially increasing the probability of detection.Item Open Access Autonomous systems imaging of aerospace structures(Unknown, 2018-12-31) Deane, Shakeb; Avdelidis, Nicolas Peter; Ibarra-Castanedo, Clemente; Zhang, Hai; Yazdani Nezhad, Hamed; Williamson, Alex A.; Maldague, Xavier P. V.; Tsourdos, AntoniosAircraft 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.Item Open Access Autonomous systems thermographic NDT of composite structures(SPIE, 2019-05-02) Deane, Shakeb; Avdelidis, Nicolas Peter; Yazdani Nezhad, Hamed; Williamson, A.; Zhang, H.; Tzitzilonis, Vasileios; Maldague, Xavier P. V.; Tsourdos, AntoniosTransient thermography is a method used successfully in the evaluation of composite materials and aerospace structures. It has the capacity to deliver both qualitative and quantitative results about hidden defects or features in a composite structure. Aircraft must 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 suggesting an autonomous thermographic imaging approach using a UAV (Unmanned Aerial Vehicle) active thermographic system. The concept of active thermography is discussed and presented in the inspection of aircraft CFRP panels along with the mission planning for aerial inspection using the UAV for real time inspection. Results indicate that the suggested approach could significantly reduce the inspection time, cost, and workload, whilst potentially increase the probability of detection of defects on aircraft composites.Item Open Access Bearing damage characteristics of fibre-reinforced countersunk composite bolted joints subjected to quasi-static shear loading(Elsevier, 2017-01-16) Yazdani Nezhad, HamedThis paper studies the progression of damage in carbon fibre-reinforced polymer (CFRP) countersunk composite bolted joints (CBJs) with neat-fit clearance, subjected to quasi-static loading. Damage mechanisms, comprising of fibre buckling and breakage, matrix damage, shear damage and inter-laminar delamination within the CFRP composite parts of the joints have been studied. Load-displacement curves, X-ray and optical microscopic images in single- and three-bolt CBJs were used to investigate damage and deformation characteristics. The observations were then employed to further investigate the type of failure and the extent of damage. The evolution of damage within the composite parts was correlated to the failure characteristics of the joints: It was found that the type and extension of damage is strongly correlated with the ultimate failure load point of the joint in single-bolt CBJs. A combined inter/intra-laminar damage consisting of fibre cluster breakage, extensive fibre buckling, debonding and delamination was observed at the ultimate failure load. This study was then extended to three-bolt CBJ where damage surrounding each bolt and its corresponding failure load was strongly correlated: The final study showed that the ultimate failure point in single-bolt CBJ and the first-bolt-failure point in three-bolt CBJ correspond to the composite plies undergoing intra-laminar damage with the size reaching to the edge of the countersunk head. This damage developed extensively through the thickness of the composite parts underneath the countersink, and in the direction opposite to the loading direction. Outside the countersunk head, debonding and delamination were found to be the dominant damage driving mechanisms. Finally, a new design rule has been proposed to predict the response of multi-bolt joints (damage area and failure load) by using the response in single-bolt CBJ as an initial baseline.Item Open Access Comparative study of strain energy storage mechanisms between carbon fibre-reinforced peek and epoxy composites subjected to static and cyclic loading(European Society for Composite Materials, 2018-06-30) Hernandez, Thibault. P. A.; Mills, Andrew R.; Yazdani Nezhad, HamedExperimental 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.Item Open Access Computational prediction of electrical and thermal properties of graphene and BaTiO3 reinforced epoxy nanocomposites(Eurasia Academic Publishing Group (EAPG), 2021-10-20) Mishra, Raghvendra Kumar; Goel, Saurav; Yazdani Nezhad, HamedGraphene based materials e.g., graphene oxide (GO), reduced graphene oxide (RGO) and graphene nano platelets (GNP) as well as Barium titanate (BaTiO3) are emerging reinforcing agents which upon mixing with epoxy provides composite materials with superior mechanical, electrical and thermal properties as well as shielding against electromagnetic (EM) radiations. Inclusion of the thesereinforcing agents shows improvedperformance;however, the extent of improvement has remained uncertain. In this study, a computational modelling approach was adopted using COMSOL Multiphysics software in conjunction with Bayesian statistical analysis to investigate the effects of including various filler materials e.g.,GO, RGO, GNP and BaTiO3 in influencing the direct current (DC) conductivity (σ), dielectric constant (ε) and thermal properties on the resulting epoxy polymer matrix composites. The simulations were performed for different volume percentage of the filler materials by varying the geometry of the filler material. It was observed that the content of GO, RGO, GNPs and the thickness of graphene nanoplatelets can alter the DC conductivity, dielectric constant, and thermal properties of the epoxy matrix. The lower thickness of GNPs was found to offer the larger value of DC conductivity, thermal conductivity and thermal diffusivity than rest of the graphene nanocomposites, while the RGO showed better dielectric constant value than neat epoxy, and graphenenanocomposites. Similarly, the percentage content and size (diameter) of BaTiO3nanoparticles were observed to alter the dielectric constant, DC conductivity and thermal properties of modified epoxy by several order of magnitude than neat epoxy. In this way, the higher diameter particles of BaTiO3showed better DC conductivity properties, dielectric constant value, thermal conductivity and thermal diffusivity.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 the paper: 'Development and testing of carbonaceous tin-based solder achieving unprecedented joint performance Item'(Cranfield University, 2021-06-21 12:53) Hawi, Sara; Gharavian, Somayeh; Burda, Marek; Goel, Saurav; Lotfian, Saeid; Khaleque, Tasnuva; Yazdani Nezhad, HamedThe paper shows that the suitable addition of carbon nanomaterials to a tin-based solder material matrix results in two fold strength of soldered joints.Item Open Access Development of carbonaceous tin-based solder composite achieving unprecedented joint performance(Springer, 2021-12-30) Hawi, Sara; Gharavian, Somayeh; Burda, Marek; Goel, Saurav; Lotfan, Saeid; Khaleque, Tasnuva; Yazdani Nezhad, HamedWeight reduction and improved strength are two common engineering goals in the joining sector to benefit transport, aerospace, and nuclear industries amongst others. Here, in this paper, we show that the suitable addition of carbon nanomaterials to a tin-based solder material matrix (C-Solder® supplied by Cametics Ltd.) results in two-fold strength of soldered composite joints. Single-lap shear joint experiments were conducted on soldered aluminium alloy (6082 T6) substrates. The soldering material was reinforced in different mix ratios by carbon black, graphene, and single-walled carbon nanotubes (SWCNT) and benchmarked against the pristine C-solder®. The material characterisation was performed using Vickers micro-indentation, differential scanning calorimetry and nano-indentation, whereas functional testing involved mechanical shear tests using single-lap aluminium soldered joints and creep tests. The hardness was observed to improve in all cases except for the 0.01 wt.% graphene reinforced solders, with 5% and 4% improvements in 0.05 carbon black and SWCNT reinforced solders, respectively. The maximum creep indentation was noted to improve for all solder categories with maximum 11% and 8% improvements in 0.05 wt.% carbon black and SWCNT reinforced ones. In general, the 0.05 wt.% nanomaterial reinforced solders promoted progressive cohesion failure in the joints as opposed to instantaneous fully de-bonded failure observed in pristine soldered joints, which suggests potential application in high-performance structures where no service load induced adhesion failure is permissible (e.g. aerospace assemblies). The novel innovation developed here will pave the way to achieving high-performance solder joining without carrying out extensive surface preparations.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 Development of leak-before-break filament wound composite structures.(Cranfield University, 2019-11) Loukodimou, Vasiliki; Skordos, Alexandros A.; Kazilas, Mihalis C.; Yazdani Nezhad, HamedA leak-before-break (LBB) concept was developed for composite pressure vessels (CPVs) to achieve a safe, predictable and controllable way of failure preventing the consequences of a catastrophic rupture. Artificial defects were introduced in the structure in prearranged patterns, acting as weak areas and enforcing failure initiation and propagation from these locations. A continuum damage constitutive model was developed through testing and simulation of tensile and compression specimens at [0°]8, specimens under cyclic in-plane shear at [±45°]2s, [+45°]₈ and [±67.5°]₂s as well as out-of-plane specimens at [0°]₁₀ and [0°]₁₂. A methodology was established for the introduction of artificial defects in the composite material for its failure control considering fibre cuts and interfacial defects. The LBB concept was investigated through the simulation of the behaviour of CPVs including defects under internal pressurisation. The assessment of the LBB behaviour was based on the ability to discern between the occurrence of two leakages; the first associated to the leakage phenomenon for pressure relief in the case of over-pressurisation and the second corresponding to ultimate failure. The influence of size and degree of damage induced through the defects was investigated, as well as the use of local reinforcing patches to enhance the LBB behaviour. The most suitable design for the optimal function of the LBB behaviour involves a circular fibre cut defective area of 87.5% fibre cut damage which results in a clear separation between leak and damage by a pressure difference of about 280 bar. The selected case was used for the manufacturing of a closed-end loaded composite pipe to validate the concept. The results of the testing showed that leakage did not occur from the introduced weak points due to manufacturing defects; however, the prediction of the damage initiation from the introduced defects was accurately identified with a difference of 2% compared to the simulation results.Item Open Access A dissection and enhancement technique for combined damage characterisation in composite laminates using laser-line scanning thermography(Elsevier, 2021-05-24) Liu, Haochen; Du, Weixiang; Yazdani Nezhad, Hamed; Starr, Andrew; Zhao, YifanImpact induced combined damage in composite laminates attracts great attention due to its significant degradation of the structural integrity. However, the provision of the quantitative analysis of each damage portion is challenging due to its bare visibility and structural mixture complexity, so-called barely visible impact damage (BVID), which is referred to as inter-laminar delamination, and is inherently coupled with in-plane transverse and matrix damage also known as combined damage. Instead of focusing on one type of damage in most of the existing studies, this paper proposes a decomposition and targeted enhancement technique based on Stationary Wavelet Transform (SWT) for such coupled BVID in composite laminates using laser-line scanning thermography. Firstly, a combined damage model composed of in-plane damage and inter-laminar delamination is established by finite element numerical modelling to predict the thermal response pattern in the laser scanning thermography. Then, a feature separation and targeted enhancement strategy based on SWT in the frequency domain is proposed to improve the contrast of the matrix crack and delamination in combined damage scenarios induced by low-velocity rigid impact via drop-tower tests, meanwhile eliminating noise and suppressing the laser pattern background. The enhanced images of in-plane damage and delamination are furtherly processed by Random Sample Consensus (RANSAC) method and confidence map algorithms to calibrate the damage profile. The proposed technique is validated through inspecting a group of unidirectional carbon fibre-reinforced polymer composite samples, impacted by a variety of energy levels, in fibre-parallel (0°), 45° and orthogonal scanning modes. The results demonstrate that the proposed technique can pertinently isolate, enhance and characterise the inspected in-plane crack and inter-laminates delamination in a flexible manner. The proposed methodology paves the way towards automated infrared thermography data analysis for quantitative dissection of actual combined damage in composite laminates.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 Fused deposition modeling-based additive manufacturing (3D printing): techniques for polymer material systems(Elsevier, 2020-02-28) Daminabo, Samuel; Goel, Saurav; Grammatikos, S. A.; Yazdani Nezhad, Hamed; Thakur, Vijay KumarWhile the developments of additive manufacturing (AM) techniques have been remarkable thus far, they are still significantly limited by the range of printable, functional material systems that meet the requirements of a broad range of industries; including the healthcare, manufacturing, packaging, aerospace and automotive industries. Furthermore, with the rising demand for sustainable developments, this review broadly gives the reader a good overview of existing AM techniques; with more focus on the extrusion-based technologies (Fused Deposition Modelling and Direct Ink Writing) due to their scalability, cost-efficiency and wider range of material processability. It then goes on to identify the innovative materials and recent research activities that may support the sustainable development of extrusion-based techniques for functional and multifunctional (4D printing) part and product fabrication.Item Open Access Graphene nanoplatelets/barium titanate polymer nanocomposite fibril: a remanufactured multifunctional material with unprecedented electrical, thermomechanical, and electromagnetic properties(Wiley, 2023-09-25) Mishra, Raghvndra Kumar; Goel, Saurav; Chianella, Iva; Yazdani Nezhad, HamedA novel, zero-waste and recycling plastic waste solution is introduced, to scalably produce graphene nanoplatelets/barium titanate (GNP/BaTiO3) polymer nanocomposite fibrils. A comprehensive investigation is performed to evaluate the compatible and non-compatible recycled polypropylene (PP)/polyethyleneterephthalate (PET) blends combined with functional (electrical, piezoelectric,and dielectric) materials for in-situ fibril production. The nanocompositefibrils made from recycled PP, PET and GNPs/BaTiO3 with high-aspect ratio disparity (400:1) are produced, which exhibit significantly enhanced electrical, thermomechanical, and electromagnetic characteristics. Single-screw extrusion is utilised to fabricate the fibrils with the in-situ fibril morphology of PET and GNPs/BaTiO3 leading to improved electrical conductivity. It is demonstrated that such fibril morphology restricts the chain mobility of polymer molecules, and ultimately increases viscosity and strain energy. Moreover, the study demonstrates a positive reinforcement effect from the utilisation of PET fibrils and GNPs/BaTiO3 in a PP matrix, dominated by the high-aspect ratio, stiffness, and thermal stability of GNPs/BaTiO3. Furthermore, it is observed that the mechanical properties and tension-bearing capacity of the PP are significantly improved by such incorporation. The study also demonstrates that the protection of the remanufactured nanocomposites against electromagnetic interference is significantly improved with the increasing GNPs/BaTiO3 content and the morphological transition from spherical to fibril-shaped PET.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 Low electric field induction in BaTiO3-epoxy nanocomposites(Springer, 2023-05-29) Mishra, Raghvendra Kumar; Li, Danning; Chianella, Iva; Goel, Saurav; Lotfian, Saeid; Yazdani Nezhad, HamedEpoxy is widely used material, but epoxy has limitations in terms of brittleness in failure, and thus researchers explore toughening and strengthening options such as adding a second phase or using electromagnetic fields to tailor toughness and strength, on demand and nearly instantaneously. Such approach falls into the category of active toughening but has not been extensively investigated. In this research, Si-BaTiO3 nanoparticles were used to modify the electro-mechanical properties of a high-performance aerospace-grade epoxy so as to study its response to electric fields, specifically low field strengths. To promote uniform dispersion and distribution, the Si-BaTiO3 nanoparticles were functionalised with silane coupling agents and mixed in the epoxy Araldite LY1564 at different content loads (1, 5, 10 wt%), which was then associated with its curing agent Aradur 3487. Real-time measurements were conducted using Raman spectroscopy while applying electric fields to the nanocomposite specimens. The Raman data showed a consistent trend of increasing intensity and peak broadening under the increasing electric field strength and Si-BaTiO3 contents. This was attributed to the BaTiO3 particles’ dipolar displacement in the high-content nanocomposites (i.e., 5 wt% and 10 wt%). The study offers valuable insights on how electric field stimulation can actively enhance the mechanical properties in epoxy composites, specifically in relatively low fields and thin, high-aspect-ratio composite layers which would require in-situ mechanical testing equipped with electric field application, an ongoing investigation of the current research.