This study examines the impact of three factors on the tensile and compressive behaviour of 3D-pr... more This study examines the impact of three factors on the tensile and compressive behaviour of 3D-printed parts: (1) the addition of short carbon fibres to the nylon filament used for 3D printing, (2) the infill pattern, and (3) the speed at which the materials are strained during testing. The results show that adding carbon fibres to the nylon filament reduces variability between tests and emphasises the effect of print orientation. When the infill pattern is aligned with the direction of loading, the tensile strength of all samples increases, with the largest increase of 100% observed in the carbon fibre-reinforced samples, compared to a 37% increase in the strength of nylon samples. The carbon fibre-reinforced samples are also highly dependent on strain rate, with a 60% increase in tensile strength observed at a faster testing speed of 300 mm/min (9 min -1 ) compared to 5 mm/min (0.15 min -1 ). Nylon samples show a decrease of approximately 10% in tensile strength at the same increased speed. The compressive strength of the composite samples increases by up to 130% when the print path is parallel to the loading direction. Increases of up to 50% are observed in the compressive modulus of the composite samples at a test speed of 255 mm/min (9 min -1 ) compared to 1.3 mm/min (0.05 min -1 ). Similar trends are not seen in pure nylon samples. This study is the first to report on the variation of Poisson's ratio of short carbon fibre-reinforced 3D-printed parts. The results show increases of up to 34% and 76% in the tensile and compressive Poisson's ratios, respectively, when printing parameters are altered. The findings from this research will contribute to the design and numerical modelling of 3D-printed composites.
Interest to crash response of vehicle parts is increasing closely related with their importance f... more Interest to crash response of vehicle parts is increasing closely related with their importance for safety of passengers. In low velocity crash case, integration of foams to tubular systems shows positive effect on the performance. While foams are classified stochastic micro lattice structures, recently, dynamic behaviour of lattices in macro size are being researched with 3D printing technique. In addition to conventional macro lattices showing positive Poisson's ratio have good energy absorbing capabilities, with only geometrical modification macro lattices with negative Poisson's ratio can be created and have better energy absorbing capability than conventional ones. In this study, in different dimensions, blocks of anti-tetrachiral metallic lattices exhibiting negative Poisson's ratio, are modelled. Crushing behaviour of them is investigated under low-velocity impact using explicit and implicit FEA tools. With the results of this study, suitable width-lenght ratio of macro level anisotropic anti-tetrachiral lattices will be able to classified. In addition to that, force-time behaviour in different impact velocities will be able to understood to use in not only tubular systems but also in sandwich structures as core part.
Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their... more Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their potential superior energy absorption capability. Because of their negative Poisson's ratio, auxetics behave counterintuitively and contract orthogonally under an applied compressive force, resulting in a densification of material in the vicinity of the applied load. This study investigates three cellular structures and compares their compressive energy absorbing characteristics under in-plane and axial loading conditions. Three unit cell topologies are considered; a conventional hexagonal, re-entrant and double arrowhead auxetic structures. The samples were additively manufactured using two different materials, a conventional Nylon and a carbon fibre reinforced composite alternative (Onyx). Finite element simulations are experimentally validated under out of and in-plane loading conditions and the double arrowhead (auxetic) structure is shown to exhibit comparatively superior energy absorption. For the carbon fibre reinforced material, Onyx, the specific energy absorbed by the double arrowhead geometry was 125% and 244% greater than the hexagonal (non-auxetic) and re-entrant (auxetic) structures respectively.
Bu çalışmada mühendislik uygulamalarında pek çok kullanım alanı olan katmanlı ... more Bu çalışmada mühendislik uygulamalarında pek çok kullanım alanı olan katmanlı kompozit plakların nonlineer dinamik davranışları parametrik olarak incelenmiştir. Çalışma esnasında dikdörtgen plak yapılar seçilmiştir. Plaklar konsol plak olarak mesnetlenmiş ve anlık basınç yükü altında test edilmiştir. Katmanlı kompozit konsol bir plağın lineer olmayan dinamik denklemleri türetilmiş ve çözülmüştür. Hareketin dinamik denklemleri virtüel iş ilkesi kullanılarak elde edilmiştir. Geometrik nonlineerlik etkileri ince plaklar için von Kármán büyük yer değiştirmeler teorisi kullanılarak hesaba katılmıştır. Uzay bölgesi için yaklaşık bir çözüm kabul edilmiştir. Zaman bölgesinde lineer olmayan diferansiyel denklemleri elde etmek için Galerkin yöntemi kullanılmıştır. Galerkin yönteminde kullanılan en uygun yaklaşım fonksiyon...
Katmanlı kompozit yapılar, mukavemet/ağırlık oranlarının yüksek olması nedeniyle havacılıkta yoğu... more Katmanlı kompozit yapılar, mukavemet/ağırlık oranlarının yüksek olması nedeniyle havacılıkta yoğun kullanım alanı bulmaktadır. Bu yapılar, ses üstü süratlerde uçan hava taşıtlarında sonik patlamalara veya civarlarında meydana gelen patlamalardan dolayı anlık basınç yüklerine maruz kalabilmektedirler. Söz konusu yapı elemanları ani yükler altında büyük hasarlar görebilmektedir. Bu yüzden yapıların bu yüklemeler altında nasıl davranacağının önceden bilinmesi önemli bir konudur. Bu tez Devlet Planlama Teşkilatının 901341998k121980 numaralı "Yapılar Üzerindeki Patlama Etkilerinin Araştırılması" adlı projesinin bir parçasıdır. Sonuçların bir kısmı bu proje kapsamında yayınlanan raporda da sunulmuştur. Tezin her aşamasında rehberliğini ve değerli vaktini benden esirgemeyen sayın hocam Prof. Dr. Zahit MECİTOĞLU'na, fikirleri ile tezin gelişmesine katkıda bulunan hocalarım Prof. Dr. Süleyman TOLUN ve Prof. Dr. Mehmet Hakkı OMURTAG'a ve yetişmemde emeği olan tüm hocalarıma, ihtiyacım olan vaktin sağlanmasında her türlü kolaylığı gösteren değerli komutanım Hv.Müh.Yb. İsmail KILINÇ'a ve onun nezdinde sıralı tüm komutanlarıma en içten saygı ve sevgilerimi sunarım. Çalışmalarım esnasında benden hiçbir zaman desteğini esirgemeyen sevgili eşim Selcen YAROĞLU KAZANCI'ya teşekkür ederim.
The dynamic behaviors of laminated flat and tapered composite plates subjected to blast loads are... more The dynamic behaviors of laminated flat and tapered composite plates subjected to blast loads are investigated. Numerical solution techniques and their computational applications which are proposed before in the literature are summarized to show the accuracy and prediction of the response of blast loaded laminated composite plates with and without damping effects. It was shown the effect of damping is not significantly effective for the first peak response. However, it is considerable with the second peak and it becomes greater as time increases. The effect of chosen displacement functions for the approximate-numerical methods is indicated. Deflection and strain–time histories of plates obtained from experiment, finite element, and approximate-numerical methods are compared and found a good agreement.
This study examines the impact of three factors on the tensile and compressive behaviour of 3D-pr... more This study examines the impact of three factors on the tensile and compressive behaviour of 3D-printed parts: (1) the addition of short carbon fibres to the nylon filament used for 3D printing, (2) the infill pattern, and (3) the speed at which the materials are strained during testing. The results show that adding carbon fibres to the nylon filament reduces variability between tests and emphasises the effect of print orientation. When the infill pattern is aligned with the direction of loading, the tensile strength of all samples increases, with the largest increase of 100% observed in the carbon fibre-reinforced samples, compared to a 37% increase in the strength of nylon samples. The carbon fibre-reinforced samples are also highly dependent on strain rate, with a 60% increase in tensile strength observed at a faster testing speed of 300 mm/min (9 min -1 ) compared to 5 mm/min (0.15 min -1 ). Nylon samples show a decrease of approximately 10% in tensile strength at the same increased speed. The compressive strength of the composite samples increases by up to 130% when the print path is parallel to the loading direction. Increases of up to 50% are observed in the compressive modulus of the composite samples at a test speed of 255 mm/min (9 min -1 ) compared to 1.3 mm/min (0.05 min -1 ). Similar trends are not seen in pure nylon samples. This study is the first to report on the variation of Poisson's ratio of short carbon fibre-reinforced 3D-printed parts. The results show increases of up to 34% and 76% in the tensile and compressive Poisson's ratios, respectively, when printing parameters are altered. The findings from this research will contribute to the design and numerical modelling of 3D-printed composites.
Interest to crash response of vehicle parts is increasing closely related with their importance f... more Interest to crash response of vehicle parts is increasing closely related with their importance for safety of passengers. In low velocity crash case, integration of foams to tubular systems shows positive effect on the performance. While foams are classified stochastic micro lattice structures, recently, dynamic behaviour of lattices in macro size are being researched with 3D printing technique. In addition to conventional macro lattices showing positive Poisson's ratio have good energy absorbing capabilities, with only geometrical modification macro lattices with negative Poisson's ratio can be created and have better energy absorbing capability than conventional ones. In this study, in different dimensions, blocks of anti-tetrachiral metallic lattices exhibiting negative Poisson's ratio, are modelled. Crushing behaviour of them is investigated under low-velocity impact using explicit and implicit FEA tools. With the results of this study, suitable width-lenght ratio of macro level anisotropic anti-tetrachiral lattices will be able to classified. In addition to that, force-time behaviour in different impact velocities will be able to understood to use in not only tubular systems but also in sandwich structures as core part.
Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their... more Auxetic cellular structures have the potential to revolutionise sandwich panel cores due to their potential superior energy absorption capability. Because of their negative Poisson's ratio, auxetics behave counterintuitively and contract orthogonally under an applied compressive force, resulting in a densification of material in the vicinity of the applied load. This study investigates three cellular structures and compares their compressive energy absorbing characteristics under in-plane and axial loading conditions. Three unit cell topologies are considered; a conventional hexagonal, re-entrant and double arrowhead auxetic structures. The samples were additively manufactured using two different materials, a conventional Nylon and a carbon fibre reinforced composite alternative (Onyx). Finite element simulations are experimentally validated under out of and in-plane loading conditions and the double arrowhead (auxetic) structure is shown to exhibit comparatively superior energy absorption. For the carbon fibre reinforced material, Onyx, the specific energy absorbed by the double arrowhead geometry was 125% and 244% greater than the hexagonal (non-auxetic) and re-entrant (auxetic) structures respectively.
Bu çalışmada mühendislik uygulamalarında pek çok kullanım alanı olan katmanlı ... more Bu çalışmada mühendislik uygulamalarında pek çok kullanım alanı olan katmanlı kompozit plakların nonlineer dinamik davranışları parametrik olarak incelenmiştir. Çalışma esnasında dikdörtgen plak yapılar seçilmiştir. Plaklar konsol plak olarak mesnetlenmiş ve anlık basınç yükü altında test edilmiştir. Katmanlı kompozit konsol bir plağın lineer olmayan dinamik denklemleri türetilmiş ve çözülmüştür. Hareketin dinamik denklemleri virtüel iş ilkesi kullanılarak elde edilmiştir. Geometrik nonlineerlik etkileri ince plaklar için von Kármán büyük yer değiştirmeler teorisi kullanılarak hesaba katılmıştır. Uzay bölgesi için yaklaşık bir çözüm kabul edilmiştir. Zaman bölgesinde lineer olmayan diferansiyel denklemleri elde etmek için Galerkin yöntemi kullanılmıştır. Galerkin yönteminde kullanılan en uygun yaklaşım fonksiyon...
Katmanlı kompozit yapılar, mukavemet/ağırlık oranlarının yüksek olması nedeniyle havacılıkta yoğu... more Katmanlı kompozit yapılar, mukavemet/ağırlık oranlarının yüksek olması nedeniyle havacılıkta yoğun kullanım alanı bulmaktadır. Bu yapılar, ses üstü süratlerde uçan hava taşıtlarında sonik patlamalara veya civarlarında meydana gelen patlamalardan dolayı anlık basınç yüklerine maruz kalabilmektedirler. Söz konusu yapı elemanları ani yükler altında büyük hasarlar görebilmektedir. Bu yüzden yapıların bu yüklemeler altında nasıl davranacağının önceden bilinmesi önemli bir konudur. Bu tez Devlet Planlama Teşkilatının 901341998k121980 numaralı "Yapılar Üzerindeki Patlama Etkilerinin Araştırılması" adlı projesinin bir parçasıdır. Sonuçların bir kısmı bu proje kapsamında yayınlanan raporda da sunulmuştur. Tezin her aşamasında rehberliğini ve değerli vaktini benden esirgemeyen sayın hocam Prof. Dr. Zahit MECİTOĞLU'na, fikirleri ile tezin gelişmesine katkıda bulunan hocalarım Prof. Dr. Süleyman TOLUN ve Prof. Dr. Mehmet Hakkı OMURTAG'a ve yetişmemde emeği olan tüm hocalarıma, ihtiyacım olan vaktin sağlanmasında her türlü kolaylığı gösteren değerli komutanım Hv.Müh.Yb. İsmail KILINÇ'a ve onun nezdinde sıralı tüm komutanlarıma en içten saygı ve sevgilerimi sunarım. Çalışmalarım esnasında benden hiçbir zaman desteğini esirgemeyen sevgili eşim Selcen YAROĞLU KAZANCI'ya teşekkür ederim.
The dynamic behaviors of laminated flat and tapered composite plates subjected to blast loads are... more The dynamic behaviors of laminated flat and tapered composite plates subjected to blast loads are investigated. Numerical solution techniques and their computational applications which are proposed before in the literature are summarized to show the accuracy and prediction of the response of blast loaded laminated composite plates with and without damping effects. It was shown the effect of damping is not significantly effective for the first peak response. However, it is considerable with the second peak and it becomes greater as time increases. The effect of chosen displacement functions for the approximate-numerical methods is indicated. Deflection and strain–time histories of plates obtained from experiment, finite element, and approximate-numerical methods are compared and found a good agreement.
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