Fatigue life prediction of composite laminates with staggered ply discontinuities: an integrated energy-based model

Delamination initiated from ply discontinuities is recognized as a critical failure mode in composite laminates, with their structural integrity being significantly compromised under fatigue loading. Although delamination has been widely studied, the specific case of staggered ply discontinuities and their role in governing progressive damage has received limited attention. In this paper, a novel integrated experimental-analytical framework is introduced to predict fatigue-driven delamination growth from such staggered configurations in glass–epoxy laminates. A comprehensive experimental program was conducted, where laminates with three distinct lay-ups ([0₃//0₂//0₃]_s, [0₅//0₂//0₅]_s, [0₇//0₂//0₇]_s) were subjected to tension–tension fatigue loading at various stress levels. Delamination growth was optically monitored, and the resultant data were used to calibrate a Paris’ law model specifically for this damage mechanism. The core analytical contribution is represented by an energy-based model that explicitly relates stiffness degradation to the evolving delamination length, enabling the derivation of closed-form expressions for fatigue life (N) as a function of damage progression. The model shows good agreement with the experimentally observed S-N behavior and delamination growth rates for the tested laminate configurations. Furthermore, the predictive capability of the framework is explored through fatigue-life predictions for three additional unseen laminate configurations not included in the calibration dataset, demonstrating its potential for application to a broader range of laminate architectures.