None

A new experimental technique involving instrumented indentation was demonstrated for the specific purpose of calibrating certain variations in elastic properties as a function of position in thermally sprayed and sintered materials. This work experimentally demonstrated for the first time that controlled gradients in elastic properties alone can lead to the suppression of damage and cracking during contact loading. New methods were developed in this work for the estimation of mechanical properties of ductile alloys and brittle ceramics by recourse to continuous measurements of load-penetration curves with spherical microindenters.

The morphology of craters resulting from high irradiance laser ablation of silicon was measured using a white light interferometry microscope. The craters show a dramatic increase in their depth and volume at a certain irradiance, indicating a change in the primary mechanism for mass removal. Laser shadowgraph imaging was used to characterize and differentiate the mass ejection processes for laser irradiances above and below the threshold value. Time-resolved images show distinct features of the mass ejected at irradiances above the threshold value including the presence of micron-sized particulates; this begins at approximately 300 {approx} 400 ns after the start of laser heating. The analysis of the phenomena was carried out by using two models: a thermal evaporation model and a phase explosion model. Estimation of the crater depth due to the thermally evaporated mass led to a large underestimation of the crater depth for irradiances above the threshold. Above the threshold irradiance, the possibility of phase explosion was analyzed. Two important results are the thickness of the superheated liquid layer that is close to the critical temperature and the time for vapor bubbles that are generated in the superheated liquid to achieve a critical size. After reaching the critical size, …