Vineta Srebrenkoska
Univerzitet Goce Delcev, Faculty of Technology, Faculty Member
The aim of this study was to investigate the mechanical and thermal properties of composite pipes based on epoxy resin and glass fibers produced by filament winding (FW) technology. Epoxy resins are widely used polymers in FW composite... more
The aim of this study was to investigate the mechanical and thermal properties of composite pipes based on epoxy resin and glass fibers produced by filament winding (FW) technology. Epoxy resins are widely used polymers in FW composite structures. The thermal characterization of the neat epoxy resin, curing, and post-curing characteristics for the determination of polymerization and glass transition temperature was performed, which is important for the mechanical properties of polymer composite pipes. In the present work, the applicability of the full factorial experimental design in predicting the hoop tensile and compressive strengths of glass fiber/epoxy resin composite pipes was investigated. The composite pipes in accordance with the 23 full factorial experimental design by using of three parameters and two levels of variation were prepared. The winding speed of the composites was taken to be the first factor, the second was the fiber tension, and the third was winding angle. T...
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The minimization of waste and reductions in material and energy inputs are the most important environmental aims. Sustainable technological development and innovations do not automatically lead to total reduction of environmental burden... more
The minimization of waste and reductions in material and energy inputs are the most important environmental aims. Sustainable technological development and innovations do not automatically lead to total reduction of environmental burden of industrial production. However, technological innovation is an important factor and seems to play a central role in the long-term initiation of cleaner production. Sustainable technology is usually connected with the design and analysis of complex, integrated management systems and sustainable development and it is a central target in environmental science and growth of global economies. Environmental improvement of companies strategy by application the idea of cleaner production linked with sustainable technologies leads to produce environmentally friendly products and leads to increase the position of company on the market. The paper describes the general cleaner production aims, which are correspond to the prevention criteria of the IPPC-Directive. It presents cleaner production practices and technologies and examines the methods of successful application of cleaner production practices in companies, which want to realize ecological targets.
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Quality control is a set of steps or guidelines designed to guarantee that a product or service meets certain performance standards. Quality control in textiles is concerned with being certain a product meets performance standards and... more
Quality control is a set of steps or guidelines designed to guarantee that a product or service meets certain performance standards. Quality control in textiles is concerned with being certain a product meets performance standards and customer expectations. In this paper one model of woman shirt is observed. For this model a working plan was made and the time that is required to perform the operations of sewing the model was also defined. The total time for each operation, the daily production capacity, the daily capacity per worker and the tact of the group were also calculated. The percentage of load per operation was also defined. The observation in the term of choosing the right operation for the operators was also done.
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Со илјадници години користењето на влакна било лимитирано само на она што го дава природата. Но, нешто повеќе од пред еден век, конечно развиено е првото вештачко влакно – рајонот (вискоза). Првото комерцијално производство на вештачки... more
Со илјадници години користењето на влакна било лимитирано само на она што го дава природата. Но, нешто повеќе од пред еден век, конечно развиено е првото вештачко влакно – рајонот (вискоза). Првото комерцијално производство на вештачки влакна го остварил францускиот хемичар Hilarie de Chardonnet. Во 1889 година неговата ткаенина од “вештачка свила“ предизвикала сензација на изложбата во Париз. Две години покасно тој го изградил првиот комерцијален погон за рајон. Во 1893 година бил пронајден уште еден целулозен продукт – ацетатот, кој во 1924 година бил произведен во вид на влакно од страна на компанијата Celanese. Целосна независност од природната целулоза била постигната со развојот на синтетичките влакна. Од нивниот почетен развој, синтетичките влакна стануваат конкурент, а во некои апликации дури ги заменуваат природните влакна. Полиестерските се денес најшироко користените влакна како за текстилни ткаенини така и, во мал дел, за технички апликации. Овие влакна прво се произведе...
Da bi do{lo do inicirawe na eksploziven proces kaj nekoja eksplozivna materija, potrebno e da i se predade odredena koli~ina energija koja ne smee da bide pomala od tnr. energija na aktivacija na tie molekuli. Koga }e zapo~ne procesot na... more
Da bi do{lo do inicirawe na eksploziven proces kaj nekoja eksplozivna materija, potrebno e da i se predade odredena koli~ina energija koja ne smee da bide pomala od tnr. energija na aktivacija na tie molekuli. Koga }e zapo~ne procesot na hemisko pretvorawe, doa|a do samozabrzuva~ki i samoraspostira~ ki reakcii. Vo zavisnost od na~inot i uslovite na aktivirawe na hemiskite reakcii, procesite na eksplozivno pretvoruvawe mo`at da se odbivaat po dva razli~ni mehanizmi: kako deflagracija (sogoruvawe) ili kako detonacija(eksplozija).
In this paper is elaborated and confirmed the need of projection and implementation of total quality management (TQM) system within Macedonian textile factories. Quality should be required not only in the production process, but in all... more
In this paper is elaborated and confirmed the need of projection and implementation of total quality management (TQM) system within Macedonian textile factories. Quality should be required not only in the production process, but in all parts of the business processes, even in the way the employees behave. An analysis is made on the situation in the textile industry in Macedonia and its progress through the four quality pillars: internal standardization, statistical process control appliance, education and motivation, and analysis of the quality costs. The results of the analysis have shown low progress of Macedonian textile companies according to the four quality pillars, therefore, this paper promotes methodology for increasing competitiveness among the textile companies and their pre- structuring in order to catch up with the new world trends
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Во овој дел се презентирани можностите за рециклирање и за обновување на енергијата од отпадни полимерни композитни материјали. Истражувањата што се презентирани во овој материјал се направени од одреден број компании кои главно се... more
Во овој дел се презентирани можностите за рециклирање и за обновување на енергијата од отпадни полимерни композитни материјали. Истражувањата што се презентирани во овој материјал се направени од одреден број компании кои главно се занимаваат со производство на производи од зајакнати полимерни композитни материјали и компании кои се занимаваат со третирање на овие материјали на крајот од нивниот животен век. Производителите на полимерни композитни материјали имаат притисок од нивните купувачи да го земат предвид влијанието на нивните крајни производи врз околината, а исто така, од нив бараат соодветни решенија за третирање на овој вид отпад. Во рамките на оваа студија ќе бидат прикажани можностите за рециклирање на ваков тип материјал и за обновување на енергијата, врз основа на економска анализа и анализа на животната средина, а истовремено ќе биде прикажана и споредбата меѓу различните постапки.
Поради зголемување на еколошките барања, особено од аспект на крајното отстранување на искористените производи, производителите и дизајнерите во иднина мора да го земат предвид справувањето и отстранувањето на нивните производи. За... more
Поради зголемување на еколошките барања, особено од аспект на крајното отстранување на искористените производи, производителите и дизајнерите во иднина мора да го земат предвид справувањето и отстранувањето на нивните производи. За конвенционалните материјали, како челик и алуминиум, постојат функционални методи за нивно рециклирање. Меѓутоа, ова не е случај со структурните полимерни композити, кои имаат сe поголема примена во голем број индустрии: автомобилската, градежната, индустријата за мебел, електроиндустријата, авионската и др. Полимерните композитни материјали покажуваат одлична јакост и цврстина во комбинација со ниска густина. Овие својства се особено атрактивни кај структурните композити наменети за транспорт на стока и луѓе кои користат необновливи горива. Намалената тежина и непроменетиот капацитет за транспорт придонесуваат за намалување на вкупните трошоци и потрошувачката на гориво. Веќе неколку години композитите зајакнати со стаклени влакна се користат во производ...
Решавањето на мноштво проблеми во хемијата и хемиската технологија, како и во останатите гранки од инженерството, често е поврзано со изведување на сложени и скапоцени експерименти. Оттука е разбирливо значењето од постоењето на начини и... more
Решавањето на мноштво проблеми во хемијата и хемиската технологија, како и во останатите гранки од инженерството, често е поврзано со изведување на сложени и скапоцени експерименти. Оттука е разбирливо значењето од постоењето на начини и методи за оптимално планирање на експериментите, кои во низа случаи овозможуваат суштествено да се скратат времето и материјалните трошоците при извршување на истражувањето. Долго време редоследот на извршување на експериментите бил базиран на личното искуство и интуиција на истражувачот. Методите на оптимално планирање на експериментите овозможуваат користење на математички методи не само за обработка на резултатите од тестовите, туку и во фазата на подготовката и спроведувањето на експериментите. Работата на истражувачите кои ги користат тие методи значително се олеснува, затоа што се изведува по логично дефинирана, редоследна постапка. Во современата математичка теорија за оптимално планирање на експериментите постојат два основни оддели: 1. План...
Во овој проект ќе биде испитувана одржлива технолошка постапка за производство на разни конструктивни материјали за примена во земјоделството, градежната и индустријата за мебел и др. Ќе бидат применети процесите на компресија и... more
Во овој проект ќе биде испитувана одржлива технолошка постапка за производство на разни конструктивни материјали за примена во земјоделството, градежната и индустријата за мебел и др. Ќе бидат применети процесите на компресија и инјекционо обликување, а како основен материјал ќе се користи текстилен и пластичен/рециклирачки отпад и биоразградлив материјал од обновливите ресурси во нашата земја. Паралелно, ќе се испитува можноста за воведување одржлива технолошка постапка за добивање на нови композити од повеќекратно рециклиран материјал. Интересот за новите композити врз основа на отпаден/рециклиран материјал расте брзо заради повисоките еколошки стандарди, потенцијално добрите својства на овие композити, ниската густина и цена, можноста за максимално искористување на реактантите и обезбедување на повратен тек на отпадниот материјал. Во рамките на предложениот проект ќе се користат различни типови на термопластичен рециклирачки отпад и природни материјали од обновливи ресурси во наш...
The changes in the environment and in the companies themselves on one hand, and the development of the organization on the other hand, can be complementary factors in the company. This can be achieved only if a dynamic process of internal... more
The changes in the environment and in the companies themselves on one hand, and the development of the organization on the other hand, can be complementary factors in the company. This can be achieved only if a dynamic process of internal changes is set in the company, which will respond to the outside changes and it will obtain a competence on the market. One of the biggest changes that the new TQM strategy (Total Quality Management) seeks, concerning the Macedonian companies, is a change of the mentality and releasing the old habits and the transitional syndrome. In this paper are shown the findings from the research concerning the approach toward quality in Macedonian companies, the abilities of the managers to create a good quality system and the directions that are needed for the development of the business processes, the products and the services. The solution should be searched for in the development of the quality system through the application of the TQM strategy, the devel...
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The search for smart self-healing materials and preventive repair methods is justified by the increasing sustainability and safety requirements of structures. The appearance of small cracks in concrete is unavoidable, not necessarily... more
The search for smart self-healing materials and preventive repair methods is justified by the increasing sustainability and safety requirements of structures. The appearance of small cracks in concrete is unavoidable, not necessarily causing a risk of collapse for the structure, but certainly accelerating its degradation and diminishing the service life and sustainability of constructions. That loss of performance and functionality promote an increasing investment on maintenance and/or intensive repair/strengthening works. The critical nature of such requirements is signified by their inclusion as priority challenges in the European Research Program. The first focus of this proposal is to compare the use of self-healing capabilities of concrete with the use of external healing methods for repairing existing concrete elements. Despite the promising potential of the developed healing technologies, they will be real competitive alternatives only when sound and comparative characterizat...
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In the composite industry for special purposes various textile materials can be apply, but in the technology of advanced composites dominate: glass, carbon, aramide and polyethylene fibers. Fiber reinforcement became dominant in many... more
In the composite industry for special purposes various textile materials can be apply, but in the technology of advanced composites dominate: glass, carbon, aramide and polyethylene fibers. Fiber reinforcement became dominant in many engineering applications due to the possibilities of designing various properties of composite materials by changing the arrangements of different fibers. But not all types of fibers can be used as reinforcement of textile composites. Fibers to be utilized in composites should have specific properties, such as high modulus of elasticity, high ultimate strength, uniform cross section, low variation of properties between individual fibers, and the ability to withstand fabrication without significant property loss. Textile composites are using high performance fibers such as glass, carbon/graphite, aromatic polyamides (aramides – Kevlar), polyesters (HM/HT PES), ceramic fibers, boron and silicon carbide fibers, etc. Textile composites are being widely used...
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The purpose of the study is to access the applicability of Taguchi Method in predicting properties of polymer composites. The preparation of the composites was conducted by applying Taguchi L9 Method. Voids are one of the most... more
The purpose of the study is to access the applicability of Taguchi Method in predicting properties of polymer composites. The preparation of the composites was conducted by applying Taguchi L9 Method. Voids are one of the most common defects in composite components and are known to degrade mechanical performance. As a result, void content measurement is often used both to assess the quality of a composite part and to determine its acceptability. For composites the calculate void in composite materials were determined in a lab according standard ASTM D 792, ASTM D 2734 and ASTM D 3171 with calculate experimental and theoretical density. From received results with minimal number of experiments and signal-to-noise ratios used as objective functions for optimization, data analysis and prediction of optimum results was shown that factor 1 has the biggest impact on the voids of manufacture samples
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Many of the processes and products associated with modern lifestyles have negative effects on the environment. Among the significant consequences are the rising costs of treating and disposing of excessive amounts of waste. Proper... more
Many of the processes and products associated with modern lifestyles have negative effects on the environment. Among the significant consequences are the rising costs of treating and disposing of excessive amounts of waste. Proper management of the large amounts of waste generated by the confection industry is of high importance to the good of society. Solving the problem of textile waste is of great importance for the garment production facilities in order to increase competitiveness, make additional profits and reduce disposal costs. In this paper were analyzed two confection companies, in order to determine the amount of textile waste that occurs in both companies, and also was made a research for utilization of the generated textile waste through its application as a raw material for the production of composite materials.
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The aim of this work was to determine the flexural properties of hybrid composites parts cut from trapezoidal core made of carbon/glass fibers impregnated in epoxy resin with help of filament winding technology. Values for stress, strain... more
The aim of this work was to determine the flexural properties of hybrid composites parts cut from trapezoidal core made of carbon/glass fibers impregnated in epoxy resin with help of filament winding technology. Values for stress, strain and module of elasticity were calculated using three point bending test. The tests were performed according to American Society for Testing and Materials (ASTM) standards. Hybrid fiber reinforced plastic (FRP) laminates exhibit progressive failure consisting of fiber failure, debonding, and delamination. Further, the paper investigates the content of voids inside the structure, the interface fiber/epoxy resin using scanning electron microscope and the procedures involved in the laminate design, fabrication, experiments and analysis of composite part for decks.
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The aim of this study is to investigate the mechanical properties of continuous glass fiber reinforced composite tubes produced by filament winding technique with three different winding angles. With help of split-disk tests hoop tensile... more
The aim of this study is to investigate the mechanical properties of continuous glass fiber reinforced composite tubes produced by filament winding technique with three different winding angles. With help of split-disk tests hoop tensile properties of selected specimens were determined, where reliable results were obtained with low standard deviations. It was observed that bigger winding angle lead to higher hoop tensile properties of filament-wound tubular samples. Also, the effect of reinforcement direction on the mechanical performances of these composites has been presented. Fiber fracture and fiber-matrix debonding is observed to be the dominant failure mechanisms by samples winded with bigger winding angles, whereas delamination in addition to these mechanisms is detected by samples with smaller winding angles. From received results it is concluded that, mechanical properties of composite specimens are depended from winding angles in filament winding technology. With help of c...
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Aim of this work is to present the thermal properties and mechanical behaviour of glass fibre/epoxy resin filament wound tubular structures winded with different winding angles. Conducted thermal analysis have demonstrated thermal... more
Aim of this work is to present the thermal properties and mechanical behaviour of glass fibre/epoxy resin filament wound tubular structures winded with different winding angles. Conducted thermal analysis have demonstrated thermal stability of used epoxy resin system even at temperatures higher than 130oC and small percent of weight loss until temperature of 350oC. With help of split-disc test hoop tensile strength of manufactured composite samples was investigated. Received results have confirmed the expectations that use of higher winding angle in filament winding technology lead to better mechanical properties of composite tubular structures subjected under internal pressure. Also, fibre-matrix deboning was determined as failure mechanisms by all samples. SEM images have confirmed good merger between reinforcement and the matrix.
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The aim of this study is to investigate the design of continuous fiber reinforced composite pipes, produced by filament winding technique. For this purpose, the full factorial experimental design was implemented. When designing filament... more
The aim of this study is to investigate the design of continuous fiber reinforced composite pipes, produced by filament winding technique. For this purpose, the full factorial experimental design was implemented. When designing filament winding composites three major factors are the most important: fiber orientation, fiber tension and velocity of the filament winding. The ultimate target is to achieve the composite pipes with good characteristics as bearing material for construction with the lowest possible weight. Preparation of the composites was done by applying the 23 full factorial experimental design. For the purposes of these investigation, eight test specimen configurations are made and on the basis that, test results should provide material properties useful in the design stage. The velocity of the filament winding was taken to be the first factor, the second – fiber tension and the third – winding angle. The first factor low and high levels were chosen to be 525 m/min and ...
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The aim of this study was to investigate the mechanical and thermal properties of continuous glass fiber reinforced composite (GFRC) pipes produced by filament winding technique with different winding speed, fiber tension and winding... more
The aim of this study was to investigate the mechanical and thermal properties of continuous glass fiber reinforced composite (GFRC) pipes produced by filament winding technique with different winding speed, fiber tension and winding angle in accordance with the 23 full factorial experimental design. The influence of each individual factor to the response function was established, as well as the influence of the interaction of the two and three factors. From received results it was concluded that, mechanical properties of composite specimens were highly effected by winding angles in filament winding technology. It was found that the estimated first-degree regression equation with the interaction gave a very good approximation of the experimental results of the hoop tensile and compressive strengths of composite pipes within the study domain. From the results of thermal characterization of the composite pipes, it was concluded that all filament wound pipes have a good thermal stabili...
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The aim of this work was to determine the flexural properties of hybrid composites parts cut from trapezoidal core made of carbon/glass fibers impregnated in epoxy resin with help of filament winding technology. Values for stress, strain... more
The aim of this work was to determine the flexural properties of hybrid composites parts cut from trapezoidal core made of carbon/glass fibers impregnated in epoxy resin with help of filament winding technology. Values for stress, strain and module of elasticity were calculated using three point bending test. The tests were performed according to American Society for Testing and Materials (ASTM) standards. Hybrid fiber reinforced plastic (FRP) laminates exhibit progressive failure consisting of fiber failure, debonding, and delamination. Further, the paper investigates the content of voids inside the structure, the interface fiber/epoxy resin using scanning electron microscope and the procedures involved in the laminate design, fabrication, experiments and analysis of composite part for decks.
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The main aim of the proposed STSM project is to perform: • Comparison of fly ash characteristics (chemical composition, granulometry and density) from different origins: Slovenia and Macedonia. • Characterization of the polymer materials:... more
The main aim of the proposed STSM project is to perform: • Comparison of fly ash characteristics (chemical composition, granulometry and density) from different origins: Slovenia and Macedonia. • Characterization of the polymer materials: thermoset and thermoplastic. • Estimate the possibilities for preparing of the composites based on fly ash as NORM material from different origins and polymers. The analyses of the inorganic fillers and organic polymer matrices will be made in order: – to find the most effective filler strengthening configuration, – to quantify the thermomechanical characteristics of the thermoset and thermoplastic polymers, – to better understand the interaction between fillers and matrix, – to estimate the contribution of the fillers, matrix and designed composite systems for the thermomechanical properties, The desired objectives of the STSM project will be achieved and guaranteed by the strong co-operation between Slovenian National Building and Civil Engineeri...
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Research and development of new fibre-based packaging materials with active and intelligent features have shown huge potential to optimise the supply chain, and increase the shelf-life of foodstuff and enhance consumer consciousness of... more
Research and development of new fibre-based packaging materials with active and intelligent features have shown huge potential to optimise the supply chain, and increase the shelf-life of foodstuff and enhance consumer consciousness of food utilisation. Very few of the potential solutions have, however, been able to reach the market.This Action aims to identify and focus on the key technical, social, economic and legislative factors relevant for a successful deployment of renewable fibre-based functional packaging solutions. This will be achieved by conducting research and development into active and intelligent packaging, encompassing both scientific and technical solutions, addressing the opportunities for, and obstacles to, market introduction. The innovative approach of this Action lies in the sharp focus on the integration of active and intelligent solutions in papermaking in order to create next-generation functional fibre-based packaging. The Action will achieve the objective...
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The aim of this study was to investigate the possibilities of utilization of the different glass fabrics and matrices for production of the composite plates. The thermoplastic and thermosetting matrices was used for production of the... more
The aim of this study was to investigate the possibilities of utilization of the different glass fabrics and matrices for production of the composite plates. The thermoplastic and thermosetting matrices was used for production of the prepreg from the fabrics. The reinforcement material was impregnated with matrix to perform a prepreg and with this process a complete wetting of fibers with the matrix. Basic parameters of the process for prepreg production like as content of matrix, uniformity of matrix along overall surface of reinforcement, gel time, matrix flow, moisture content and volatiles materials were tested. The composite plates were fabricated from the prepreg materials by thermo -compression in an open mold on a semi - industrial press machine. The basic mechanical and physical properties of the composite plates were investigated. The laminated composite structures have wide application in aerospace, mechanical, civil and other areas of engineering chiefly due to the low v...
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Because of increasing environmental demands, especially on dealing with products end of life phase, product manufacturers and designers must consider the future disposal of their products. For conventional materials like steel and... more
Because of increasing environmental demands, especially on dealing with products end of life phase, product manufacturers and designers must consider the future disposal of their products. For conventional materials like steel and aluminium well-functioning recycling methods exists. This is not the case for structures of polymer composites, which are used more extensively, especially for structures like vehicles and vessels. Several techniques do exist but they are not yet commercially available. The current disposal methods of polymer composites are landfill and incineration. Polymer composites are materials, which consist of several materials like fibre, matrix, and additives. This circumstance complicates the waste treatment of composite materials. Therefore, it is necessary to develop adequate waste treatment techniques for polymer composites including sandwich structures. Recommendations for waste treatment have been formed for a number of polymer composites. These recommendati...
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Because of increasing environmental demands, especially on dealing with product life phase end, manufacturers and designers must consider future disposal of their products. In recent years, an increased emphasis on developing recycling... more
Because of increasing environmental demands, especially on dealing with product life phase end, manufacturers and designers must consider future disposal of their products. In recent years, an increased emphasis on developing recycling techniques for industrial waste products has been placed, with the goals of protecting the environment. The aim of the work is investigation of the possibilities of reusing of cotton textile waste, generated during the manufacture in garment industry, as reinforcement in production of composite materials. The main focus has been put on the preparation and characterization of composites based on cut waste from garment industry. The materials have been cotton fabric and cotton textile waste as reinforcements and phenol phormaldehyde resin as matrix. The composites containing 60 % wt. reinforcement were manufactured by compression molding. For the composites, the mechanical and thermal properties were analyzed and compared to those of commonly used conti...
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In this study hoop tensile properties of continuous fiber reinforced composites pipes are investigated. The test pipes were manufactured of glass fiber and epoxy resin by filament winding method with three different winding angle... more
In this study hoop tensile properties of continuous fiber reinforced composites pipes are investigated. The test pipes were manufactured of glass fiber and epoxy resin by filament winding method with three different winding angle configurations (10°, 45° and 90°). Three specimens from each model of filament wound pipes with help of split-disk tests were tested and the hoop tensile strengths and modulus of elasticity were determined. From received results it is concluded that, mechanical properties of composite specimens are depended from winding angles in filament winding technology, whereas that bigger winding angle lead to higher hoop tensile properties of filament-wound tubular samples. The optimal values for the hoop tensile strength are obtained for the samples winded with 45° winding angle.
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The aim of this study is to investigate the mechanical properties of continuous glass fiber reinforced composite tubes produced by filament winding technique with three different winding angles. With help of split-disk tests hoop tensile... more
The aim of this study is to investigate the mechanical properties of continuous glass fiber reinforced composite tubes produced by filament winding technique with three different winding angles. With help of split-disk tests hoop tensile properties of selected specimens were determined, where reliable results were obtained with low standard deviations. It was observed that bigger winding angle lead to higher hoop tensile properties of filament wound tubular samples. Also, the effect of reinforcement direction on the mechanical performances of these composites has been presented. Fiber fracture and fiber-matrix debonding is observed to be the dominant failure mechanisms by samples winded with bigger winding angles, whereas delamination in addition to these mechanisms is detected by samples with smaller winding angles. From received results it is concluded that, mechanical properties of composite specimens are depended from winding angles in filament winding technology.With help of co...
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This paper investigates the behaviour of Concrete-Filled FRP Tubes (CFFT) as columns. The experimental programme consists of preparing and testing one steel column acting as control sample and three columns made with GFRP. The GFRP tubes... more
This paper investigates the behaviour of Concrete-Filled FRP Tubes (CFFT) as columns. The experimental programme consists of preparing and testing one steel column acting as control sample and three columns made with GFRP. The GFRP tubes were produced by filament winding method where the amount and orientation of the fibres was changed. The tubes had dimensions of 1000x100 mm (length x diameter) and were filled with C25/30 concrete. The columns were tested under compression and the load was applied at a pace rate of 0.5 mm/min. It was found that the GFRP tubes can efficiently confine the concrete and could be used as alternative material to steel tubes. The steel and GFRP samples developed a high level of strain throughout the testing. The GFRP sample with fibre orientation of 90° failed by FRP rupture, whereas the remaining samples failed by buckling. The orientation of the fibres at 90° was more efficient than orientation of fibres at 45° in terms of increasing the ultimate capaci...
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Influences of chemical oxidation polymerization conditions on the yields of polyaniline powder were investigated. These chemical oxidation polymerization conditions included polymerization time, concentration of HNO3, mol ratio of... more
Influences of chemical oxidation polymerization conditions on the yields of polyaniline powder were investigated. These chemical oxidation polymerization conditions included polymerization time, concentration of HNO3, mol ratio of ammonium persulfate/aniline (APS/AN), and polymerization temperature. If polymerization time, concentration of HNO3, mol ratio of APS/AN, and polymerization temperature were 60 min, 1.0 M, 1.0, and 0°C, respectively, then the yield of emeraldine base form polyaniline powder was around 78.1%. The yield of polyaniline powder increased significantly with the polymerization time, concentration of HNO3, and the mol ratio of APS/AN. A 23 factorial experimental design was applied to study the main, two-factor interaction, and three-factor interaction effects of polymerization time, concentration of HNO3, and mol ratio of APS/AN on the yield of polyaniline powder. According to the definition, the sequence of the main effects on the yield of polyaniline powder, in ascending order, is concentration of HNO3 < mol ratio of APS/AN < polymerization time. The sequence of the two-factor interaction effects on the yield of polyaniline, in ascending order, is concentration of HNO3 vs. mol ratio of APS/AN < polymerization time vs. concentration of HNO3 < polymerization time vs. mol ratio of APS/AN. Meanwhile, the prediction equation by definition is: Ŷ = 0.287+0.145X1+0.091X2+0.121X3+0.023X1X2+0.111X1X3+0.002X2X3+0.003X1X2X3. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1571–1580, 2002