Josh E. Loukus

Application of data dependent systems approach for evaluation of fracture modes during a single-grit scratching

Brittle fracture and the associated material removal mechanisms in model brittle materials were investigated using single-grit scratch experiments. The objective was to develop a fundamental understanding of the mechanisms of brittle material removal during machining (e.g., grinding) processes and mathematically describe the induced topological features. Initial experiments were conducted on metals and the ductile material removal response was captured in the form of smooth lenticular shaped scratch trace and a smooth semi-sinusoidal force profile. Scratch experiments on model brittle materials, namely, Homalite-100 and Pyrex glass, revealed intermittent material removal patterns and oscillatory force profiles. In Homalite, material removal occurred in periodic bursts with the size of the burst proportional to the instantaneous depth of cut, and accordingly the force profiles reflected periodic oscillations. In Pyrex glass, the material removal occurred in random bursts at irregular intervals and accordingly the force profiles reflected irregular/random force oscillations. To further characterize the nature of material removal process, the experimentally obtained force data were analyzed using data dependent systems (DDS) approach. The analysis revealed that the physical features of the induced damage in the scratch groove are effectively captured in the respective Greens functions. Based on the energy contributions arising from the characteristic roots of the DDS models, a brittleness measure, that characterizes the propensity for brittle fracture in ceramics, has been proposed. This measure can be used in more complex machining situations for on-line monitoring of the nature of material removal process.