Browsing by Author "Li, Danning"

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    Accelerated microwave curing of fibre-reinforced thermoset polymer composites for structural applications: A review of scientific challenges
    (Elsevier, 2018-09-12) Mgbemena, Chinedum Ogonna; Li, Danning; Lin, Meng-Fang; Liddel, Paul Daniel; Katnam, Kali Babu; Kumar, Vijay Thakur; Nezhad, Hamed Yazdani
    Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided.
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    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-Fang
    This 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 powers
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    ItemOpen 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, Hamed
    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.
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    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, Hamed
    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 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.
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    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, Hamed
    For 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.
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    ItemOpen 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, Hamed
    Epoxy 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.