Evaluation of Fatigue Strength of AISI 4340 Steel Under Hydrostatic Pressure
TL;DR: In this article, the authors presented the comparison of fatigue life data evaluated for a structural steel material under ambient conditions and under hyperbaric pressure conditions, and the results suggest that hydrostatic pressure has a significant influence on fatigue life.
Abstract: The presence of hydrostatic pressure in the range of 10 to 600 bar (typical of sea depths from 100 meters to 6 kilometers) and cyclic wave loading in off-shore structures and equipments operating in deep-water environment requires suitable criteria accounting for high hydrostatic load during design of such structural elements The presence of corrosive species due to sea water and marine organisms also adds complexity to this problem Plain fatigue data evaluated under ambient conditions or fatigue data evaluated in atmospheric conditions under soaked sea water environment may not be appropriate for the design of systems subjected to hydrostatic pressure High hydrostatic pressure alters the yield criterion of materials Thus, it becomes essential to generate the fatigue strength data of structural steel in pressurized simulated sea water (35% NaCl solution) conditionsThis paper presents the comparison of fatigue life data evaluated for a structural steel material under ambient conditions and under hyperbaric pressure conditions A special hyperbaric chamber was designed for this purpose and 35% NaCl solution was pressurized into the chamber by a manual pump Mechanical fatigue loading was applied on the specimen in the presence of two pressures, viz, 30 bar and 50 bar hydrostatic pressure The results suggest that hydrostatic pressure has a significant influence on fatigue life data of steel The fracture surfaces were examined using a scanning electron microscope which suggests change in fracture mode from being pure ductile to mixed mode of fracture Work is in progress to evaluate the strength degradation of welded joints subjected to hyperbaric fatigueCopyright © 2014 by ASME
TL;DR: A novel sealing method is proposed, which adopts the combination of anti-shear block device and four O-ring seals and has the advantage of no need of manual pre-tightening and of sufficient shear resistance.
Abstract: A high-pressure chamber is the main equipment required for simulating deep-sea operational environment and used for evaluating the performances of underwater equipment such as underwater vehicles under a preset pressure so that the possible malfunctions could be alarmed before deep-sea commissioning. In this paper, due to its current unavailability, a high-pressure chamber with the maximum working pressure of 60 MPa was designed, which has the inner diameter of 3 m and the height of 4 m, possesses the video transmission function and allows most of the small-scale underwater vehicle's overall stability and capacity to be tested possible. To tackle the leakage and ensure the stability of the chamber, this paper proposes a novel sealing method, which adopts the combination of anti-shear block device and four O-ring seals and has the advantage of no need of manual pre-tightening and of sufficient shear resistance. The performance and strength analysis of the chamber were carried out by Ansys/Workbench finite element analysis software. Furthermore, The high-pressure chamber was manufactured and its experiment verification results indicate that with larger containment volume and more advanced control system it could work reliably, which made it feasible for its engineering application.