PSI - Issue 2_A

2838 Z.S. Metaxa et al. / Procedia Structural Integrity 2 (2016) 2833–2840 6 Z.S. Metaxa, E.D. Pasiou, I. Dakanali, I. Stavrakas, D. Triantis, S.K. Kourkoulis / Structural Integrity Procedia 00 (2016) 000–000

(a)

(b)

36

36

E F

C D

B

27

27

9 Load [kN] . 18

18

Central SG

9

Load [kN] .

A

0

0

-0.010 -0.005 0.000 0.005 0.010 Strain

0

900

1800

2700

3600

Time [sec]

Fig. 5. (a) Typical load-time curve; (b) the variation of the strains at the central region of the connector (orange line) and at the region which belongs to the moving block (light blue line).

(a) (b) the relative opening of the blocks (“value of the lower clip gauge” minus “value of the upper clip gauge”) are plotted versus time in Fig.6b, again in conjunction to the load level. Although the maximum value recorded by the lower clip reaches 1 mm, the parasitic bending in the xy plane is clear at a first glance, especially after the load is approxi mately equal to 8.5 kN. Excluding its initial portion, the qualitative similarity of the relative opening-time plot to the respective load-time curve is astonishing. The relative opening of the volumes reaches a maximum value at the time instant when the load is equal to ~27.5 kN (point C). Afterwards, a small decrease is observed (until the load becomes equal to about 26.5 kN) indicating a temporary bending tendency in the xy plane the direction of which is opposite to the so far recorded bending tendency. This change of the rotation tendency could perhaps explain the unstable behavior of the ERC-time curve, since it designates an inversion of the tendency of the two blocks to approach each other (or equivalently an inversion of the parasitic loads mutually exerted by the two blocks on each other). Indeed a tendency of the blocks to approach each other corresponds to parasitic compressive forces which are in favour of closing microcracks while on the other hand a tendency to move away from each other corresponds to parasitic tensile loads which create additional microcracks increasing the electric resistance. From this point on, the opening of the epistyles gets continuously higher values. When load reaches point E (~29.5 kN) the slope of the relative opening-time curve increases slightly denoting acceleration of the separation of the two blocks. The specific point will be further discussed in next section taking advantage of the data gathered by the DIC and AE techniques.

36

20

36

1200

electrical resistance change load

clip gauge-lower level clip gauge-upper level blocks' relative opening load

2

0 Electrical resistance change Δ R / R 0 [-] 5 10 15

27

27

800

3 ~18,80kN

Load [kN]

L oad [kN]

1

18

400

18

Opening [μm]

9

0

9

0

-400

0

0

900

1800

2700

3600

0

900

1800

2700

3600

Time [sec]

Time [sec]

Fig. 6. (a) Electrical resistance change of the nanomodified mortar versus time (some characteristic points are included); (b) the recordings and the relative opening of the marble blocks (for comparison purposes the load-time curve is included in both graphs).