Fatigue tests of full scale models of rectangular hollow section (RHS) T-joints were carried out to obtain a design hot-spot S-N curve. The component was also analyzed by the finite element method, using several modeling techniques and element types. The results from both experimental tests and finite element analysis are discussed. Recommendations on the procedure of fatigue assessment of rectangular hollow section T-joints using the hot-spot stress approach including S-N curve to be used are also presented.
Fatigue design codes for welded aluminum structures are often based on a nominal stress range S-N curve approach, where the design stress is the local nominal stress range at the weld toe. This nominal stress does not include any stress raisers due to joint geometry, thus local geometry effects are implicitly included in S-N curves available for standard detail classes. Welded structures may, however, deviate significantly from such detail classes, both in terms of geometry and loading. To overcome this, a design principle based on a hot-spot stress range S-N curve has been suggested as a more suitable fatigue assessment procedure. The hot-spot stress range includes the influence of joint geometry, thus the designer avoids using a large varieties of joint depend S-N curves since the geometrical features of the design classes are included in the design stress range rather than in the design S-N curves. However, the local notch effects (including fabrication defects and workmanship) are still embedded/inherent in the design S-N curves. The main object of this paper is to verify the fatigue assessment of fillet welded rectangular hollow section (RHS) T-joints by the use of a hotspot stress approach. A series of RHS aluminum T-joints were tested in bending fatigue to obtain a design S-N curve. Literature test data of similar joint configurations were also included in the data analysis, yielding 39 data points in total. Commonly used FEM discretizations and extrapolation methods for finding hot-spot stresses are investigated, using both shell and solid elements.
