Buket Okutan Baba

Buckling Behavior of Laminated Composite Plates

In this study, the influence of boundary conditions on the buckling load for rectangular plates of various cutout shape, length/thickness ratio, and ply orientation is examined. Boundary conditions consisting of clamped, pinned, and their combinations are considered. Numerical and experimental studies are conducted to investigate the effect of boundary conditions, cutout shape, length/thickness ratio, and ply orientation on the buckling behavior of E-glass/epoxy composite plates under in-plane compression load. Buckling analysis of the laminated composites is performed by using finite element analysis software ANSYS. Tests have been carried out on laminated composites with circular and semicircular cutouts under various boundary conditions. Comparisons are made between the test results and predictions based on finite element analysis. The results show a complex interaction between plate orthotropy and boundary conditions.

An experimental investigation of free vibration response of curved sandwich beam with face/core debond

The aim of this research was to investigate the curvature and face/core debond influence on the vibration behavior of curved composite sandwich beams made up of carbon/epoxy laminate skins over a polyurethane foam core. Flat and curved sandwich beams with debond were prepared by keeping the arc length of the sandwich beams equal to the length of the flat sandwich beams. Sandwich specimens with three different curvatures and debond between the top and bottom face/core were manufactured. Systematic vibration and static experiments were carried to determine the response and to study the effect of curvature and debond. Flexural stiffness and strength of the sandwich beams were determined by four-point bending tests. The natural frequencies and damping loss factors of the sandwich beams were determined using impulse frequency response technique under free—free boundary conditions. Four-point bending test results indicate that stiffness of the beams decrease with presence of debond. Vibration test results show that face/core debond causes reduction of the natural frequencies whereas damping loss factor values increase with presence of debond. The effects of debond and curvature on damping loss factor is higher than that on natural frequency.

Impact response of sandwich beams with various curvatures and debonds

This article presents experimental results of the impact response and failure characteristics of curved composite sandwich beam with debond. The objective of this study is to determine how the curvature and debond affects the contact force, displacement, absorbed energy, and damage type under impact loading. An instrumented drop-weight impact test are performed on sandwich beams made of carbon/epoxy face sheets and polyurethane foam core material with four different radii of curvature and debonds between the top and bottom interface of face sheet and foam core. Impact energy was kept constant of 4 J. The contact force and displacement histories of curved sandwich composites with debond are measured to determine the impact response. The results are compared with those of flat beams with the same dimensions and no debond. They indicate that the value of the contact force increases as the curvature angle increases for the beam with no debond. Opposed to the beams with no debond, the contact force decreases as the curvature angle increases for the beam with debond. These results show that curvature angle and debond are important mechanical parameters that must be considered in the design of structures.

Free Vibration Analysis of Curved Sandwich Beams with Face/Core Debond Using Theory and Experiment

This work deals with vibration behavior of sandwich beams made of fiber-glass laminate skins wrapped over polyurethane foam core. Experimental and numerical investigations on the natural frequencies of both flat and curved beams with and without debond were carried out. The vibration tests were performed for clamped-clamped end conditions using an impulse-frequency response method. Finite element analysis was carried out using ABAQUS. Results indicate that fundamental natural frequencies are seriously affected by curvature angle and debond, whereas the higher order natural frequencies show relatively small changes. Face/core debond causes reduction of the natural frequencies.

Experimental and numerical analysis of vibration frequency in sandwich composites with different radii of curvature

In this study, free vibration responses of sandwich composite panels with different radius of curvature were presented numerically. The studies were carried out on square flat and curved sandwich panels made of E-glass/epoxy face sheets and polyvinyl chloride foam with three different radii of curvature. Experimental studies were used to verify the numerical results. Vibration tests were performed on flat and curved sandwich panels under free–free boundary conditions. The experimental data were then compared with finite element simulation, which was conducted by ANSYS finite element software and it was shown that the numerical analysis results agree well with the experimental ones. Effect of the curvature on natural frequencies under different boundary conditions (all edge free, simply supported, and fully clamped) was investigated numerically. Results indicated that the natural frequencies and corresponding mode shapes were affected by boundary conditions and curvature of the panel. For all boundary conditions, the variation of curvature had smaller effect on the natural frequency of the first mode than those of the other modes.

Buckling Response of Rectangular Laminated Composite Plates with Cutouts

Results from numerical and experimental study of buckling response of compression-loaded E/glass>xy composite plates with centrally located circular 1 semicircular cutouts are presented. The effects of orientation angle and cutout shape on the buckling ponse of laminates subjected to uniaxial static loads investigated. The laminated composites are analyzed ng the finite element analysis software ANSYS. The inge in critical buckling response of thin rectangular nmetric and antisymmetric laminates with respect to ply orientation angle and cutout shape has been died. In addition, results are presented from buckling ilysis and these results are compared to jerimentally measured results. ;ywords: Layered Structures, Finite Element alysis. Buckling, Cutout