PSI - Issue 52

Ruben I. Erives et al. / Procedia Structural Integrity 52 (2024) 600–610 Ruben Erives et al./ Structural Integrity Procedia 00 (2019) 000–000

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displacements. In the Fig. 4, the raw measurements are shown in blue circles, with the green circles representing the section of the data used for a linear fit (10%-80% of 0 ). The blue solid curve represents a fit of the measurements (using gaussian process models), while the green curve shows the extrapolated fit of the linearised region. The blue start indicates the opening according to the AE measurements, while the red star indicates the opening corresponding to the linear fit. The horizontal red line that joins the blue and red stars shows the deviation from linearity (i.e., difference between 0 and ℓ ) of the load (moment)-displacement curve.

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Fig. 5. Delamination from linearity for specimen under a) (near) pure normal opening displacements, b) mixed mode, and c) (near) pure shear opening displacements.

In Fig. 5, the deviation from linearity measured from all the tested specimens is plotted against their respective measured phase angle, . The solid blue circles are the individual measurements, while the red curve is a fit (obtained using gaussian process models) of ∆ℓ as a function of the phase angle. The measured deviation from linearity is very small for low phase angles (normal opening dominated), and much larger (about one order of magnitude) for large (shear opening dominated). It can be noted that all the measurements lay within the 95% confidence intervals, showing a good correlation.