Research on Engineering Structures and Materials

99-105

Authors: Ebru Baser, Alper Incesu, Sedef Sismanoglu, Ali Gungor

Aluminum silicon alloys are the most preferred alloys for industrial applications due to their ease of production and lightness. It is important to improve the mechanical properties of these materials in order to increase their usage. Wear properties are one of these mechanical properties that can be improved. In this present investigation, 3 different artificial aging durations; 2hrs, 4 hrs, 8 hrs aging at 200 °C were applied after solution heat treatment for 4 hrs. at 540 °C to the AlSi8Cu3Fe alloy. Microstructural analysis, mechanical tests were applied to understand the effect of aging parameters on wear performance and also hardness values of AlSi8Cu3Fe alloy. According to the results obtained from tests and analyzes, the highest wear resistance was reached on the 4 hrs. aged sample.

115-125

Authors: Ahmet C. Tatar, Halil B. Kaybal, Hasan Ulus, Okan Demir and Ahmet Avcı

Epoxy based fiber reinforced composites are widely utilized in aerospace applications due to mechanical properties, thermal stability and, chemical resistance. However, it is known that materials become brittle and due to the poor crack resist restricts their applications in cryogenic engineering applications. The purpose of this paper is to experimentally investigate the cryogenic temperatures’ effect on the low-velocity impact (LVI) test of composite laminates. In addition, the effect of matrix modification in the studied composites was investigated. The LVI tests were conducted at RT (room temperature), 0 °C, -50 °C, -150 °C and -196 °C (liquid nitrogen temperature) on the composite laminates to measure influence on their energy absorption capacity. LVI tests performed according to ASTM-D-7136 standard under 10, 20 and 30 J impact energy levels. The results show that the contact forces and energy absorption capacities are improved by adding SiO2 nanoparticles into the epoxy matrix. The absorbed energy at cryogenic temperatures is increased by 24.87% from 18.1 J of pure epoxy resin to 22.7 J of modified epoxy. For the purpose of comparison, the LVI properties of composites at room temperature (RT) are also investigated. It is noted that the energy absorption capacity is not higher at cryogenic temperatures than that at RT for the modified and neat epoxy composites. Moreover, the peak contact forces are reduced in low-temperature conditions.

137-146

Authors: Serkan Islak, Uğur Çalıgülü, Husain R.H. Hraam, Cihan Özorak, Vahdettin Koç

In this study, Cu–Mo composite coatings were produced on copper substrate by plasma spray technique. Electrical conductivity, microstructure and wear properties of the composite coatings were investigated. Microstructure and phase composition of the coatings were examined by using optical microscopy (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). The microhardness experiments were also performed by using a microhardness machine. The electrical conductivity properties of the coatings were evaluated with eddy current instruments. Wear tests were performed by pin-on-disc method. Although the electrical conductivities of the coatings are very small compared to the substrate, it has been determined that the coatings exhibit very good tribological property and high hardness in comparison to the substrate.

155-165

Authors: Bedriye Ucpinar Durmaz, Ayse Aytac

The aim of the present work was to investigate the effect of glycerol (GLY) concentration on the properties of poly (vinyl alcohol) (PVA)/casein (CAS) blend films. The films were prepared by solution casting method at the different concentrations of GLY. The structural, mechanical, thermal, barrier and hydrophilic-hydrophobic properties of the films were determined by various methods. The structural analysis indicated that there were some interactions between the components. Tensile test results release that tensile strength of the film decreased with the addition of GLY while strain at break values increased. According to thermogravimetric analysis (TGA) results, the GLY included films exhibited lower thermal stability than GLY-0 film. The residual weight decreased by increasing GLY content. The contact angle measurements showed that all films were hydrophilic structure. Also, the water vapor barrier property of the GLY-0 film was developed with the addition of GLY.

175-188

Authors: Mehmet Akçair, Melih Savran, Levent Aydın, Ozan Ayakdaş, Savaş Öztürk, Nilay Küçükdoğan

Stacking sequence design and optimization of 64 layered symmetric-balance graphite/epoxy laminated composite have been performed. The optimization problems aim to find the optimum stacking sequence maximizing the critical buckling load by single objective optimization approach. Differential Evolution (DE) and Simulated Annealing (SA) optimization algorithms are proposed to solve the problems. The effect of the aspect ratios (a/b) and in-plane biaxial compressive loading ratios (Nx/Ny) on critical buckling load are investigated. In order to see the effect of discrete increments of fiber orientation angle on critical buckling load, 1°, 5°, 15°, 30° and 45° fiber angle increments are also considered. The results show that (i) the proposed algorithms DE and SA exhibit comparable performance in terms of critical buckling load when compared Genetic algorithm (GA) and Generalized pattern search algorithm (GPSA), (ii) DE and SA find distinct stacking sequence configurations in terms of buckling load for the same laminated structure design problems.