Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
Browse
3 results
Search Results
Doctoral Thesis Effects of Fiber Discontinuity in Fiber Reinforced Polymer Matrix Composites(01. Izmir Institute of Technology, 2024) Kılıçoğlu, Ahmet Süha; Tanoğlu, MetinBu tez, cam elyaf takviyeli kompozit plakaların mekanik davranışları üzerindeki yapısal süreksizliklerin etkisini araştırmaktadır. Bu süreksizlikler, kompozit mikro yapısındaki geometrik kısıtlamalar nedeniyle katmanlar arası (inter-ply) ve katman içi (intra-ply) olarak sınıflandırılmıştır. Süreksizlikler kürleme öncesi ilave edilmiştir. İlk olarak, malzeme özellikleri kupon seviyesinde testlerle belirlenmiştir. Daha sonra, bilgisayarlı sayısal kontrol kesimi ve manuel uygulama ile katman içi süreksizlikler oluşturularak iki tam ölçekli kompozit numune üretilmiştir. Bu numunelerin mekanik özellikleri, servo-hidrolik aktüatörler kullanılarak üç nokta eğme testi ile değerlendirilmiştir. Deneysel test sonuçları, kesitsel fiber hacim oranı değerlendirilerek CAE analiz tahminleriyle karşılaştırılmış ve yerel süreksizliklerin mikroskopik analizi ile desteklenmiştir. Çalışma, yer değiştirme bölgelerinin reçine açısından zengin alanlara yol açtığını ve ekzotermik kürleme sürecinin reçinenin rengini şeffaftan sarıya dönüştürdüğünü, bunun da mekanik dayanıklılığı azalttığını ortaya koymuştur. Ayrıca, fiber süreksizlikleri ve reçine boşlukları, cam elyaf takviyeli polimer (GFRP) kompozit yaprak yayların yapısal bütünlüğünü olumsuz etkilemektedir. Üretim sürecindeki düzensizlikler, malzeme dayanıklılığını ve boşluk doldurma kapasitesini etkilemektedir. Isı transferi ile ilgili sorunların ele alınması, reçine boşluklarını ve ısı kaynaklı çatlakları azaltmak için önemlidir. Bulgular, iç yapısal kusurlar ve reçine boşlukları arasındaki ilişkiyi anlamanın, kiriş tasarımı ve üretim süreçlerini önemli ölçüde iyileştirebileceğini önermektedir. Bu çalışma, mühendislik uygulamalarında kompozit malzemelerin yapısal performansını ve güvenilirliğini optimize etmek için kritik bilgiler sunmaktadır.Doctoral Thesis Examination of Fatigue Behaviour of Carbon Fiber Reinforced Polymer Composites(Izmir Institute of Technology, 2021) Güneş, Mehmet Deniz; Tanoğlu, Metin; Tanoğlu, MetinThis PhD thesis aims to examine the fatigue behavior of sandwich panels fabricated from adhesively bonded aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Initially, sandwich panels were manufactured with three different amounts of adhesive in their interface. Static flexural behavior was characterized with three-point bending tests. Load-displacement curves and static flexural failure modes were obtained and utilized to compare the static flexural behavior of fabricated sandwich. Fatigue behavior of sandwich panels were characterized with the three-point bending fatigue tests. Stiffness degradation curves were used to identify the failure cycles of sandwich panels. Fatigue failure modes and S-N curves were obtained to find out the effect of amount of adhesive on fatigue behavior of sandwich panels. The other study within this thesis was made to investigate the effect of core thickness on the fatigue behavior of the sandwich panels based on aluminum honeycomb core and carbon fiber reinforced polymer composite face sheets. Sandwich panels were fabricated by using three different aluminum honeycomb core thickness. Static flexural tests were carried out to determine the static flexural behavior of developed sandwich panels. Load-displacement curves and failure modes were obtained from flexural tests. In addition to this, core shear tests were performed to investigate the core shear strength of the honeycomb cores with different core thickness. Effect of core thickness on fatigue behavior of sandwich panels were characterized with fatigue failure modes and S-N curves. Stiffness degradation method was used to determine the fatigue failure cycles of the sandwich panels.Doctoral Thesis Modeling, Simulation and Analysis of Type-Iii Composite Overwrapped Pressure Vessels for High-Pressure Gas Storage(Izmir Institute of Technology, 2019) Kangal, Serkan; Tanoğlu, MetinIn this thesis, multi-layered composite overwrapped pressure vessels (COPVs) for high-pressure gaseous storage were modeled by finite element (FE) method and manufactured by filament winding technique. Two liners with distinct geometries were utilized for containing gas and forming a basis for composite filament winding. 34CrMo4 steel as a load-sharing metallic liner was selected for investigation of hybridization effects. Glass and carbon filaments were overwrapped to the liner with a winding angle of [±11°/90°2]3 to obtain a fully overwrapped composite reinforced vessel with non-identical front and back dome endings. The other type of liner was made of Al 6061-T6 and chosen for containing high-pressure gas such as hydrogen and its better strength-to-weight ratio suitable for onboard applications. Doily layers were implemented to the structure for inducing safe burst modes and increasing the burst pressure of the aluminum-based COPVs. All vessels were hydrostatically loaded with increasing internal pressure up to the burst pressure. The mechanical performances of pressure vessels were investigated by both experimental and numerical approaches. In numerical approaches, FE analysis was performed featuring a simple progressive damage model available in ANSYS for composite section. The metal liners were modeled as elastic-plastic material with two different hardening approaches; bilinear and multilinear hardening. The results from steel based COPV indicate that the FE model provided a good correlation between experimental and numerical strain results for the vessels with indications that the composite interlayer hybridization has positive effects on radial deformation of the COPVs. The constructed model for aluminum-based COPVs was also able to predict experimental burst pressures within a range of 8%.