Research on Engineering Structures and Materials

203-212

Authors: Seçkin Erden, Mustafa Ertekin, Gözde Ertekin, Arzu Marmaralı

Two-(biaxial and triaxial) and three-dimensional braided fabric structures are generally used as structural components in various industries such as ballistic, aerospace, automotive, energy, medical, marine, construction, and sports applications. Due to the advantages of braided structures like high level of uniformity, near net-shape manufacturing, design flexibility, repairability, low manufacturing cost, and damage resistance capability, braiding process have been preferred widely in the manufacturing of composite products. This study reports the influence of the braiding angle on the compression behaviour of carbon/epoxy tubular composites manufactured based on 2D biaxial braided fabrics, and also their comparison with that of the circular knitted ones. In order to determine the effect of braiding angle, 2D biaxial braids were manufactured by using three different braiding angles (62°, 67°, and 75°). Composite tube specimens were manufactured by vacuum bagging technique and their compression tests were performed. The results imply that braided carbon/epoxy tubes could be more suitable for the cases requiring smaller deformation and higher compressive stresses when compared to the circular knitted ones.

233-247

Authors: Engin Burgaz, Okan Gencoglu, Mert Goksuzoglu

Carbon black reinforced natural rubber (NR)/butadiene rubber (BR), NR/styrene-butadiene rubber (SBR) and NR/BR/SBR composites were prepared by using two types of BR with highly linear (higher viscosity and molecular weight) and branched chain structures. In NR/BR composite with a higher viscosity BR, the presence of both polysulphidic and monosulphidic types of crosslinking was confirmed based on FT-IR data. NR/BR composite consisting of BR with higher viscosity has the lowest Payne effect and compression set values. NR/BR/SBR composites have much lower Payne effect values compared to NR/SBR system. Also, the addition of BR to NR decreases the tan d value and leads to lowest values of tan d in NR/BR composites. Tensile strength and elongation at break values in NR/BR/SBR composites are improved with the addition of BR with a lower viscosity. In comparison with NR/SBR, NR/BR/SBR composites exhibit much less compression set and stress relaxation values because NR/SBR composite exhibits more permanent deformation due to its more rigid styrene content. Here, these results clearly show that blending carbon black reinforced NR or NR/SBR composites with BR having different degrees of viscosity is quite favorable in terms of using these NR composites as anti-vibrational rubber bushings in automotive applications.

263-278

Authors: A. Pınar Tüzüm Demir

Poly (vinyl chloride) (PVC) is a rigid polymer that can also be used in flexible applications by the addition of plasticizers. When plasticized PVC (p-PVC) film is heated, plasticizer evaporates from the surface of the film and it degrades by the loss of hydrogen chloride (HCl) gas. Plasticizers are not chemically bound to the polymers, easily diffuse to the contact media during its life-time and contaminate the environments which are in contact. The aim of this study is to reduce the diffusion of plasticizer by means of boron waste sludge (BWS) and clay filler (CF, kaolinite) to assess the effects of BWS and CF on the diffusion of plasticizer. Plastisols were prepared by mixing of plasticizer, heat stabilizer, BWS and CF into PVC resin and were cured in plastigel films. Thus obtained plastigel films were subjected to heat treatment in an oven at 100, 130 and 150°C. During heat treatment diffusion of plasticizers from p-PVC films into air was studied. In addition, migration of plasticizers into hexane was compared with the migration of plasticizers into air during the heat treatment. For this purpose, the effects of BWS and CF on the migration of the plasticizer to different environments were examined. Diffusion coefficient of plasticizer was evaluated according to the Fick’s law and to determine related activation energies according to the Arrhenius relation. Oxidation index (OI) values were determined by using FTIR spectroscopy. The addition of boron waste was reduced the diffusion of the plasticizer into air and increased the activation energy value. Its determined that, the mass loss of the films decreased with increasing amount of BWS and CF.

299-310

Authors: Gizem Tufaner, Açelya Çalışkan, Huriye Banu Yener, Şerife Şeref Helvacı

In the study, silica particles were synthesized from rice husk ash by calcination method in the presence of activating agents. The parameters which are effective in calcination method on structure and morphology of synthesized silica particles, activating agent type (NaOH and KOH), the calcination temperature (500-850°C), the calcination time (1-3 hours) and the weight ratio of activating agent to ash (4:1 and 5:1), were investigated. The crystal structures of the silica particles were determined by XRD, agent structures by FTIR, sizes and shapes by SEM, surface areas and porous structures by N2 adsorption-desorption analysis. Amorphous silica particles were synthesized in all experimental conditions. Optimum weight ratio, calcination temperature and time were determined as 4:1, 750°C and 2 hours, respectively. The activating agent NaOH was found to be more active than KOH in the preparation of silica.

321-333

Authors: Hayri Baytan Ozmen, Hakan Yilmaz, Hakan Yildiz

Dynamic analyses are important tools for seismic evaluation of structures in which the features of the used ground motion records have a key role. For proper estimation, the record set should have the desired extent and variability. However, when present literature is examined, it may be seen that difficulties still exist to have a record set with preferred properties. To ease these difficulties, a study conducted in scope of a project supported by The Scientific and Technological Research Council of Turkey (TUBITAK) under the title of “Change of Earthquake Ground Motions Depending on Soil Properties” and grant number 215M357. A set of acceleration records having different frequency content and soil classes based on average top 30 m shear velocity are given. Set includes 8400 records generated from 84 base rock acceleration passing through 100 different soil cases. The set is assumed to provide a wide range of frequency content, amplitude and soil classification option to researchers. Also, properties of devastating earthquakes in Turkey are investigated. Depth-average shear wave velocity relations are given for sand and clay materials. It is observed that; scaling real earthquake records in 0.7-1.3 range does not alter the frequency-amplitude relationship, records with a PGA of more than 0.4g have higher amplification ratios for waves larger than roughly 1.0 s periods when compared to records with smaller PGA.