Hibrit fiber kompozit malzemelerin mekanik özelliklerinin deneysel olarak incelenmesi = Experimental investigation of mechanical properties of hybrid fiber composite materials

Abstract

Mekanik özelliklerin iyileştirilmesi ve maliyetlerin azaltılması için geliştirilen yeni imalat teknolojileri ve alternatif malzemelerin kullanımı en önemli araştırma konularındandır. Savunma sanayi, havacılık sektörü, otomotiv endüstrisi, uzay teknolojileri ve enerji gibi pek çok sektöre ait çalışmalarda kullanılan mevcut malzemelere alternatif malzeme olarak araştırılan malzemelerden biri de hibrit kompozit malzemelerdir. Hibrit kompozitler, günümüzde farklı elyaf türlerinin takviye elemanı olarak kullanılabilmesi ile ilgi çekici hale gelmiştir. Hibrit kompozitler farklı takviye malzemelerinin sahip oldukları özellikleri tek bir yapıda bulundurdukları için mekanik özellikleri üstünlük göstermektedir. Bu malzemelerin özellikleri ile ilgili sürekli araştırma yapılmaktadır. Bu malzemelerin performanslarını arttırmak için farklı elyaflar, farklı diziliş sıraları aynı kompozit yapıda kullanılarak hibrit kompozit yapılar elde edilecektir. Bu çalışmada takviye malzemesi olarak aramid fiber, karbon fiber ve cam fiber kullanılmıştır. Karbon fiber olarak plain dokuma ve yoğunluğu 200 g/mm2 olan serisi kullanılmıştır. Aramid fiber olarak twill dokuma ve yoğunluğu 170 g/mm2 olan serisi kullanılmıştır. Cam fiber olarak twill dokuma ve yoğunluğu 280 g/mm2 olan serisi kullanılmıştır. Epoksi reçine ağırlıkça 100/40 oranında sertleştirici ile homojen bir karışım hazırlanmıştır. Karbon fiber, cam fiber ve aramid fiberler epoksi reçinesi ile birleştirilerek farklı kombinasyonlarda 6 adet hibrit plaka oluşturulmuştur. Hazırlanmış olan hibrit yapıdaki kompozit plakalar 6 katmanlıdır. Oluşturulan hibrit plakalar elle yatırma yöntemi ile üretilmiştir. Karbon fiber, aramid fiber ve cam fiberler ile oluşturulan farklı kombinasyonlardaki 6 hibrit plaka 1 gün boyunca oda sıcaklığında bekletilmiştir. Oluşturulan hibrit plakalar CNC dikey işleme merkezinde kesilerek numuneler elde edilmiştir. Bu çalışmada el yatırma yöntemi ile cam, karbon ve aramid fiberlerin farklı diziliş sıraları için mekanik özellikleri incelenmiştir. Mekanik özellikleri incelemek amacıyla çekme, üç nokta eğme ve darbe deneyleri gerçekleştirilmiştir. Çekme testinde gerilme-birim şekil değiştirme grafikleri oluşturulmuştur. Üç nokta eğme testinde kuvvet-deplasman grafikleri oluşturulmuştur. Darbe testinde ise farklı hibrit kompozit yapıların darbe dayanımları incelenmiştir. Çekme deneyi sonuçları incelendiğinde 3K+3C numunesi en yüksek çekme dayanımına, 2K+2C+2A numunesi ise en düşük çekme dayanımına sahip olduğu görülmüştür. Elastiklik modülü en yüksek olan numune 3K+3C, en düşük olan numune ise 3A+3C numunesinde elde edilmiştir. Eğme deneyi sonuçları incelendiğinde en yüksek yük taşıma kapasitesine sahip olan numune 2C+2A+2K kombinasyonuna, en düşük yük taşıma kapasitesine sahip olan numune ise 3A+3C kombinasyonuna aittir. Eğme deneyinde kombinasyonların diziliş sırasının yanında kombinasyonların ters çevrilmesi mekanik özellikleri etkilediği görülmüştür. xx Darbe deneyinden elde edilen verilerde ise darbe enerjisi en yüksek olan kombinasyon 2K+2C+2A, en düşük darbe enerjisine sahip kombinasyon ise 3K+3C'dir. Elde edilen sonuçlara göre farklı fiber türlerinin diziliş sırasının hibrit kompozit malzemeler üzerinde etkisinin olduğu görülmüştür.

The use of new manufacturing technologies and alternative materials developed to improve mechanical properties and reduce costs are among the most important research topics. Hybrid composite materials are one of the materials researched as an alternative material to existing materials used in studies in many sectors such as the defense industry, aerospace industry, automotive industry, space technologies and energy. Hybrid composites have become interesting with the use of different fiber types as reinforcement elements today. Hybrid composites have superior mechanical properties because they contain the properties of different reinforcement materials in a single structure. Hybrid composites formed by two or more different fibers in the same matrix form a new fiber-reinforced composite material group, unlike other composite types. Hybrid composites have better mechanical properties in all respects than composites consisting of only a single fiber in the matrix. In hybrid composites where very different matrix and fiber combinations are used, the most preferred hybrid is the type consisting of a polymer-based matrix that combines carbon fiber and glass fiber. Carbon fiber, with its stronger and higher rigidity, provides low density reinforcement, but is expensive. However, although glass fiber is cheap and easily available, it does not have the strength values provided by carbon fiber. The combination of glass fiber and carbon fiber provides stronger, tougher and higher impact resistance. This feature; can be obtained at a lower cost than all carbon fiber or all glass fiber reinforced plastics. Hybrid composites are more advanced than other fiber-reinforced composites and have a wider range of potential applications. Two different fibers, which have a significant impact on the overall properties of the composite, can be combined in many different ways. For example, both types of fibers can be mixed together and placed all in the same direction, or it can be prepared by sequentially placing layers, each containing a single type of fiber, one after the other. The properties of almost all hybrid composites are direction dependent. When hybrid composites are subjected to a tensile type of stress, damage usually does not occur suddenly. First, the reinforcing element with a high strength value meets the load, and then this load is transferred to the other reinforcing elements. Matrix phase fracture also occurs after all the reinforcement phases have undergone fracture. Ultimately, damage to the composite occurs simultaneously with damage to the matrix. There is constant research on the properties of these materials. In order to increase the performance of these materials, hybrid composite structures will be obtained by using different fibers in the same composite structure. In this study, aramid fiber, carbon fiber and glass fiber were used as reinforcement materials. Among the properties of carbon fibers, we can count high impact resistance, abrasion resistance and fatigue resistance. Carbon fibers are resistant to high temperatures. The disadvantage is that it causes impact resistance problems due to the limited elongation properties of its fibers. Aramid fiber is lighter and more rigid than glass fiber. Aramid fibers have low compressive strength. Therefore, it finds usage area by creating hybrid composite with carbon fiber. Due to their low compressive strength, aramid reinforced epoxy matrix composites also have poor moisture retention. The basis of glass fiber is silicon dioxide (SiO2). However, it can also contain oxides of elements such as aluminum, calcium, sodium boron and iron in a certain amount. Glass fibers have high resistance to chemicals and poor moisture absorption properties. Glass fiber is an inexpensive reinforcing material and is commonly used in plastic-based composites. Plain weave and the series with a density of 200 g/mm2 were used as carbon fiber. Twill weaving and the series with a density of 170 g/mm2 are used as aramid fiber. Twill weaving and the series with a density of 280 g/mm2 were used as glass fiber. A homogeneous mixture was prepared with epoxy resin and hardener at a weight ratio of 100/40. Carbon fiber, glass fiber and aramid fibers were combined with epoxy resin to form 6 hybrid plates in different combinations. The created hybrid plates are 400×400 mm in size. The prepared hybrid composite plates have 6 layers. The created hybrid plates were produced by hand lay-up method. 6 hybrid plates in different combinations formed with carbon fiber, aramid fiber and glass fibers were kept at room temperature for 1 day. The created hybrid plates were cut in CNC vertical machining center and samples were obtained. In this study, the mechanical properties of glass, carbon and aramid fibers for different arrays were investigated by hand lay-up method. The purpose of the tensile test; To determine the elastic and plastic behavior of materials under static load. For this, a circular or rectangular test piece with dimensions in accordance with the standards; By connecting to the pulling device, axial and variable forces are applied. The bending test is performed to determine the design information about the strength of the material and to determine the mechanical properties of the material against bending. Izod impact test determines the energy consumed to break the sample with the impact of a hammer at the tip of a pendulum at a certain height from a vertical and cantilevered gripping jaw and the effect of multiaxial stresses occurring at the bottom of the notch. Tensile, three-point bending and impact tests were carried out to examine the mechanical properties. Stress-strain graphs were created in the tensile test. Forcedisplacement graphs were created in the three-point bending test. In the impact test, the impact strength of different hybrid composite structures was investigated. The tensile test was carried out on a Dartec brand test device with a load capacity of 30 tons. Tensile test was performed according to ASTM D3039 standard. In the tensile test, samples of 250x25 mm dimensions were prepared from each combination. In the tensile test, the samples were tested with a tensile speed of 2 mm/min. Three point bending tests were carried out on a Zwick/Roell test device with a load capacity of 5 tons. Test samples of 125x13 mm dimensions were prepared from each combination in accordance with ASTM D790 standard. In the three-point bending test, the samples were tested with a bending speed of 2 mm/min. Izod impact test was performed according to ASTM 4812 standard. Samples of 65x13 mm dimensions were prepared from each combination. Alerge brand izod impact tester was used. The experiment was carried out with a 5.5 Joule hammer. When the tensile test results were examined, it was seen that the 3K+3C sample had the greatest tensile strength with a tensile strength of 351.47 MPa. The 3A+3C sample is in second place with a tensile strength of 301.03 MPa. The 2K+2C+2A sample has the lowest tensile strength of 225.47 MPa. The sample with the highest modulus of elasticity was 3K+3C, and the sample with the lowest was obtained from the 3A+3C sample. The combination of 3K+3C with a high modulus of elasticity is more rigid than other combinations. In the bending test, the highest load carrying capacity was obtained with 259.41 N in combination with 2C+2A+2K. The lowest load carrying capacity was observed in the 3A+3C sample with 87.74 N. In the bending test, it was seen that the order of the combinations as well as the inversion of the combinations affected the mechanical properties. In the data obtained from the impact test, the combination with the highest impact energy is 2K+2C+2A, and the combination with the lowest impact energy is 3K+3C. Impact resistance is high in groups with aramid fiber in impact tests. The reason for this is thought to be the high tensile strength and percent elongation values of aramid fiber. According to the results obtained, it was seen that the order of the different fiber types had an effect on the hybrid composite materials.