Issue 30

P.N.B. Reis et alii, Frattura ed Integrità Strutturale, 30 (2014) 431-437; DOI: 10.3221/IGF-ESIS.30.52 435 According with Tab. 1, it is possible to observe that only a small decrease of the interlaminar fracture toughness occurs, around 7.5%, which means that the G IC parameter is practically independent of the initial delamination length. Therefore, for the present laminates, the average value of G IC is around 281 J/m 2 . Initial crack length (a 0 ) 30 mm 45 mm 50 mm G IC [J/m 2 ] 292.3 279.6 270.4 SD [J/m 2 ] 65.6 63.6 58.1 Table 1 : G IC values versus delamination length. Fig. 6 presents the energy release rate for mode II specimens and the formulation used to obtain G can be found in the work of Morais and Pereira [9]. Therefore, G IIC was calculated by the following equation: 3 1 2 2 e 2 .h .E 16.b .a 9.P IIG  (2) where P is the load, b is the specimen width, h is the specimen thickness, E 1 is the flexural modulus a e is expressed by the Eq. (3): 3 3 f 3 1 e 3 2.L .C b.h 8.E . a   (3) where L is half of the spam length (50 mm) C f given by Eq. (4): .b.h 10. 3.L C C 13 f    (4) where  13  is the shear moduli C the specimen compliance expressed by Eq. (5): .b.h 10 3.L .b.h 8.E ) 3.(a 2.L C 13 3 1 3 II 3 .      (5) and, finally, for carbon fibers, Δ II is expressed by the following equation: 13 72. 1E h. II   (6)