Issue 40

E. D. Pasiou et alii, Frattura ed Integrità Strutturale, 40 (2017) 41-51; DOI: 10.3221/IGF-ESIS.40.04 43 therefore it doesn’t react with other chemicals when they come into contact with it. Soda glass in usually used to make windows, bottles, jars, vials and other laboratory equipment. The chemical composition of this type of glass is presented in Tab. 1. In the present experimental protocol three prismatic blocks (30 mm x 30 mm x 80 mm) were used. Components SiO 2 Al 2 O 3 Na 2 O K 2 O CaO MgO Fe 2 O 3 TiO 2 P 2 O 5 ZrO 2 % 72.4 1.26 13.4 0.24 8.53 3.95 0.16 0.063 0.018 0.05 Table 1 : Chemical composition of soda-lime-silica glass [31]. Experimental set up Before testing, one Kyowa strain gauge (of 5 mm gauge length and of 120 Ω gauge resistance) was glued on the front surface of the specimen (at the middle of its height and of its width as it is seen in Fig.1a) in order to measure the axial strain during the tests. In addition, one acoustic sensor R15α (denoted by number 3 in Fig.1b) was coupled on the opposite surface of the specimen by means of silicone and one preamplifier with 40 dB gain was also used (the equipment and the software used were by Mistras Group, Inc.). Finally, a pair of electrodes was attached on the two side opposite surfaces of each specimen (orange ellipses in Fig.1a and numbers 1,2 in Fig.1b) in such a way so as the imaginary line connecting them to be perpendicular to the loading axis. A sensitive programmable electrometer (Keithley, 6517A), capable of resolving currents as low as 0.1 fA and as high as 20 mA in 11 ranges, was used to record the electric signals. It should be underlined that thin teflon plates were placed between the specimen and the loading platens for the specimen’s electrical isolation. All specimens were subjected to compressive loading under load control conditions (dσ/dt=0.3 MPa/s) simulating quasi-static loading. Figure 1 : (a) A sketch of the experimental set up, (b) A typical marble specimen. The pair of electrodes (1, 2) and the acoustic sensor (3) are also presented. R ESULTS AND DISCUSSION Mechanical behaviour ypical stress-strain curves of each material are presented in Fig.2. The commonly observed “bedding error” during compressive tests is obvious in all three materials. Ignoring this initial part, the curves of both marble and cement mortar are mainly characterized by linearity up to about 80% of their maximum stress (points A and B in Fig.2a,b). The mean value of the fracture stress is ~95 MPa for marble and ~50 MPa for cement mortar. The modulus of elasticity obtained was equal to ~70 GPa and ~20 GPa for marble and mortar, respectively, which are very close to the respective ones from literature [10, 22]. Afterwards both curves deviate from linearity. On the other hand, the stress-strain curve of soda glass is linear almost up to 90% of the maximum stress of the specimens (point C in Fig.2c). Its modulus of elasticity was calculated equal to ~70 GPa as it is also mentioned in [31, 32] and its maximum stress was found to be equal to ~20 MPa. It is also to be noted that ductility of soda glass specimens is one order of magnitude lower than the respective ones of both marble and mortar. The mechanical characteristics obtained from all specimens are recapitulated in Tab. 2. Teflon plates Pair of electrodes Strain gauge (a) (b)