ラウンドロビン解析によるASME及びEN圧力容器設計規格における溶接継手疲労強度評価手法の比較

Fatigue strength evaluation methods for welded joints specified in the pressure vessel codes of ASME and EN have been comparatively studied by a round robin analysis，in which ５ independent parties participated．ASME Code provides three types of methods，i．e．(1)Elastic stress analysis based notch stress method using smooth bar design fatigue curve，(2)Elastic-plastic stress analysis based notch strain method using smooth bar design fatigue curve，and(3)Elastic stress analysis based structural stress method using welded joints fatigue master curve．In the method(1)，the notch stress can be determined by two different approaches using，(a)the raw stress value as-computed by FEA or(b)the membrane plus bending stress multiplied by FSRF，fatigue strength reduction factor．Meanwhile，EN Code provides so-called(4)hot spot stress method with a series of welded joint fatigue curves．These ４ methods are applied to a single problem for fatigue life assessment on as-weld welded joints for a pressure vessel，and then the differences among the methods and those characteristics have been discussed through the round robin analysis．It is found that the(4)EN hot spot stress method gives quite equal results regardless of the mesh density as well as the FEA software adopted．The(1-b)FSRF notch stress method and the(3)master curve method also show less scattered results in a certain level．Contrarily，the results obtained from the(1-a)direct notch stress method and the(2)notch strain method largely depend on the mesh density because of stress singularity due to the sharp corner discontinuity at the weld toe．In addition，the applicability of effective notch stress method，which introduces fictitious notch root rounding with the radius of １mm，is also examined for the pressure vessel fatigue evaluation and found the result almost agrees with that from the(4)hot spot stress method．