Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 9 Fatigue - Section 1 General Considerations - 2 Definition
2 Definition
2.1 Hot spots
2.1.1 Hot spots are locations in the structure where fatigue cracks may initiate due to the combined effect of nominal structural stress fluctuation and stress raising effects due to the weld geometry or similar effects due to notch in the base material.
Hot spots may be located at:
- Weld toe.
- Weld root of partial penetration or fillet weld.
- Base material at free edge of plate.
2.2 Nominal stress
2.2.1 Nominal stress is the stress in a structural component taking into account macro-geometric effect but disregarding the stress concentration due to structural discontinuities and the presence of welds. Nominal stress is to be obtained either using coarse or fine mesh FE analysis, as required in Ch 9, Sec 5 or using analytical calculation based on beam theory, as required in Ch 9, Sec 4.
2.3 Hot spot stress
2.3.1 Hot spot stress is the stress at the weld toe taking into account the stress concentration due to structural discontinuities and presence of welded attachments but disregarding the non-linear stress peak caused by the notch at the weld toe. The hot spot stresses to be considered correspond to the two principal stresses on the surface plating at the weld toe. The first principal stress acts within ±45°, perpendicular to the weld and the second principal stress acts outside ±45°.
The hot spot stress is to be obtained by multiplying the nominal stress by a Stress Concentration Factor (SCF), according to Ch 9, Sec 4, [5] or directly by a very fine mesh FE analysis, according to Ch 9, Sec 5, [3] and Ch 9, Sec 5, [4].
2.4 Local stress at free edge
2.4.1 Local stress at free edge is the stress at the plate free edge derived using finite element analysis according to Ch 9, Sec 5, [3.2].
2.5 Fatigue stress
2.5.1 Fatigue stress is the stress relevant for fatigue assessment purpose, i.e.:
- Maximum of the two principal hot spot stress for weld toe with the mean stress effect and thickness effect corrections.
- Local stress at free edge with corrections due to the base material surface finishing, mean stress effect, thickness effect and material strength.
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