Dynamic behavior of zirconia ceramics in uniaxial compression

A novel Split Hopkinson Pressure Bar (SHPB) method called the stress reversal Hopkinson technique developed at UCSD, is successfully used to subject ceramic samples to predetermined compressive stress pulses. The advantage of the technique is that the ceramics are subjected to a single well-defined compressive stress pulse of approximately 60 {dollar}mu{dollar}s duration, and then recovered for further analysis. Unlike the traditional SHPB method, in this technique the compressive pulse is immediately followed by a tensile pulse. After the compressive pulse loads the sample, all other pulses which travel towards the sample are tensile and hence the sample is not reloaded.; Transformation plasticity in Magnesia-Partially Stabilized Zirconia (Mg-PSZ) and Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) is investigated in this study. The samples tested in SHPB show a tri-linear stress-strain behavior. The longitudinal and transverse strains are measured by strain gages mounted on the samples. The lateral surfaces of Mg-PSZ samples show extensive surface rumpling and microcracking parallel to the loading axis after the test. Reloading of these samples to higher stress levels did not reveal additional inelasticity. Cuboid samples which have been loaded initially to attain transformation saturation, are then reloaded in a direction perpendicular to the first loading. The second loading produces additional inelasticity and microcracking (parallel to this loading direction), indicating the formation of transformation texture in each loading under uniaxial compression. Scanning electron microscope (SEM) observations on suitably etched samples reveal evidence of isolated and correlated transformations. Transmission electron microscope (SEM) observations reveal crack deflection around the precipitates and microcracking around transversely twinned precipitates. X-ray diffraction (XRD) on these samples shows significant monoclinic peaks and reduced tetragonal peaks. Ultrasonic measurements on samples subjected to different stress levels indicate decreased modulus due to microcracking. A micromechanical damage model for modulus degradation of a cracked body is developed using the assumption of dilute distribution of cracks, and the results are compared with the ultrasonic measurements. A micromechanical phenomenological model is also developed to predict the transformation strains and uniaxial stress-strain behavior assuming a potency distribution for the particles. The resulting stress-strain curves are in good agreement with the experimentally obtained curves.