http://yetl.yabesh.ir/yetl1/handle/yetl/19036 2026-04-04T01:13:45Z http://yetl.yabesh.ir/yetl1/handle/yetl/4310671 Failure Analysis of the Threaded Connection of the Top Inlet Pipe for the High-Pressure Polyethylene Reactor Gao, Bingjun; Wang, Hao; Wang, Tong; Wang, Chuanzhi To investigate the thread failure issue of the top inlet pipe end of a high-pressure polyethylene reactor, a fluid–structure interaction (FSI) numerical model was developed for the reactor's top inlet pipe. Bidirectional FSI analysis revealed that, although fluid pressure pulsations are the primary cause of pipeline vibrations, asymmetric secondary flow at the double elbows induces out-of-plane structural vibrations, leading to an out-of-plane deviation of the crack locations at the threaded pipe end. A localized numerical model of the threaded straight pipe segment was developed, and the reaction forces and moments at the fixed end of the pipe segment were directly applied based on results from the FSI analysis to assess the very high cycle fatigue (VHCF) life of the structure. A parametric analysis was performed by replacing the real threads with a virtual thread structure, and the simulation results were refined to identify optimized reinforcement strategies for the inlet pipe segment. The results indicate that adding support at the end of the inlet elbow enhances the fatigue life by a factor of 4.35 relative to the original structure. Fractographic analysis using scanning electron microscopy revealed the presence of shallow nonmetallic inclusions at the crack initiation site, characterized by atypical “fish-eye” features. Based on a high-strength steel VHCF life prediction model, recommendations were provided to improve the fatigue life of the pipe segment by limiting the size of nonmetallic inclusions. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4310667 Mixed Mode Stress Intensity Factors for a Slanted Edge Crack Under Remote Uniform Tension Affected by an Adjacent Horizontal Crack Levy, Cesar; Perl, Mordechai; Ma, Qin Fracture mechanics has been used in Fitness-for-Service (FFS) assessments of structures containing cracks. The stress intensity factors (SIFs) at the crack tip are the key information in assessing the remaining service life of a cracked component. Extensive studies have been carried out on the mutual influence of adjacent parallel cracks. However, to date no solutions are available for nonparallel cracks. In the present analysis mode I (KI) and Mode II (KII) SIFs of a slanted-edge-crack affected by an adjacent nonparallel horizontal crack are obtained. KI and KII are evaluated for a wide range of the slanted edge crack angle β = 0 deg–70 deg, for various normalized horizontal (S/a2 = −0.4 to 2) and vertical (H/a2 = 0.4 and 2) separation distances and for several crack lengths. The problem is solved using a two-dimensional, plane strain, finite element model, which was successfully validated against presently available solutions. It is found that the presence of the horizontal crack always amplifies KI of the edge crack while KII might be either amplified or attenuated depending on the crack configuration. Furthermore, the present results indicate that, for the purpose of Fitness-for-Service, the effective SIF at the tip of the slanted crack always increases due to the presence of the horizontal crack. 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4310665 Formulation of the Stress Corrosion Crack Growth Rates Based on the Theoretical Strain Rate Model for Light Water Reactors Koshiishi, Masato; Akazawa, Dan; Miura, Yasufumi; Kako, Kenji 2025-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4310663 Application of Fracture Assessment Method Considering Constraint Effect to Ductile-Brittle Transition Temperature Region Hojo, Kiminobu; Hirota, Takatoshi; Nagoshi, Yasuto; Fukahori, Takuya; Sakima, Kimihisa; Ohata, Mitsuru; Minami, Fumiyoshi With the long-term operation of nuclear power plants, evaluating the integrity of reactor pressure vessels (RPVs) against neutron irradiation has become increasingly important. In the context of pressurized thermal shock (PTS) evaluation, the flaw stability of the reactor vessel has been assessed using fracture mechanics for a postulated flaw. Neutron irradiation may reduce the safety margins of certain plants, potentially raising concerns regarding nuclear safety. For this countermeasure, the applicability of the Beremin model, which is a statistical procedure considering the stress multi-axiality, has been investigated to mitigate excessive conservatism in the conventional fracture mechanics and to perform a realistic fracture evaluation using a physical model for cleavage fracture. In this paper, the applicability of a model coupled with the Beremin model with the Gurson–Tvergaard–Needleman (GTN) models was examined to establish a more precise fracture evaluation method for realistic structures in which cleavage fracture occurs after a small ductile crack growth in the ductile-brittle transition temperature (DBTT) region. After determining the parameters of the Beremin model to characterize cleavage fracture and the GTN model parameters to characterize ductile fracture with the C(T) and SE(B) specimens, these parameter values were used in the coupled model to predict the 5% and 95% confidence limits of critical cleavage fracture of a surface-flawed plate specimen with a thickness of 50 mm under bending or tensile load with nearly the same constraint as a reactor vessel. When the fracture tests using a flat plate with a surface flaw of depth/thickness 0.1 under bending or tensile load were performed at temperatures –80 °C and –120 °C, most of all the critical Ks of the specimens were within the upper and lower bounds of the predicted critical K values. At the temperature –80 °C which caused a small ductile crack, the predicted critical K values by the coupled model were better than those by the Beremin model comparing with the test data. As a result, it was confirmed that the coupled model was a proper procedure for the cleavage fracture associated with small ductile crack growth. 2025-01-01T00:00:00Z