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Article
Effect of Water Absorption on Some Electrical and Dielectrical Properties of Epoxy Resin Reinforced with Chopped Carbon Fibers

Authors: E.A.Al-Ajaj --- S.I.Husaen --- H.I.Jafar
Journal: Al-Nahrain Journal of Science مجلة النهرين للعلوم ISSN: (print)26635453,(online)26635461 Year: 2011 Volume: 14 Issue: 4 Pages: 87-94
Publisher: Al-Nahrain University جامعة النهرين

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Abstract

In this research, we study a.c electrical conductivity (σa.c ( ) and dielectric properties (dielectric constant (έ), and dissipation factor ( tanδ) ), with frequency change (102 -107 Hz) for the epoxy resin and composites reinforced with chopped carbon fiber ,prepared by hand lay –up method (EP +5% CF), (EP +10% CF), (EP +15% CF), (EP +20% CF), Were measured electrical conductivity of epoxy and composites with frequency change and at room temperature the results showed a.c electrical conductivity dependence with frequency relationship σ (ω)=Aωs to the values of the exponential factor (s)of less than one all samples, and adopted the theory of filtration for the interpretation of data conductivity for composites reinforced with carbon fibers was selected epoxy+20% C.F showed a higher electrical conductivity (13.6 * 10-7 (ohm.cm)-1). The composites were immersed in water at room temperature for 6, 10,15,20,27 days.The results showed that the electrical conductivity of (σ (ω)) increasing with increasing weight gain(M%) due to water absorption. Itwas found that dielectric constant increases when the percentage moisture absorption increase, whereas dielectric constant (έ) is dependent on capacity of composite materials.

تـم في هـذا البحث دراسـة التوصيليـة الكهربائيـة المتناوبـة ()(σa.c وخـواص العـزل الكهربائـي (έ,tan (مـع تغيـر التردد (102 -107 Hz) لراتنـج الايبوكسي ومتراكباته المدعمة بالياف الكاربون المقطعة والمحضرة بطريقة التشكيل اليدوية(EP+5%C.F)، (EP+10%C.F)، (EP+15%C.F)، (EP+20%C.F) تم قياس التوصيلية المتناوبة للايبوكسي ومتراكباته في مدى التردد وفي درجة حرارة المختبر اظهرت النتائج اعتماد التوصيلية على التردد وفق العلاقة σ(ω)=Aωs بقيم للعامل الاسي اقل من الواحدلكل العينات, واعتمدت نظرية الترشيح لتفسير بيانات التوصيلية لمتراكبات الايبوكسي المدعم بالالياف الكاربون. كما تم دراسة تأثير التردد في قيمة ثابت العزل الكهربائي وفقد العزل فقد وجد بان السماحية ( ( έتقل في حالة التقوية بالياف الكاربون المقطعة، تم اختيار المتراكب ايبوكسي -20% الياف الكاربون المقطعة الافضل من بين المتراكبات باعتبـاره اظهـر اعلـى توصيليـة كهربائيـة( (ohm.cm )-1 13.6*10-7 ). تم تغطيس المتراكبات في الماء بدرجة حرارة الغرفة لمدة 20,1510,6, 7, 2 يوم، اظهـرت النتائـج العمليـة ان التوصيليـة الكهربائيـة((ω)σ) تزداد بزيادة التردد وزيادة النسبة المئوية لامتصاصية الماء بينما ثابت العزل (έ) يزداد عند زيادة النسبة المئوية لامتصاصية الماء اعتمادا على السعة الكهربائية للمواد المتراكبة.


Article
Mechanical Properties of High Performance Carbon Fiber Concrete
الخواص الميكانيكية لخرسانة ألياف الكاربون العالية الأداء

Authors: Wasan I. Khalil --- Akar Abdulrazaq
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2011 Volume: 29 Issue: 5 Pages: 906-924
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

In this research mechanical properties of high performance carbon fiber concreteare studied. The experimental work includes, producing high performance concreteusing superplasticizer and condensed silica fume reinforced with different volumefractions (0%, 0.2%, 0.3%, 0.4% and 0.5%) of carbon fibers. The effect of choppedcarbon fibers on the mechanical properties (compressive strength, splitting tensile andflexural strengths, and modulus of elasticity) of high performance concrete was alsostudied. Generally, the results show that the addition of carbon fibers improves themechanical properties of high performance concrete. Also the results show that Usingcondensed silica fume as addition by weight of cement increases the compressivestrength more than that as replacement by weight of cement. The percentages increasein compressive strength of concrete containing 15% silica fume as replacement and asaddition by weight of cement are about 14% and 26% respectively. The addition ofcarbon fibers causes a slight increase in compressive strength and modulus ofelasticity of high performance concrete when the fiber volume fraction increases,while the splitting tensile and flexural strengths shows a significant increase relativeto the reference high performance concrete (without fiber). The percentage increase insplitting tensile and flexural strengths for high performance concrete with fibervolume fraction 0.5% at 28 days is about 45% and 46% respectively.


Article
The Effect of Addition of Carbon Fibers on Some Properties of Self Compacting Concrete
تأثير أضافة ألياف الكاربون على بعض خواص الخرسانة ذاتية الرص

Authors: شاكر أحمد صالح --- غزوان عبد الصمد سلمان
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2011 Volume: 29 Issue: 14 Pages: 576-596
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

To Study the possibility of producing self compacting concrete (SCC), 10% by weight of cement of metakaoline and silica fume were used and carbon fiber with two volume fraction (0.1%, 0.5%) and two fiber lengths (6mm, 12mm) were add . the effect of these variables on most properties of SCC containing fibers has been studied.Test results show that concrete mixes containing metakaoline and silica fume required higher superplastizer content to 9% and 10% by weight of cement compared with 8% by weight of cement for mixes without Pozzolanic materials to maintain the self compatibility of mixes .A significant improvement was observed in the mechanical properties of mixes including compressive and splitting tensile strength, Moduls of rupture, static Modulus of elastisity, and impact resistance. the improvment percentage at 28 days were (6.74% , 5.37% , 4.5% , 3.2% , 6.07%) respectively for SCC with silica fume mixes and (8.43% , 7.6% , 6.08% , 4.03% , 30.30%) respectively for SCC with Highreactive metakaolin mixes. Test results indicate that the addition of carbon fibers led to reduce the workability of mixes and the reduction was increased with fiber length and fiber content. mixesreinforced with carbon fibers, the compressive and splitting tensile strength, modulus of rupture, static moduls of elastisity, and impact resistance at failure were higher than the reference mixes by not more than (25.75% , 66.18%, 38.26% , 14.14% and 1195%) respectively .

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