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Öğe Experimental and numerical analysis of fracture parameters of adhesively bonded joints at low temperatures(Pergamon-Elsevier Science Ltd, 2019) Rahmani, A.; Choupani, N.In this work, the fracture parameters of the adhesive joints were investigated at low temperatures. The results of the tensile experiments showed that by decreasing the temperature, the ultimate strength, yield strength and elastic modulus have increasing trends. The effect of temperature and loading mode on the fracture toughness parameters of adhesive joints were examined by using the special test loading device in which by varying the loading angle, pure mode I, II and mixed mode data were obtained experimentally. The results showed that by decreasing the temperature, critical stress intensity factors and critical strain energy release rates increased. However, the increasing trend in mode I was gentle and in mode II was significant. Non-dimensional stress intensity factors were also determined by using finite element method at low temperatures and different loading modes. In order to understand the failure mechanism of adhesive joints, fracture surfaces of samples were analyzed, which showed that, in mode I, the failure mechanism was of a cohesive type and by decreasing the temperature, the joint became brittle and the fracture surface became smooth. The interfacial failure in mode II revealed that the fracture toughness of the adhesive was greater than that of the interface, which leads to deviation of crack growth path from the cohesive to the interfacial fracture.Öğe Fracture assessment of pipeline girth weld at low temperature(Springer Heidelberg, 2020) Khajedezfouli, M.; Choupani, N.; Torun, A. R.; Yengejeh, E. AlipourThe results of long-distance oil and gas pipeline failure analysis are important to the industry in order to maintain the reliability and safety of them. Seam welding in these pipes is done with good accuracy at place of work, while girth welding is carried out in the installation site and usually causes the main failure problem. Therefore, the most vulnerable and crucial part of these pipes is the girth welding. Investigating the fracture behavior of girth weld in high-pressure gas pipeline systems at low temperatures is important because these products are hazardous and may lead to explosion, leading to economic losses and environmental pollution. In the present study, the fracture behavior of girth-welded API 5L X65 natural gas transportation pipes was experimentally investigated at low temperatures. The fracture parameters were obtained using Arcan fixture in which all of the in-plane modes including pure tensile mode to pure shear mode can be created by altering the loading angle from 0 degrees to 90 degrees. Finite element analysis was also conducted by ABAQUS finite element software in order to determine geometrical coefficients which are required in calculating the fracture toughness. Results revealed that by decreasing the temperature and increasing the mode II loading contribution, the fracture toughness values were also decreased.Öğe 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.Öğe 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
