Finite element analysis for large displacement J-integral test method for Mode I interlaminar fracture in composite materials

The presence of surface and internal cracks in monolithic and composite materials is known to reduce the fracture strength of the material. Due to the inherent complexity of composites, a wide array of fracture analysis has been developed to quantify the stress field at the crack tip. In this paper, an expression of instantaneous evaluation of J-Integral (Paris and Paris, 1988 [1]; Williams, 1987 [2]; Nilsson, 2006 [3]) is compared to finite element output as a method of analysis for the Mode I interlaminar fracture toughness of composite materials for large displacements of the double cantilever beam using empirical data. The outputs of the proposed exact method and finite element method are also compared with two ASTM methods; Modified Beam Theory (MBT) and Modified Compliance Calibration (MCC) methods. The results show close alignment with MBT method and MCC method, and therefore, suggest that the exact (J-integral) method may be used as an alternative over relatively costly and time consuming testing procedures for evaluating fracture toughness of fiberglass-epoxy composites. In addition, finite element simulations show relatively constant value of fracture toughness as compared to exact method, MBT method, and MCC method if extracted remotely from the crack tip.