Ertan Kosedag

In this study, the effects of graphene and halloysite fillers on the mechanical properties of GFRPC were experimentally investigated. A reference composite unfilled was produced; in addition, six different composites were prepared containing graphene and halloysite at 0.5, 1, 1.5 wt.%. All samples were prepared according to ASTM standards and subjected to tensile and compressive tests in the directions parallel to the fibers (0°) and perpendicular to the fibers (90°), as well as bending tests. In tensile tests, both filler types increased strength in the 0° direction but decreased ductility values. In the 90° direction, graphene filler decreased strength, while 1.5 % halloysite filler provided a limited increase in tensile strength. In compressive tests, both filler types showed improvements, especially in the 90° direction; graphene filler provided the highest increase in strength. In the 0° direction, graphene increased compressive strength, while halloysite addition significantly improved deformation capacity. In bending tests, fillers generally reduced strength; however, graphene filler increased deformation capability, exhibiting more elastic behavior. SEM analyses showed that graphene has a leaf-like and sometimes agglomerated morphology, while halloysite has a tube-like structure and is more homogeneously distributed within the matrix. The findings reveal that the type, ratio, and loading direction of the filler significantly affect the composite performance.

Composite materials continue to be an indispensable part of engineering applications. Their use is increasing due to their strength, lightness, and good performance in energy absorbing components. In this study, composite tubes were produced by infusing jute fiber, a natural fiber, with epoxy resin. Unlike traditional production methods for cylindrical composites, the vacuum infusion method was used. Three different types of filler materials, produced using a 3D printer, were placed inside the tubes, and their peak force, energy absorption, and specific energy absorption values were compared. The filler geometries used were linear, hilbert, and hexagonal honeycomb structures. Comparisons were made between jute fiber reinforced epoxy resin matrix composite (JFRP) without filler and the composite itself. The highest peak strength value was determined to be 1.94 kN in the JFRPHH sample with hexagonal honeycomb filler. The highest energy absorption and specific energy absorption were also obtained with the hexagonal honeycomb filled composite sample. The obtained values were 12.85 joules and 0.331 J/g, respectively. The lowest energy absorption value was obtained with the sample without filler; the obtained value was 6.70 joules. It was observed that the addition of filler material affected the peak strength and energy absorption values of the composite samples.

Vehicle crash boxes are elements that protect the integrity of vehicles and ensure the safety of occupants in potential vehicle accidents. These crash boxes are mounted on the chassis of vehicles. In this study, composite crash boxes fabricated from aluminum, which is known for its lightweight properties, as well as denim and ultra-high-molecular-weight polyethylene, both of which are widely available on the market, were investigated experimentally. Composite crash boxes composed of an epoxy resin matrix reinforced with denim fabric (DenimFRP) and ultra-high-molecular-weight polyethylene (UHMWPEFRP) fibers, as well as aluminum (Al), were produced. The crash boxes were manufactured using a vacuum infusion method. This combination was produced by wrapping these fibers around an aluminum core. The energy absorption values, peak force values, and specific energy absorption values of the manufactured crash boxes were obtained through quasi-static compression tests and then compared. The best energy absorption value was achieved with the Al+denimFRP composite crash box manufactured by wrapping denim around aluminum at a workload of 1645.22 J, and its specific energy absorption value was also calculated as 15.52 J/g. The difference between the highest and lowest energy absorption was determined to be 244.61%. The highest peak strength value was obtained with the Al+denim+UHMWPEFRP sample, which contained a combination of aluminum on the inside, denim fabric in the middle, and UHMWPE fabric on the outside. Among the individually produced samples, the Al+denimFRP composite crash box manufactured with denim fiber exhibited higher results compared with the UHMWPEFRP composite box manufactured with ultra-high-molecular-weight polyethylene.

In this study, the flexural behavior and microstructural characteristics of pure polylactic acid (PLA) and graphene nanoparticle (GNP)‐reinforced PLA composites produced via melt processing were systematically investigated. Composite filaments containing different GNP weight fractions (0.4, 0.8, 1.2, and 1.6 wt%) were fabricated through controlled mixing and extrusion and subsequently processed into test specimens using additive manufacturing. The flexural response revealed that increasing graphene content led to a gradual reduction in strength, stiffness, and energy absorption capacity, typically in the range of 10%–20%; however, this behavior was governed primarily by the dispersion quality within the matrix rather than filler content alone. While relatively uniform distributions were observed at lower loadings, higher graphene contents promoted particle agglomeration, interlayer discontinuities, and weakened interfacial bonding, thereby limiting effective load transfer. Morphological analyses confirmed that the mechanical performance is directly controlled by microstructural integrity, particularly, the dispersion state of graphene and the continuity of interlayer bonding. Overall, the results demonstrate that optimizing graphene‐reinforced PLA systems requires not only controlling filler content but, more critically, maintaining a homogeneous microstructure.

Composite materials are widely used as structural and machine components due to their high strength-to-weight ratio. Their lightweight nature is one of the most significant characteristics driving their increasing adoption. During service, composite structures may experience damage depending on operating conditions. In addition, mechanical joining to other components is often required. Adhesive bonding is generally preferred to avoid fiber damage during joining; however, in certain applications, mechanical fastening becomes unavoidable, necessitating machining operations such as drilling. In this study, composite cylindrical tubes reinforced with natural jute fibers were manufactured to promote sustainability. An epoxy resin matrix was used, and uniform resin distribution was ensured during production. Circular holes were drilled diametrically opposite each other in the fabricated composite tubes. The hole diameters were selected as 3, 5, and 7 mm. The peak force and energy absorption capacities of the perforated tubes were compared with those of an unperforated reference specimen to evaluate the mechanical performance degradation associated with drilling and potential fastening applications. The highest peak force was obtained from the unperforated specimen (S1), reaching 1.312 kN. Similarly, the maximum energy absorption value was recorded for S1 at 11.65 J. The lowest energy absorption value, 9.94 J, was measured for specimen S4, which contained two opposite holes of 7 mm diameter. An increase in hole diameter resulted in a nearly linear reduction in the energy absorption capacity of the composite tubes.

This study investigates the effects of graphene nanoplatelets and halloysite nanotubes on the low-velocity impact behavior of glass fiber–reinforced polymer composites manufactured via ultrasonic-assisted dispersion and vacuum infusion. Unfilled, graphene filled (0.5, 1.0, and 1.5 wt%), and halloysite nanotube filled (0.5, 1.0, and 1.5 wt%) composites were fabricated and tested using a drop weight impact system to assess their peak contact force, deformation response, and overall energy absorption characteristics. Graphene reinforced samples exhibited a substantial increase in peak contact force, particularly at 1 wt%, indicating enhanced stiffness and load transfer due to the high aspect ratio and superior intrinsic strength of graphene. However, the 1.5 wt% graphene specimens showed a reduction in maximum force. In contrast, Halloysite nanotube filled composites displayed a more progressive and ductile response. The 1 wt% HNT sample achieved the best balance between load bearing capacity and displacement, demonstrating improved energy dissipation through micro crack deflection, crack bridging, and nanotube pull-out mechanisms. Microscobic analyses confirm that graphene is more effective for increasing peak load, whereas halloysite nanotubes provide superior impact resilience and damage tolerance. Overall, low nano filler loadings (0.5–1 wt%) significantly enhanced the impact performance of polymer based composites, while excessive filler content led to dispersion-related performance losses.

Vehicle crash boxes, mounted on the chassis before the bumper, absorb impact energy to protect passengers, but their metal construction adds weight, prompting increased research into lightweight composite alternatives with comparable strength. In this study, energy absorption values (EA), specific energy absorption (SEA), peak forces (PF) and crashing force efficiency (CFE) of carbon fiber, glass fiber, and aramid fiber reinforced composite crash boxes with epoxy resin matrix were compared. Composite crash boxes with different geometries were fabricated using vacuum infusion method in three different geometries: hexagonal, circle, and square. Unlike hand lay‐up and prepreg winding methods, vacuum infusion method was chosen because it provides homogeneous distribution of epoxy resin. The crashworthiness of the samples was evaluated through quasi‐static compression tests. The best energy absorption performance was obtained with the hexagonal carbon fiber‐reinforced composite crash box (246.17 J), corresponding to a specific energy absorption of 8.57 J/g. Although aramid fiber‐reinforced specimens showed lower energy absorption, they exhibited the highest crash force efficiency among all tested configurations. These results confirm the significant influence of both fiber type and geometry on the crashworthiness of polymer‐based composite crash boxes. The study highlights that hexagonal geometry consistently provided superior energy absorption across all fiber types, while carbon fiber‐reinforced composites demonstrated the best overall mechanical performance, making them strong candidates for lightweight crashworthiness applications.

This study investigates the ballistic behaviors of a novel sandwich structure produced from metal matrix composites (MMCs) and polymer matrix composites (PMCs). Utilizing the powder metallurgy method, specifically the hot pressing technique, superior-quality MMC samples were created by applying pressure and heat simultaneously. The MMC materials underwent surface preparation, including grinding and polishing, to ensure cleanliness and enhance bonding with the PMC layers. Aramid fiber reinforced prepregs were used for the PMC layers in hybrid laminates. Pre-cut prepregs were placed on MMC plates and bonded together using vacuum and hot press methods to produce PMC-MMC hybrid laminates. Five distinct hybrid laminates were developed, including configurations of equal thickness consisting entirely of PMC and MMC, to assess their performance under ballistic tests at three different velocity levels of approximately 600 m/s, 660 m/s, and 765 m/s. The results indicate that none of the samples fully penetrated at the first velocity level (600 m/s), with the resistance ranking from most to least penetrated being S-5-1 (MMC) (10 mm), S-2-1 (MMC-PMC) (11.5 mm), S-1-1 (PMC-MMC) (12 mm), S-3-1 (PMC-MMC-PMC) (13.5 mm), and S-4-1 (PMC) (18 mm). Notably, the S-2 sample exhibited no penetration across all test speeds. At the second velocity level (660 m/s), while some samples experienced penetration, the S-2-2 (MMC-PMC) remained intact, highlighting its resilience. The third velocity level (765 m/s) demonstrated that the S-2 sample continued to withstand penetration, further establishing its superiority successfully. The findings underscore the significant role of the material configuration in ballistic resistance and provide foresight into optimizing composite structures for enhanced performance in defense applications.

In this study, 48 polylactic acid (PLA) samples were produced via 3D printing, incorporating four infill geometries (gyroid, lattice, honeycomb, and linear), four infill rates (15%–60%), and three printing directions ( x , y , z ). Tensile testing revealed anisotropic mechanical behavior, with the x ‐direction consistently outperforming y ‐ and z ‐directions due to layer adhesion dynamics. A machine learning framework leveraging copula‐based data augmentation was developed to predict tensile strength at untested infill rates. The framework employed least squares regression, support vector machines (SVM), Gaussian process regression (GPR), and artificial neural networks (ANNs), augmented with 20,000 synthetic data points to enhance model robustness. Results demonstrated that gyroid geometry in the x ‐direction achieved the highest tensile strength (53.4 MPa at 60% infill), while Lattice patterns underperformed. Data augmentation improved prediction accuracy across all models, with SVM achieving the lowest RMSE (1.53 MPa) and R ² values exceeding 0.87. This study highlights the critical interplay of infill parameters, directional anisotropy, and machine learning in optimizing 3D‐printed PLA components for industrial applications, offering a data‐driven pathway to reduce experimental costs and accelerate material design.