Mete Onur Kaman

Experimental and Numerical Analysis of Critical Buckling Load of Honeycomb Sandwich Panels

The critical buckling loads for various core densities and materials of honeycomb composite panels are experimentally and numerically investigated in this study. The surface plates of honeycomb composite panels are of polyester/glass fiber composite. Polyester resin-impregnated paper or aluminum is used as the honeycomb core material. Honeycomb panels with different cell sizes, but approximately the same volume, are produced and the effect of the honeycomb core density on the critical buckling load is investigated by compression tests. The critical buckling load of paper core panels is determined to be higher than that of aluminum core panels. It is seen that the buckling strength of the specimens increases by the increase of core density. As the critical buckling load exceeds a certain limit, regional core cell buckling and core crushing are seen in aluminum core panels. In paper core panels, regional cracks are seen, in addition to these failures. The study also calculates the numeric buckling loads of the panels using the ANSYS finite element analysis program. The achieved experimental and numerical results are compared with each other and the results are provided in tables.

Progressive Failure Analysis of Pin-Loaded Unidirectional Carbon-Epoxy Laminated Composites

In this study, a research was carried out to determine the failure modes and failure loads at pinned joint unidirectional laminated carbon/epoxy composite plates. To evaluate the effects of joint geometry and fiber orientation on the failure loads and failure modes, parametric studies were performed experimentally and numerically. A numerical study was performed by using 3D APDL codes with ANSYS fem software and Hashin Failure Criteria was used for predicted failure mode and failure load. The experimental and numerical results showed that the failure loads of composite plates were increased with increasing E/D and W/D ratios.

Effects of Ductile Fiber Size on the Fracture Toughness of Copper/Polyester Composites

The objective of this study is to examine the effect of fiber size on the fracture toughness of ductile fiber reinforced composite materials. For this purpose, pull-out tests of copper fiber embedded in polyester matrix have been conducted, as a result of which load—displacement graphics for different fiber diameters and embedded lengths have been obtained. Using the derived load—displacement graphics, debonding load of each specimen has been found, and sliding shear stress, bond shear stress, and pull-out work have been calculated. Then, fracture energy increments per unit cross-sectional area have been determined. In the numeric part of the study, pull-out test was modeled using finite element package program ANSYS (11.0). With the help of this model, load—displacement graphic obtained in the test has been repeated in numeric terms. Obtained results have been presented in the form of tables and graphs and interpreted. It has been observed that the fracture energy increment increases with increase in the diameter of the copper fiber.

Progressive Failure Analysis of Laminated Composite Plates With Two Serial Pinned Joints

This study presents experimental and numerical failure analyses for two serial pin loaded holes in unidirectional carbon fiber/epoxy resin composite laminates. The failure loads and failure modes of composite laminates are determined for different geometrical parameters and different stacking sequences. Three-dimensional ANSYS Parametric Design Language codes are developed in the ANSYS® finite element software. Hashin Failure Criteria and material degradation rules are used to determine failure loads and failure modes in the numerical analysis. Experimental and numerical results show that failure loads and failure modes were affected with geometrical parameters.

Nonlinear stress analysis of v-notched aluminum plates repaired with the wet patch technique

ABSTRACT In this study, V-notched aluminum plates were repaired using the wet patch technique. Two different repair operations, single-side and double-side composite patches, were applied to the notched plates. Four layers of woven carbon fiber textile and with the same reinforcement angle were used as a composite patch. Previously, the epoxy was saturated onto the prepared carbon fiber textiles and glued to the plates, and then those plates were placed in a vacuum medium. The repaired plates were experimentally tested under tension load. A nonlinear stress analysis was carried out using the finite element methodology in addition to the experimental results. As major foci of the study, the effects of repair type and notch size on failure behavior and plastic stress distribution were examined. As a result, it was found that the notch depth affects the repair performance far more than the notch width. Debonding failure load between the patch and the plate in plates repaired with a single-side patch was found to be two times higher than the yield load. For the double-side patch, the yield load was close to the debonding load and this repair method increases the debonding load more than a single-side patch.

Effect of Curing Conditions on the Interface Strength of Single- Fibre Composite Specimens

Abstract The purpose of this paper is to examine the effect of curing conditions on interface strength in single-fibre composites. Test specimens produced by using polyester resin and single glass fibre were cured under four different temperatures, which were room temperature, 40°C, 55°C and 70°C for three different curing periods, which were 1 hour, 4 hours and 8 hours. Afterwards they were subjected to tensile test. As a result of the examination under optic microscope, it has been observed that the major damage formations are in the form of matrix cracks and fibre fragments. Young modulus and therefore mechanical properties of single-fibre composite specimens improved after a treatment above 40°C.