Fatigue strength assessment of laser stake‐welded T‐joints subjected to reversed bending

Abstract

The paper investigates the fatigue strength of laser stake‐welded T‐joints subjected to reversed bending. The fatigue tests are carried out with the load ratio, R ≈ −0.8. The experimental data is firstly analysed using the nominal stress approach and then by the J‐integral as the local fatigue strength parameter in the finite element (FE) assessment. The nominal stress approach demonstrated that the fatigue strength of the investigated T‐joints is lower than encountered for any other steel joint under reversed tensile loading. The results also showed that the fatigue strength of this joint under the load ratio R ≈ −0.8 increases with respect to R = 0 bending by 22.6% in the case of the nominal stress approach and 13% in the case of the J‐integral approach. However, the slopes of the fatigue resistance curves for different load ratios appear very similar, suggesting that the load ratio has an insignificant influence to the slope. In contrast to the similar slopes, the scatter indexes were different. The nominal stress approach shows that the scatter index is 3.4 times larger for R ≈ −0.8 than R = 0 bending. The J‐integral approach showed that the scatter index for R ≈ −0.8 is only 67% larger than in the R = 0 case because the weld geometry is modelled in the FE analysis.

Fatigue failure modes of rib‐to‐deck joints under the multiaxial stress states caused by various wheel loading characteristics

“…Considering the diversity of fatigue failure modes, it is crucial to determine the dominant failure mode for fatigue life prediction. 8 Owing to the complexity of the bridge deck structure, it is difficult to accurately calculate the nominal stress at the fatigue failure location based on classical mechanics methods 9 ; similarly, owing to the characteristic of the evaluation method, the hot spot stress method can only be applied to the issues that fatigue cracks originate from the weld toe 10 ; comparatively, the structural stress method, which is based on the mechanic's principle of the free body cut, could evaluate the fatigue performance of complex structures in the case of both toe failure and root failure. 11 Yang et al 12 analyzed the fatigue behavior of welded joints in OSBD through the above-mentioned evaluation methods; the traction structural stress with 95% confidence intervals is more accurate than those calculated by the other S-N curves based on nominal, hotspot, and effective notch stresses.…”

The Effect of Numerical 2D and 3D Fem Element Modelling on Strain and Stress Distributions at Laser Weld Notches in Steel Sandwich Type Panels

“…The present state of the art in this area has not permitted development of a comprehensive calculation method for structures of this type. The calculated fatigue life of the analysed structures heavily depends on the assumed loading condition [30], [36], [37]. From among numerous possible methods to assess the fatigue life, the most frequent approach bases on local strains, or local stresses [38], [39], [40], [41], [42].…”

Factors affecting the fatigue strength of thin-plates in large structures

“…Furthermore, the scatter of experimental data is larger for thin plates in comparison to thick plates [12]. In steel sandwich panels, where the plate thickness is significantly smaller, neither the structural or notch stress approaches give reasonable results for fatigue strength, and an energy or J-integral based assessment method has to be used instead [19], [20], [21], [22]. However, it is seen that the slope of the fatigue resistance curve can be even higher than with structural and notch stress approaches.…”