Recep Ekici

Motorcycle use is increasing and becoming widespread every day in the world, especially in Turkey. As the need for motorcycles increases, the basic structural parts of motorcycles, especially the frames, are desired to be stronger and cheaper as well as lighter. For this reason, although motorcycle frame materials are mostly steel or aluminum, in recent years hybrid materials consisting of composites and various alloys, especially in frame construction, have become widespread in the motorcycle industry. In this study, a preliminary design of two separate motorcycle frames consisting of steel and hybrid (steel, aluminum alloy and carbon fiber reinforced polymer (CFRP) composites) materials were made with solid modeling, and a finite element model of both frames was created. Thus, the deformations and stresses created by the static and dynamic loads acting on the frame were analyzed, and the frames were compared in terms of static and acceleration loading.

In this study, the low‐velocity impact behavior of polymer composites produced separately by reinforcing with natural fiber fabrics such as linen, hemp, jute, and bamboo was investigated for three different thicknesses (2.5 ± 0.1, 5 ± 0.1, and 7.5 ± 0.1 mm) by vacuum infusion method. Low‐speed impact tests were performed at three different energy levels of 20, 35, and 50 J by striking the geometric center of the composite samples with a hemispherical impactor. The impact strengths of the composites were evaluated by comparing the contact force‐displacement, contact force‐time graphs, and impacted sample images. The types of damage occurring in each experimental sample were evaluated. Increasing the thickness had a positive effect on the impact strength of the composites. When the thickness of the composite plates increases, the peak contact force increases, the displacement decreases and capacity to carry impact loads increases due to the increased stiffness of the composites. However, except for the damaged 5 ± 0.1 mm thick bamboo and jute samples, the energy absorption ability of the samples generally increases with the increase of impact energy. Bamboo, jute, and hemp reinforced samples with a thickness of 2.5 ± 0.1 mm were completely perforated under 20 J impact energy. Also, it was determined that linen reinforced composites have the best impact resistance among natural fabric reinforced composites.Highlights: Low‐velocity impact behavior of natural fiber fabric reinforced PMCs was studied. The impact strength of PMCs increased as the thickness increased. Linen reinforced composites had the best impact resistance. The main damage modes are matrix cracking and delamination at low‐impact energies. As the impact energy increases, perforation and fiber breakage or separations are observed.

This study experimentally investigates the mechanical properties of carbon fiber reinforced epoxy composites (CFRECs) filled with Graphene (Gr) and Silicon Carbide (SiC) nanoparticles. Gr and SiC nanoparticle filled CFREC plates at 0%, 0.5%, 1%, and 2% weight ratios were fabricated using a vacuum infusion technique from unidirectional carbon fiber fabric with both 0 and 90° fiber orientation. According to ASTM standards, tensile, compression, and three point bending tests were performed to determine the effects of additive type and weight ratios. CFRECs with Gr additive exhibit improved tensile properties compared to the unfilled composites, especially at higher filler contents and at specific fiber orientations. Also, the Gr additive showed a better improvement in the tensile behavior of the CFRECs than the SiC additive. In general, it was found that the elastic modulus values of nanoparticle additive samples were higher than that of the unfilled composite material in both fiber orientations. Except for the 0.5% SiC ratio with 0° fiber orientation, the particle added nanocomposites did not exceed the value of the unfilled composite and did not make a positive effect on the compressive strength. It has been observed that Gr additives give more positive results on the bending strength of CFRECs than SiC, especially at a 2% weight ratio. Highlights: Effects of nanoparticle types on mechanical properties of CFRECs were compared. Weight ratio effects on the properties of nanoparticle‐filled CFRECs were studied. The load‐bearing capacity decreased as the additive ratio increased. Additives and ratios should be carefully selected for the intended applications. Overall, presence Gr resulted in enhanced properties much prominently for composites.

In this study, the thermo-mechanical behavior of rectangular plates functionally graded (FG) in two directions along the plane is investigated with three-dimensional (3D) elasticity equations. In numerical analysis, the finite difference method (FDM) is used and the directional variation of the derivatives of the material properties is taken into account. The thermo-mechanical behavior of the plates is investigated for different compositional gradient exponents and it is emphasized that the variation of the compositional gradient exponent in both directions significantly changed the thermal stress distribution and the results are confirmed.

This study investigates the low-velocity and ballistic impact responses of SiC-reinforced Al6061 metal–matrix composites in different reinforcement volume fractions. Low-velocity impact (LVI) tests were performed with samples having SiC particle volume fractions of 0, 5, 10, 15, 20, 30, and 40%, while ballistic tests were carried out with samples having volume fractions of 0, 10, 20, and 30%. The weight-drop test method was used for LVI by applying 50 J (4.45 m/s) energy to all samples. Ballistic tests were carried out under the same conditions on all samples with the projectile launched at an average velocity of 500 m/s. For the determination of the ballistic resistance of the samples, the projectile penetrations in the witness structures were taken into consideration. The damage and deformations caused by both the LVI and the ballistic test in composites were examined. By the LVI test results, composite samples have absorbed less impact energy by increasing the reinforcement volume fraction, as well as demonstrated superior performance compared to unreinforced samples. In addition, the crack formation was mainly observed in the samples containing 30% reinforcement, while the composite material with a 40% volume fraction was completely broken. With the increase in the reinforcement volume fraction, the ballistic resistance of the samples increased significantly.

Thanks to their superior mechanical properties, polymer matrix composites have gained considerable importance. In order to improve the impact resistance of polymer matrix composite materials, a new hybrid material known as fiber metal laminate (FML) has been developed. The aim of this study was to reveal the effect of stacking sequence (SS), metal volume fraction (MVF), and number of layers on ballistic resistance in fiber metal laminates (FMLs). Four types of FMLs in different sequences and MVF (25% and 50%) were produced with hot press and vacuum. Ballistic tests were carried out with a single stage gas gun system. The absorbed energy was calculated from the energy difference that occurred by taking into account the FMLs entry and exit velocity of the projectile and the projectile mass. Damage types were examined after ballistic testing. It was determined that the stacking sequence and MVF significantly affect the impact resistance of FMLs. It was determined that the metal layer, which first encounters the projectile, compared to the polymer matrix composite, is more effective on the impact resistance of FMLs, and the impact resistance increased with the increase of MVF. In addition, the increase in the number of layers, if the top layers remain the same, adversely affected the impact resistance. It was observed that the first layer that encounters the projectile and the amount of MVF have a significant effect on the ballistic impact strength. As the amount of MVF increases, the ballistic impact resistance increases.

The objective of this research was to evaluate the stress and damage occurring on the bone model of D2 quality during implant insertion procedure using a novel dynamic finite element analysis (FEA) modeling. Three-dimensional finite element method was used to simulate the implant placement into the mandible. The cross-sectional model of the implant was created in SolidWorks 2007 software. The implant model was created to resemble a commercially available fine thread bone level dental implant (Bilimplant®, Turkey). 3 D bone models created with and without cortical bone drilling were specified according to D2 bone (Misch's Bone Classification) with a 1.5 mm cortical bone thickness. The stress patterns in both cancellous and cortical crestal bone were examined during implant insertion by using a novel dynamic FEA in ABACUS/Explicit (ABAQUS/Explicit version 6.14). According to the results of the dynamic FEA, it was reduced stress and damage significantly on the crestal bone region using the cortical drill before the implantation. Also, implant placement time was shorter when the cortical drill was used. The present research is a pilot study using a novel dynamic FEM to model and simulate the dental implant insertion process. This study showed that the use of cortical drills decreased the stress in the bone, especially crestal region, and shortened the whole implant insertion time.

The low‐velocity impact behavior of SiC nanoparticle‐glass fiber‐reinforced polymer matrix composites (PMC) in terms of different weight fraction of nanoparticle, artificial aging time, and impact energy was investigated in this article. In this context, silicon carbide (SiC‐70 nm) ceramic nanoparticle in weight fractions of 0%, 0.1%, 1%, 2%, 3% filled glass fiber‐reinforced PMCs were produced by vacuum infusion technique. The specimens were artificially aged in 0, 750, and 1500 h, 85% relative humidity and 70°C in air conditioning cabinet. The after‐impact damage regions were obtained using ultrasonic scanning technique for three different impact energies of 10, 20, and 30 J. The weight of specimens was measured at certain periods during aging and the weight change was examined. As the weight fraction and aging time were increased, the impact resistance of specimens decreased. At the beginning of aging period, the weight of specimens increased; however, the increase in weight decreased over time. Ultrasonic scanning results showed that the damage geometry changed and increasing discontinuity with increasing weight fraction and artificial aging time.