Experimental and numerical analysis of abrasive waterjet drilling of brittle materials

The interaction between abrasive waterjet (AWJ) and brittle materials, as well as lated machining mechanisms, was studied using a hybrid experimental - numerical analysis approach. First, the machineability of ceramic materials, such as alumina, silicon nitride, silicon carbide, and titanium diboride, was studied by varying the AWJ input parameters. The AWJ machining forces on these materials were measured and discussed. First, an SEM study was conducted to investigate the AWJ machining mechanisms on continuous fiber-reinforced ceramic composites (CFCC). Second, a moire interferometry experimental setup and procedure were developed, as well as a 3-D finite element model. The measured surface displacement distributions were used to drive the finite element modeling. In this inverse problem, the measured reaction forces of the specimen during AWJ drilling were matched the reaction forces from the finite element simulation. Three pressure loads of the AWJ exerted on the cavity were assumed for the FEA model, and their effects on the surface displacement distribution were studied through numerical experiments. The verification of the finite element model was carried out by studying a statically loaded specimen, both experimentally and numerically, in which the moire fringe patterns from the experiments and the displacement contour plots from the FEA were compared.; The test results from the machineability study indicated that structural ceramics can be machined by AWJ at a reasonable material removal rate. Under certain conditions a threshold supply pressure exists. The impact force on a specimen by pure waterjet is about 20% greater than that by an AWJ. There exists a basic fluctuation frequency that is low in value and associated with the AWJ system. The material removal mechanisms for AWJ cutting on CFCC consist of a combination of bending, shearing, micromachining, and erosion. The micro-mechanisms associated with AWJ drilling are micro-fracture of fibers and matrix, delamination, and fragmentation of fiber bundles. The results from the numerical experiments demonstrated that the shear applied on the kerf surface, simulating the AWJ return flow, most profoundly affects the surface displacement distribution. The optical experimental data from both polycarbonate and alumina indicated that the horizontal strain, {dollar}varepsilonsb{lcub}x{rcub}{dollar} increases as the depth of hole is increased. The AWJ drilling process was numerically modeled reasonably well with the three assumed pressure loads, i.e. jet pressure, normal pressure, and shear. The numerical modeling demonstrated that the principal stresses at the bottom of the hole increase as the depth of hole increases. The material removal mechanism is a process of micro crack initiation, micromachining and erosion, as proposed by Ramulu{dollar}sp{lcub}17{rcub}.{dollar} This can be substantiated quantitatively by the study results. The micro-crack can be activated by the impingement of the AWJ by the condition of {dollar}rm Ksb{lcub}I{rcub}ge Ksb{lcub}Ici{rcub}.{dollar}...