Modeling of microcrack formation in orthogonal machining

• Defined failure strain-based criterion to identify microcracks in shear zone.
• Developed finite element model to simulate microcrack formation in the shear zone.
• Evaluated effect and contribution of cutting parameters to specific shear energy.
• Evaluated contribution of micro-cracks to specific shearing energy and size-effect.
• Validated simulation based cutting forces by orthogonal micro-cutting experiments.

Researchers have observed formation of microcracks during metal cutting and attributed their occurrence to various phenomena. Shaw postulated that under the combined shear and normal stress conditions on shear plane, microcracks could occur when strain in the shear plane exceeds the failure limit of material. However, the phenomenon of microcrack formation is difficult to capture experimentally. Therefore, this paper presents a finite element (FE) model to simulate the microcrack formation during orthogonal cutting. The model has been validated by performing orthogonal micro-cutting experiments and error in cutting force prediction is less than 11.5%. The simulation helps identify locations at which microcracks are formed in the shear zone using the mathematical and FEA models. Furthermore, the contribution of the specific energy (energy/volume) associated with the microcrack formation to the total specific energy of the shear zone has been evaluated. Contribution of microcracks to specific shear zone energy is found to be in the range of 0–20% for AISI 1215 and 0–15% for AISI 1045 under different machining conditions.