Mechanics analysis and predictive force models for the single-diamond grain grinding of carbon fiber reinforced polymers using CNT nano-lubricant

Machining of carbon fiber-reinforced polymer (CFRP) with less damage remains to be a challenge because of anisotropy and inhomogeneity issues. Flood cooling will reduce the mechanical properties of CFRPs due to its hygroscopicity, however, dry grinding will result in thermal damage and deterioration of surface integrity, which cause it not suitable in aeroengine and aerostructure applications. Aiming to resolve the above gaps, the grinding mechanics for a single grain of CFRPs involving CNT nano-lubricant minimum quantity lubrication (MQL) is explored. To reveal the various fundamental mechanisms in machining CFRP of special transversal grinding and lubrication conditions, four sub-models were developed based on the unique geometries of grain and fiber in contact due to the random fiber arrangements and grain edge shapes under different undeformed chip thicknesses. Specifically, the models account ⅰ) the contact force model between the grain tip and fibers, ⅱ) the local contact stress model of elliptical region between the spherical grain edge and cylindrical fiber, ⅲ) the tensile fracture force model of single fiber regarded as an bending beam fixed at both ends and constrained on the elastic foundation, and ⅳ) the extrusion and shearing force model on the cut fiber section at the grinding groove. Furthermore, the grinding force model is obtained by integrating these sub-models, in which the grain-fiber friction coefficient and grinding mechanics are accurately introduced. Finally, the model is numerically simulated and the trend of force along the entire grinding arc length is obtained. Experimental verifications demonstrate the approach for predicting the grinding force have acceptable accuracy and can successfully capture the mechanics of CFRPs. The model reveals that the tensile fracture force of single fiber has the most contributions to the grinding force.