Mete Onur Kaman

In this study, composite plates with circular holes cracked on both edges were repaired using a composite patch. Epoxy adhesive was used to bond the patch to the plate. Low-velocity impact tests were applied to repaired specimens with varying crack lengths. Compared to specimens without holes, the maximum reaction force of repaired specimens without cracks increased by up to 50%. When the crack length reached its maximum, the maximum impact force of repaired specimens increased by 36% compared to the specimens without holes.

Three-dimensional woven composites eliminate the critical delamination weakness of conventional laminated composites through z-directional reinforcement, which is essential for aerospace and automotive structures where both intralaminar and interlaminar failures pose unacceptable safety risks. This study systematically investigated the shear behavior of 3D woven composites using three fiber types (glass, carbon, high-strength polyester) and three architectures (Type I: orthogonal, Type II: layer-to-layer angle interlock, Type III: through-thickness angle interlock). V-notched shear tests following the ASTM D7078 standard revealed that GG (glass warp-glass weft filament) homogeneous composites achieved the highest shear strength across all architectures, with GG-Type II demonstrating optimum performance (70 ± 3 MPa) compared to GG-Type I (55 ± 3 MPa) and GG-Type III (68 ± 2.5 MPa). Carbon fiber systems showed inferior performance due to weak fiber-matrix adhesion, while glass fiber systems exhibited 50% higher ductility. Increased weaving density reduced deformation capacity by 41%. Microscopic analyses revealed controlled fiber pull-out and progressive damage in glass systems, contrasting with widespread fiber splitting and premature interfacial separation in carbon systems. Production evaluation showed Type I (vertical weaving) to be the most economical (12 h, 198.4 m filament) compared to Type III (17.5 h, 261.9 m filament). The PG-Type II (polyester warp-glass weft filament) combination proved optimal for aerospace/automotive applications when considering cost-performance trade-offs. The developed structure-property relationships provide universal design guidelines for 3D woven composite optimization.

This study presents an experimental and numerical investigation into the axial crushing performance of hybrid sandwich pipes designed for energy absorption applications. The aim is to enhance the specific energy absorption (SEA) characteristics of crashworthy structures while maintaining low weight, which is critical in transportation and aerospace industries. Hybrid specimens were fabricated by placing carbon fiber–reinforced polymer (CFRP) pipes inside aluminum tubes to create a sandwich configuration. Axial crushing tests were conducted to assess the energy absorption behavior, and the results were compared with those of full aluminum tubes. A finite element model was developed using LS-DYNA to simulate the progressive crushing behavior and validate the experimental findings. The numerical model incorporated the Johnson–Cook and Hashin failure criteria for the aluminum and composite materials, respectively. Results demonstrate that the hybrid sandwich structure significantly improves SEA compared to conventional aluminum tubes, indicating its potential for lightweight, high-performance energy absorbers in crash scenarios.

This study evaluated the stress distribution in maxillary incisors with internal resorption (IR) filled with various root canal filling materials using fin

In this study, the behavior of circular perforated and pin-loaded models of laminated composites under cyclic loads was obtained by progressive damage analysis. Experimental studies were also carried out to verify the numerical results the specimens. The strength and stiffness changes of the experimental specimens were obtained, and residual strength and stiffness graphs, which changed according to the number of cycles, were created. These parameters were used in the progressive damage analysis. In the numerical study, Hashin Damage Criterion was used for progressive damage analysis and the results were also compared with Puck Damage Criterion. Different damage criteria and problem types can be solved under fatigue load with the help of the subprogram written in ANSYS APDL. In this direction, after the verification of the numerical study with the experimental study, a parametric study was also carried out for the numerical analysis. At high cycle numbers for low loads in the experiments, crushing damage around the hole and shear damage at the plate edge became evident along with matrix damage. This damage behavior was consistent with the analyses performed with Puck. In the Hashin damage criterion, fiber compression damages were dominant, especially on the pin contact surface around the hole.

In this study, the impact resistance of reinforced composite panels with unsupported, and U profile supported by I profile was numerically examined. For this purpose, firstly, unsupported glass fiber/epoxy composite panels were designed, and then I-profile composite supports were added to these panels. The impact strength, and damage behavior of supported, and unsupported specimens under low-velocity impact were compared numerically. In the analysis, the MAT22 material card, also known as the Chang-Chang damage model for composite material, was used in the LS-DYNA program. As a result of the analysis, maximum damage load of the unsupported specimen is determined to be approximately 294 N. It was determined that by adding an I profile to the structure, the maximum damage load increased to 543 N. It was seen that the added I profile supports increased the maximum contact force of the composite structure by approximately 85%. Fiber breakage damages were observed in both supported, and unsupported specimens. However, with the use of I profile support, the damaged area was further reduced. It has been determined that under low-velocity impact, supported specimens exhibit more rigid material behavior than unsupported specimens.

In this study, the failure behavior of carbon fiber‐reinforced pin‐jointed composite plates were analyzed for different criteria. For this purpose, composite plates with a single and double pin joints were prepared from four layers carbon fiber composites. The effect of pin number, pin position on plate damage load and type was investigated experimentally and numerically under the tensile test. Numerically, progressive damage analysis was performed using Hashin and Puck failure criteria, and the approach rates to the experimental results were determined. It was observed that the experimental results obtained for single pin joint composites and the numerical data obtained using the Puck damage criterion were at least 87 % compatible, and this rate was determined as 85 % for the Hashin failure criterion. For the double pin jointed composites, it was seen that the experimental results and the results of the Puck damage criterion were compatible with at least 90 %, and this rate was obtained as 84 % for the Hashin failure criterion. The dominant damage type seen in the specimen is matrix shear and fiber compression according to the Hashin damage criterion, inter fiber failure in transverse tension for Puck.