Additive Manufacturing of Polymer Matrix Composites

Due to the developments and the interest of leading aerospace companies, additive manufacturing (AM) has become a highly discussed topic in the last decades. This is mainly due to its capability of producing parts with high geometrical complexity, short manufacturing lead times, and suitability for customization as well as for low-volume production. As is the case with aircraft fuselage body where weight reduction while keeping the demanding mechanical properties is of uttermost importance, modern technology applications sometimes need materials with unusual combinations of properties that cannot be solely provided by metals, polymers, or ceramics. In this case, composite materials combining two or more materials allow having the preferred properties in one material. Thus, AM of composites is becoming more and more important for critical applications. Fiber reinforcement can significantly enhance the properties of resins/polymeric matrix materials. Although continuous fiber composites even present higher mechanical performance, the manufacturing methods for chopped fibers are more commercially available. This chapter reviews the studies in the field involving many aspects spanning from design, process technology, and applications to available equipment

Psychometric Properties of the Gifted Students’ Coping with Anger and Decision Making Skills Scale

The purpose of this study is to develop the scale concerning gifted children's’ skills for making decisions and coping with anger and to examine the validity and reliability of the scale. A total of 324 students, which 151 were female and 173 were male, studying in 3 different Science and Arts Center’s (BILSEM) in Istanbul during 2014-2015 academic period participated in the study. Content and construct validity tests were conducted for the validity of the scale, internal consistency and test-retest tests were conducted for the reliability and total correlation analysis was conducted. 48.19% of the total variance was explained with the factor analysis. The scale, which consisted of 16 items, demonstrated a two-factor structure titled as coping with anger and decision making. Factor loads of the scale were between .54 and .78.  The Cronbach alpha reliability coefficient was .76 for the whole scale, and .88 and .73 for the coping with anger and decision making sub-scales respectively. The test-retest reliability coefficients for the whole scale was .81, and .88 and .70 for the coping with anger and decision making sub-scales respectively. It was observed that the item-total correlations of the scale ranged between .44 and .72. Based on these findings, it can be concluded that the Scale for Gifted Children's’ Coping with Anger and Decision Making Skills is a valid and reliable assessment instrument that can be used for education and psychology. Keywords: Gifted children, coping with anger, decision making, reliability, validit

Assessment of Adolescent Perceptions on Parental Attitudes on Different Variables

The purpose of this study is to examine secondary school student perceptions of parental attitudes with regards to specific variables. Independent samples t test for parametric distributions and one-way variance analysis (ANOVA) was used for analyzing the data, when the ANOVA analyses were significant Scheffe test was conducted on homogeneous variance and Tamhane’s T2 test was conducted when the analyses were not homogeneous. Kruskall Wallis H test was conducted on non-parametric distributions and Mann Whitney-U test was conducted when the Kruskall Wallis H analyses were significant. It was observed that the democratic attitude dimension, which is a sub-dimension of parental attitudes that students perceive, does not significantly differ from the gender, number of siblings and income level variables; but is significantly different according to the parental educational status, whether parents are alive and marital status of the parents’ variables. It was observed that the protective-willing dimension, which is a sub-dimension of parental attitudes that students perceive, does not significantly differ from the gender, income level, whether parents are alive and marital status of the parents’ variables; but is significantly different according to the parental educational status and number of siblings’ variables. It was observed that the authoritarian dimension, which is a sub-dimension of parental attitudes that students perceive, does not significantly differ from the educational status of mother, number of siblings, income level, whether parents are alive and marital status of parents variables; but is significantly different according to the gender and educational status of the father variables

Sodium perborate usage instead of hydrogen peroxide for the reinforcement of oxygen delignification

Oxygen has always been an attractive oxidant for the pulp and paper industry due to it being cheap and harmless for the environment. However, it has lower lignin-cellulose selectivity, therefore the degree of delignification achieved at the oxygen stage is ultimately limited by its industrial pulp strength – 45-50% . In this study, to enhance the degree of delignification, the addition ofsodium perborate and hydrogen peroxide at the oxygen stage was examined. At the same active oxygen (approximately 0.5%) content, the degree of delignification increased from 45.56% to 49.42% using hydrogen peroxide and to 52.96% with sodium perborate. For the same selectivity parameter with control, the delignification degree can be increased to 57.59% with the addition of sodium perborate, which includes 1% active oxygen. Moreover, the costs of using sodium perborate and hydrogen peroxide were compared with respect to commercial employability. It was determined that the use of sodium perborate was more effective than that of hydrogen peroxide for delignification of the oxygen stage

Üstün Yetenekli Çocukların Öfkeyle Başa Çıkma ve Karar Verme Becerilerinin Bazı Değişkenler Açısından İncelenmesi

Bu araştırmanın amacı Bilim ve Sanat Merkezleri’ne devam eden üstün yetenekli çocukların öfkeyle başa çıkma ve karar verme becerilerinin bazı değişkenler açısından incelenmesidir. Araştırmada tarama (betimsel) modeli kullanılmıştır. Araştırmanın örneklemini İstanbul’da bulunan üç farklı Bilim ve Sanat Merkezi’nde öğrenim gören toplam 276 5.6.7 ve 8. Sınıf öğrencisi oluşturmaktadır. Araştırmada Ersoy ve Deniz (2015) tarafından geliştirilen Üstün Yetenekli Çocukların Öfkeyle Başa Çıkma ve Karar Verme Becerileri Ölçeği ve Kişisel Bilgi Formu kullanılmış, veriler SPSS 22.0 istatistik paket programı ile analiz edilmiştir. Yapılan analiz sonucunda üstün yetenekli çocukların öfkeyle başa çıkma becerisi ve karar verme becerisi boyutlarının anne ve baba eğitim düzeyi, kardeş sayısı, gelir düzeyi, anne-babanın hayatta olup olmaması ve anne-babanın medeni durumu değişkenine göre anlamlı düzeyde farklılaşmadığı; buna karşılık cinsiyet değişkenine göre anlamlı düzeyde farklılık gösterdiği görülmüştür

Investigation of the NH4OH-KOH pulping possibilities of banana pseudo-stem wastes

Artan nüfus talepleri nedeniyle kağıt hamuru ve kağıt endüstrisi hızla büyümektedir. Bu talepleri karşılamak için, çevresel kaygılara bağlı olarak, kağıt hamuru ve kağıt üretiminde alternatif hammaddelerin ve yeni teknolojilerin kullanımı artmıştır. Bu çalışmada, muz bitkisinin (Musa sapientum) meyve hasadı sırasında büyük miktarlarda oluşan muz yalancı gövde atıklarından NH4OH-KOH yöntemi ile kağıt hamuru üretim olanakları araştırılmıştır. Pişirme çözeltisinin muz yalancı gövde atığına oranı, maksimum pişirme sıcaklığı ve maksimum sıcaklıkta pişirme süresi sırasıyla 6, 165 °C ve 60 dakika olarak sabit tutulmuştur. Çalışmada %20 ve %22 olmak üzere iki farklı alkali oranı kullanılmış olup, pişirme çözeltisindeki NH4OH ve KOH oranları sistematik olarak değiştirilerek hamur ve kağıt özelliklerindeki değişim gözlemlenmiştir. Artan KOH ve NH4OH oranlarına bağlı olarak hamurların kappa numaralarının azaldığı ancak bu azalışın yeterli delignifikasyon sağlayacak şekilde olmadığı görülmüştür. Üretilen hamurların viskozite değerleri korunmuş ancak lignin içeriğinin yüksek olmasından dolayı hamurların parlaklık değerleri düşük olmuştur. Bununla birlikte, muz yalancı gövde atıklarının NH4OH-KOH yöntemi ile kopma indisi (60,95 Nm/g), yırtılma indisi (14,94 mNm2/g) ve patlama indisi (4,28 kPa.m2/g) değerleri yüksek kağıtların üretildiği tespit edilmiştir. Elde edilen sonuçlara göre muz yalancı gövde atıklarından NH4OH-KOH yöntemi ile üretilen kağıtların ambalaj endüstrisi için uygun olabileceği düşünülmüştür.The pulp and paper industry has been growing fast due to the increasing population demands. In order to meet these demands, the use of alternative raw materials and new technologies for pulp and paper manufacture has increased depending on environmental concerns. In this study, pulp production possibilities of the banana plant (Musa sapientum) were investigated by the NH4OH-KOH method from banana pseudo-stem wastes formed in large quantities during fruit harvest. The liquid to banana pseudo-stem ratio, the maximum cooking temperature, and the cooking time at the maximum temperature were kept constant as 6, 165 °C, and 60 min., respectively. In the study, two different alkaline ratios, 20%, and 22%, were used and the changes in pulp and paper properties were observed by systematically changing the NH4OH and KOH ratios in the cooking liquor. It was observed that, the kappa numbers of the pulps decreased due to the increasing KOH and NH4OH ratios, but sufficient delignification could not be achieved. The brightness values of the produced pulps were low due to the lignin content of the pulps, while the viscosity values were preserved. Although, it has been determined that papers with values high tensile index (60,95 Nm/g), tear index (14,94 mNm2/g), and burst index (4,28 kPa.m2/g) were produced by the NH4OH-KOH method from banana pseudo-stem wastes. According to the results obtained, it was thought that the papers produced from banana pseudo-stem wastes by the NH4OH-KOH method could be suitable for the packaging industry

Vertical Anatolian mavoment project

TÜBİTAK ÇAYDAG01.09.201

Bacterial cellulose as reinforcement in paper made from recycled office waste pulp

Bacterial cellulose, produced during fermentation of Kombucha tea, was investigated relative to its ability to modify the characteristics of pulp from recycled office wastepaper. The produced bacterial cellulose wet films were dispersed and added rates of 5%, 10%, and 15% to the recycled office wastepaper. The Fourier-transform infrared spectroscopy analyses, scanning electron microscopy images and thermogravimetric analysis values were determined in order to characterize the pulp samples. The results of these analyses showed similar changes as the amount of added bacterial cellulose increased, which also meant an increased amount of filler attaching to the fiber matrix. The burst index and tensile index values were protected while the tear index value partially decreased as the amount of added bacterial cellulose increased. The brightness values of the bacterial cellulose reinforced papers did not change after thermal aging, while the changes in the yellowness values were quite limited. Higher water absorption rates, and lower air permeability values were obtained from bacterial cellulose reinforced recycled office wastepaper sheets, which corresponded to the addition of increased bacterial cellulose amounts. Considering the mechanical and physical properties of the reinforced paper, bacterial cellulose represents a promising alternative for the reinforcement of office wastepaper

A Review of the Additive Manufacturing of Fiber Reinforced Polymer Matrix Composites

Additive manufacturing (AM), also referred to as 3D printing, has gained popularity due to the recent developments and market trends especially in the last decades. The main advantages of AM are its capability of producing parts with high geometrical complexity at almost no added cost, short lead times, weight reduction, less efforts for assembly and suitability for customization as well as for low volume production or even single parts. Moreover, some applications may need materials with unusual combinations of properties, which cannot be provided only by metals, polymers or ceramics. For such applications, composite materials combining two or more materials allow having the preferred properties combined in a single material. Thus, AM, which can be defined as a process of adding materials to produce objects directly from its CAD model in successive layers in contrast to subtractive processes, is gaining significance for critical applications using composite materials. This paper thus presents a detailed review of AM of polymers reinforced with chopped / continuous fibers and the influence of this reinforcement on the mechanical performance of composite parts, mainly focusing on the Fused Deposition Modelling (FDM) process. On one hand, the reviewed studies on the FDM of composites mainly point out that that the mechanical performance is significantly enhanced in contrast to polymers with no reinforcement. Yet, it is also evident that the mechanical performance of FDM composites is highly dependent on the build direction and porosity. Thus, there is still a wide range of gaps to be studied for replacing metallic components by AM composites.Mechanical Engineerin

Dimensional Accuracy and Mechanical Properties of Chopped Carbon Reinforced Polymers Produced by Material Extrusion Additive Manufacturing

Fused Filament Fabrication (FFF), classified under material extrusion additive manufacturing technologies, is a widely used method for fabricating thermoplastic parts with high geometrical complexity. To improve the mechanical properties of pure thermoplastic materials, the polymeric matrix may be reinforced by different materials such as carbon fibers. FFF is an advantageous process for producing polymer matrix composites because of its low cost of investment, high speed and simplicity as well as the possibility to use multiple nozzles with different materials. In this study, the aim was to investigate the dimensional accuracy and mechanical properties of chopped carbon-fiber-reinforced tough nylon produced by the FFF process. The dimensional accuracy and manufacturability limits of the process are evaluated using benchmark geometries as well as process-inherent effects like stair-stepping effect. The hardness and tensile properties of produced specimens in comparison to tough nylon without any reinforcement, as well as continuous carbon-reinforced specimens, were presented by taking different build directions and various infill ratios. The fracture surfaces of tensile specimens were observed using a Scanning Electron Microscope (SEM). The test results showed that there was a severe level of anisotropy in the mechanical properties, especially the modulus of elasticity, due to the insufficient fusion between deposited layers in the build direction. Moreover, continuous carbon-reinforced specimens exhibited very high levels of tensile strength and modulus of elasticity whereas the highest elongation was achieved by tough nylon without reinforcement. The failure mechanisms were found to be inter-layer porosity between successive tracks, as well as fiber pull out