Browsing by Author "Yeke, Melisa"

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Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites
(Sage Publications Ltd, 2023) Iplikci, Hande; Barisik, Murat; Turkdogan, Ceren; Martin, Seckin; Yeke, Melisa; Nuhoglu, Kaan; Iris, Mehmet Erdem
Removal of contaminants and top polymer layer from the surface of carbon -fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/-45/90](2s) stacking of carbon/epoxy prepregs (HexPly (R) -M91), 100 mJ/mm(2) generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition.
Improving adhesive behavior of fiber reinforced composites by incorporating electrospun Polyamide-6,6 nanofibers in joining region
(Sage Publications Ltd, 2022) Esenoglu, Gozde; Barisik, Murat; Tanoglu, Metin; Yeke, Melisa; Turkdogan, Ceren; Iplikci, Hande; Iris, Mehmet Erdem; Tanoğlu, Metin
Adhesive joining of fiber reinforced polymer (CFRP) composite components is demanded in various industrial applications. However, the joining locations frequently suffer from adhesive bond failure between adhesive and adherent. The aim of the present study is improving bonding behavior of adhesive joints by electrospun nanofiber coatings on the prepreg surfaces that have been used for composite manufacturing. Secondary bonding of woven and unidirectional CFRP parts was selected since this configuration is preferred commonly in aerospace practices. The optimum nanofiber coating with a low average fiber diameter and areal weight density is succeed by studying various solution concentrations and spinning durations of the polyamide-6.6 (PA 66) electrospinning. We obtained homogeneous and beadles nanofiber productions. As a result, an average diameter of 36.50 +/- 12 nm electrospun nanofibers were obtained and coated onto the prepreg surfaces. Prepreg systems with/without PA 66 nanofibers were hot pressed to fabricate the CFRP composite laminates. The single-lap shear test coupons were prepared from the fabricated laminates to examine the effects of PA 66 nanofibers on the mechanical properties of the joint region of the composites. The single-lap shear test results showed that the bonding strength is improved by about 40% with minimal adhesive use due to the presence of the electrospun nanofibers within the joint region. The optical and SEM images of fractured surfaces showed that nanofiber-coated joints exhibited a coherent failure while the bare surfaces underwent adhesive failure. The PA66 nanofibers created better coupling between the adhesive and the composite surface by increasing the surface area and roughness. As a result, electrospun nanofibers turned adhesive failure into cohesive and enhanced the adhesion performance composite joints substantially.
Improving mechanical properties of adhesive joints in carbon fiber reinforced polymer composites by incorporation of graphene added electrospun polymeric nanofibers
(01. Izmir Institute of Technology, 2023-07) Yeke, Melisa; Tanoğlu, Metin; Tanoğlu, Metin
Since composites joined with mechanical fasteners cause severe delamination damage, stress concentration in the joint area, and weight increase, joining composite materials with innovative methods have recently gained more importance. These joining methods prevent delamination damage, provide a uniform distribution of stress, and do not cause considerable weight increases. However, modifying the surface of composite parts joined by innovative methods is critical. In this study, the bonding surface was modified by coating carbon/epoxy prepregs with electrospun nanofibers with 10% wt/v ratio of PA 66 and 1%, 2% and 3% wt/v ratio of rGO added. Composite parts were joined in the hot press by the secondary bonding method using 3 plies of FM 300K film adhesive. The morphological structure of nanofibers and the dispersion of rGO were analyzed by SEM. The thermal properties of nanofibers were analyzed by DSC. The contact angle measurement device was used to determine the hydrophilic and hydrophobic properties of the unmodified prepreg and nanofiber-modified prepreg surface. The most hydrophilic surface was observed on the nanofiber-coated surface with 2% rGO added. Single Lap Joints (SLJ), and Charpy Impact tests were performed to examine the mechanical properties of modified and unmodified composite plates. According to the SLJ and Charpy Impact results, an improvement of 17.89% and 30.59% was observed in carbon/epoxy composite plates whose surface was modified with 2% rGO, respectively.
Investigating the Effects of PA66 Electrospun Nanofibers Layered within an Adhesive Composite Joint Fabricated under Autoclave Curing
(Amer Chemical Soc, 2023) Esenoglu, Gozde; Tanoglu, Metin; Barisik, Murat; Iplikci, Hande; Yeke, Melisa; Nuhoglu, Kaan; Iris, Mehmet Erdem; Tanoğlu, Metin
Enhancing the performance of adhesively joined composite components is crucial for various industrial applications. In this study, polyamide 66 (PA66) nanofibers produced by electrospinning were coated on unidirectional carbon/epoxy prepregs to increase the bond strength of the composites. Carbon/epoxy prepregs with/without PA66 nanofiber coating on the bonding region were fabricated using the autoclave, which is often used in the aerospace industry. The single lap shear Charpy impact energy and Mode-I fracture toughness tests were employed to examine the effects of PA66 nanofibers on the mechanical properties of the joint region. Scanning electron microscopy (SEM) was used to investigate the nanofiber morphology and fracture modes. The thermal characteristics of Polyamide 66 nanofibers were explored by using differential scanning calorimetry (DSC). We observed that the electrospun PA66 nanofiber coating on the prepreg surfaces substantially improves the joint strength. Results revealed that the single lap shear and Charpy impact strength values of the composite joint are increased by about 79 and 24%, respectively, by coating PA66 nanofibers onto the joining region. The results also showed that by coating PA66 nanofibers, the Mode-I fracture toughness value was improved by about 107% while the glass transition temperature remained constant.