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Chapter 1
1.2 Research gaps
The following research gaps have been identified from the review of literature:
· Researchers have observed formation of microcracks during micro-cutting and attributed their occurrence to various phenomena. Moreover, the phenomenon of microcrack formation along the shear plane is difficult to capture experimentally. In literature, there is no specific analytical or numerical formulation to estimate the number, the location and the contribution of the microcracks to the size effect during micro-cutting.
· The specific work of fracture (R) has been widely used to quantify the fracture energy consumed during metal cutting as suggested by Atkins. R becomes a significant portion of total cutting energy in micro-cutting thereby influencing the phenomenon of the size effect. Therefore, it is necessary to evaluate R as a function of various parametric conditions such as cutting speed (V), uncut chip thickness (to), rake angle (a) and tool edge radius (r).
· Fracture in cutting of ductile as well as brittle materials in various zones of deformation, has been characterized analytically using parameters such as K, G, R and J-integral. To accurately evaluate the contribution of fracture energy in the size effect, it is understood that J-integral would be appropriate. The J-integral would characterize the fracture energy accurately in the presence of mixed mode, material plasticity and nonlinear behavior conditions that prevail during micro-cutting of ductile materials.
· Most of the past studies have either used phenomological models to predict work material properties or developed approximate multi-phase models without taking into account actual nature, size and distribution of grains along with the grain boundaries. Moreover, there are various challenges to model actual grain and grain boundaries using traditional numerical formulations due to very small sizes of these microstructural features. To overcome these challenges, Smoothed Particle Hydrodynamics (SPH) formulation is expected to provide suitable results.
To address the research issues thus identified, the main goal of this research work is to determine the size effect due to presence of microcracks, gross fracture and workpiece microstructures during micro-cutting of ductile materials within the framework of numerical modeling and evaluate the contribution of each aspect to the size effect followed by an appropriate experimental validation.
