Alaattin Aktaş

Buckling and compressive failure of stepped-lap joints repaired with composite patches

In this study, the buckling and compressive failure of adhesively-bonded stepped-lap joints (with/without composite patches) composed of pultruded glass fiber-reinforced polymer composite laminates was investigated experimentally and numerically. Two-component epoxy adhesive was used for bonding purposes. Composite patches were woven glass-epoxy layer. They were added onto the conventional stepped-lap joints so that additional load transfer paths were created and localized stress concentrations near joint edge were reduced. The axial compression tests were performed and the results revealed that the buckling and failure load of new stepped lap composite joints with composite patches were significantly higher than the conventional stepped lap joints. The influence of the overlap length was evaluated. For both types of joints, a small increase was observed in failure loads by increase of the overlap length. Numerical results showed a very good agreement with experimental results.

Effect of Knitting Tightness on Mechanical Properties of Weft-knit Glass Fiber Reinforced Epoxy Composites

In the presented article, an experimental study has been carried out to investigate the effect of tightness level on mechanical properties of weft-knit 1 × 1 rib glass fiber reinforced epoxy composites. Three different glass fiber reinforced epoxy composites with different tightness level were produced. Mechanical properties of the composites have been determined. The results show that tensile strength, compression strength, and shear strength of the composites increase with increasing of tightness level.

Solid particle erosion of glass epoxy composite strengthened by metal powder

In the present study, the solid particle erosion behavior of glass-epoxy composite strengthened by metal powder has been studied. Four types of specimens were tested; one is composite specimen without metal powder, the others with metal powder, the percentages of which were 5%, 10%, and 20% by weight, respectively. Steady state erosion rates of these composites have been evaluated at various impingement angles (changed from 15° to 90° by 15° increments) with different impact velocities (34 m/s, 53 m/s and 80 m/s). The erosion experiments have been carried out by using silica sand particles (450 ± 50 μm) as erodent. The results show that the erosion rate of the composites with and without powder is the highest when the particles impact angle is between 15° and 30°. In addition, the erosion quantity of the composites were nearly the same for the specimens with and without metal powder.

Solid particle erosion behaviour of glass mat-based polyester laminate composite materials:

In this study, solid particle erosion behaviour of glass fibre mat-based polyester laminate composite materials was investigated by varying the impact velocity and the impingement angle and sizes of the abrasive particles. Impact velocities used in the tests were 23, 34 and 53 m/s, while the impingement angles were 15°, 30°, 45°, 60°, 75° and 90°. Silicon dioxide particles with average diameters of 250, 500 and 1000 μm were used as abrasive particles. Experimental data were taken as reference and values of erosion rates were obtained as functions of impact velocity, impingement angle and the size of the abrasive particles. The results obtained exhibited typical ductile behaviour of glass fibre-reinforced composites, where the maximum erosion rate was recorded at an impingement angle of 30°, and the erosion rates decreased as the impingement angle increased. Moreover, the erosion rates increased with the increase in impact velocity and particle size. Finally, the worn out surfaces of the test specimens were investigated on two different devices, optical microscope and scanning electron microscope.

Enhancement of flexural performance of wood beams using textile fabrics

Abstract The aim of this study was to investigate the flexural performance of wood beams (beech — Fagus orientalis Lipsky) reinforced with woven and selected weft knitted glass fabrics, namely, Milano and plain knit. Some physical and mechanical properties of the beech wood and the textile fabrics were determined in accordance with relevant ASTM standards. Twenty-four wood beams which have two different cross sections (I-shaped and square hollow) were manufactured and tested under a three-point load. They were divided into two groups: Group A specimens were not reinforced to serve as a reference, whereas Group B specimens were reinforced with textile fabrics combined with adhesion. The flexural behavior of the specimens was studied through their load-deflection characteristics. The modes of failure were identified and categorized. The experimental results showed that the load-bearing capacity of reinforced beams increased significantly compared to the beam without reinforcement. This method can be used to repair and strengthen damaged wood beams.

Enhancement of Single-Lap Composite Joints Strength at Different Temperatures

Abstract In this study a novel reinforcing method was examined for glass-fiber reinforced composites consisted of inter-adherend glass fibers which acted as pins to pierce the composite adherend. Two types of interadherends were investigated. One of the types involved fibers which acted as pins (type B), and the other type was made up of pin like fibers with bent edges which stuck to the surface of the adherend (type C). Static tensile tests were performed on both types of single-lap joints (SLJ) and for joints without interadherend fibers (type A) at four different temperatures (20, 40, 60 and 80°C) in accordance with ASTM standards. The results showed that the fibers improved the ultimate static strength of the single-lap joints over the entire temperature range.

Shear strength of pultruded composite pins with external confinement

Weight reduction using composites has gained increasing attention in recent times. In this study, pultruded composite pins (unconfined and confined) were manufactured and tested by using a custom double shear testing fixture. Different configurations were applied for confinement of the composite pins, including weft-knitted fabrics (plain, 1 × 1 rib, and Milano), woven fabrics and E-glass 130 tex fibers/adhesive cloth. They were externally wrapped and bonded to the unconfined composite pins. In each case, five identical specimens were tested, and shear strength data were analyzed by using two-parameter Weibull statistics. The results showed that the maximum shear strength took its highest value in the unconfined case for both average values of the test results and for 99% reliability under Weibull distribution. The confinement had a negative effect on the average shear strength of the unconfined pins. It was also seen that the 99% reliability values of shear strength were approximately equivalent to the 0.7 average value of the shear strength.

The Effect of the Hole Diameter on Residual Stress and Plastic Zone Expansion in Aluminum Metal-Matrix Laminated Plates

This study aims to investigate the effect of the hole diameter on elasto-plastic stress analysis and the expansion of plastic zone of steel fiber reinforced aluminum metal matrix laminated composite plates with various hole diameters. The width plate-tothe hole diameter, W/D, ratios are changed as 6, 8 and 10. The plates are assumed to be clamped and subjected to different transversely distributed loads. Loading is gradually increased from the yield point of the plate by 0.001 MPa at each load steps up to 42 kN total load on the plates. Laminated plates are composed of four orthotropic layers oriented with different angles in symmetric manner. Residual stress and the expansion of plastic zone are obtained for small deformations by using finite element method (FEM) and including firstorder shear deformation theory. In order to obtain residual stresses and plastic regions, a computer program was developed. The results show that the propagation of the plastic regions decrease while W/D ratios decrease for [0°/90°]s, [30°/-30°]s, and [60°/-60°]s fiber directions. However, the propagation of the plastic regions increase by decreasing W/D ratios for [45°/45°]s fiber direction. K e y w o r d s : Metal-matrix composite, Plastic zone, Finite element analysis, Residual stress, Elasto-Plastic analysis. INTRODUCTION Metal-matrix composites have been used in many structures and commercial applications for a long time due to their specific stiffness, high temperature performance and low density. Residual stresses in matrix are particularly important, because they lead to premature failure. Prediction and measurement of residual stresses are important in relation to production, design and performance of composite components. For creating permanent deformations and residual stresses in laminated plates, the loads applied on the plate must exceed the yield point of the laminate. The use of the residual stresses obtained is a way to raise the yield point of the machine components. Bahaei-EI-Din and Dvorak /1/ have investigated the elasto-plastic behavior of symmetric metal-matrix composite laminates for the case of in plane loading conditions. Non and Clarke 121 examined the influence of particle size on particle fracture and the elastic-plastic deformation of metal-matrix composites. Palazotto and Witt /3/ have investigated nonlinear analysis of laminated composites under a variety of loading and boundary conditions. Karakuzu and Sayman /4/ have studied the elasto-plastic stress analysis of rotating discs with holes that was subjected to inner pressure. Karakuzu et al. 15/ have been developed a twodimensional finite element program for analyze the elastic-plastic behavior of steel fiber reinforced aluminum metal matrix laminated composite plates with * Corresponding author: Fax: +90-276-263-41-95, E-mail: aaktas@aku.edu.tr. * Co-author: E-mail: maktas@aku.edu.tr.