PSI - Issue 3

Stavros K. Kourkoulis et al. / Procedia Structural Integrity 3 (2017) 316–325 S. K. Kourkoulis and I. Dakanali / Structural Integrity Procedia 00 (2017) 000–000

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In order to gain a better overview of the relative response of the two fragments a detailed view of the crack open ing (as recorded by both the two clip-gauges and the DIC system - as it will be described in next paragraph) is plotted versus time in Fig.9a, in juxtaposition to the respective variation of the load applied. Three time intervals can be clearly distinguished: The fault starts opening at about t=400s. At the same moment the load-time curve exhibits a clear slope change. Similar behavior is observed at t≈950s. Finally, at t≈1085s when the third change of the crack opening plot appears, an abrupt load drop is observed and the crack starts opening very rapidly. The deformed shape of the epistyle’s lower edge, as recorded by the five LVDTs, is shown in Fig.9b for the as above mentioned character istic time instants. The increasing asymmetry of the indications of the LVDTs, placed on either side of the fault, with increasing time (or equivalently with increasing load), probably attributed to the fault’s inclination, is worth noticing. (a) (b)

1085s

Fragment’s separation

950s

406s

Fig. 9. (a) The load and the crack opening versus time; (b) The deformed shape of the lower edge of the restored epistyle.

3.2. Digital image correlation The full-field axial (horizontal) displacement of the two fragments, as recorded by the DIC system, is shown in Fig.10 for characteristic time instants. In excellent accordance with the previously mentioned data the epistyle behaves as an intact structure up to about t=400s. Then the fragments are separated from each other and their distance starts increasing. This trend is smoothly intensified until t=1085s when it becomes rapid denoting the onset of final failure. For the quantitative correlation of the data recorded by the DIC and the clip-gauges, two pairs of elementary areas of the fragments on either side of the fault were isolated in the immediate vicinity of the clips and the distance

Fig. 10. The contours of the horizontal specimen’s deformation for four characteristic time instants.