PSI - Issue 79

Benjamin Möller et al. / Procedia Structural Integrity 79 (2026) 493–500

499

Since ships and maritime structures in general are subjected to corrosive environments, in addition to fatigue testing under CAL in ambient atmosphere (air) a corrosive environment, sodium chloride solution of 5 % in this case, has been applied to the laser-welded adapters. A housing made of stainless steel encapsulates the adapter (and clamping) from the surroundings. According to DIN EN ISO 9227 (2017), in parallel to the constant amplitude loading at f =5Hz, the sodium chloride solution is sprayed for 5 minutes horizontally into the housing, follow by 20 minutes residence time without spraying. The procedure is repeated until failure of the specimen, Figure 5 (right). A load-dependent S - N curve ( Wöhler curve) has been evaluated from the results of the fatigue tests in air, while three test results under corrosive environment were performed for direct comparison, as shown by Figure 6. The load amplitudes applied were divided by the thickness of the adapters of 15 mm to derive a related force amplitude. The S N curve evaluated from the test results in air is defined by the related force amplitude F a / t a =139 N/mmat cycles to failure of N f =5·10 6 , slope k =5.0(in the high cycle fatigue regime) and to the scatter T F =1:1.25. A knee point, usually defined by N k and F a ( N k ) as well as a differing slope k * (in the long life fatigue regime), could not be identified. The three fatigue test results under combined CAL and corrosive environment are within the scatter of the results under CAL in ambient atmosphere (air), indicating no fatigue reduction under corrosive media. Additionally, the fatigue test results of adapters without form fit from Möller et al. (2019) are included. It can be seen that the fatigue strength in the range 1·10 5 ≤ N f ≤ 5·10 6 of the adapter with form fit is about a factor of 2 to 3 higher than the one without form fit. This confirms that the developed laser beam welding process is an appropriate solution for joining steel to aluminum sheets of increased thickness.

Figure 6. S - N curve for LBW steel-aluminum adapters tested in air and under corrosive media.

5. Conclusions Research, starting from development of a laser beam welding process to realize steel-aluminum adapters with a form fit as well as tensile and fatigue investigations have been conducted with the following main findings: • A laser beam welding process has been developed using two intersecting beams and additional material in order to generate a form fit and advantageous microstructure which has the potential to have a positive effect not only on the (tensile and fatigue) strength under orthogonal loading of the sheets, but also in an adapter design which has the potential to function as a local steel-to-aluminum-joint for ship construction.