Issue 31

R.D.S.G. Campilho et alii, Frattura ed Integrità Strutturale, 31 (2015) 1-12; DOI: 10.3221/IGF-ESIS.31.01 8 R ESULTS Configuration 1 or the bonded specimens with jute-epoxy adherends,  n and  o were defined as specified previously. The values of G n c for the bonded joints were defined by plotting the G n -  n curves, considering G n c as the steady-state value of G n in the G n -  n curve [13]. Fig. 7 plots the experimental G n -  n law and the corresponding 6 th degree polynomial fitting curve for a given specimen. At the beginning of the test, G n slowly increases with  n , but the growth rate of G n rapidly increases up to nearly  n =0.02-0.04 mm, and a steady-state value of G n is attained at approximately  n = 0.09 mm. For this specimen, the measured value of G n c is 1.429 N/mm. For the six bonded specimens, the obtained data gave G n c =1.182±0.215 N/mm. Fig. 8 shows the obtained experimental t n -  n law, showing the ductile characteristics of the adhesive after the peak value of t n is attained. For this specimen, the following values were found: t n 0 =20.73 MPa and  nc =0.0935 mm. For the complete batch of tested specimens, average values and deviations were as follows: t n 0 =23.18±3.57 MPa and  nc =0.0843±0.156 mm. Proposed triangular and trapezoidal simplified CZM laws are also presented, allowing concluding that for the adhesive SikaForce ® 7888 a trapezoidal law is particularly suited, since it accounts the best for the adhesive ductility. G n = 7.1158E+06  n 6 - 2.8985E+06  n 5 + 4.3017E+05  n 4 - 3.1299E+04  n 3 + 1.1496E+03  n 2 + 2.9621E-01  n - 6.2813E-04 R² = 9.9999E-01 0 0.4 0.8 1.2 1.6 2 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 G n [N/mm]  n [mm] Experimental law Polinomial (Experimental law) 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 y i l ( ri t l l ) Figure 7 : Experimental G n -  n law for one test specimen and polynomial fitting curve (configuration 1). 0 5 10 15 20 25 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 t n [MPa]  n [mm] Experimental CZM law Triangular aprox. Trapezoidal aprox. 1 . . . . . . . Figure 8 : Experimental t n -  n law for one test specimen. Configuration 2 G n c was calculated by Eq. (1). The experimental G n -  n laws were identical in shape to Fig. 7, and an example for h =3 mm is presented in Fig. 9. The G n c results by applying this procedure for all tested specimens are shown in Fig. 10 as a F