Basic Study on Fatigue Strength Evaluation:second report: SN diagram to structural details from a viewpoint of attaining FEM direct strength calculation

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In these days, direct strength calculation methods has been increasingly and effectively used in ship design for preventing structural members from buckling and yielding. However, regarding to fatigue strength assessment, it is generally known that it is not clear how FEM stress output ought to be used and that how FEM input ought to be prepared for fatigue strength estimation sake.In order to attain direct strength calculation, in this report, it is emphasized that an adaptation step is needed from a SN curve as a material strength characteristics to equivalently converted SN curve in which the vertical axis value is expressed by a local stress range and is made compatible to stress calculation tool.This is because that SN curve is the essence of fatigue life and that the vertical index of a conventional SN diagram, that is nominal stress range, is difficult to calculate of an actual ship structural details due to the complexity of stress distribution and the non-flat shape of the actual optimized details.And also in the study a consideration was made on the limit of FEM modeling, and eventually it is made clear that the plate element FEM, which is not able to allow the plate thickness to change during calculation, may underestimate the stress concentration factor when it is accompanied with large sectional deformation of plate and weld bead. An example of the case was verified by the series fatigue test of T-shaped fillet weld joint by adopting the three point bend loading with small distance of supporting ends compared with the plate thickness.
社団法人日本船舶海洋工学会の論文

Basic Study on Fatigue Strength Evaluation:second report: SN diagram to structural details from a viewpoint of attaining FEM direct strength calculation

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