| An introduction on the development history and the state-of-the-art of abrasive waterjet technology is presented. An intensive review of literature is given on the published experimental and theoretical studies of both ductile and brittle material erosion. The review is presented in a tabular format for quick referencing. A study using scanning electron microscopy (SEM) is conducted to give the first-hand information on the erosion mechanisms associated with abrasive waterjet processes. It reveals that the erosion mechanisms of brittle materials include plastic flow at the immediate impact site and a surrounding crack network. For polycrystalline ceramics, the cracking occurs along grain boundaries. Based on this observation, an elasto-plastic theory is used to model the brittle material removal applied to abrasive waterjet process. By analogy to the damage patterns by small detonation, the network cracking phenomenon is attributed to fractures caused by impact induced stress waves. A crack network model to evaluate the fractured volume is derived in terms of the input stress wave energy and the required fracture surface energy. The stress wave energy is expressed with a modified Hutchings' equation for normal incidence and with an equation derived in this study for low incidence, respectively. The crack network model combined with Bitter's deformation wear model gives the total material removal for a single particle impact at normal incidence, and, combined with Finnie's microcutting model, gives the total material removal for low incidence impacts. Observations on the abrasive waterjet cutting front reveal that the cutting process is associated with abrasive particle impacts at glancing angles. The energy dissipation phenomena in abrasive waterjet cutting are characterized. Consequently, the individual particle removal model for low incidence impacts, combined with the analytical results from the energy dissipation study, is used to derive an equation which predicts the depth of cut. By analogy to this theoretical equation, an empirical equation is also derived which narrows the gap between the theories and applications. Based on this empirical equation, a new material parameter, called "Machinability Number", is defined. The "Machinability Number" is applied to the parameter prediction of abrasive waterjet processes. |
