Fatigue Experiments on Very High Strength Steel Base Material and Transverse Butt Welds

Abstract

Very High Strength Steels (VHSS) with nominal strengths up to 1100 MPa have been available on the market for many years. However, the use of these steels in the civil engineering industry is still uncommon, due to lack of design and fabrication knowledge and therefore limited inclusion in codes. Moreover, in a fatigue loaded VHSS structure absolute and relative stress variation will be higher compared to stresses in structures made of lower grade steels. According to current design codes the fatigue strength of welded connections mainly depends on the applied detail, plate thickness and machining condition, not on steel grade. Recently experiments on plates made of S690 and S1100, with and without transverse butt welds, have been performed in order to study the fatigue strength. Test results show that the characteristic fatigue strengths of plates with and without transverse butt weld lay well above the values according to EN 1993-1-9, mainly because of higher slope of the S-N curves. Crack initiation phase of S1100 specimens is relatively long compared to S690 specimens, while crack propagation is relatively short. An efficient application of VHSS in welded connections requires high fabrication quality and avoidance of large stress concentration in joints.

Matching effect on fatigue crack growth behaviour of high-strength steels GMA welded joints

“…& The welding causes unfavourable effects both on the mechanical properties and the fatigue crack growth resistance of the high-strength steels. This statement has good correspondence with previous high cycle fatigue experiments [25][26][27]. & The average values of the Paris-Erdogan exponents (n) of Weldox 700E and Alform 960M base materials in the T-L and L-T directions and of the Weldox 960Q base material in the T-S and L-S directions are significantly not different, which means equal fatigue crack growth resistance in these orientations.…”

Fatigue Properties of Cruciform and Flange-gusset Joints Using Normal and High Strength Steels

“…The final part of the lifetime is the crack propagation region. Thus the measured stress range varies close to the weld toe [13].…”

“…Analyzing these values during the whole fatigue lifetime (Fig. 14), the border between the crack initiation and the crack propagation region can be observed [13]. The stress range-load cycle diagrams show, that the crack nucleation and the crack propagation part of the lifetime are also dominant and have significant impact on the fatigue behavior of the test specimens.…”

Re‐evaluation and extension of fatigue test data for welded attachments and butt joints

“…For most known experimental data, the geometric properties of the weld convexity are not documented. However, experimental studies in [16], [17], [18] show that the weld convexity has a significant influence on the fatigue strength. Therefore, it is nevertheless recommended to keep the current classification, see Table 4.…”