Coke drums are major production equipment in petroleum refineries. In this presentation, failure mechanisms of the coke drums are analyzed. A statistical fatigue life estimation method is then proposed for the coke drums.
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A small-scale hybrid glass beam-column connection prototype is tested in order to assess its rotational characteristics and post-fracture performance. To simulate fracture process in glass, possibility of using two numerical Finite Element (FE) approaches is explored and the results are compared to the experimental findings focusing on the connections failing in a brittle manner.
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In this paper, the contribution of surface effect to the anti-plane deformation of a magnetoelectroelastic medium weakened by a crack is investigated. The surface magnetoelectroelasticity is incorporated by using the extended surface/interface model of Gurtin and Murdoch. The mixed boundary value problem of the mode-III crack is formulated by using a continuous distribution of screw dislocations and the dislocations of electric potential and magnetic potential on the crack, and the problem is finally reduced to solving a system of coupled Cauchy singular integro-differential equations, which can be numerically solved by the decoupling and collocation methods. The results show that the stresses, eldctric displacements and magnetic induction near the crack tips exhibit the logarithmic singularity when the surface effect is considered. When there is no surface effect on the crack face, the classical square-root singularity of the near crack-tip fields can be observed.
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Accurate stress intensity factor (SIF) solutions for cylindrical specimens with different wire aspect ratios and crack aspect ratios are required to determine the fracture toughness of rods and wires. The mode I geometric factor solutions of various crack configurations in a cylindrical fracture specimen in tension have been determined using liner elastic fracture mechanics. Finite element analysis (FEA) is applied to compute this as a function of wire aspect ratio (𝐻/𝐷), crack aspect ratio (𝑎/𝑏), and relative crack depth (𝑎/𝐷). It is found that the geometric factor is independent of wire aspect ratio for shallow cracks but has a major influence for deeper cracks. Also, the geometric factor is higher for concave cracks which facilitates the crack propagation. The mechanistic causes of the same are explained. Fracture toughness measurements on polymethylmethacrylate (PMMA) were carried out for the experimental validation of the solutions. The application of these solutions to fracture toughness measurements at the micro- and nanoscale, particularly in ceramic fibers and high strength metallic wires, is discussed.
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In this study a thorough evaluation of the toughening mechanism in cement-based nanocomposites reinforced with hybrid networks of carbon nanofibers (CNFs) and polypropylene microfibers (PPs) took place. The critical values of fracture toughness/stress intensity factor, KIC, were experimentally determined on prismatic notched specimens of nano and micro scale fiber reinforced cementitious composites using the two parameter fracture model (TPFM). The post-crack energy absorption capacity of the hybrid-composites was assessed by evaluating the dimensionless toughness index, I20, calculated through linear elastic fracture mechanics (LEFM) tests. The addition of CNF/PP networks at low volume fractions of about 0.1 vol% in cementitious matrix results in a significant improvement in the KIC (85-240%) and 1.6 – 10x higher I20 compared to the CNF or PP reinforced materials. Relative to the single-scale fiber reinforcement, the synergy between the nano- and micro- scale fibers results in a multi-scale crack arresting distinctively increasing the toughening effect in the hybrid fiber-cementitious mortar nanocomposites.
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