Influence of confinement on the deformation behavior of zirconium diboride-silicon carbide (ZrB2-SiC) composite

Zirconium Diboride-Silicon Carbide (ZrB2-SiC) is a structural ceramic and its widespread use in diverse applications requires a fundamental understanding of its constitutive response under a range of loading conditions. In this context, confined compression experiments are of particular interest because of their ability to withstand higher loads. However, it is important to know the confinement load as precise as possible for accurate characterization. Taking advantage of a Raman active secondary Silicon Carbide (SiC) phase within the primary ZrB2 phase, a framework is derived to estimate the biaxial compressive stresses generated due to the application of an externally applied radial load. The relationship derived relates Raman peak-shift on a confined SiC particle to the magnitude of imposed confinement using phonon deformation potentials for 3C-SiC diamond and zinc-blende crystal structure. External pressure is applied on cylindrical specimens of ZrB2-SiC, using thermal shrink fitting metallic sleeves. The peak-shift relation derived is then verified by utilizing the classical formulations for thick walled pressure vessels in the first step and comparing the measured strains using digital image correlation (DIC) in the second step. The two independent techniques compared well with the stresses measured through the peakshift relation.;In the later part of the manuscript multiaxial compression tests were conducted on confined ZrB2-SiC under quasi-static and high strain rates. The applied pressure was varied by using different sleeve materials to achieve different levels of shrink-fit. Postmortem analysis on the recovered specimens revealed formation of a shear plane under multiaxial stress with a high crack density beneath the leading edge of the fault as opposed to axially oriented columnar fragments under uniaxial stress. The highest compressive strength achieved in the confined specimen was measured to be 5.6 GPa and 9.8 GPa under quasi-static and dynamic loading conditions, respectively. Moreover, ZrB2-SiC samples loaded at a strain rate of epsilon =102 s-1 and confined at ≥ 300 MPa exhibited slip lines induced through bulk confinement. Johnson and Holmquist (JH-2) model parameters were determined for future simulations. The experimental results were found to fit Mohr-Coulomb failure surface in the pre-HEL and Von-Mises type yield surface in the post-HEL regime.