Meso-scale cracks initiation of Nomex honeycomb composites in orthogonal cutting with a straight blade cutter

Cracks generated in micro and meso-scales pose a potential threat to the full product. Numerous reports on microscale voids and cracks in Nomex honeycomb composites (NHCs) have focused on the process of co-curing and co-bond. Practically, substantial meso-scale cracks were introduced in the machining without sufficient attention. To fill this gap, the study explored a new phenomenon (i.e., transverse and longitudinal cracks) in meso-scales, with a special focus on formation mechanism and evolution. A meso-scale numerical model of NHCs was developed for the analysis of fracture inducing mechanisms in ultrasonic vibration machining (i.e., multi -source loading conditions). During model establishment and validation, not only the friction model of the cut-ter and NHCs was amended, but also the cutting force system was evaluated and compensated. Analytical and experimental validation indicated that the cell deformation and the peak value of the cutting force showed a reasonable agreement with the numerical results. Further understanding based on the numerical model can obtain the cracks initiation mechanisms that: (i) Transverse cracks are induced by longitudinal tensile stress, which is generated by tool vibration, while (ii) longitudinal cracks are induced by transverse tensile stress, which is caused by tool feed. The findings of meso-scale cracks not only enhance the significance of curing-induced microcracks and voids, but also provide theoretical guidance for the evolution of macroscopic defects after machining.