Yazar "Kurtaran, H." seçeneğine göre listele

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    Fracture Characterization of Base Metal, Seam Weld, and Girth Weld of Welded Line Pipe Steel at Room and Low Temperatures
    (Springer, 2021) Choupani, N.; Asghari, V.; Kurtaran, H.
    For fitness-for-service assessment of pipeline cracks, it is necessary to examine toughness values of pipeline steels and their variations with temperature. In this study, experimental values of toughness (K-JC) at room temperature have been obtained for base metal (BM), seam weld (SW), and girth weld (GW) in an API X65 gas transportation pipeline in order to investigate the structural integrity of whole structure. The toughness tests employed side-grooved compact tension specimens, obtained from the original pipe, to characterize the resistance to crack extension curves based on the unloading compliance technique. The values of J(IC) for tested specimens were found, and then, K-JC values are obtained using ASTM E1820 guideline as 302, 262, and 166 MPam(1/2) for BM, SW, and GW materials, respectively. Charpy V-notch (CVN) impact tests at room and low temperatures were also conducted to determine low-temperature effects on the toughness, and to examine ductile-brittle transition temperature values in the samples under study. The capability of CVN test for prediction of toughness in the tested specimens was also investigated. The error values in using CVN test results are large enough to justify that the CVN test is not suitable for prediction of toughness accurately.
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    Frequency study of functionally graded multilayer graphene platelet-reinforced polymer cylindrical panels
    (Polish Acad Sciences Inst Fundamental Technological Research, 2021) Farsadi, T.; Asadi, D.; Kurtaran, H.
    IN THIS STUDY, NONLINEAR FUNDAMENTAL NATURAL FREQUENCIES of Functionally Graded (FG) multilayer Graphene Platelet-reinforced Polymer Composite (GPL-RPC) curved cylindrical panels are studied. It is considered that the Graphene Platelet (GPL) nanofillers are distributed in the matrix either uniformly or non uniformly along the thickness direction. Four GPL distribution patterns namely, UD, FG-O, FG-X, and FG-A are considered. The effective material properties of GPL-RPC layers are obtained via the modified Halpin-Tsai micromechanics model and the rule of the mixture. A nonlinear structural model is utilized based on the virtual work principle. Green's nonlinear kinematic strain relations are used to account for the geometric nonlinearities and the First-order Shear Deformation Theory (FSDT) is adopted to generalize the formulation for the case of moderately thick cylindrical panels including transverse shear deformations. The Generalized Differential Quadrature (GDQ) method of solution is employed to solve the nonlinear governing equations of motion. The present study aims to study the effect of GPL weight fraction for the proposed distribution patterns on the nonlinear fundamental frequency of functionally graded GPL-RPC cylindrical panels with different boundary conditions.
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    Thermo-fracture analysis of composite-aluminum bonded joints at low temperatures: Experimental and numerical analyses
    (Elsevier Ltd, 2019) Rahmani, A.; Choupani, N.; Kurtaran, H.
    Adhesive joints have found extensive applications in aerospace structures because of important advantages such as uniform stress distribution, thermal, acoustic and electrical insulation as well as capability of joining dissimilar materials. These joints in aerospace structures frequently experience severe low temperatures. Lack of experimental data in this field motivated the study of the fracture of adhesive joint at low temperatures in this paper. Fracture parameters of carbon-fibre-reinforced polymer-based composites (CFRP) and aluminum bonded joints were investigated in a temperature range of ?80 to +22 °C. In order to understand the mechanical behavior of different components of the bonded joint, firstly, the components (adhesive, composite, and aluminum) were characterized by conducting tensile tests. Subsequently, specimens of cracked bonded joint were tested at low temperatures in different loading modes (mode I, mode II, and mixed mode I/II). The finite element model of the bonded joint was developed in order to obtain the dimensionless functions of stress intensity factors at lower temperatures. The results showed that a reduction in temperature down to a particular value contributes to improved critical stress intensity factors, while any further reduction in the temperature tends to lower the critical stress intensity factors, eventually leading to decreased fracture energy absorption capacity of the structure. In the final section of this paper, a study on fracture surfaces and fracture mechanisms was performed via macroscopic and scanning electron microscopic (SEM) analyses. © 2019 Elsevier Ltd