Publication: Static and dynamic behavior of polymer based biocomposites
Abstract
Bu tezin birden fazla amacı bulunmaktadır. Birinci amaç, termoplastik keçe biyokompozitlerin mekanik olarak karakterizasyonudur. 4 farklı tip keçe sıcak preslenmiş, su jeti ile kesilmiş ve mekanik özelliklerini belirlemek için mekanik olarak test edilmiştir. Tüm keçeler, farklı polimer elyaf matrisleri ile takviye malzemesi olarak kısa kenevir elyafları kullanmaktadır. Bu matrisler polipropilen, geri dönüştürülmüş polipropilen, polilaktik asit ve düşük erime noktalı polyester elyaflardır.İkinci amaç, tek yönlü prepreg katmanlı biyokompozitlerin eklenmesiyle kenevir – polipropilen biyokompozitte mekanik performanstaki artışı görmektir. Tek yönlü prepregler, takviye olarak uzun keten lifleri ve matris malzemesi olarak polipropilen kullanmaktadır. 7 farklı tasarım sıcak preslenmiş, su jeti ile işlenmiş ve mekanik olarak test edilmiştir. Bu tasarımlar, keçeye göre farklı pozisyonlarda yerleştirilmiş farklı sayıda prepreg katmanından oluşmaktadır.4 keçe ve 7 tek yönlü keçe tasarımı ile toplam 11 farklı biyokompozit test edilmiştir. Bu malzemeler üzerinde 7 adet mekanik test tamamlanmıştır. Bu testlerden 4 tanesi statik testler olup çekme, basma, eğilme ve kesme testleridir. Geri kalan testler, ölçü aletli Charpy darbe, düşen ağırlık darbe ve yüksek hızlı darbe testleri olan dinamik testlerdir. Bu testlere ek olarak, yüksek hızlı darbe testlerinde elde edilen sonuçları simüle etmek için bir malzeme üzerinde sayısal analizler yapılmıştır.Mekanik karakterizasyon testleri tamamlanmış ve tüm biyokompozitlerin statik ve dinamik davranışları incelenmiştir. Keçeler ve tek yönlü prepreg katkılı keçelerin test sonuçları, kendi tasarım grupları ve diğer tasarım grupları ile karşılaştırılarak yüksek mukavemet ve kabul edilebilir ağırlıkta en uygun biyokompozitin bulunması sağlanmıştır. Keçelere tek yönlü prepreg biyokompozitlerin eklenmesiyle mekanik özelliklerde ciddi bir artış görülmüştür. Sayısal çalışmalar yapılmış ve hasar davranışlarının deneylerde karşılaşılan hasarlar ile benzer olduğu görülmüştür.
This thesis has multiple aims with the first one being the mechanical characterization of thermoplastic felt biocomposites. 4 different types of felts have been hot pressed, water jet machined and mechanically tested to determine their mechanical characteristics. All felts use short hemp fibers as reinforcement material with different polymer fiber matrices. These matrices are polypropylene, recycled polypropylene, polylactic acid and low melt polyester fibers.Second aim is to reveal the improvement in mechanical performance in the hemp – polypropylene biocomposite with the addition of unidirectional prepreg layers. Unidirectional prepregs use long flax fibers as reinforcement material and polypropylene as matrix material. 7 different designs have been hot pressed, water jet machined and mechanically tested. These designs consist of different number of prepreg layers placed in different positions relative to the felt.With 4 felts and 7 unidirectional-felt designs, a total of 11 different biocomposites were tested. 7 mechanical tests were carried out on these materials. 4 of these tests are static tests, namely, tensile, compression, flexural and shear tests. Remaining tests are dynamic tests, which are instrumented Charpy impact, drop weight impact and high velocity impact tests. In addition to these tests, numerical analyses have been conducted on one material to simulate the results obtained in high velocity impact tests.The mechanical characterization tests have been completed and static and dynamic behaviors of all biocomposites have been investigated. Test results of felts and unidirectional prepreg added felts were compared with their own design groups and other design groups to find the most suitable biocomposite with high strength and acceptable weight. A drastic increase in the mechanical properties were seen with the addition of unidirectional prepreg biocomposites to felts. The numerical studies were carried out and the failure behaviors were found to be similar as those seen in experiments.
This thesis has multiple aims with the first one being the mechanical characterization of thermoplastic felt biocomposites. 4 different types of felts have been hot pressed, water jet machined and mechanically tested to determine their mechanical characteristics. All felts use short hemp fibers as reinforcement material with different polymer fiber matrices. These matrices are polypropylene, recycled polypropylene, polylactic acid and low melt polyester fibers.Second aim is to reveal the improvement in mechanical performance in the hemp – polypropylene biocomposite with the addition of unidirectional prepreg layers. Unidirectional prepregs use long flax fibers as reinforcement material and polypropylene as matrix material. 7 different designs have been hot pressed, water jet machined and mechanically tested. These designs consist of different number of prepreg layers placed in different positions relative to the felt.With 4 felts and 7 unidirectional-felt designs, a total of 11 different biocomposites were tested. 7 mechanical tests were carried out on these materials. 4 of these tests are static tests, namely, tensile, compression, flexural and shear tests. Remaining tests are dynamic tests, which are instrumented Charpy impact, drop weight impact and high velocity impact tests. In addition to these tests, numerical analyses have been conducted on one material to simulate the results obtained in high velocity impact tests.The mechanical characterization tests have been completed and static and dynamic behaviors of all biocomposites have been investigated. Test results of felts and unidirectional prepreg added felts were compared with their own design groups and other design groups to find the most suitable biocomposite with high strength and acceptable weight. A drastic increase in the mechanical properties were seen with the addition of unidirectional prepreg biocomposites to felts. The numerical studies were carried out and the failure behaviors were found to be similar as those seen in experiments.