Equivalent Solid Based Fatigue Analysis of Perforated Plates with Triangular Perforation Pattern

The current fatigue assessment method of the ASME B&PV Code uses an elastic stress multiplier to determine the total stress in perforated plates with triangular pattern. This method contains several simplifications and shortcomings. The present paper shows that the perforation pattern symmetry imposes constraints on the total stress multipliers that can be used to simplify the elastic analysis, particularly of three-dimensional (non-axisymmetric) plates. For thin ligament conditions, the very conservative Code analysis can be replaced by a more accurate stress multiplier approach for which the stress concentration around the hole is derived from an elastic Finite Element analysis. This can result in a significant reduction of the calculated fatigue usage factor. Finally, the issue of strain concentration is addressed. When the total stress range at a location around the ligament exceeds 2Sy, the elastically predicted strain range is potentially unconservative. The elastic-plastic strain at this location can be estimated from the elastic result using simplified methods. The corresponding predictions are compared to elastic-plastic analysis results.