This study aims to elucidate the crack-tip plastic deformation, closure response and stress evolution of I-II/I-III mixed-mode fatigue cracks in compact tension shear (CTS) specimens, focusing on the roles of in-plane shear and out-of-plane tearing.
Using standard CTS cracked specimens, a three-dimensional elastic-plastic finite element model was established based on ABAQUS software, with an initial prefabricated crack length of 5 mm. A cyclic constant-amplitude harmonic load with a load ratio of R = −1 was applied for 50,000 cycles. By changing the combined loading angle, I-II/I-III mixed-mode fatigue cracks were generated and the plastic characteristics and stress evolution laws of mixed cracks under different load application points and loading angles were systematically analyzed.
Numerical results show that increasing the mode II/III components enhances shear or torsional deformation and promotes equivalent plastic strain (PEEQ) accumulation near the crack tip, but the degree of crack closure and its influence gradually decrease. For I-II mode cracks, as the mode II component increases, the plastic strain and Mises stress fields become increasingly asymmetric, while variations in the thickness direction remain limited. For I-III mode cracks, the PEEQ field retains a symmetric butterfly-shaped distribution, but due to anti-plane shear, the Mises stress exhibits stronger thickness dependence.
This study reveals the plastic propagation characteristics and mechanical behavior of I-II/I-III mixed-mode crack tip under fatigue load, which is of great significance for an in-depth study of the fatigue crack failure mechanism and ensuring the long-term life and safe operation of mechanical equipment.
