Simulation analysis of progressive damage of helical milling holes in CFRP laminates based on strain Hashin criterion

Due to the progressive damage involving multiple coexisting failure modes during the helical milling of carbon fiber reinforced polymer (CFRP) laminates, the finite element simulation accuracy based on Hashin criterion stress form is difficult to guarantee. In this study, the Hashin criterion was modified by introducing strain and applied to the simulation of helical milling of CFRP laminates. The results show that the stress and strain peaks under the strain Hashin criterion can reach a high level. The aperture deviation at the entrance/export is reduced by 36% and 43% respectively compared with that before correction, which indicates that the criterion can fully reflect the continuous damage evolution process of “crack initiation-propagation-failure”. The strain Hashin criterion is further applied to explore the influence of fiber orientation on the hole quality. It is found that the average cutting force, entrance damage factor and aperture deviation can reach the minimum values at 0°, which are 39.52 N, 0.21 and 12 μm, respectively; The average cutting force corresponding to 90° is up to 52.12 N; The export damage factor and aperture deviation at 135° can reach the maximum values of 0.28 and 27 μm, respectively. Finally, it is verified by experiments that the prediction errors of axial force F_z and circumferential force F_r under the strain Hashin criterion are small, which are 6.4% and 12.7% respectively. And its hole entrance/export morphology and hole wall quality are in good agreement with the experimental results. Compared with the traditional Hashin criterion stress form, the strain Hashin criterion gradually determines the damage failure based on strain accumulation, which effectively suppresses the premature failure caused by stress concentration in CFRP helical milling holes, thus significantly improving the prediction accuracy of its simulation.