PSI - Issue 75

Philippe Thibaux et al. / Procedia Structural Integrity 75 (2025) 546–554 P. Thibaux et al. / Structural Integrity Procedia (2025)

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At the start of the test, the excitation frequency was 19.6 Hz but decreased during the test to 15 Hz at the end (figure 3). This frequency drop was caused by a loss of stiffness of the specimen. At the start of the test, the horizontal displacement amplitude was close to 2mm, but increased progressively to 3.8mm at the end of the test. This stiffness loss was caused by the presence of very large cracks at the end of the test. The hot spot stresses were determined from the strain gauge measurements with the two rosette arrangements. The hot spot stress amplitude on the chord was found to be between 100 and 110MPa, depending on the location and using the principal stress values. Using only the perpendicular strain gauges, the extrapolated stress would be between 87 and 97MPa, highlighting that the loading is bi-axial close to the weld toe. The hot spot stresses on the brace were around 15% lower than on the chord. This difference is slightly smaller than would be expected from the stress concentration factors.

Fig. 3. Measured displacements and applied excitation frequency during the out-of-plane test.

Fig. 4. Crack revealed by dye penetrant inspection at the end of the out-of-plane test, position at 3h on the right brace.