Browsing by Author "Lotfian, Saeid"

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    Assessment of mechanical and fatigue crack growth properties of wire+arc additively manufactured mild steel components
    (Wiley, 2022-07-20) Shamir, Muhammad; Igwemezie, Victor C.; Lotfian, Saeid; Jones, Rhys; Asif, Huzaifa; Ganguly, Supriyo; Mehmanparast, Ali
    A study has been conducted to evaluate the mechanical and fatigue crack propagation properties of wire + arc additively manufactured ER70S-6 components. A parallel-built deposition strategy was employed to fabricate the additively manufactured wall. The hardness values were slightly higher at the bottom and top of the wall due to the presence of Widmanstätten ferrite and carbides. The characterization of mechanical properties in both orientations; parallel and perpendicular to the deposition direction showed a marginal difference in yield strength and ultimate tensile strength. The crack growth rates were correlated with linear elastic fracture mechanics parameter ΔK and compared with an oscillation-built deposition strategy from the literature. The crack growth rates of both deposition strategies were found to be very similar to each other. Furthermore, it has been demonstrated that the variability in the crack growth histories can be reasonably well captured by using the NASGRO crack growth equation.
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    Chemically graded Fe–Al/steel samples fabricated by laser metal deposition
    (Cambridge University Press, 2017-01-30) Lotfian, Saeid; Rolink, Gesa; Weisheit, Andreas; Palm, Martin
    By laser metal deposition (LMD) samples from Fe–28Al (at.%) have been built on iron and various steels. Chemically graded iron aluminium and Fe–28Al/steel samples were fabricated with intended concentration gradients by controlling the feed rates of the powders. All samples were subsequently heat treated at 700 °C for 1000 h to study possible reactions between Fe–28Al and the steels and the long-term stability of the composition gradients. Microstructures were characterized by scanning electron microscopy (SEM) and concentration profiles along the building direction were analysed by energy- and wavelength-dispersive spectrometry (EDS, WDS).
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    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, Hamed
    The paper shows that the suitable addition of carbon nanomaterials to a tin-based solder material matrix results in two fold strength of soldered joints.
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    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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    Electrospun piezoelectric polymer nanofiber layers for enabling in situ measurement in high-performance composite laminates
    (American Chemical Society, 2018-08-09) Lotfian, Saeid; Giraudmaillet, Claire; Yoosefinejad, Ata; Thakur, Vijay Kumar; Hamed, Yazdani Nezhad
    This article highlights the effects from composite manufacturing parameters on fiber-reinforced composite laminates modified with layers of piezoelectric thermoplastic nanofibers and a conductive electrode layer. Such modifications have been used for enabling in situ deformation measurement in high-performance aerospace and renewable energy composites. Procedures for manufacturing high-performance composites are well-known and standardized. However, this does not imply that modifications via addition of functional layers (e.g., piezoelectric nanofibers) while following the same manufacturing procedures can lead to a successful multifunctional composite structure (e.g., for enabling in situ measurement). This article challenges success of internal embedment of piezoelectric nanofibers in standard manufacturing of high-performance composites via relying on composite process specifications and parameters only. It highlights that the process parameters must be revised for manufacturing of multifunctional composites. Several methods have been used to lay up and manufacture composites such as electrospinning the thermoplastic nanofibers, processing an inter digital electrode (IDE) made by conductive epoxy–graphene resin, and prepreg autoclave manufacturing aerospace grade laminates. The purpose of fabrication of IDE was to use a resin type (HexFlow RTM6) for the conductive layer similar to that used for the composite. Thereby, material mismatch is avoided and the structural integrity is sustained via mitigation of downgrading effects on the interlaminar properties. X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and scanning electron microscopy analyses have been carried out in the material characterization phase. Pulsed thermography and ultrasonic C-scanning were used for the localization of conductive resin embedded within the composite laminates. This study also provides recommendations for enabling internally embedded piezoelectricity (and thus health-monitoring capabilities) in high-performance composite laminates.
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    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.
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    A review of challenges and opportunities associated with bolted flange connections in the offshore wind industry
    (MDPI, 2020-06-01) Mehmanparast, Ali; Lotfian, Saeid; Vipin, Sukumara Pillai
    The use of bolted flange connections in the offshore wind industry has steeply risen in the last few years. This trend is because of failings observed in other modes of joints such as grouted joints, coupled with enormous economic losses associated with such failures. As many aspects of bolted flange connections for the offshore wind industry are yet to be understood in full, the current study undertakes a comprehensive review of the lessons learned about bolted connections from a range of industries such as nuclear, aerospace, and onshore wind for application in offshore wind industry. Subsequently, the collected information could be used to effectively address and investigate ways to improve bolted flange connections in the offshore wind industry. As monopiles constitute an overwhelming majority of foundation types used in the current offshore wind market, this work focusses on large diameter flanges in the primary load path of a wind turbine foundation, such as those typically found at the base of turbine towers, or at monopile to transition piece connections. Finally, a summary of issues associated with flanges as well as bolted connections is provided, and insights are recommended on the direction to be followed to address these concerns.
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    Towards the use of electrospun piezoelectric nanofibre layers for enabling in-situ measurement in high performance composite laminates
    (European Society for Composite Materials, 2018-06-30) Lotfian, Saeid; Kumar, Vijay Thakur; Giraudmaillet, Claire; Yoosefinejad, Ata; Brennan, Feargal; Yazdani Nezhad, Hamed
    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.
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    Ultra-thin electrospun nano-fibres for damage tolerant composite laminates
    (Cranfield University, 2019-11-08 12:34) An, Donglan; Lotfian, Saeid; Mesbah, Daria; Ayre, David; Yoosefinejad, Ata; Kumar, Vijay; Yazdani Nezhad, Hamed
    Raw data and calculation of Mode-I fracture toughness at initiation and propagation for different densities of electrospun nanofibres embedded for toughening of composite laminates
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    Ultra-thin electrospun nanofibers for development of damage-tolerant composite laminates
    (Elsevier, 2019-11-05) An, Donglan; Lotfian, Saeid; Mesbah, Daria; Ayre, David; Yoosefinejad, Ata; Thakur, Vijay Kumar; Yazdani Nezhad, Hamed
    The present article overcomes existing challenges in inter-laminar toughening of novel multifunctional fiber-reinforced polymer composites via development and embedment of highly stretched, ultra-thin electrospun thermoplastic nanofibers made of polyamide 6.6. The nanofibers exhibit significant enhancement of the composite laminate's structural integrity with almost zero weight penalty via ensuring a smooth stress transfer throughout the plies and serving tailoring mechanical properties in desired directions, with no interference with geometric features, e.g., thickness. The findings for 1.5 g per square meter electrospun nanofibers have demonstrated, on test coupon specimens, improvements up to 85% and 43% in peak load and crack opening displacement, respectively, with significant improvement (>25%) and no sacrifice of fracture toughness at both initiation and propagation phases. The initial stiffness for the modified specimens was improved by nearly 150%. The enhancement is mainly due to nanofibers contributing to the stiffness of the resin-rich area at the crack tip adjacent to the polytetrafluoroethylene (PTFE) film. Glass fiber-reinforced woven phenolic pre-impregnated composite plies have been modified with the nanofibers (each layer having an average thickness of <1 micron) at 0.5, 1.0, 1.5, 2.0 and 4.0 gsm, electrospun at room temperature on each ply, and manufactured via an autoclave vacuum bagging process. Inter-laminar fracture toughness specimens were manufactured for Mode I (double cantilever beam) fracture tests. It was found that there is threshold for electrospun nanofibers density, at which an optimum performance is reached in modified composite laminates. The threshold is influenced by the plastic deformation mechanism at the crack tip, the fiber bridging between the adjacent plies afforded by the nanofibers, and the density of the electrospun fibers. Such optimum performance was found linked to the nanofibers at a specific density. Excessively increasing above the threshold (herein >2.0 gsm) degrades the adhesion properties (chemical bonding) between glass fibers and the phenolic matrix. The density of nanofibers increases, so does the likelihood of forming a physical barrier between the plies resulting in the loss of resin flow and poor adhesion. Such an effect was evident from microscopic investigations and reduction in fracture toughness data at the initiation and propagation phases.