Kadir Turan

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 Reinforced-Adhesively Single-Lap Joint

The failure behavior of reinforced-adhesively single-lap joints was investigated experimentally and numerically. The reinforced adhesive was produced by mixing waste composite particles and an epoxy-based commercial adhesive. The single-lap joint was prepared with an adhesive and unidirectional fiber glass/epoxy composite plates with a (0°/90°)3 stacking sequence. Three types of adhesive were used: an un-reinforced adhesive (ADH), an adhesive mixed with glass fiber-reinforced epoxy resin composite plate particles (GFRC), and an adhesive mixed with carbon fiber-reinforced epoxy resin composite plate particles (CFRC). The adhesive thickness (ta) and overlap length (lap) were 0.4, 0.8, 1.2, and 1.6 mm and 10, 20, 30, and 40 mm, respectively. Progressive failure analysis was performed with the ANSYS™ 11.0 finite element program using ANSYS™ parametric design language (APDL) code. In the numerical study, the failure loads of the composite and the adhesive were determined with the Hashin failure criteria and the Tresca failure criteria, respectively. The difference between the experimental and numerical studies ranged from 2% to 10%. The failure load of reinforced-adhesively single-lap joints was 1.3–22.8% higher than that of the un-reinforced adhesive.

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.

Buckling behavior of adhesively patch-repaired composite plates

In this study, buckling behavior of adhesively patch repaired composite plates was investigated experimentally and numerically. Unidirectional carbon/epoxy composite plates with circular cutout were repaired with an adhesively bonded patch. Critical buckling loads of composite plates were researched without cutout, circular cutout, single patch-repaired, and double patch-repaired conditions. In addition to circular hole dimensions, patch length and adhesive thickness were used as geometrical parameters. Numerical study was performed in ANSYS finite element software three dimensionally. As a result, the critical buckling loads of single and double patch-repaired composite plates were increased from 96 and 263 ratios higher than circular-cutout composite plates. The percentile errors between experimental and numerical studies were determined from 2 to 11.5.

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.

Joint angle effect on the failure behavior of pinned joint composite plates

In this study, the failure behaviors of composite plates with double-pin joints were investigated with experimental and numerical methods. The effects of joint angle, fiber orientation angle, and numerical modeling techniques on failure behavior were examined for composite plates consisting of epoxy matrix resin reinforced with woven glass fiber in four layers. The numerical study was performed in ANSYS 11.0 using two- and three-dimensional modeling techniques. Progressive failure analysis was performed by means of a subprogram. Tsai–Wu and Hashin failure criterion were used for two- and three-dimensional solutions, respectively. Material properties degradation rules were adopted for modeling the failure progress. As a result studies, a convergence ranging between 1% and 6% was obtained between the predicted and experimented failure loads. At the end of the study, it has been discovered that the failure loads, due to increment of the joint angle, cause decrease ranging between 16% and 43%.

Failure analysis of adhesive-patch-repaired edge-notched composite plates

ABSTRACT In this study, failure behaviors of edge-notched composite plates which were repaired with using patch and adhesive were investigated experimentally and numerically. The composite plates had a (0°/90°)3 anti-symmetric stacking sequence; the patches were obtained from the same plates and were bonded using an epoxy-based adhesive. The effects of the geometry of the notch were investigated using U-, V-, and square-shaped notches. We varied the notch geometry, investigated single-lap and double-lap repairs, and varied the patch fiber-stacking sequence. Simulations were carried out to analyze the three-dimensional failure progression using ANSYS. The failure loads of the repaired plates increased by 170–304% for single-lap repairs and 240–476% for double-lap repairs compared with the notched plates. The simulated and measured failure loads were in agreement within 0.2–23.6%.

Progressive failure analysis on two parallel pinned joint glass/epoxy composite plates under the effect of seawater

This study investigates failure behaviors of woven glass fiber-reinforced epoxy resin composite plates with two parallel pins jointed and under the effect of seawater. The effects of joint geometry and immersion time in seawater were analyzed by experimental and numerical methods. In order to observe the effects of seawater, the samples were kept in seawater for periods of zero, three, and six months. For the observation of the joint geometry effect on the failure behaviour, the edge distance-to-upper hole diameter (E/D), the two hole-to-hole centre diameter (K/D), the distance from the upper or the lower edge of the specimen to the center of the hole-to-hole diameter (M/D), and the width of the specimen-to-hole diameter (W/D) ratios were selected as geometrical parameters. The numerical study where the progressive failure analysis was employed was carried out through a sub-program running in ANSYS 11.0 finite elements program. In order to predict the failure loads and failure types in the numerical analysis, the Tsai-Wu failure criterion was used along with material degradation rules. At the end of the study, it was determined that increase of the immersion time in seawater caused weaker mechanical properties and decrease in failure loads of samples. It was also found that the results of progressive failure analysis were consistent with the experimental results.

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.