Mechanical behaviour of SiC fibre-reinforced titanium/titanium aluminide hybrid composites

The viability of developing an SiC fibre-reinforced titanium/titanium aluminide hybrid matrix composite was explored. The hybrid composites are expected to be used at temperatures beyond those attainable in conventional titanium matrix composites while improving the damage tolerance of the titanium aluminide matrix composites. The room-temperature mechanical characteristics studied were tensile strength, fracture toughness, low-cycle fatigue life and fatigue crack growth rate. The mechanisms of damage initiation and propagation under various loading conditions were also characterized. The directions for developing a satisfactory composite with hybrid titanium/titanium aluminide matrix are also addressed.     

Preparation of hybrid PU/PCL fibers from steviol glycosides via electrospinning as a potential wound dressing materials

In this study, the synthesis and application of biocompatible steviol glycosides based polyurethane/poly (ε-caprolactone) (PU/PCL) fibers was performed by electrospinning as a potential wound dressing materials that can be used for the closure of nonhealing wounds. During electrospinning, steviol glycoside-based polyurethane structures were used in blend formation with poly (ε-caprolactone) for easy producibility. Steviol glycosides are a natural abundant and easily accessible source as the main component of the wound dressing material due to their free hydroxyl groups, high biocompatibility, and hydrophilicity. The structure of steviol glycosides is composed of saccharide units and the free OH groups. Thus, steviol glycosides act as a crosslinker within the polyurethane structure and provides mechanical strength. For the production of steviol glycosides based PU/PCL fibers first, the steviol glycosides as a monomer were isolated from the stevia rebudiana. Then, polyurethane structures containing stevia glycoside were synthesized with hexamethylene diisocyanate, lactose and PEG-200 by solution polymerization technique. PCL was added to the prepared polyurethanes in a ratio of 1:2 and formation of nanofiber structure. The prepared wound dressing material was characterized by Fourier transform infrared, atomic force microscopy, and scanning electron microscope techniques. Swelling degree, water content and oxygen permeability assay of the steviol glycosides based PU/PCL wound dressing material was determined. In biocompatibility test, cell viability value of PU/PCL fibrous materials in indirect cytotoxicity test was determined as 86.9% and cell adhesion on hybrid PU/PCL fibers was showed as morphological. In accordance with this target, the steviol glycosides based PU/PCL wound dressing material can be produced easily and low cost. As a result, the wound dressing materials obtained with their high biocompatibility and low costs will be an effective and fast method for the healing of open wounds of diabetics.     

Synthesis of Quaternary,Long-Chain N-Alkyl Amides and Their Corrosion Inhibition in Acidic Media

New cationic surfactants were synthesized by the quaternization of a number of straight-chain amide derivatives with triethylamine or pyridine. The corrosion inhibition tests of the surface-active compounds were performed at room temperature for 24 h on carbon steel coupons in acidic media using the gravimetric method. The acidic media used were 1.5 M HCl and 1.5 M H₂SO₄. Almost all of the synthesized cationic surfactants showed efficient inhibition of corrosion in the test. To establish the inhibition efficiencies of the inhibitors, surface characterization studies (contact angle measurements, SEM analysis and optical profilometer images) of the metal coupons used were performed.     

Three-parameter (3P) weibull distribution for characterization of strength of ceramics showing R-Curve behavior

Strength distribution of advanced ceramics is commonly characterized by two-Parameter (2P) Weibull distribution. However, deviation of strength distribution from 2P-Weibull distribution may occur in ceramics due to various mechanisms. R-curve behavior is one of these mechanisms where increase of fracture resistance with the extension of crack occurs. In such cases, 2P-Weibull distribution may not be the best fitting distribution function based on the goodness-of-fitness tests. This article examines the effectiveness of three-parameter (3P) Weibull distribution function for fitting the strength variation due to R-curve effect by using experimental and virtual strength data. The effect of Weibull parameters, degree of increase in crack resistance and number of samples on effectiveness of fitting via 3P-Weibull distribution is investigated. It is reported that 3P-Weibull distribution function fits the strength distribution better than 2P-Weibull distribution function for materials showing R-curve behavior when the crack resistance curve is steep and Weibull modulus is high. Furthermore, it is shown that at least 100 samples should be used for a reliable estimate when the material exhibits R-curve behavior.     

Determination of the quality and purity characteristics of olive oils obtained from different regions of Turkey,depending on climatic changes

Virgin olive oils (VOOs) obtained from olives grown in different regions of Turkey under changing climatic conditions sometimes show different sensory and chemical properties. This study was planned to determine whether these deviations are due to climatic changes or not. For this purpose, five different olive varieties (Ayvalık, Memecik, Gemlik, Nizip Yağlık, Kilis Yağlık) of commercial importance were harvested from the provinces/districts (four different region) where cultivation is intense during the 2017/2018–2020/2021 harvest years. Every year, olive samples were collected from 3 orchards from 13 provinces/districts. One hundred and fifty-six samples were subjected to the purity, quality and sensory analysis. Basic climatic values (average, minimum and maximum temperature, humidity and precipitation) were examined for four consecutive years. All of the examined olive oil samples were determined within the legal limits in terms of fatty acid composition and fatty acid ethyl ester values. However, delta-7-stigmastenol value from the sterol composition was found to be above 0.5% in some samples in all the years studied (total 21 samples). Delta-7-stigmastenol values of olive oil samples varied between 0.16% and 1.14%. Multiple linear regression analysis was applied using a genetic algorithm-based inverse least squares method to determine whether there is a relationship between climate data and delta-7-stigmastenol values. According to this result, it has been determined that the delta-7-stigmastenol value is high when the annual average relative humidity is low and the annual average temperature is high. There is an urgent need to make forward-looking plans due to climate change.