Mehmet Aktaş

Impact Behavior of Glass/Epoxy Laminated Composite Plates at High Temperatures

The objective of this study is to investigate the impact behavior of laminated glass/epoxy composite plates with [0/90/0/90]S and [0/90/45/- 45] S stacking sequences at room (~20°C) and high temperatures (60°C and 100°C). The maximum contact force between the impactor and the composite plate, the maximum deflection at the maximum contact force at the center of the composite, and the contact time history were plotted as a function of impact energy. In order to determine the energy absorbing capability of the plates, energy profiling method was used. The results show that the perforation threshold increases with increasing temperature.

Thermal Impact Behavior of Glass-Epoxy-Laminated Composite Plates:

The aim of this study is to investigate the experimental and numerical characterizations of the glass/epoxy composite plates at room temperature (approximately 20°C) and high temperatures (40°C, 60°C, 80°C, and 100°C). Two stacking sequences were selected as [0/90/0/90] S and [0/90/45/—45]S. Numerical analysis was carried out using 3DIMPACT finite element code. The maximum contact force between the impactor and the composite plate, the maximum deflection at the center of the composite, and the percentage of damage area versus impact energy were drawn. Overall damage patterns were found using a light table and obtained by 3DIMPACT code. The numerical predictions showed good agreement with the experimental results.

Failure load prediction of adhesively bonded pultruded composites using artificial neural network

Mechanical joining and adhesive bonding provide convenience for manufacturing of complex structures, which made of composite materials. Failure load is directly related with process parameters of mechanical joining or adhesive bonding. In this study, the effects of bonding angle, patching type (single side and double side) and patching structure on the failure load were investigated in the pultruded composite specimens. For this aim, the pultruded composite specimens, which bonded with five different bonding angles (45°, 51°, 59°, 68° and 90°) and five different bonding types as unpatched, single-side woven patch, single-side knitting patch, double-side woven patch and double-side knitting patch were exposed to tensile loads at room temperature. In the view of experimental results, the failure loads of bonded pultruded composite specimens were predicted by training six different artificial neural network algorithms. The only three best prediction results of Bayesian regularization, Levenberg–Marquardt and scaled conjugate gradient were given in the figures for better understanding.

Strength enhancement of notched composite pultruded shafts by repairing with woven and knitting fabrics

Composite shafts can be damaged because of unsuitable production, mistaken assemblage, and excessive strain. Repairing of damaged composite shafts with patch or an alternative approach is an economical solution. This study aims to enhance the tensile, compressive, and four-point bending loads of notched E-glass/vinylester composite pultruded shafts by repairing with different patch materials. For this purpose, the notched composite shafts having 1 mm, 1.5 mm, and 2 mm notch depths were repaired with E-glass woven fabric, rib knitting fabric, and milano knitting fabric with 30 mm, 50 mm, and 70 mm widths by winding method. The results of the repaired composite shafts were compared with unrepaired composite shaft to better understand the influence of type and width of patch and notch depth on the critical damage load. The results showed that the repairing with E-glass woven and knitting patches increased the critical damage load of notched composite shafts by about 67%.

Surface Modification Effects on the Mechanical Properties of Woven Jute Fabric Reinforced Laminated Composites

ABSTRACT During recent years, crude material costs and increasing environmental concerns have led to the search for new reinforcement materials for composites. Consequently, interest on natural fiber reinforced polymer composites has increased significantly owing to their easy availability, light weight, and low price. In this study, surface modification effects were investigated on the mechanical properties of woven jute fabric reinforced laminated composite plates, experimentally. The woven jute fabrics were retained at the rates of 0%, 5%, 10%, and 15% NaOH solution for 15 days at room temperature for surface modification process. Then, woven jute/epoxy (WJE), woven jute/polyester (WJP), and woven jute/vinylester (WJV) laminated composite plates having six layers were produced using modified woven jute fabric. The mechanical properties of woven jute reinforced laminated composites, such as tensile, compression, and shear properties, were determined at room temperature. The experimental results were analyzed statistically with Weibull distribution having 85% reliability level. The statistical results showed that the surface modification process and type of matrix material have dramatically affected the mechanical properties of woven jute fabric reinforced laminated composites.

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.