Ahmet Erkliğ

Investigation of RPIM Shape Parameter Effects on the Solution Accuracy of 2D Elastoplastic Problems

The effects of radial point interpolation method (RPIM) shape parameters on the solution accuracy of 2D elastoplastic problems are investigated. The RPIM algorithm is adapted for the solution of 2D elastoplastic problems using the multi-quadric radial basis function. The convergence rates after yielding are investigated for perfectly plastic and hardening cases with various shape parameters. Both regular and irregular node distributions are used by considering the standard Gauss integration and nodal integration schemes. It is shown that the solutions after yielding can be improved using appropriate shape parameters. The propagation of plastic region and solution time of each case are presented against load increments.

The effects of cutouts on buckling behavior of composite plates

Abstract Cutouts such as circular, rectangular, square, elliptical, and triangular shapes are generally used in composite plates as access ports for mechanical and electrical systems, for damage inspection, to serve as doors and windows, and sometimes to reduce the overall weight of the structure. This paper addresses the effects of different cutouts on the buckling behavior of plates made of polymer matrix composites. To study the effects of cutouts on buckling, loaded edges are taken as fixed and unloaded edges are taken as free. Finite element analysis is also performed to predict the effects of different geometrical cutouts, orientations, and position of cutouts on the buckling behavior. The results show that fiber orientation angle and cutout sizes are the most important parameters on the buckling loads. For all types of cutouts the buckling loads decrease dramatically by increasing the fiber orientation angle. It is observed that minimum buckling load is reached when 45° fiber angle is used, and after this angle critical buckling load begins to increase. Also, it is concluded that while fiber orientation angle is 0°, elliptical cutout has the highest buckling load and while fiber orientation angle is 45°, circular cutout has the highest buckling load.

Boundary element analysis of contact problems using artificial boundary node approach

An improved version of the regular boundary element method, the artificial boundary node approach, is derived. A simple contact algorithm is designed and implemented into the direct boundary element, regular boundary element and artificial boundary node approaches. The exisiting and derived approaches are tested using some case studies. The results of the artificial boundary node approach are compared with those of the existing boundary element program, the regular element approach, ANSYS and analytical solution whenever possible. The results show the effectiveness of the artificial boundary node approach for a wider range of boundary offsets.

A comparative study on industrial waste fillers affecting mechanical properties of polymer-matrix composites

This paper investigates the mechanical properties of the various inorganic filler-filled polymer composites. Sewage sludge ash (SSA), fly ash (FA) and silicon carbide (SiC) micro-particles were used as filler in the polyester resin. Composite samples were prepared with various filler content of 5, 10, 15 and 20 wt%. The results indicated that the tensile and flexural strength increased at the particle content of 5 wt% and then followed a decreasing trend with further particle inclusion. The tensile and flexural modulus values of the particulate polyester composites were significantly enhanced compared with the unfilled polyester composite. SEM micrograph results showed good indication for dispersion of FA, SSA and SiC particles within the polymer matrix.

The effect of hybridization and boundary conditions on damping and free vibration of composite plates

Abstract In this study, the influence of hybridization on natural frequency and damping properties of laminated composite plates consisting of various combinations of fibers and boundary conditions are examined. Carbon (C), Kevlar® (K), and S-glass fibers are used as reinforcement with epoxy resin for hybridization. Experiments are conducted on hybrid composites under the combinations of clamped, free, and simply supported boundary conditions. Natural frequency analyses of hybrid composites are performed using finite element analysis software ANSYS. Vibration test results obtained from experimental and numerical studies are compared with each other. Results show that hybridizations with three different fibers and their substitutions in the layers have strongly effected the damping and vibration characteristics of composite plates.

A comparative study on the interlaminar shear strength of carbon, glass, and Kevlar fabric/epoxy laminates filled with SiC particles:

The present article investigates the interlaminar shear strength of the woven carbon, glass, and Kevlar fiber reinforced epoxy (CFRE, GFRE, and KFRE) composites filled with SiC particles. The work covers the samples preparation, testing, and analyzing. The samples were fabricated using the regular addition of the SiC particles as 0, 5, 10, 15, and 20 wt% of the total weight of epoxy resin. Samples of the short beam shear test were cut using CNC machine. The experiments were conducted according to the ASTM-D-2344 standard. The fracture surfaces of the laminate samples were observed by scanning electron and optical microscopy. The major benefits of the current study are that the modification process by adding a certain amount of the SiC particles significantly enhanced the interlaminar shear strength of CFRE, GFRE, and KFRE composites as the comparison to the conventional ones.

Damping and vibration characteristics of basalt-aramid/epoxy hybrid composite laminates

Abstract Damping and vibration characteristics of basalt-aramid/epoxy hybrid composites with different basalt/aramid fiber mixing ratios were investigated. Unidirectional basalt and twill weave aramid fibers were used as reinforcement. Non-hybrid basalt/epoxy and aramid/epoxy composite laminates were also fabricated for comparison. Dynamic characteristics of the composite laminates were determined experimentally using dynamic modal analysis. Damping properties were calculated with the logarithmic decrement method using a vibration response envelope curve. Loss modulus, storage modulus and damping ratio of the structures were also considered. It was observed that the results of hybrid configurations showed a distribution between non-hybrid basalt/epoxy and aramid/epoxy composites. Furthermore, the employment of aramid fibers in composite laminates enhances the damping properties of laminates, but reduces the strength values.

Experimental investigation on influence of Kevlar fiber hybridization on tensile and damping response of Kevlar/glass/epoxy resin composite laminates

This study investigates the tensile and damping behavior of Kevlar/glass/epoxy hybrid laminates. Hybrid Kevlar/glass with epoxy resin composites is fabricated considering different fiber volume fractions in combinations to show the influence of hybridization. Mechanical properties were inspected by an instrumented tensile test machine. A series of vibration tests were conducted to determine dynamic characteristics of the samples. Damping properties are calculated from logarithmic decrement method by using vibration response envelope curve. In addition, effects of fiber angle on natural frequencies were examined using ANSYS. The results show that the hybridization of relatively brittle material S-glass fibers with tough and high performance Kevlar fibers has showed to be highly effective in improving damping capacity of S-glass fiber composite laminates.

Vibration-damping characterization of the basalt/epoxy composite laminates containing graphene nanopellets

Abstract The present study investigates the influence of graphene nanopellets (GnPs) on the damping and vibration characteristics of fiber-reinforced basalt/epoxy composites for different weight contents of GnPs particles (0.1, 0.2 and 0.3 wt%). The variation of dynamic properties in terms of loss and storage modulus was explored by using the experimental modal analysis. The damping properties were determined by using logarithmic decrement method from the acceleration-time envelope curves. Results showed that the incorporation of GnPs at weight contents of 0.1% and 0.2% significantly affected the damping and vibration characteristics of the samples as a result of the interfacial strength between the GnPs particles-fiber-matrix interactions. The natural frequencies increased by 20.7% and 25% at GnPs contents of 0.1 and 0.2 wt%, whereas the damping ratios increased by 28.5% and 57.1%, respectively.

Mixed-mode I/III fracture toughness of polymer matrix composites toughened with waste particles

Abstract Fracture toughness of particle-filled polymer composite beams with different particle content for varying of crack inclination angles was investigated in mode I and mode III loading conditions. The beams were tested using three-point bending test with crack inclination angles of 30°, 45°, 75°, and 90°. Sewage sludge ash (SSA), fly ash (FA), and silicon carbide (SiC) microparticles were used as toughening fillers with 5, 10, 15, and 20 wt% contents of the total weight of the polymer composites. The scanning electron microscope (SEM) micrographs showed that a good indication was observed for dispersion of FA, SSA, and SiC particles within the polymer matrix. The critical crack tip stress intensity factors KIc (crack angle 90°) and KIIIc, and the critical strain energy release rates GIc and GIIIc were calculated and their results were compared. The mode I and mode III fracture toughness of the particulate polyester composite were improved by addition of particulate fillers. The maximum values of fracture toughness mode I (KIc and GIc) and mode III (KIIIc and GIIIc) were recorded at particle content of 5 wt% polymer composites.