Yazar "Kefal, Adnan" seçeneğine göre listele

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    A novel isogeometric beam element based on mixed form of refined zigzag theory for thick sandwich and multilayered composite beams
    (Elsevier Sci Ltd, 2019) Kefal, Adnan; Hasim, Kazim Ahmet; Yildiz, Mehmet
    This study presents a highly accurate, computationally efficient, and novel isogeometric beam element, named as IG - RZT((m)), whose formulation is derived by using the kinematic assumptions and a priori transverse-shear stress continuity conditions of mixed form of the refined zigzag theory, known as RZT((m)). Both the displacement field and geometry of the beam is approximated by using non-rational B-spline (NURBS) basis functions and the IG - RZT((m)) element accommodates only four degrees-of-freedom at each control point. Since the present formulation incorporates isogeometric analysis into the RZT((m)) theory, it provides various advantages for displacement and stress analysis of thin/thick composite beams such as high-order continuity representation and simple mesh refinement. Furthermore, the utilization of RZT((m)) theory within the current beam formulation enables the calculation of nonlinear transverse-shear stress variations through the thickness of highly anisotropic beams without any post-processing. Various numerical analysis are performed to validate the accuracy of the IG - RZT((m)) element and its wide range of applicability including beams with a resin-rich damage zone. Comparisons with analytic solutions and high-fidelity finite element models demonstrate the superior accuracy and practical applicability of the present formulation, especially making the IG - RZT((m)) element as an attractive candidate for modelling delamination initiation and propagation in composite structures.
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    Isogeometric plate element for unstiffened and blade stiffened laminates based on refined zigzag theory
    (Elsevier Sci Ltd, 2019) Hasim, Kazim Ahmet; Kefal, Adnan; Madenci, Erdogan
    This study presents an isogeometric plate element, IG-RZT based on the refined zigzag theory (RZT) to model bending behavior of blade stiffened and unstiffened thick or thin laminates. This element is free of shear-locking and shear correction factors due to the use of Non-Uniform Rational B-Splines (NURBS) functions which satisfy the requirement of C-1 continuity in the computation of transverse shear stresses. Comparison of the predictions with IG-RZT element with the previous benchmark solutions reveals fast convergence and high accuracy for general laminate layups under different loading and boundary conditions. Thus, the IG-RZT element can be adopted for computationally efficient and accurate analysis of unstiffened and stiffened flat laminates.