Browsing by Author "Al-Maharma, Ahmad Yousef Mohammad"

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Critical review of the factors dominating the fracture toughness of CNT reinforced polymer composites
(IOP Publishing, 2019-01) Al-Maharma, Ahmad Yousef Mohammad; Şendur, Polat; Al-Huniti, N.; Mechanical Engineering; ŞENDUR, Polat; Al-Maharma, Ahmad Yousef Mohammad
In this study, the main factors, which have substantial influence on fracture toughness of carbon nanotubes (CNTs)-based composites both at nano and macro scales, are discussed in detail. Based on the findings from the reviewed literature, the improvement obtained on fracture toughness of CNTs multi-scale composites are due to the effect of CNTs on crack bridging and pullout toughening mechanisms. It is highly recommended to reinforce raw composites with low content of CNTs in order to improve the dispersion and interfacial adhesion of CNTs with surrounding polymer. Long aligned MWCNTs with small diameters (high aspect ratio) are recommended to be used to reinforce FRP composite in order to obtain superior fracture resistance toward initiated cracks. We found out that the factors, which govern the fracture toughness in multi-scale composites, are strongly correlated to each other. The most critical factors that affect the fracture toughness include the alignment and structure (length of nanotube) followed by the type of functionalization conducted on the surface of CNTs.
Open Access
Critical review of the parameters affecting the effectiveness of moisture absorption treatments used for natural composites
(MDPI AG,, 2019) Al-Maharma, Ahmad Yousef Mohammad; Al-Huniti, N.; Al-Maharma, Ahmad Yousef Mohammad
Natural composites can be fabricated through reinforcing either synthetic or bio-based polymers with hydrophilic natural fibers. Ultimate moisture absorption resistance at the fiber–matrix interface can be achieved when hydrophilic natural fibers are used to reinforce biopolymers due to the high degree of compatibility between them. However, the cost of biopolymers is several times higher than that of their synthetic counterparts, which hinders their dissemination in various industries. In order to produce economically feasible natural composites, synthetic resins are frequently reinforced with hydrophilic fibers, which increases the incompatibility issues such as the creation of voids and delamination at fiber–matrix interfaces. Therefore, applying chemical and/or physical treatments to eliminate the aforementioned drawbacks is of primary importance. However, it is demonstrated through this review study that these treatments do not guarantee a sufficient improvement of the moisture absorption properties of natural composites, and the moisture treatments should be applied under the consideration of the following parameters: (i) type of hosting matrix; (ii) type of natural fiber; (iii) loading of natural fiber; (iv) the hybridization of natural fibers with mineral/synthetic counterparts; (v) implantation of nanofillers. Complete discussion about each of these parameters is developed through this study.
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The effect of interlaminar graphene nano-sheets reinforced e-glass fiber/ epoxy on low velocity impact response of a composite plate
(IOP Publishing, 2018-05) Al-Maharma, Ahmad Yousef Mohammad; Şendur, Polat; Mechanical Engineering; ŞENDUR, Polat; Al-Maharma, Ahmad Yousef Mohammad
In this study, we compare the inter-laminar effect of graphene nano-sheets (GNSs) and CNTs on the single and multiple dynamic impact response of E-glass fiber reinforced epoxy composite (GFEP). In the comparisons, raw GFEP composite is used as baseline for quantifying the improvement on the dynamic impact response. For that purpose, finite element based models are developed for GNSs on GFEP, graphene coating on glass fibers, inter-laminar composite of CNTs reinforced polyester at 7.5 vol%, and combinations of all these reinforcements. Comparisons are made on three metrics: (i) total deformation, (ii) the contact force, and (iii) internal energy of the composite plate. The improvement on axial modulus (E1) of GFEP reinforced with one layer of GNS (0.5 wt%) without polyester at lamination sequence of [0]8 is 29.4%, which is very close to the improvement of 31% on storage modulus for multi-layer graphene with 0.5 wt% reinforced E-glass/epoxy composite at room temperature. Using three GNSs (1.5 wt%) reinforced polyester composite as interlaminar layer results in an improvement of 57.1% on E1 of GFEP composite. The simulation results reveal that the interlaminar three GNSs/polyester composite at mid-plane of GFEP laminated composite can significantly improve the dynamic impact resistance of GFEP structure compared to the other aforementioned structural reinforcements. Reinforcing GFEP composite with three layers of GNSs/polyester composite at mid-plane results in an average of 35% improvement on the dynamic impact resistance for healthy and damaged composite plate under low velocity impacts of single and multiple steel projectiles. This model can find application in various areas including structural health monitoring, fire retardant composite, and manufacturing of high strength and lightweight mechanical parts such as gas tank, aircraft wings and wind turbine blades.
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Numerical assessment of the factors controlling the acoustic response of wind turbine blades
(Canadian Acoustical Association, 2019) Al-Maharma, Ahmad Yousef Mohammad; Şendur, Polat; Mechanical Engineering; ŞENDUR, Polat; Al-Maharma, Ahmad Yousef Mohammad
The blades of wind turbine are the most critical parts of the wind turbine system, which contribute to noise generated by wind turbine due to excitation from air streams across them. In this numerical study, the effect of various design factors for both horizontal and vertical wind turbines is analysed in order to determine the most critical design factors. The knowledge of such information is important to control and reduce the noise level from wind turbine. The simulation results show that the pitch angle, which is the summation of angle of attack and twist angle, along with the height of air foil section have the most significant effect on the overall sound pressure level. The results also reveal that the overall sound pressure level is least sensitive to the size of the blade and shell thickness.
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Review of the main factors controlling the fracture toughness and impact strength properties of natural composites
(IOP Publishing, 2019-02) Al-Maharma, Ahmad Yousef Mohammad; Şendur, Polat; Mechanical Engineering; ŞENDUR, Polat; Al-Maharma, Ahmad Yousef Mohammad
The main critical factors, which have direct influence on the fracture toughness and imapct strength properties of natural fibers composites, are reviewed in details in this paper. Considering the vast body of literature on the aforementioned subject, there are six main factors controlling these properties: (i) Intrinsic properties of the constituents related to packing arrangements, length, loading and orientation of the fibers; (ii) Type of physical and chemical treatment on natural fibers; (iii) Environmental conditions such as temperature and moisture; (iv) Material properties of reinforcing fiber and hosting resin, which constitute the natural composites; (v) The type of hybridization of natural composites such as self-hybridization based on same natural fiber and hybridization of natural fiber with another natural or synthetic fibers; (vi) Type of nano reinforcements, which is used to improve the fracture toughness of natural composites at nano and micro scale levels. Among the aforementioned factors, it is found out that the most critical factors affecting the fracture toughness and impact strength of natural composites are the type of physical and chemical treatments used to improve interfacial adhesion at fiber-matrix interface and the type of hybridization process.