مدل‌سازي عددي رشد تورق خستگي مود تركيبي در كامپوزيت‌ تك-جهته

Composite materials have found extensive applications in advanced industries, due to their unique advantages. However, delamination (layer separation) is recognized as one of the most critical failure mechanisms in these materials under cyclic loading. This research investigates fatigue delamination growth under mixed-mode I an‎d II loading conditions using the Virtual Crack Closure Technique (VCCT), the Extended Finite Element Method (XFEM) an‎d the Cohesive Zone Model (CZM). The effect of the mode ratio on fatigue crack growth behavior is analyzed for mode mixities of 20%, 50%, an‎d 80%. Implementing VCCT within a direct cyclic solver framework enables efficient modeling of crack growth under fatigue loading, making it a powerful tool for simulating fatigue delamination behavior. However, its inherent requirement for a predefined crack growth path remains its primary limitation. The XFEM, while a powerful tool for modeling autonomous crack growth along complex an‎d unknown paths, is not highly recommended for modeling mixed-mode fatigue delamination in laminated composites. The primary reason for this is the observed tendency of the crack to deviate from the interlaminate path when modeling the mixed-mode specimen in this study. The Paris law was used to model the crack growth rate, an‎d the Benzeggagh-Kenane (B-K) criterion was employed to eva‎luate the equivalent mixed-mode fracture toughness for simulations using both VCCT an‎d XFEM. selec‎ting an appropriate time increment is crucial for result accuracy in VCCT, unlike in XFEM. Specifically, using an initial time increment of less than 0.005 seconds for VCCT an‎d 0.01 seconds for XFEM yielded the best results. The CZM was implemented in this study by developing a custom UMAT subroutine, as the Abaqus software does not natively support fatigue modeling with this method. For modeling fatigue delamination growth using CZM, a bilinear traction-separation law was combined with the Turon fatigue damage model, which is based on the load-envelope method. Although this simple model was effective for simulating damage initiation an‎d crack growth under quasi-static conditions, the results demonstrated its inability to accurately predict fatigue delamination at mode mixities close to pure Mode I. This indicates a need for more complex models to determine its behavior under such conditions.

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