One of the main challenges encountered in modeling the behavior of metal matrix composites (MMCs) during machining is the availability of a suitable constitutive equation. Currently, the Johnson–Cook (J–C) constitutive equation is being used, even though it was developed for homogeneous materials. In such a case, an equivalent set of homogeneous parameters is used, which is only suitable for a particular combination of particle size and volume fraction. The current work presents a modified form of the J–C constitutive equation that suits MMCs, and explicitly accounts for the effects of particle size and volume fraction, as controlled parameters. Also, an energy-based force model is presented, which considers particle cracking and debonding based on the principles of fracture mechanics. In order to validate the new approach, cutting forces were predicted and compared to experimental results, where a good agreement was found. In addition, the predicted forces were compared to other analytical models available in the literature.