High signal-to-noise-ratio ultrasonic imaging of crack defects in particles filled composite explosives

<sec>Polymer bonded explosive (PBX) is a kind of composite material with highly filled molding particles (normally more than 95%) and small quantity binders (less 5%). The effective detection internal cracks in PBX great significance evaluating structural integrity safety reliability .</sec><sec>Ultrasonic phased array imaging methods show advantages potential detecting crack defects. But acoustic test results indicate that the has unique characteristics low longitudinal wave velocity (~3000 m·s<sup>–1</sup>) strong attenuation (attenuation coefficient ~400 dB·m<sup>–1</sup> for 2.5 MHz ultrasound). When defect imaged by traditional ultrasonic total focusing method (TFM) , noises at boundaries between lead to signal-to-noise ratio (SNR) FMC signals background noise reconstructed image, which will disturb cracks.</sec><sec>To realize high SNR defects PBX, an algorithm based on baseband nonlinear synthetic (BB-NSF) proposed. By utilizing spatial coherence received full matrix capture (FMC) data, pixel intensity position can be enhanced while drastically weakened. delay rule modified according surface configuration. In this way, different orientations configuration realized, quality images compared evaluated quantitatively. Meanwhile, base band transformation calculation process optimization could significantly reduce burden increase efficiency.</sec><sec>Experimental proposed effectively suppress improve ability detect cracks. suppression makes highlighting distinguished easily. For BB-NSF algorithm, <i>p</i> crucial parameter used dynamically regulating image. value 2.0, image improved 10 dB linear imaging. With value, further improved, efficiency single almost kept stable. Moreover, some extent far-field capability.</sec><sec>Besides, flexible transducer inhibits depths curved specimens. large orientation angle buried depth, tip, root shape completely present. part contour features lost.</sec><sec>In conclusion, shows advantage cracks, exhibits application prospect other strongly attenuated composites.</sec>