Fracture of elastomers under static

Thiswork dealswith the fracture of rubbers under a mixed mode loading (I+II) and it is an extension of our previous papers on that subject [Aït Hocine N, Naït AbdelazizM, Imad A (2002) Int J Fract 117:1- 23; AïtHocine N, Naït AbdelazizM(2004) In: Sih GC, KermanidisB, PantelakisG(eds) 6th international conference for mesomechanics. Patras (Greece), May 31- June 4, pp 381-385]. An experimental and a numerical analysis were carried out using a Styrene Butadiene Rubber (SBR) filled with 20 and 30% of carbon black. Sheets with an initial central crack (CCT specimens) inclined with a given angle compared to the loading direction were used. The J -integral and its critical values Jc (fracture surface energy) were determined by combining experimental data and finite element results. These critical values, determined at the onset of crack growth, were found to be quite constant for each elastomer tested, which suggests that Jc represents a reasonable fracture criterion of such materials. Then, the strain-stress field and the strain-energy-density factor S, earlier introduced by Sih [Sih GC (1974) Int J Fract 10(3):305-321; Sih GC (1991) Mechanics of fracture initiation and propagation. Kluwer Academic Publishers, Dordrecht, 428 pp] were numerically calculated around the crack tip. According to the experimental observations, the plan of crack propagation is perpendicular to the direction of the maximum principal stretch. Moreover, as suggested by Sih in the framework of linear elastic fracture mechanics (LEFM), the minimum values Smin of the factor S are reached at the points corresponding to the crack propagation direction. These results suggest that the concept of the maximum principal stretch and the one of the strainenergy- density factor can be used as indicators of the crack propagation direction.