A computational approach for fatigue crack propagation in ship structures under random sequence of clustered loading |
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Authors: | T Okawa Y Sumi |
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Institution: | (1) Steel Products Lab.-II, Steel Research Laboratories, Nippon Steel Corporation, 20-1 Shintomi, Futtsu, Chiba 293-8511, Japan;(2) Department of Systems Design for Ocean-Space, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan |
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Abstract: | The authors have developed a simulation program, CP-System, for multiple cracks propagating in a three-dimensional stiffened
panel structure, where through-the-thickness crack propagation is formulated as a two-dimensional in-plane problem, and the
crack propagation behavior is simulated by step-by-step finite element analyses. In order to evaluate the fatigue lives of
marine structures accurately, it is necessary to take into account the load histories induced by sea waves, which may be composed
of a random sequence of certain clustered loads with variable stress range. In the proposed crack growth model, the crack
opening and closure behavior is simulated by using the modified strip yielding model, and the effective tensile plastic stress
intensity range, ΔK
RP, is calculated by considering the contact of plastic wake along the crack surfaces. The adequacy of the proposed crack growth
model is examined by comparison with fatigue tests under non-constant-amplitude loading. The usefulness of the developed method
is demonstrated for a ship structural detail under certain simulated load sequences. It is shown that the fatigue crack growth
of a ship structure is significantly retarded due to the load interaction effects, so that the conventional method for fatigue
life assessment may predict a relatively conservative fatigue life of a structure. |
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Keywords: | Fatigue crack propagation Ship structures Clustered random loading Plastic stress intensity range |
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