Okan Ozdemir

Low-velocity impact response of sandwich composites with different foam core configurations

In this study, the low-velocity impact response of sandwich composites consisting of different foam core configurations is investigated experimentally. Polyvinyl chloride foam core and glass fibers were used as core material and face sheets, respectively. A number of tests under various impact energy levels for three different sandwich composite configurations were conducted with Ceast 9350 Fractovis Plus impact testing machine in order to improve the energy absorption capacity of sandwich composites panels. Absorbed energies, maximum loads and the maximum deflection of sandwich panels were obtained for each impact energy level. As the impact energy was increased, fiber fractures at face sheets, delaminations between glass-epoxy layers, core fractures, and indentations failures were observed by visual inspection. According to the obtained results, the sandwich composite with proposed new foam core design with two internal face sheets exhibits high energy absorption capacity compared to sandwich panels formed by sandwiching a polyvinyl chloride foam core between glass fabric face sheets. Maximum contact force values decrease by increase of number of core material.

Core-thickness effect on the impact response of sandwich composites with poly(vinyl chloride) and poly(ethylene terephthalate) foam cores

The objective of this study was to investigate the effects of core material and its thickness on impact behavior of sandwich composite plates subjected to low-velocity impact, experimentally. Poly(vinyl chloride) (PVC) and poly(ethylene terephthalate) (PET) foams were selected as the core material, having approximate density of 65 kg/m3 and 60 kg/m3, respectively, and thicknesses of 5, 10, and 15 mm. The stacking sequence of the sandwich composites is [ ± 45 ∘ / 0 ∘ / 90 ∘ / core / 90 ∘ / 0 ∘ / ∓ 45 ∘ ] . Impact tests were carried out by using Ceast 9350 Fractovis Plus impact testing machine under room temperature. Various impact energies were selected ranging from 10 J to 70 J to analyze the impact energy level. The dimensions of the specimens are 100 mm × 100 mm. After the impact tests, contact-force deflection curves and also maximum contact force, maximum contact time, and maximum deflection versus impact energy curves were obtained for mentioned impact energies for sandwich composites with PVC and PET foams and [ ± 45 ∘ / 0 ∘ / 90 ∘ ] s -laminated composites. As a result, it is seen that the core material and its thickness have notable effects on the impact behavior of sandwich composite plates. Sandwich composites also have higher absorbed energy, penetration, and perforation thresholds.

Experimental analysis of single-lap composite joints with two different adhesives at various conditions

Composite materials have been used in the transport industry in the recent years. The assembly of composite materials has been performed with either adhesive joints or other mechanical fasteners. Adhesive joints are more preferred because of their easy usages, lightness and the stress concentration, which is very important in the design, occurs less than the other type joints. In this study, load-carrying capacity of single-lap joints bonded with different adhesives was found, experimentally. Woven glass fibre–epoxy composites manufactured by using vacuum assisted resin infusion method (VARIM) were used as adherends. FM73 epoxy film adhesive and DP-460 paste adhesive were used as adhesive materials. Several loading conditions, 5, 10 and 15 J, that possibly happen in the operation life were considered. The tests were carried out room temperature (25℃), 50℃ and 80℃. From the results, it is observed that the load-carrying capacity of single-lap joints significantly varies with adhesive types and temperature.

Electromechanical characterization of multilayer graphene-reinforced cellulose composite containing 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid

Abstract In this study, multilayer graphene (Gr)-reinforced cellulose composites were synthesized by using 1-ethyl-3-methylimidazolium diethylphosphonate ionic liquid. The composites were fabricated via dissolving the cellulose in 1-ethyl-3-methylimidazolium diethylphosphonate and Gr loading at different ratios (0.2, 0.4, and 0.6 wt.%). Both sides of the composites were coated with gold leaf to generate electrodes. The effect of Gr loading on chemical functional groups, crystallographic properties, thermal stability, and morphological and mechanical properties of cellulose film was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and tensile test, respectively. Electromechanical behavior of the cellulose composite films reinforced with Gr (0.2, 0.4, and 0.6 wt.%) was investigated under DC excitation voltages of 1, 3, 5 and 7 V. Gr loading of 0.2 wt.% increased maximum tip displacement by 400% when the actuator is excited with 3 V.

Investigation of the effects of PWM parameters on ionic polymer metal composite actuators

The effects of the PWM excitation signal parameters, such as frequency and magnitude, on the Nafion-based ionic polymer metal composite (IPMC) actuator response were found out. The first set of experiments was designed to observe the actuator response when the actuators were biased with constant DC voltages. These experimental results were exploited to build an experimental data based dynamic model. The model and these results were also used as references to evaluate the experimental results in the proceeding experiments. The second set of experiments was designed to observe the actuator response when the DC square wave signals at different frequencies (0 to 1000 Hz) were applied. The third set of experiments was designed to observe the actuator response when the PWM signals at different magnitudes (6, 8 and 10 V) were applied. It is observed that back relaxation reduces with increasing frequency, but after a certain frequency value, it remains approximately constant. It is seen that the input output relationship of the actuators are linear only for a range of PWM signal magnitudes. The observations in both the PWM frequency and the magnitude experiments indicated that the performance of the Nafion-based IPMC actuator could be improved by selecting a magnitude of PWM signals between 6–8 Volts and by selecting a frequency between 400–1000 Hz.

Cam Lifi Takviyeli Polipropilen Kompozitlerde Kalınlığın ve Sıcaklığın Darbe Davranışına Etkileri

Bu calismada, uzun cam elyaf takviyeli polipropilen granullerden olusan termoplastik kompozitlerin dusuk hizli darbe davranislari deneysel olarak incelenmistir. Bu kompozitlerin dusuk hizli darbe davranisini iyilestirmek amaciyla cam elyaf takviyeli polipropilen kompozit prepregler kullanilarak sandvic yapida yeni bir dizilime sahip kompozitler uretilmistir. Kalinligin ve sicakligin dusuk hizli darbe davranisina olan etkilerini incelemek amaciyla 4 ve 6mm kalinliga sahip kompozitlerin oda sicakliginda ve 50˚C’de deneyleri gerceklestirilmistir. Elde edilen sonuclara gore, iki farkli dizilime sahip kompozitlerin kalinligin artmasiyla maksimum temas kuvvetinin arttigi, sicakligin yukselmesiyle ise dustugu gozlemlenmistir.

Characterization and analysis of motion mechanism of electroactive chitosan-based actuator

In order to analyze the bending mechanism of the electroactive​ chitosan-based actuator, different amounts of poly(diallyldimethylammonium chloride) (PDAD) were incorporated in chitosan solution. The effects of PDAD concentration on electromechanical performance of chitosan actuator were investigated under various excitation voltages. With the incorporation of PDAD into chitosan solution, crosslinked chitosan film acts as an actuator showing a considerable displacement behavior. However it can be noted that higher incorporation of PDAD into chitosan solution decreased the performance of the actuators. Thermal, viscoelastic, and crystallographic properties of the chitosan films were examined by thermogravimetric analysis, dynamic mechanical analysis, and X-ray diffraction analysis, respectively. The effect of incorporation of PDAD in chitosan-based film on morphological properties of chitosan film was determined by scanning electron microscopy. It was observed that the films involving PDAD have larger pore size than the PDAD free film.