PSI - Issue 75

Ralf Glienke et al. / Procedia Structural Integrity 75 (2025) 474–488

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Ralf Glienke et al. / Structural Integrity Procedia 00 (2019) 000 – 000

outer specimen edge was analysed. In addition, microsections are shown with 200x magnification in the centre of the plate after etching with Nital. The edge of the hole (A) shows a work hardening depth of approx. 39 µm as a result of the blast-cleaning. At the outer edge, the work hardening depth was ≈ 82 µm. The lower work hardening in the hole leads to the assumption that the blast-cleaning medium cannot penetrate sufficiently into the hole, resulting in less work hardening of the material and thus low compressive residual stresses. Nevertheless, blast-cleaning leads to higher surface roughness in the hole, which favours crack initiation in the area of the highest principal normal stress during the fatigue test and thus reduces the lifetime.

Fig. 6. Microsections of specimen from test series #18: A – edge of hole, B – plate edge

3.5.5. Effect of overloads on the fatigue strength For HFMI post-weld treatment, there is an application limit for the S-N curve (-0.8 f y ≤  ≤ f y ), which indicates that compressive loads reduce the fatigue strength (Marquis et al. (2016), Deutscher Ausschuss für Stahlbau (2019)). A similar effect would be expected for the blast-cleaning process, which is comparable in terms of work hardening and inducing compressive residual stresses. Older investigations by Bignonnet et al. (1987) show a sensitivity to compressive loads on the detail T-joint with shot-peening treatment. For this purpose, tests with tensile and compressive preloads (N = 50 load cycles) prior to the fatigue test itself were carried out on the blast-cleaned specimens from series #03 and #10. The results are shown in Fig. 6 b), f) and l). Tensile preloads have no negative effect on the fatigue strength. In contrast, the fatigue life of butt-welded joints is significantly reduced by compressive preload of -85% ∙ f y and -90% ∙ f y . Furthermore, for specimens with oxy-fuel edges, compressive preloads of -95 % ∙ f y and -100 % ∙ f y lead to an early failure. This is attributed to the reduction of compressive residual stresses by compressive loads.