Stress redistribution analysis of egg-shaped pressure shell fabricated by dieless free hydroforming
The stress redistribution characteristics of the welded egg-shaped pressure shell fabricated by dieless free hydroforming will affect the accurate evaluation of its fatigue life.In this paper,according to the egg-shaped contour curve function,an egg-shaped pressure shell for working at 4 000 meters underwater was designed.A numerical model was established to study the stress distribution of the weld of the unexpanded eggshell under dif-ferent external pressure loads.Combined with dieless free hydroforming theory,the effect of internal expansion deformation on the tendency of segmented eggshell to egg-shape was studied,and the stress distribution of egg-shell weld before and after dieless free hydroforming was compared.The results show that the stress at the egg-shell weld increases with the increase of external load,the busbar curvature has a great influence on the bending stress at the eggshell weld.Dieless free hydroforming has a good effect on the improvement of the egg shape of the segmented eggshell,60 MPa is the best internal expansion load.It can not only reduce the bending stress at the eggshell weld,but also reduce the bending stress difference of each weld.
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