Interlaminar Fatigue Life Estimation of Composite Laminates and Substructures Under HCF and VHCF Loads: A Generalized Computational Framework

ABSTRACT

The current research work presents a generalized and thoroughly validated finite element (FE) methodology to predict the mixed-mode delamination-induced fatigue life (S–N curve) of composite laminates and substructures under high cycle fatigue (HCF) and very high cycle fatigue (VHCF) loads. A novel fatigue damage initiation (FDI) model is developed using the G–N curve obtained from coupon-level fracture fatigue tests. The proposed FDI model is coupled with a fatigue damage propagation (FDP) model to predict the fatigue life of composite laminates and substructures. Besides, contrary to the typical ΔG = (G_max − G_min)/G_c approach used as a crack driving force in FDP formulations, to capture the load ratio (R ratio) effects on the fatigue failure, based on the similitude principles, $\mathrm{\Delta G}={\left(\sqrt{G_{\max }}-\sqrt{G_{\min }}\right)}^2/G_c$ is used as the crack driving force. The proposed fatigue damage algorithm is implemented using the cohesive zone formulations in Abaqus/Explicit via a VUMAT subroutine and validated against the experimental G–N curve at damage initiation and S–N curve until final failure for both individual and mixed-mode loading conditions. Finally, the implemented FE methodology is extended to predict the fatigue life of a composite cylinder subjected to Brazier-like crushing forces, demonstrating the proposed model's applicability to complex substructures under the loads that induce mixed-mode failure.

Highlights

• A novel fatigue damage initiation (FDI) model is proposed based on experimental G (energy release rate)–N (number of cycles to damage onset) curves and validated under individual modes.
• Mixed-mode G–N curves at damage initiation are successfully predicted using individual-mode G–N curves, eliminating the need for mixed-mode experimental fracture fatigue tests.
• Contrary to the typical $\mathrm{\Delta G}=\frac{\left(G_{\max }-G_{\min }\right)}{G_c}$ formulations used as a crack driving force in the propagation damage model, $\mathrm{\Delta G}=\frac{{\left(\sqrt{G_{\max }}-\sqrt{G_{\min }}\right)}^2}{G_c}$ is adopted based on similitude principles to capture the R ratio effects on the crack growth rate.
• The FDI model is coupled with a fatigue damage propagation (FDP) model and validated for predicting the S–N curves of composite laminates and substructures.