PSI - Issue 64

Julian Unglaub et al. / Procedia Structural Integrity 64 (2024) 918–924 Julian Unglaub / Structural Integrity Procedia 00 (2019) 000–000

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displacement sensor. These are used to record the forces that are occurring. During the course of the welding tests, the slide movement is controlled and recorded by two displacement sensors of the NCDT 3300 type. The fine displacement sensors are positioned on either side of the specimens at the height of the seam flanks to be welded. The mean displacement signal of the two sensors is employed for displacement control during the welding experiments. Two clip-on extensometers (manufacturer MTS, model 632-02F-20) are utilized to record local gap opening movement during the initial phase of welding the first layers. Each clip-on extensometer is attached to the rear at the height of the seam flanks. The experiments were carried out in displacement control and force control conditions in order to investigate the different welding boundary conditions at the bridge. It can be stated that hot cracking will invariably occur, irrespective of the chosen control technique, even when the amplitude is small. The defective root layer must therefore be removed by grinding in order to prevent further deterioration. The experiments have shown that up to an amplitude of ±0.1 mm amplitude at a frequency of 2 Hz, defect-free welds can be produced. At larger amplitudes, the hot cracks connect to continuous cracks during welding. Therefore, a weld cannot be established. The results are summarized in Fig. 3. frequency [Hz] 0 1 2 4 8

0

+ +

0,05

+ +

0,1

+

- -

0,125

-

0,15

- - - -

amplitude [mm] 0,25

Fig. 3. Parameter field for welding under cyclic load

To characterize the achieved seam quality, the fatigue samples were divided into the evaluation groups according to (2014). The seam flank angle, seam camber and edge offset were each evaluated as quality criteria. The fatigue specimens were measured in advance using a laser triangulation sensor (Micro-Epsilon optoNCDT1800) and aligned according to the existing angular distortion by limiting the angular deviation to 0.2°. For detailed explanations on the evaluation of the weld seam quality, please refer to Begemann et al. (2024) 3.2. Fatigue Performance A total of 22 fatigue tests were conducted as part of welding experiments under displacement control conditions, along with 41 fatigue tests under force control conditions. Additionally, 18 fatigue tests were performed on reference welds without service loading. The fatigue tests were executed in force-controlled mode, maintaining a threshold tensile stress (stress ratio R = 0.1), exploring stress ranges between 190 MPa and 350 MPa. The testing frequency reached up to 15 Hz, and the tests were conducted until reaching either 5 Mio load cycles or complete fracture. The results of the fatigue tests on the welds subjected to different loading conditions during welding and the reference welds are presented in Fig. 4. The experimental data are transformed to 2 Mio. load cycles, resulting in a one-dimensional distribution. Additionally, the 90% confidence interval is given. It can be seen that all individual tests are above fatigue detail 90 for construction detail 5 - transverse joints of plates or flat steels from DIN EN 1993 1-9 (2010) and thus comparable fatigue strengths can be achieved.