Experimental investigation on the penetration characteristics of low-frequency impact of pulsed water jet

Abstract

In this paper, experiments were conducted to investigate the penetration characteristics of low-frequency impact of pulsed water jet. The pulsed jet was generated with pulse length of 217 mm at the frequency of 120 Hz, using a round nozzle with diameter of 1 mm within the standoff distance of 40 mm. The macro characteristics (entrance shape, cross-section features, penetration depth, entrance area, and penetration rate), inner wall roughness, and micro morphology of penetration cavity on different targets (sandstone and granite) were measured to investigate the penetration performance and mechanism of low-frequency liquid impact. Results showed that there were two different penetration patterns on different targets based on the macro characteristics and the analysis of flow field loading characteristics in penetration cavity. The penetration cavities were present as funnel-shaped pits with narrow entrance and large depth on sandstone samples, and shallow craters with wide entrance and small depth on the granite samples. The roughness on entrance zone and bottom zone of penetration cavity on sandstone decreased with impact time and impact velocity, and that of middle zone increased. The roughness of cavity wall for granite increased with the expansion of penetration cavity. It was found that the main destruction pattern of sandstone was in the form of intergranular fracture, and transgranular fracture for granite. Radial confined holes were observed on the cavity wall at different depths, and the holes mainly existed along the grains boundary of sandstone, present on the transgranular fracture surface of granite. Based on the study about the macro failure characteristics, roughness, and micro morphology of penetration cavity, it was expected to provide some useful information for the application of penetration technology by low-frequency liquid jet.