Shock wave-material interaction in ZrB2–SiC based ultra high temperature ceramics for hypersonic applications

We investigate the thermochemical stability of ZrB₂–SiC based multiphase ceramics to hypersonic aerothermodynamic conditions in free piston shock tube with an objective to understand quantitatively the role of thermal shock and pressure. The developed ceramics sustained impulsive thermomechanical shock, under reflected shock pressure of 6.5 MPa and reflected shock temperature of 4160 K in dissociated oxygen, without structural failure. The conjugate heat transfer analysis predicts the surface temperature of ZrB₂–SiC to reach a maximum of 693 and 865 K, for ZrB₂–SiC–Ti. The transient shock-material response is characterized by surface oxidation of the investigated ceramics, when exposed to high enthalpy gaseous environment, as a consequence of the interaction with ultrafast-heated (10⁶ K/s) gas for ~5 ms. Spectroscopic and structural characterization reveals that addition of Ti improves thermomechanical shock resistance, which is attributed to the assemblage of refractory phases. Taken together, ZrB₂–SiC–Ti based multiphase ceramics exhibit favorable shock-material response under impulse loading.     

Experimental approach to probe into mechanisms of high-temperature erosion of NbB2-ZrO2

In the backdrop of potential applications of boride-based materials in high-speed supersonic aircrafts, the present investigation probes in comprehending the mechanisms of high-temperature erosive wear of spark plasma sintered NbB₂-ZrO₂ composite. The solid particle erosion experiments were performed at different temperatures starting from room temperature (25°C) to 800°C using Al₂O₃ particles (50 μm). The air-erodent particle mixture was impinged toward the target surface at normal impact with a velocity of 50 m/s. The detailed microstructural analysis using HRTEM reveals the generation and accumulation of a large number of dislocations within NbB₂ and ZrO₂ grains of the eroded surfaces. Such observations indicate the activation of dislocation plasticity during erosion at 800°C. XRD-based analyses provided residual stress-based interpretation for the enhancement of erosion resistance at high temperatures. In contrast, substantial material loss via brittle failure, involving the generation and intersection of the lateral/radial cracks, was recorded after room temperature erosion. In case of erosion at 400°C and 800°C, the residual stress relaxes as a consequence of high-temperature exposure prior to erosion. The accumulation of dislocations near the crater region and shot peening phenomena play a dominant role in decreasing erosion rate with increasing erosion test temperature.     

Detection,tracking, and recognition of isolated multi-stroke gesticulated characters

Pattern Analysis and Applications - The detection and tracking of the bare hand are the most vital stages in the bare hand gesticulated character recognition system. Applying detection and tracking...