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  • Küçük Resim
    Öğe
    Çoklu çatlayan lifli kompozitlerin birim şekil değişiminin dijital görüntü korelasyonu ile analizi: Parametre etkilerinin değerlendirilmesi
    (TMMOB İnşaat Mühendisleri Odası, 2020) Yıldırım, Tarık; Keskinateş, Muhammer; Gödek, Eren; Tosun Felekoğlu, Kamile; Felekoğlu, Burak; Önal, Okan
    Bu çalışmada çekme yüklemesi altında çoklu çatlak davranışı sergileyen lifli kompozitlerin birim şekil değiştirmeleri geleneksel deformasyon ölçer (LVDT) ve dijital görüntü korelasyonu (DIC) yöntemiyle incelenerek kıyaslanmıştır. DIC yönteminde ışık etkisi (kontrollü aydınlatma varlığı), görüntü çözünürlüğü, alt küme boyutu ve adım aralığı parametreleri ile iki farklı korelasyon yöntemi dikkate alınarak analizler gerçekleştirilmiştir. Uygun alt küme boyutunun seçilmesi ve görüntülerin kontrollü aydınlatma ile yüksek çözünürlük koşullarında alınması durumunda, DIC analizi sonucu elde edilen birim şekil değiştirme değerleri, LVDT’lerden elde edilen değerler ile örtüşmektedir.
  • [ X ]
    Öğe
    Development of flaw tolerant fiber reinforced cementitious composites with calcined kaolin
    (Elsevier Ltd, 2017) Gödek, Eren; Tosun Felekoğlu, Kamile; Keskinateş, Muhammer; Felekoğlu, Burak
    Flaws naturally occur in the structure of the cementitious composites or concrete. When brittle composites (ceramics, concrete) are loaded up to their ultimate capacity, micro-cracks initiate and propagate from these flaws in a sudden manner. As an exception, Engineered Cementitious Composite (ECC) surprisingly has an ability to transform its flaw structure into an advantage by exhibiting multiple cracking behavior with improved mechanical properties. On the other hand, presence of polymeric fibers in ECC design can rise some challenging situations such as workability and fiber distribution. Both flaw structure and workability of ECC can be improved by using inert and pozzolanic powders in matrix phase. In this study, five sets of composites were prepared at three different water to cement and fine material to cement ratios by using high tenacity polypropylene fibers (HTPP). Calcined kaolin was used for the first time in order to improve fresh state properties and fiber distribution performance of composites. The flaw tolerances of composites were studied by adding polyethylene beads (diameter of 3 mm by 6% of total volume) as artificial flaws into matrix. Results showed that, flaw tolerant ECCs exhibiting saturated multiple cracking with a flexural strength of 10.9 MPa and a deflection capacity of 13.2 mm can be prepared successfully by using HTPP fibers and calcined kaolin. © 2017 Elsevier B.V.
  • [ X ]
    Öğe
    Role of matrix structure and flaw size distribution modification on deflection hardening behavior of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC)
    (Central South University of Technology, 2019) Tosun Felekoğlu, Kamile; Gödek, Eren
    The multiple cracking and deflection hardening performance of polyvinyl alcohol fiber reinforced engineered cementitious composites (PVA-ECC) under four-point flexural loading have been investigated. Matrices with different binder combinations and W/B ratios (from 0.44 to 0.78) providing satisfactory PVA fiber dispersion were specially designed. Effect of pre-existing flaw size distribution modification on deflection hardening behavior was comparatively studied by adding 3 mm diameter polyethylene beads into the mixtures (6% by total volume). Natural flaw size distributions of composites without beads were determined by cross sectional analysis. The crack number and crack width distributions of specimens after flexural loading were characterized and the possible causes of changes in multiple cracking and deflection hardening behavior by flaw size distribution modification were discussed. Promising results from the view point of deflection hardening behavior were obtained from metakaolin incorporated and flaw size distribution modified PVA-ECCs prepared with W/B=0.53. The dual roles of W/B ratio and superplasticizer content on flaw size distribution, cracking potential and fiber-matrix bond behavior were evaluated. Flaw size distribution modification is found beneficial in terms of ductility improvement at an optimized W/B ratio.