A Novel Numerical Methodology for Mode I Fatigue Delamination with Fibre Bridging Retardation of Composite Laminates

Fatigue delamination growth (FDG) is one of the most important failures in composite structures during their long-term operation. The presence of fibre bridging at the behind of delamination front can have significant retardation effects on FDG behavior. With the change of certification philosophy of composite structures from no crack growth to slow crack growth that recommended by the US federal aviation administration (FAA) since 2009, how to appropriately represent FDG performance, especially with significant fibre bridging, has become a critical issue for composite material development, characterization and structural life evaluation. Both European Society of Structural Integrity Technical Committee 4 (ESIS TC4) and the American Society for Testing and Materials Subcommittee D30.06 (ASTM D30.06) have provided separated round-robin programs in the past decades for the development of this test protocol for mode I fatigue delamination in composite laminates. The relevant ISO standard has been under discussions at this moment. Even a large number of experimental studies on mode I fatigue delamination with fibre bridging have been reported by different researchers, there is few numerical model for characterizing this specific damage. Thus, the aim of the present study is to develop an accurate numerical model for mode I fatigue delamination with significant fibre bridging. A superposition strategy was employed to respectively represent damage propagation around the delamination front as well as in bridging fibres under cyclic loading. Particularly, fatigue damage evolution concentrated at the crack front was determined via a fatigue cohesive constitutive proposed in literature [1-2], in which fatigue damage is linked to the fracture mechanics Paris resistance curve. And a new bridging constitutive was proposed to determine failures occurring in bridging fibres via an optimization algorithm. These two constitutive was subsequently implemented in a numerical model via programming the user defined material subroutine of ABAQUS software, and finally result in a new numerical model for FDG with fibre bridging. The predicted results clearly demonstrate that the use of this new model can well account for bridging retardation effects in mode I FDG of composite laminates. This model therefore can be used for composite structural design and life evaluation.